Search

In this study nanostructured MoO3 and WO3 promoted SnO2 solid acid catalysts were explored for the production of glycerol carbonate via carbonylation of bioglycerol with urea. The investigated reference SnO2 and promoted catalysts were synthesized by fusion and wet-impregnation methods, respectively. The physicochemical properties of the prepared catalysts were thoroughly analyzed by XRD, Raman, BET surface area, TEM, FTIR, pyridine adsorbed FTIR, NH3-TPD, and XPS techniques. It was found from the characterization studies that integration of SnO2 with MoO3 and WO3 promoters leads to remarkable structural, textural, and acidic properties. Especially, a high quantity of acidic sites were observed over the MoO3/SnO2 catalyst (~ 81.45 μmol g−1) followed by WO3/SnO2 (61.81 μmol g−1) and pure SnO2 (46.47 μmol g−1), which played a key role in the carbonylation of bioglycerol with urea. The BET specific surface area and oxygen vacancies of SnO2 were significantly enhanced after the addition of MoO3 and WO3 promoters. TEM images revealed the formation of nanosized particles with a diameter of around 5–25 nm for the synthesized catalysts. The MoO3/SnO2 catalyst exhibited a high conversion and selectivity towards glycerol carbonate in comparison to other catalysts. The observed better performance is attributed to unique properties of MoO3/SnO2 catalyst including smaller crystallite size, high specific surface area, abundant oxygen vacancies, and more number of acidic sites. This catalyst also exhibited remarkable stability with no significant loss of activity in the recycling experiments. Nanostructured MoO3/SnO2 solid acid catalyst exhibited an excellent catalytic activity and a high selectivity to glycerol carbonate in the carbonylation of bioglycerol with urea under solvent-free and mild conditions.

TiO2 nanorods-supported MnOx, FeOx, CrOx, and MnOx-FeOx-CrOx catalysts have been prepared by a deposition-precipitation method, with the aim of investigating the combination of ternary metal oxides effect on elemental mercury (Hg0) removal. The TiO2 nanorods-supported MnOx-FeOx-CrOx catalyst manifested the superior Hg0 removal efficiency (∼80-83%) at low temperatures (100–200 °C) in the presence of O2. The addition of NO promoted the Hg0 removal efficiency under the same reaction conditions. Further, SEM, HRTEM, XRD, BET surface area, and XPS characterization were carried out to explore the physicochemical properties of the catalysts. It was found that the integration of three active metal oxides contributed to the enrichment of active sites and the surface adsorbed oxygen species, thereby improving the catalytic activity. Additionally, both the large surface area and high crystallization of the obtained TiO2 nanorods resulted in uniform dispersion of the manganese-iron-chromium mixed metal oxide nanoparticles and a high activity. Further, XPS data of spent MnOx-FeOx-CrOx/TiO2 catalyst indicated that the presence of Mn4+, Cr6+, and Fe3+ could promote Hg0 oxidation due to the strong synergistic interaction between the TiO2 nanorods-incorporated MnOx, FeOx, and CrOx nanoparticles.

A series of Ce1 − x–ZrxO2 − δ (x = 0.2, 0.5, and 0.8) mixed oxides were prepared by coprecipitation method and explored for selective oxidation of vanillyl alcohol employing O2 and acetonitrile as the oxidant and solvent, respectively under base-free conditions. To ascertain the key factors responsible for vanillyl alcohol oxidation, the physicochemical properties of the synthesized catalysts were investigated by various characterization techniques namely, XRD, BET surface area, Raman, XPS, and H2-TPR. It was observed from this exercise that the catalytic activity dependents on the Ce:Zr mole ratio, which is related to the degree of reducibility of the catalyst. Interestingly, the catalytic activity is enhanced with the increase of Ce content in the Ce–Zr mixed oxide. Among the investigated catalysts, the Ce0.8Zr0.2O2 combination exhibited a high catalytic activity with ~ 98% conversion and ~ 99% selectivity to vanillin. Smaller crystallite size, large BET surface area, more number of oxygen vacancies, improved redox properties, and strong synergetic interaction are found to be the key factors to promote the oxidation ability of Ce0.8Zr0.2O2 catalysts towards vanillyl alcohol oxidation. Further, the influence of reaction parameters such as time, solvent, temperature, and oxygen pressure were also studied to optimize the catalytic process for vanillyl alcohol oxidation. As revealed by these studies, the high activity of Ce0.8Zr0.2O2 catalyst could be retained up to five cycles without appreciable loss in the activity and selectivity. Nanosized Ce0.8Zr0.2O2 catalyst exhibited an excellent catalytic activity and superior selectivity to vanillin in the liquid phase oxidation of vanillyl alcohol under ecofriendly conditions

A series of Cr-TUD-1 catalysts with various loadings of chromium (3, 5, 7, and 9 wt%) were prepared by microwave irradiation and explored for oxidative dehydrogenation of propane to propylene utilizing CO2 as soft oxidant. The microwave irradiation reduced the synthesis time and the resulting Cr-TUD-1 catalysts exhibited a high specific surface area of more than 600 m2 g−1. The synthesized catalysts were characterized by various techniques including XRD, XPS, TEM, UV–vis DRS, BET surface area, and pore size distribution to understand the physicochemical properties, and to correlate with the catalytic activity. Among various compositions, the 7% Cr-TUD-1 catalyst exhibited a high propane conversion (~ 45%) with better propylene product selectivity (~ 75%). The Cr-TUD-1 catalyst was also found to be quite stable up to 8 h of time-on-stream investigated. As revealed by the characterization techniques, the inter-convertible Cr6+ to Cr3+/2+ species are very crucial for the observed better catalytic activity of these materials. The TUD-1 enables to encapsulate the chromium nanoparticles in the porous silica structure with high dispersion which help in maintaining the better catalytic performance.

This work reports a thorough investigation of nanosized Mn-doped ceria (Ce 0.7 Mn 0.3 O 2-δ , CM) as an efficient catalyst for oxidation of benzylamine under solvent-free conditions. These catalysts were prepared by a coprecipitation method followed by calcination at 773 and 1073 K. Effect of Mn doping was examined by a variety of characterization techniques. XRD results confirmed formation of single-phase Ce-O-Mn solid solution, and TEM studies showed nanosized nature of particles. BET surface area of CeO 2 was significantly enhanced after Mn incorporation. Raman, XPS and H 2 -TPR results revealed that Mn cations in ceria lattice increase concentration of structural oxygen vacancies and reducibility of ceria. Among various catalysts, the CM calcined at 773 K exhibited a high conversion (∼71%), product selectivity (∼99.8%), and excellent stability. The better performance has been proved to be due to synergetic interaction between Ce and Mn ions thereby enhanced surface area, improved reducibility, and increased surface adsorbed oxygen species.

This article represents a comparative study of a series of doped ceria catalysts towards environmental applications like CO and soot oxidation catalysis. Transition and rare earth metals of varying size and reducibility property have been selected namely, zirconium (Zr), hafnium (Hf), iron (Fe), manganese (Mn), praseodymium (Pr), and lanthanum (La) as dopants. A facile coprecipitation approach has been used to incorporate the dopants into ceria lattice.The formation of homogeneous solid solutions and their respective physicochemical properties have been confirmed by employing XRD analysis, BET surface area measurements, TEM, Raman, UV-DRS, XPS, and TPR techniques. All the doped CeO2 samples exhibited smaller crystallite size, larger BET surface area, and higher amounts of oxygen vacancies than that of pure CeO2. CO oxidation has been performed in the presence of oxygen under atmospheric pressure, and 300–850 K temperature range in a fixed bed microreactor. Soot oxidation was carried out in presence of air using a thermo gravimetric analyzer within a much wider temperature window of 300–1273 K. The physicochemical properties of the doped ceria materials have been comparatively analyzed to correlate the influence of dopants with their improved behaviour in both the oxidation reactions. Vital role of ‘lattice oxygen’ in CO oxidation and ‘active oxygen species’ in soot oxidation on the catalyst surface has been considered, assuming that Mars and van Krevelen mechanism and active oxygen mechanism play the key role in CO and soot oxidation, respectively. The O 1s XP spectra confirmed that Mn doped ceria (denoted as CM) exhibited most loosely bound lattice oxygen and highest concentration of surface adsorbed oxygen species compared to other materials. Accordingly, a superior CO and soot oxidation activity have been observed for manganese doped ceria. Significant lowering of T50 (390 K and 669 K for CO and soot oxidation respectively) temperature have been observed in both the oxidation reactions; which is primarily attributed to the considerable lowering of lattice oxygen binding energy and higher concentration of surface adsorbed oxygen species.

Ceria is the hub of constant and diverse research interest due to its wide industrial applications. In the present work, we have developed Mn-doped CeO 2 catalysts for vanillyl alcohol oxidation. Accordingly, we synthesized nanostructured Mn-doped CeO 2 catalysts with various concentration of MnO x by an economical coprecipitation method and characterized using XRD, ICP-OES, BET surface area, Raman spectroscopy, TEM, XPS, and H 2 -TPR techniques. XRD and TEM results confirmed formation of nanocrystalline solid solutions with the incorporation of Mn into ceria lattice. ICP-OES analysis confirmed actual amount of MnO x loadings in the respective catalysts. The BET surface area of CeO 2 significantly enhanced after the incorporation of MnO x dopant. Raman results disclosed that the incorporation of MnO x into ceria lattice greatly enhances the oxygen vacancies, which are responsible for the improved catalytic activity. XPS analysis revealed that Ce and Mn exist in +3, +4 and +2, +3, +4 oxidation st a tes, respectively, on the surface of the samples. H 2 -TPR results showed pronounced enhancement in the reduction of CeO 2 by MnO x doping. Catalytic activity studies confirmed that among all the catalysts, the Ce 0.7 Mn 0.3 O 2−δ showed superior activity for vanillyl alcohol oxidation with 89% conversion and 95% selectivity, which could be attributed to higher concentration of oxygen vacancies, a high BET surface area, low temperature reducibility, and facile synergetic interaction between CeO 2 and MnO x .

The selective hydrogenolysis of bioglycerol to 1,2-propanediol was investigated over a series of Ce-promoted Cu/Mg catalysts, namely, Cu/Mg (1/9), Cu/Ce/Mg (1/1/5), Cu/Ce/Mg (1/3/5), and Cu/Ce/Mg (1/5/5) prepared by a coprecipitation method. The physicochemical properties of the synthesized catalysts were analyzed by XRD, Raman, BET, BJH, XPS, NH3- and CO2-TPD, and H2-TPR techniques. The XRD and BET surface area results indicated that addition of Ce to Cu/Mg sample remarkably inhibits the crystal growth of CuO and improves the specific surface area. More number of oxygen vacancy defects were found in the Cu/Ce3/Mg sample, as evidenced from Raman studies. The reducible nature of the Cu/Mg sample was significantly enhanced after the Ce-incorporation. The NH3- and CO2-TPD results show that the acid–base properties of the Ce-promoted Cu/Mg samples are highly dependent on the Ce-loading. Among the synthesized samples, the Cu/Ce3/Mg sample exhibited higher concentration and superior strength of acidic sites. The achieved activity order of various catalysts for glycerol hydrogenolysis is Cu/Mg

The development of promising solid acid catalysts alternative to hazardous liquid acids is essential towards a sustainable chemical industry. This work reports the synthesis of nanostructured CeO2–MoO3/SiO2 and CeO2–WO3/SiO2 solid acids, along with CeO2–MoO3, CeO2–WO3 and CeO2 for continuous-flow oxidative coupling of benzylamine using O2 as a green oxidant. A systematic physicochemical characterization has been undertaken using XRD, Raman, N2 adsorption–desorption, TEM, NH3-TPD, and XPS techniques. It was found that the dispersion of CeO2–MoO3 and CeO2–WO3 species on the SiO2 support leads to remarkable structural and acidic properties, due to the synergetic effect of the respective components. TEM analysis reveals the presence of highly dispersed WO3 (0.8–1.2 nm) and MoO3 (0.8–1 nm) nanoparticles in the synthesized catalysts. Among the various catalysts developed, the CeO2–MoO3/SiO2 sample exhibited higher BET surface area (248 m2 g−1), abundant oxygen vacancy defects, and large amounts of strong acidic sites. Owing to improved properties, the CeO2–MoO3/SiO2 solid-acid showed a superior catalytic performance in the continuous-flow oxidative coupling of benzylamine: the obtained benzylamine conversions for 1 h are ∼11.8, 55, 70, 76, and 96%, respectively, for CeO2, CeO2–WO3, CeO2–WO3/SiO2, CeO2–MoO3, and CeO2–MoO3/SiO2 catalysts. Importantly, the CeO2–MoO3/SiO2 solid acid exhibited a remarkable steady performance in terms of benzylamine conversion (∼88–96%) and selectivity of N-benzylbenzaldimine product (∼96–97.8%) up to 6 h. The outstanding catalytic performance of CeO2–MoO3/SiO2 solid acid coupled with the application of continuous-flow synthesis, economical benefits of the respective oxides, and eco-friendly oxidant is expected to bring new opportunities in the design of industrially-favourable chemical processes.

Surface active sites such as oxygen vacancies, Ce3+ ions, and unsaturated coordinated sites on nano ceria (CeO2) are significant in catalytic oxidation reactions. The recent development in nanoengineered CeO2 made a pathway to extend its use in various catalytic applications. In this study, transition metals (Mn2+, Ni2+, and Co2+) doped CeO2 nanorods (NRs) were prepared by hydrothermal method and tested towards CO oxidation. Furthermore, the samples were characterized by various physicochemical techniques, namely, TEM and HR-TEM, SEM-EDX, XRD, ICP-OES, BET surface area, Raman spectroscopy, XPS, and H2-TPR. The results demonstrated that the incorporation of dopants greatly enhances the surface defective sites (Ce3+ ions and a high degree of surface roughness) and redox properties of CeO2 NRs and thereby improved catalytic activity. Especially, the Co–CeO2 NR catalyst exhibited better CO conversion (T50 ∼ 145 °C) when compared to pure CeO2 NR (T50 ∼ 312 °C).

In this work, the influence of trivalent rare-earth dopants (Sm and La) on the structure-activity properties of CeO2 was thoroughly studied for diesel soot oxidation. For this, an optimized 40% of Sm and La was incorporated into the CeO2 using a facile coprecipitation method from ultra-high dilute aqueous solutions. A systematic physicochemical characterization was carried out using X-ray diffraction (XRD), transmission electron microscopy (TEM), Brumauer-Emmett-teller method (BET) surface area, X-ray photoelectron spectroscopy (XPS), Raman, and H2-temperature programmed reduction (TPR) techniques. The soot oxidation efficiency of the catalysts was investigated using a thermogravimetric method. The XRD results suggested the formation of nanocrystalline single phase CeO2-Sm2O3 and CeO2-La2O3 solid solutions. The Sm- and La-doped CeO2 materials exhibited smaller crystallite size and higher BET surface area compared with the pure CeO2. Owing to the difference in the oxidation states of the dopants (Sm3+ and La3+) and the Ce4+, a number of oxygen vacancies were generated in CeO2-Sm2O3 and CeO2-La2O3 samples. The H2-TPR studies evidenced the improved reducible nature of the CeO2-Sm2O3 and CeO2-La2O3 samples compared with the CeO2. It was found that the addition of Sm and La to the CeO2 outstandingly enhanced its catalytic efficiency for the oxidation of diesel soot. The observed 50% soot conversion temperatures for the CeO2-Sm2O3, CeO2-La2O3 and CeO2 were ∼790, 843 and 864 K (loose contact), respectively, and similar activity order was also found under the tight contact condition. The high soot oxidation efficacy of the CeO2-Sm2O3 sample was attributed to numerous catalytically favourable properties, like smaller crystallite size, larger surface area, abundant oxygen vacancies, and superior reducible nature.

This work demonstrates that MoOx/CeO2–ZrO2 solid acid acts as a promising catalyst in the solvent-free oxidative-coupling of benzylamine into dibenzylimine with O2 as the oxidant. The benzylamine conversions were found to be ~27, 51, 74, and 99 % for CeO2, CeO2–ZrO2, MoOx/CeO2, and MoOx/CeO2–ZrO2 catalysts, respectively. The MoOx/CeO2–ZrO2 catalyst also efficiently converts various substituted- and secondary-benzylamines under solvent-free conditions with O2 resulting in moderate to excellent yields. Remarkably, a high selectivity of ~99.6–99.9 % towards the dibenzylimine product was found for all reaction conditions. The outstanding performance of MoOx/CeO2–ZrO2 catalyst was attributed to high specific surface area, improved structural defects, and superior acid properties. The MoOx/CeO2–ZrO2 catalyst show an outstanding performance in the oxidation of benzylamine and its derivatives, which is attributed to abundant acidic sites, large number of oxygen vacancies, and superior BET surface area.

This work presents the synthesis and characterization of alumina supported ceria–manganese solid solutions (Ce–Mn/Al), which were prepared by a deposition coprecipitation method followed by calcination at different temperatures from 773 to 1073 K. The physicochemical properties of the synthesized samples were deeply investigated by various characterization techniques, namely, XRD, ICP-OES, BET surface area, TEM-HRTEM, Raman, XPS, and H2-TPR. The catalytic activity was evaluated for CO oxidation. BET surface area measurements revealed that synthesized samples exhibit reasonably high specific surface area. XRD and Raman results confirmed that the present Ce–Mn/Al samples are single-phase solid solutions with good structural homogeneity and high thermal stability up to 1073 K. TEM analyses showed that the particle sizes of Ce–Mn/Al samples are in the range of ∼5–14 nm. XPS analysis revealed that Ce is in the form of Ce4+ and Ce3+, and Mn existed in the form of Mn4+, Mn3+, and Mn2+ on the surface of the samples. The solid solution particles in the nanosize form are well distributed over the support surface. As a result of solid solution formation and high dispersion over the support, the Ce–Mn/Al samples exhibited better redox behaviour. The CO oxidation results revealed that the Ce–Mn/Al samples show an excellent CO oxidation performance compared with alumina supported undoped CeO2 (Ce/Al) and MnOx (Mn/Al) samples. Among various samples, the Ce–Mn/Al calcined at 773 K showed outstanding CO activity with T50 = ∼340 K. The enhanced catalytic activity was mainly attributed to high surface area, large amount of oxygen vacancies, and excellent redox behaviour. The metal–support interaction also seems to play a decisive role in their high catalytic activity by stabilizing the Ce–Mn–O dispersion.

In this work, nanosized Ce0.7M0.3O2−δ (M = Mn, Fe, Co) solid solutions were prepared by a facile coprecipitation method and evaluated for CO oxidation. The physicochemical properties of the synthesized samples were investigated by various characterization techniques, namely, XRD, ICP-OES, BET surface area, SEM-EDX, TEM and HRTEM, Raman, XPS, and H2-TPR. XRD studies confirmed the formation of nanocrystalline single phase Ce0.7M0.3O2−δ solid solutions. ICP-OES analysis confirmed actual amount of metal loadings in the respective catalysts. The BET surface area of Ce0.7M0.3O2−δ samples significantly enhanced after the incorporation of dopants. TEM studies confirmed nanosized nature of the samples and the average particle sizes of Ce0.7M0.3O2−δ were found to be in the range of ∼8–16 nm. Raman studies indicated that the incorporation of dopant ions into the CeO2 lattice promote the formation of more oxygen vacancies. The existence of oxygen vacancies and different oxidation states (Ce3+/Ce4+ and Mn2+/Mn3+, Fe2+/ Fe3+, and Co2+/Co3+) in the doped CeO2 samples were further confirmed from XPS investigation. TPR measurements revealed an enhanced reducibility of ceria after the incorporation of dopants. The catalytic activity results indicated that the doped CeO2 samples show excellent CO oxidation activity and the order of activity was found to be Ce0.7Mn0.3O2−δ > Ce0.7Fe0.3O2−δ > Ce0.7Co0.3O2−δ > CeO2. The superior CO oxidation performance of CeO2-MnOx has been attributed to a unique Ce-Mn synergistic interaction, which facilitates materials with promoted redox properties and improved oxidation activity.

This work attempts to gain information about the role of trivalent and tetravalent dopants on the structural and catalytic properties of ceria (CeO2). In this study, we have prepared Zr4+, La3+, and Eu3+ doped ceria (CZ, CL, and CE) by coprecipitation method and calcined at 773 K. The physicochemical characterization was achieved by using various techniques, namely, X-ray powder diffraction (XRD), Brunauer-Emmett-Teller (BET) surface area, high resolution transmission electron microscopy (HRTEM), Raman spectroscopy, temperature programmed reduction (TPR), X-ray photoelectron spectroscopy (XPS), and electron spin resonance (ESR) spectroscopy. The catalytic efficiency for soot oxidation was evaluated by thermogravimetric (TG) method and compared with undoped CeO2. Doped CeO2 catalysts decreased the soot oxidation temperature by more than 158 K compared to pure ceria. This is ascribed to mutual interaction and synergistic effect between the dopant species and the ceria. Among the synthesized nanocatalysts, the CE sample exhibited better performance. The observed better activity of CE was attributed to the presence of more number of oxygen vacancies, a high specific surface area, and easy reducibility as confirmed from Raman, BET surface area, and TPR measurements, respectively.

The development of noble-metal-free catalysts is currently a topic of paramount research investigation in the chemical industry. In this work, a promising CeO2–MoO3/SiO2 catalyst was synthesized for the oxidation of a wide variety of benzylamines with O2 as the oxidant under solvent-free conditions. For comparison, the efficiency of CeO2 and CeO2–MoO3 catalysts were also studied for the oxidation of benzylamine under identical conditions. The physicochemical properties of the catalysts were thoroughly analysed using X-ray diffraction, Raman spectroscopy, Barrett–Joyner–Halenda pore size distribution, Brunauer–Emmet–Teller (BET) surface area, Fourier-transform infrared spectroscopy, ammonia-temperature programmed desorption (NH3-TPD), and X-ray photoelectron spectroscopy techniques. Characterization studies revealed that the CeO2–MoO3/SiO2 catalyst shows favourable structural, textural and acidic properties, which are due to strong interaction between the Ce–Mo mixed oxide and the SiO2. In particular, the CeO2–MoO3/SiO2 sample exhibits smaller crystallite size and highest BET surface area compared with the CeO2–MoO3 and bare CeO2. Raman analysis revealed that the CeO2–MoO3/SiO2 sample exhibits greater number of oxygen vacancy defects. The NH3-TPD studies indicated that the CeO2–MoO3/SiO2 sample has large amount of acidic sites. Owing to the beneficial properties, the CeO2–MoO3/SiO2 sample exhibited an outstanding catalytic performance for the aerobic oxidation of various benzylamines. The achieved benzylamine conversions are ~16, 65 and 98 %, respectively, for CeO2, CeO2–MoO3 and CeO2–MoO3/SiO2 samples. Despite the nature of the catalyst used and the reaction conditions employed, almost ~100 % selectivity for the dibenzylimine product was found in the present study. Remarkably, the CeO2–MoO3/SiO2 catalyst can be repeatedly used up to 5 cycles without any considerable variation in the benzylamine conversion and imine product selectivity. The CeO2–MoO3/SiO2 catalyst showed an outstanding efficiency in the oxidation of benzylamine, which is attributed to abundant acidic sites, large number of oxygen vacancies, and superior BET surface area.

Nanosized CeO2-MnOx mixed oxides with different Ce/Mn ratios were prepared by a citric acid-assisted sol-gel method. The effect of the MnOx content on structural, redox, and surface properties of the CeO2-MnOx was investigated by various techniques, namely, BET surface area, SEM, XRD, ICP-OES, Raman and FT-IR spectroscopy, H2-TPR, and XPS. Catalytic activity was evaluated with soot-catalyst mixture under tight contact conditions. BET surface area analysis indicated that Mn doping favors an enhancement in the surface area of pure CeO2. Raman active peaks for both pure CeO2 and CeO2-MnOx mixed oxides were determined at ca. 460 cm-1. The observed Raman shift can also be assigned to Raman active modes of CeO2 that are shifted from the original position due to different Mn doping. Formation of Ce1-xMnxO2-δ solid solutions was further confirmed by XRD and FT-IR analysis. H2-TPR results demonstrate that Ce1-xMnxO2-δ solid solutions significantly improved the redox property over the pure CeO2 or MnOx. XPS analysis reveal that Ce is in the form of Ce4+ and Ce3+, and Mn existed in the form of Mn4+, Mn3+, and Mn2+ on the surface of the samples. Catalytic activity results indicate that the oxidation temperature of soot can be significantly reduced by CeO2-MnOx mixed oxides, which render higher Ce3+ concentration and more surface oxygen vacancies compared with pure CeO2. Particularly, the Ce0.7Mn0.3O2-δ sample exhibited highest activity (a shift of T50 by ca. 122 K) compared to pure ceria.

Y-doped ceria–zirconia (Ce0.8Zr0.12Y0.08O2−δ, CZY) and ceria–lanthana (Ce0.8La0.12Y0.08O2−δ, CLY) ternary oxide solid solutions were synthesized by a facile coprecipitation method. Structural, textural, redox, and morphological properties of the synthesized samples were investigated by means of X-ray diffraction (XRD), inductively coupled plasma-optical emission spectroscopy (ICP–OES), Raman spectroscopy (RS), UV–visible diffuse reflectance spectroscopy (UV–vis DRS), X-ray photoelectron spectroscopy (XPS), temperature-programmed reduction by hydrogen (H2-TPR), high resolution transmission electron microscopy (HRTEM), and Brunauer–Emmett–Teller surface area (BET SA) techniques. The formation of ternary oxide solid solutions was confirmed from XRD, RS, and UV–vis DRS results. ICP–OES analysis confirmed the elemental composition in the ternary oxide solid solutions. HRTEM images revealed irregular morphology of the samples. RS, UV–vis DRS, and XPS results indicated enhanced oxygen vacancies in the Y doped samples. H2-TPR profiles confirmed a facile reduction of CZY and CLY samples at lower temperatures. BET analysis revealed an enhanced surface area for CZY and CLY samples than the respective CZ and CL undoped mixed oxides. All these factors contributed to a better CO and soot oxidation performance of CZY and CLY samples. Particularly, the CLY sample exhibited highest catalytic activity among the various samples investigated.

Ceria (CeO2) is a well-known material for various industrial applications due to its unique redox properties. Such properties, dominated by structural defects that are primarily oxygen vacancies associated with the Ce3+/Ce4+ redox couple, can be easily modulated and optimized by different approaches. In this paper, nanosized Mn and Fe codoped CeO2 solid solutions, Ce0.7−xMn0.3FexO2−δ (x = 0.05–0.2), were prepared by a simple coprecipitation method and tested towards elemental mercury (Hg0) oxidation and adsorption. The obtained solid solutions were characterized in detail at the structural and electronic level by various techniques, namely, XRD, ICP-OES, BET surface area, TEM, Raman, H2-TPR, and XPS. The XRD results suggest that the Mn and/or Fe dopant cations are effectively incorporated into the CeO2 lattice. BET surface area results suggest that the addition of Mn and/or Fe dopants to CeO2 significantly reduces its crystallite size and thereby improves the surface area. Raman, H2-TPR, and XPS results reveal that the Mn and/or Fe dopant cations in the ceria lattice increased the concentration of structural oxygen vacancies and the reducibility of the redox pair Ce4+/Ce3+. The Hg0 oxidation and adsorption studies indicate that Ce0.7−xMn0.3FexO2−δ solid solutions exhibited the highest activity compared to pure CeO2. In particular, the Ce0.5Mn0.3Fe0.2O2−δ (CMF20) solid solution shows an Hg0 oxidation efficiency (Eoxi) of 86.5%. It was found that the doping of both Mn and Fe led to lattice distortion and restrained growth of CeO2, resulting in synergistic increase in oxygen vacancies and catalytic activity.

Noble metal-free nanostructured Ce 0.7 Mn 0.3 O 2−δ (CM) solid solutions were prepared by a simple, facile, and high yielding coprecipitation method from aqueous solutions of cerium and manganese nitrates. The influence of calcination temperature from 773 to 1073 K on the structural features and catalytic behaviour of the CM solid solutions has been thoroughly investigated. The synthesized materials were characterized using XRD, ICP-OES, BET surface area, TEM and HRTEM, UV–vis DRS, Raman, XPS, EPR, and H 2 -TPR techniques. The XRD results indicated that the samples calcined at various temperatures from 773 to 973 K did not show any diffraction peaks corresponding to manganese oxides and thereby ensured the formation of Ce 0.7 Mn 0.3 O 2−δ solid solution. However, the diffraction peak corresponding to Mn 2 O 3 was clearly observed at 1073 K due to the occurrence of phase segregation between Mn–oxide and ceria. The TEM and HRTEM observations showed the nanocrystalline nature of the solid solutions with a particle size in the range of ∼7–20 nm. The doping of Mn into the ceria lattice increased the concentration of structural oxygen vacancies, which are beneficial for oxidation reaction as revealed by UV–vis DRS and Raman results. XPS analysis confirmed that Ce and Mn exist in +4 or +3 and +3 or +2 oxidation states, respectively on the surface of the samples. The EPR studies showed the presence of isolated Mn 2+ and Mn 3+ species in different structural locations such as ceria-lattice defect sites, framework of Ce 4+ locations, interstitial locations, and at the surface of the ceria. H 2 -TPR measurements showed a pronounced enhancement in the reduction of ceria by manganese doping. Among the various catalysts examined, the CM catalyst calcined at 773 K exhibited superior CO oxidation activity at much lower temperature with T 50 = 390 K and 100% CO conversion at ∼470 K in comparison to pure ceria and MnO x . The observed remarkable enhancement in the reactivity for CO oxidation at lower temperatures has been attributed to a highly dispersed state of Mn 2+ /Mn 3+ in the ceria matrix, facile redox behaviour, and a synergistic Mn–Ce interaction.

Nanostructured Ce 0.7 Mn 0.3 O 2− δ (CM) and Ce 0.7 Fe 0.3 O 2− δ (CF) solid solutions were prepared by a facile coprecipitation method and evaluated for soot oxidation. The structural, morphological, and surface properties were investigated by various techniques, namely, XRD, ICP-OES, BET surface area, SEM-EDX, TEM-HRTEM, UV–vis DRS, Raman, FT-IR, XPS, H 2 -TPR, and TGA-DTA. XRD and TEM results confirmed formation of nanocrystalline solid solutions with the incorporated Mn and/or Fe cations in the ceria lattice. SEM studies ensured nanoparticle nature of Ce–Mn–O and Ce–Fe–O solid solutions with homogeneous distribution. ICP-OES and EDX analysis confirmed actual amount of metal loadings in the respective catalysts. UV–vis DRS and Raman results revealed the formation of more oxygen vacancies, which lead to the creation of more surface active species (Ce 4+ /Ce 3+ and O*). XPS results revealed that the doping of Mn and/or Fe into the ceria lattice makes some Ce 4+ transferred into Ce 3+ in order to maintain the electrical neutrality, thereby facilitate the reduction of Ce 4+ → Ce 3+ and the formation of oxygen vacancies. TPR results showed that the mixed oxides reduce at lower temperatures than pure ceria. This observation confirmed that there is a synergetic interaction between Ce–O and M–O (M = Mn, Fe). The catalytic activity of CM and CF samples towards soot oxidation has been evaluated under tight contact conditions and compared with the well-established CeO 2 –ZrO 2 (CZ) catalyst. Among the investigated catalysts, the Mn and/or Fe doped ceria solid solutions showed improved catalytic activity. The order of activity is as follows: CM > CF > CZ > C. Further, the CM and CF catalysts were found to be thermally quite stable compared to pure ceria. In particular, the CM sample exhibited superior catalytic activity ( T 50 = ∼665 K) and thermal stability towards soot oxidation.

The aim of the present investigation was to ascertain the role of Al2O3, SiO2, and TiO2 supports in modulating the catalytic performance of ceria-based solid solutions. In this study, we prepared nanosized Ce-Gd/Al2O3, Ce-Gd/SiO2, and Ce-Gd/TiO2 catalysts by a deposition coprecipitation method and evaluated for soot oxidation. The synthesized catalysts were calcined at two different temperatures to assess their thermal stability and extensively characterized by various techniques, namely, XRD, Raman, BET surface area, TEM, H2-TPR, and UV–vis DRS. XRD and TEM results indicate that Ce-Gd-oxide nanoparticles are in highly dispersed form on the surface of the supports. Raman results show a prominent sharp peak and a broad peak corresponding to the F2g mode of ceria and the presence of oxygen vacancies, respectively. The presence of a significant number of oxygen vacancies in all samples is also confirmed from UV–vis DRS measurements. The H2-TPR results suggest that Gd-doping facilitates the reduction of the materials and decreases the onset temperature of reduction. Among the prepared samples, Ce-Gd/TiO2 catalyst exhibited the highest activity, suggesting the existence of strong interfacial metal support interaction between the active metal oxide and the support.

Owing to significant environmental and economical concerns of fossil fuels, the search for alternative renewable fuels has received a explicit research interest in recent times. In this work, we prepared efficient solid acid catalysts, namely, SnO2, WO3/SnO2, MoO3/SnO2, and SO42–/SnO2 for the production of bioadditive fuels from bioglycerol under ecofriendly conditions. The synthesized samples were meticulously analyzed by means of X-ray diffraction, X-ray photoelectron spectroscopy, Brunauer–Emmett–Teller (BET) surface area, Barrett–Joyner–Halenda pore size distribution, Fourier transform infrared (FT-IR) spectroscopy, FT-IR analysis of adsorbed pyridine, NH3-temperature programmed desorption, and other techniques. The catalytic efficiency of these solid acids was investigated for esterification and acetalization of glycerol with acetic acid and benzaldehyde, respectively. Characterization studies revealed that the textural properties (crystallite size and BET surface area) of pristine SnO2 were outstand...

Ceria is an important rare earth metal oxide for numerous catalytic applications. In the present work, a combined study of structural characterization and catalytic activity of nanocrystalline Ce–Gd–O mixed oxides was thoroughly investigated towards CO oxidation. The Ce–Gd mixed oxides with different Gd-doping amounts (10 and 20 mol% Gd with respect to Ce) were prepared by means of an economical and simple coprecipitation method with aqueous NH3 solution as the precipitant. The resulting samples were treated at different calcination temperatures to evaluate their structural homogeneity and thermal stability. An extensive physicochemical characterization was done by means of XRD, Raman, TEM, BET analysis, H2-TPR, XPS, and UV–Vis DRS techniques. XRD studies revealed the formation of nanocrystalline single phase Ce–Gd solid solutions. Raman studies further disclosed the formation of Ce–Gd solid solutions associated with deformed F2g band and additional bands pertaining to oxygen vacancy defects. The Gd-doping remarkably reduced the CeO2 crystallite size, which is in nanoscale range as evidenced by TEM images. The BET surface area and oxygen vacancy defects of CeO2 were significantly enhanced after Gd3+ incorporation. The ability of CeO2 to store and release of oxygen (oxygen storage capacity, OSC) is markedly improved 3 and 4 times for Ce0.9Gd0.1O2−δ and Ce0.8Gd0.2O2−δ samples, respectively. Among the investigated catalysts, the Ce0.8Gd0.2O2−δ sample calcined at 773 K showed better catalytic activity due to smaller crystallite size, higher BET surface area, enhanced reducible nature, and superior OSC. It is found that the catalytic performance of the Ce–Gd sample strongly depends on the Gd-loading and calcination temperature.

The present investigation was undertaken to know the influence of different dopants on the physicochemical properties and catalytic behavior of nano-Au/CeO2 catalyst for CO oxidation. Accordingly, various metal ions namely, Fe3+, La3+ and Zr4+ were incorporated into the ceria lattice by a facile coprecipitation approach using ultra-high dilute aqueous solutions. An anion adsorption method was used to prepare the Au/doped-CeO2 catalysts in the absence of any base, reducing and protective agents. The physicochemical characterization was performed by XRD, BET surface area, ICP-AES, TG-DTA, FT-IR, TEM, UV–vis DRS, Raman, XPS and TPD techniques. Doped CeO2 exhibited smaller crystallite size, higher BET surface area and larger amount of oxygen vacancies than the pure CeO2. These remarkable properties showed a beneficial effect toward gold particle size as confirmed by XRD and TEM studies. XPS results revealed that Au is present in the metallic state and Ce in both +3 and +4 oxidation states. Incorporation of Zr into the Au/CeO2 resulted in high CO oxidation activity attributed to the presence of more Ce3+ ions and oxygen vacancies. In contrast, the La-incorporation caused an opposite effect due to the presence of carbonate species on the surface of Au/CeO2–La2O3 catalyst, which blocked the active sites essential for CO oxidation. It was shown that accumulation of carbonate species strongly depends on the acid–base properties of the supports. The catalytic performance of Au catalysts is highly dependent on the nature of the support.

The development of an efficient doped CeO2 material is an active area of intense research in environmental catalysis. In this study, we prepared highly promising Ce–Fe nano-oxides by a facile coprecipitation method and their catalytic performance was studied for CO oxidation. Various characterization techniques, namely, XRD, BET surface area, pore size distribution, Raman, FT-IR, TEM, H2-TPR, and XPS were used to correlate the structure–activity properties of the Ce–Fe catalysts. XRD results confirmed the formation of nanocrystalline Ce1−xFexO2−δ solid solution due to doping of Fe3+ into the CeO2 lattice. The BET surface area and lattice strain of CeO2 are significantly improved after the Fe-incorporation. Raman studies revealed the presence of abundant oxygen vacancies in the Ce–Fe sample. TEM images evidenced the formation of nanosized particles with an average diameter of 5–20 nm in the prepared samples. Interestingly, despite the thermal treatment at higher temperatures, the Ce–Fe sample showed remarkable reducible nature compared to pure CeO2 ascribed to existence of strong interaction between the CeO2 and FeOx. The synthesized Ce–Fe nano-oxides calcined at 773 K exhibited excellent CO oxidation performance (T50 = 480 K), with a huge difference of 131 K with respect to pure CeO2 (T50 = 611 K). The outstanding activity of the Ce–Fe catalyst is mainly due to smaller crystallite size, facile reduction, enhanced lattice strain, and ample oxygen vacancies. The superior CO oxidation performance of Ce–Fe nano-oxides with the advantages of low cost and easy availability could make them potential alternatives to noble metal-based oxidation catalysts.

The design of promising heterogeneous catalysts is an urgent task for protecting the environment from automotive exhaust pollutants. In this work, the catalytic efficiency of nanosized Ce–Sm and Ce–Sm/γ-Al2O3 samples synthesized using economical coprecipitation and deposition coprecipitation methods, respectively, was investigated for diesel soot oxidation. The physicochemical properties of the synthesized materials were systematically analyzed by means of XRD, BET surface area, Raman spectroscopy, TG-DTA, FT-IR spectroscopy, HRTEM, ICP-OES, XPS, and UV-vis DRS techniques. XRD studies confirmed the formation of nanocrystalline single-phase Ce–Sm oxide solid solutions. HRTEM images showed the presence of small-sized nanocrystals (∼4–15 nm) in the synthesized samples. The Ce–Sm/γ-Al2O3 sample exhibited remarkable thermal stability compared with the Ce–Sm oxide and CeO2 samples, as evidenced by an insignificant variation in the crystallite size and BET surface area with high temperature thermal treatments. Owing to the disparity in the oxidation state of Sm3+ and Ce4+, abundant oxygen vacancies were formed in both the Ce–Sm and Ce–Sm/γ-Al2O3 samples. Interestingly, the oxygen vacancy concentration substantially decreased with increased calcination temperature, attributed to the high level of order of the samples. The catalytic activity results revealed that both the Ce–Sm and Ce–Sm/γ-Al2O3 samples show excellent soot oxidation performance compared with pristine CeO2 due to the presence of abundant oxygen vacancies and superior BET surface area. A 50% soot conversion was achieved at ∼690, 697 and 835 K with the Ce–Sm, Ce–Sm/γ-Al2O3 and CeO2 samples calcined at 773 K, respectively. It was found that the soot oxidation efficiency of the Ce–Sm and Ce–Sm/γ-Al2O3 samples strongly depends on the calcination temperature. Despite its trivial activity difference with respect to the Ce–Sm sample, the outstanding thermal stability of the Ce–Sm/γ-Al2O3 sample is vital in view of the practical working conditions of diesel engines.

A nanosized Ce–Sm/SiO2 catalyst was found to show an outstanding performance in the oxidation of benzylamines into valuable dibenzylimine products with almost 100% selectivity with O2 as the green oxidant under solvent-free conditions, which is attributed to the presence of abundant strong acidic sites, enhanced oxygen vacancy concentration, and superior BET surface area.

In this work, we systematically investigated the structure–activity performance of nanosized Au/CeO2 and Au/Ce0.9Fe0.1O2−δ catalysts, along with nanocrystalline CeO2 and Ce0.9Fe0.1O2−δ supports, for the oxidation of carbon monoxide and benzylamine. An extensive physicochemical characterization was undertaken using XRD, BET surface area, BJH analysis, TG-DTA, XPS, TEM, Raman, AAS and CHN analyses. XRD studies confirmed the formation of smaller sized Ce0.9Fe0.1O2−δ nanocrystallites due to the incorporation of Fe3+ ions into the CeO2 lattice. Interestingly, Raman analysis revealed that the addition of Au remarkably improves the structural properties of the supports, evidenced by F2g peak shift and peak broadening, a significant observation in the present work. TEM images revealed the formation of smaller Au particles for Au/Ce0.9Fe0.1O2−δ (∼3.6 nm) compared with Au/CeO2 (∼5.3 nm), attributed to ample oxygen vacancies present on the Ce0.9Fe0.1O2−δ surface. XPS studies indicated that Au and Fe are present in metallic and +3 oxidation states, respectively, whereas Ce is present in both +4 and +3 oxidation states (confirming its redox nature). Activity results showed that the incorporation of Fe outstandingly enhances the efficacy of the Au/CeO2 catalyst for both CO oxidation and benzylamine oxidation. A 50% CO conversion was achieved at ∼349 and 330 K for Au/CeO2 and Au/Ce0.9Fe0.1O2−δ catalysts, respectively. As well, the Au/Ce0.9Fe0.1O2−δ catalyst showed ∼99% benzylamine conversion with ∼100% dibenzylimine selectivity for 7 h reaction time and 403 K temperature, whereas only 81% benzylamine conversion was achieved for the Au/CeO2 sample under similar conditions. The excellent performance of the Au/Ce0.9Fe0.1O2−δ catalyst is mainly due to the existence of smaller Au particles and an improved synergetic effect between the Au and the Ce0.9Fe0.1O2−δ support. It is confirmed that the oxidation efficiency of the Au catalysts is highly dependent on the preparation method.

The present study was undertaken to develop a novel and easy practical approach for synthesis of cyclopentanone, a versatile industrial ingredient. Accordingly, ceria–zirconia based nano-oxide catalysts, namely, CexZr1−xO2 and CexZr1−xO2/M (M = SiO2 and Al2O3) were prepared and evaluated for the title reaction. The physicochemical characterization has been achieved using different techniques, namely, XRD, BET surface area, XPS, Raman, OSC, and HREM. The catalytic results revealed that CexZr1−xO2 based nano-oxides are promising heterogeneous catalysts for synthesis of cyclopentanone. Amongst, the CexZr1−xO2/Al2O3 catalyst exhibited ∼100% conversion with 75% desired cyclopentanone product selectivity owing to its favorable physicochemical characteristics.

The heterogeneous green solid acid catalyzed acetalization of glycerol with various benzaldehydes was investigated under solvent‐free conditions. The investigated catalysts namely ZrO 2 and TiO 2 –ZrO 2 , and the respective MoO 3 promoted catalysts were prepared by a facile precipitation and wet‐impregnation method, respectively. The physicochemical characteristics were achieved using X‐ray diffraction, BET surface area, ammonia–temperature programmed desorption, Raman spectroscopy and FT–infrared spectroscopy techniques. Characterization results revealed that addition of MoO x enhances the surface acidic properties of the oxide supports. The MoO x /TiO 2 –ZrO 2 catalyst exhibited a superior 74% glycerol conversion with 51% 1,3‐dioxane product selectivity. Various reaction parameters were investigated to enhance the glycerol conversion as well as product selectivity. Particularly, the reaction temperature showed a significant influence on the glycerol conversion, whereas the effect of solvents was negligible. The conversion of glycerol was considerably decreased with substituted benzaldehydes due to steric hindrance. On the other hand, a high selectivity (71%) of 1,3‐dioxane was obtained in the case of p ‐anisaldehyde. These interesting results suggest that MoO x /TiO 2 –ZrO 2 is a highly promising green solid acid catalyst for environmentally benign synthesis of bio‐additive fuels from glycerol.

Development of highly promising solid acids is one of the key technologies to meet the essential challenges of economical and environmental concerns. Thus, novel molybdenum and tungsten promoted SnO2 solid acids (wet-impregnation) and pure SnO2 (fusion method) were prepared. The synthesized catalysts were systematically analyzed using various techniques, namely, XRD, BET surface area, pore size distribution, XPS, FTIR, FTIR of adsorbed pyridine, Raman, NH3-TPD, and H2-TPR. XRD results suggested formation of nanocrystalline SnO2 solid solutions due to the incorporation of molybdenum and tungsten cations into the SnO2 lattice. All the materials exhibited smaller crystallite size, remarkable porosity, and high specific surface area. Raman measurements suggested the formation of more oxygen vacancy defects in the doped catalysts, and the TPR results confirmed facile reduction of the doped SnO2. NH3-TPD studies revealed the beneficial role of molybdenum and tungsten oxides on the acidic properties of the SnO2. FTIR studies of adsorbed pyridine showed the existence of a larger number of Bronsted acidic sites compared to Lewis acidic sites in the prepared catalysts. The resulting catalysts are found to be efficient solid acids for acetalization of glycerol with acetone, furfural, and its derivatives under solvent-free and ambient temperature conditions. Particularly, the Mo6+-doped SnO2 catalyst exhibited excellent catalytic performance in terms of both glycerol conversion and selectivity of the products. The increased presence of acidic sites and enhanced specific surface area, accompanied by notable redox properties and superior lattice defects are found to be the decisive factors for better catalytic activity of the Mo6+-doped SnO2 sample. The investigated SnO2 solid acids represent a novel class of heterogeneous catalysts useful for the transformation of glycerol to value-added products in an eco-friendly manner.

The feasibility of acetylation of glycerol with acetic acid was investigated employing CeO2–ZrO2, CeO2–Al2O3, SO42−/CeO2–ZrO2, and SO42−/CeO2–Al2O3 solid acid catalysts to synthesize monoacetin, diacetin and triacetin having interesting applications as bioadditives for petroleum fuels. Intensive physicochemical and surface characterization of the prepared catalysts were performed using XRD, BET surface area, ammonia-TPD and Raman spectroscopy techniques. Characterization results revealed that impregnated sulfate ions strongly influence the physicochemical characteristics of the investigated mixed oxide catalysts. Among various catalysts investigated, the SO42−/CeO2–ZrO2 combination catalyst exhibited superior catalytic activity under mild conditions. The effect of various parameters such as reaction temperature, molar ratio of acetic acid to glycerol, catalyst wt% and time-on-stream were studied over the SO42−/CeO2–ZrO2 catalyst to optimize the reaction conditions. Catalyst reusability was also carried out to understand its stability.

A series of TiO2–ZrO2 supported V2O5 catalysts with vanadia loadings ranging from 4 to 12 wt% were synthesized by a wet impregnation technique and subjected to various thermal treatments at temperatures ranging from 773 to 1,073 K to understand the dispersion and thermal stability of the catalysts. The prepared catalysts were characterized by X-ray powder diffraction (XRD), BET surface area, oxygen uptake, and X-ray photoelectron spectroscopy (XPS) techniques. XRD results of 773 K calcined samples conferred an amorphous nature of the mixed oxide support and a highly dispersed form of vanadium oxide. Oxygen uptake measurements supported the formation of a monolayer of vanadium oxide over the thermally stable TiO2–ZrO2 support. The O 1s, Ti 2p, Zr 3d, and V 2p core level photoelectron peaks of TiO2–ZrO2 and V2O5/TiO2–ZrO2 catalysts are sensitive to the calcination temperature. No significant changes in the oxidation states of Ti4+ and Zr4+ were noted with increasing thermal treatments. Vanadium oxide stabilized as V4+ at lower temperatures, and the presence of V5+ is observed at 1,073 K. The synthesized catalysts were evaluated for selective oxidation of o-xylene under normal atmospheric pressure in the temperature range of 600–708 K. The TiO2–ZrO2 support exhibits very less conversion of o-xylene, while 12 wt% V2O5 loaded sample exhibited a good conversion and a high product selectivity towards the desired product, phthalic anhydride.

Nanosized ceria–zirconia, ceria–hafnia and ceria–terbia solid solutions were synthesized by a modified coprecipitation method and evaluated for oxygen storage/release capacity (OSC) and CO oxidation activity. The physicochemical characteristics were investigated by various techniques namely, XRD, Raman, XPS, ISS, UV–vis DRS, TEM and BET surface area. XRD and Raman results revealed formation of Ce0.75Zr0.25O2, Ce0.8Hf0.2O2 and Ce0.8Tb0.2O2−δ solid solutions typical of fluorite like cubic structure. Variation in the lattice parameter confirmed the successful incorporation of dopant cations into the ceria lattice. XPS measurements revealed that Ce is present in both 3+ and 4+ oxidation states in all samples. UV–vis DRS studies suggested the presence of Ce3+ ← O2− charge transfer transitions attributed to oxygen defects in all the samples. ISS measurements indicated surface enrichment of cerium in ceria–hafnia solid solutions. The ceria–hafnia solid solutions exhibited a high OSC and better CO oxidation activity among the investigated samples. Systematic investigation of these materials provided valid information about the key factors that control the catalytic efficiency of the solid solutions for OSC and CO oxidation.

Acetalisation of biomass derived glycerol was performed with acetone over zirconia and promoted zirconia catalysts to synthesize solketal. The catalytic experiments were carried out at room temperature. It was observed that the promoted zirconia catalysts exhibit promising catalytic activity. The activity increased in the order of ZrO 2 x /ZrO 2 x /ZrO 2 4 2− /ZrO 2 . All catalysts exhibited an excellent selectivity of ∼97% towards solketal. The effect of different parameters, such as molar ratio of acetone to glycerol, catalyst wt.% and time-on-stream was studied over zirconia and promoted zirconia catalysts. The synthesized catalysts were characterized by XRD, BET surface area, ammonia-TPD and FT-Raman techniques. Characterization results revealed that the addition of promoters strongly influences the surface acidity of ZrO 2 and enhances the tetragonal zirconia phase.

The vapour phase selective conversion of glycerol to acetol at normal atmospheric pressure in a fixed-bed micro reactor was investigated over SO4 2� and WOx promoted ZrO2 and M-ZrO2 (M = Al2O3 or TiO2) solid acid catalysts. The investigated sulfate and tungstate ion promoted zirconia-based catalysts were prepared by both coprecipitation and impregnation methods and calcined at 923 K. The synthesized catalysts were characterized by means of X-ray powder diffraction, X-ray photoelectron spectroscopy, BET surface area and ammonia temperature-programmed desorption methods. Characterization results suggest that SO4 2� promoter strongly influences the physicochemical properties of the support oxides than WOx. However, the WOx promoted catalysts exhibited better catalytic activity than SO4 2� promoted catalysts. Among various catalysts investigated, the WOx/Al2O3-ZrO2 catalyst exhibited stable catalytic activity with the highest glycerol conversion of 99% and acetol selectivity of 74%.

Nanosized CexM1−xO2−δ (M = Zr, Hf, Tb and Pr) solid solutions were prepared by a modified coprecipitation method and thermally treated at different temperatures from 773 to 1073 K in order to ascertain the thermal behavior. The structural and textural properties of the synthesized samples were investigated by means of X-ray diffraction (XRD), high resolution transmission electron microscopy (HRTEM), BET surface area, X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy (RS) techniques. The catalytic efficiency has been performed towards oxygen storage/release capacity (OSC) and CO oxidation activity. The characterization results indicated that the obtained solid solutions exhibit defective cubic fluorite structure. The solid solutions of ceria–hafnia, ceria–terbia and ceria–praseodymium exhibited good thermal stability up to 1073 K. A new Ce0.6Zr0.4O2 phase along with Ce0.75Zr0.25O2 was observed in the case of ceria–zirconia solid solution due to more Zr4+ incorporation in the ceria lattice at higher calcination temperatures. The reducibility of ceria has been increased upon doping with Zr4+, Hf4+, Tb3+/4+ and Pr3+/4+ cations. This enhancement is more in case of Hf4+ doped ceria. Among various solid solutions investigated, the ceria–hafnia combination exhibited better OSC and CO oxidation activity. The high efficiency of Ce–Hf solid solution was correlated with its superior bulk oxygen mobility and other physicochemical characteristics.

The influence of ceria on structural and catalytic properties of TiO2–ZrO2 mixed oxide was investigated for oxidative dehydrogenation (ODH) of p-diethylbenzene (DEB) to p-divinylbenzene (DVB) utilizing CO2 as soft oxidant. The investigated catalysts were synthesized by coprecipitation and impregnation methods involving microwave treatment. Catalyst characterization was achieved using X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), BET surface area and temperature programmed desorption/oxidation (TPD/TPO) methods. The XRD and TEM results revealed that the prepared samples are in nanocrystalline form with 10–20 nm size. The presence of acid–base sites and their distribution was examined by NH3 and CO2 TPD measurements. The ceria promoted sample exhibited more number of acid sites. The TPO measurements revealed that CO2 dissociates over the reduced surface of the catalysts. Among various catalysts investigated, the microwave treated CeO2/TiO2–ZrO2 sample exhibited better conversion and a high product selectivity. The time-on-stream studies revealed that ceria promoted TiO2–ZrO2 catalysts exhibit higher stability for ODH of DEB.

Acetylation of glycerol with acetic acid was investigated over ZrO2, TiO2–ZrO2, WOx/TiO2–ZrO2 and MoOx/TiO2–ZrO2 solid acid catalysts to synthesize monoacetin, diacetin and triacetin having interesting applications as bio-additives for petroleum fuels. The prepared catalysts were characterized by means of XRD, BET surface area, ammonia-TPD and FT-Raman techniques. The effect of various parameters such as reaction temperature, molar ratio of acetic acid to glycerol, catalyst wt.% and time-on-stream were studied to optimize the reaction conditions. Among various catalysts investigated, the MoOx/TiO2–ZrO2 combination exhibited highest conversion (~ 100%) with best product selectivity, and a high time-on-stream stability.

In this investigation, CuO/CeO2–MxOy (MxOy = Al2O3, ZrO2 and SiO2) nanocomposite oxide catalysts were prepared by deposition-precipitation and wet impregnation methods, and evaluated for CO oxidation. Catalysts were characterized by XRD, TEM, UV–vis DRS, BET surface area and H2-TPR techniques. The synthesized catalysts exhibited high specific surface area, and uniform particle size distribution over the supports. The nanocrystalline texture of mixed metal oxides is clearly evidenced by TEM analysis. TPR and XRD results revealed synergetic interactions between copper oxide and ceria. Among various catalysts investigated, the CuO/CeO2–Al2O3 combination exhibited excellent CO oxidation activity with T1/2 = 374 K and 100% CO conversion at below 420 K.

Catalytic activity of CoO, NiO, CuO−CoO, and CuO−NiO nanocrystalline mono- and bimetallic catalysts over a thermally stable and high surface area ceria−alumina mixed oxide support was evaluated for oxidation of carbon monoxide at normal atmospheric pressure and lower temperatures. The content of Co or Ni in the respective monometallic catalysts was 10 wt % and the Cu-promoted samples contained 5 wt % each. These catalysts were prepared by a wet impregnation procedure and the CeO2−Al2O3 support was obtained by a deposition precipitation method. The synthesized catalysts were characterized by BET surface area, X-ray diffraction (XRD), energy dispersive X-ray microanalysis (EDX), temperature-programmed reduction (TPR), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS) techniques. XRD patterns of 773 K calcined samples revealed the presence of metal oxide phases, namely, CeO2, CuO, NiO, and Co3O4 in the respective catalysts. However, after calcination at 1073 K, the XRD lines ...

Ceria−praseodymia (CP) nanocrystalline solid solutions were prepared by a coprecipitation method and calcined at various temperatures to understand the thermal effects on the physicochemical properties of the nano-oxides. The structural and redox properties of the synthesized samples were investigated by means of X-ray diffraction (XRD), transmission electron microscopy (TEM-HREM), BET surface area (SBET), Raman spectroscopy (RS), X-ray photoelectron spectroscopy (XPS), UV−visible diffuse reflectance spectroscopy (UV−vis DRS), and temperature programmed reduction (TPR) techniques. The catalytic efficiency toward oxygen storage capacity (OSC) and CO oxidation activity have been investigated. The XRD results confirmed the successful incorporation of praseodymium into the ceria lattice through the formation of nanoscale face-centered cubic solid solutions. The TEM-HREM observations supported the nanocrystalline nature of the solid solutions, as indicated by XRD results. XPS results revealed the presence of c...

Titania–silica, titania–alumina, and titania–zirconia mixed oxides (1:1 molar ratio) were prepared by a microwave-induced solution combustion synthesis technique. The prepared materials were characterized by thermogravimetry/differential thermal analysis, X-ray diffraction (XRD), Raman spectroscopy, BET surface area, X-ray photoelectron spectroscopy (XPS), ultraviolet–visible diffuse reflectance spectroscopic (UV–Vis DRS), and Fourier transform infrared (FTIR) techniques to assess their physicochemical properties. Their photocatalytic activity for the degradation of phenol in aqueous solution under sunlight was studied. XRD and Raman studies revealed the presence of titania in the form of anatase phase in all the mixed oxides synthesized. The XRD studies further suggested that titania–zirconia contains an additional (Ti,Zr)O2 phase. UV–Vis DRS results reveal that all samples exhibit absorption maxima near visible region. FTIR results revealed the presence of Ti–O–Si linkages in the titania–silica sample, which are responsible for its higher activity in the photocatalytic degradation of phenol under sunlight.

Various CeO2–MxOy (MxOy = SiO2, TiO2, ZrO2, and Al2O3) mixed oxides were prepared by microwave induced solution combustion method and analyzed by different complimentary techniques, namely, X-ray diffraction (XRD), Raman spectroscopic (RS), UV–Vis diffuse reflectance spectroscopy (UV-DRS), X-ray photoelectron spectroscopy (XPS), thermogravimetry (TG-DTA), and BET surface area. XRD analyses revealed that CeO2–SiO2 and CeO2–TiO2 mixed oxides are in slightly amorphous form and exhibit only broad diffraction lines due to cubic fluorite structure of ceria. XRD lines due to the formation of cubic Ce0.5Zr0.5O2 were observed in the case of CeO2–ZrO2 sample. RS results suggested defective structure of the mixed oxides resulting in the formation of oxygen vacancies. The UV-DRS measurements provided valid information about Ce4+ ← O2− and Ce3+ ← O2− charge transfer transitions. XPS studies revealed the presence of cerium in both Ce3+ and Ce4+ oxidation states. The ceria–zirconia combination exhibited better oxygen storage capacity (OSC) and CO oxidation activity when compared to other samples. The significance of present synthesis method lays mostly on its simplicity, flexibility, and the easy control of different experimental factors.

In this investigation, ceria–zirconia composite oxide based monometallic (CoO/CeO2–ZrO2 and NiO/CeO2–ZrO2) and bimetallic (CuO–CoO/CeO2–ZrO2 and CuO–NiO/CeO2–ZrO2) catalysts were evaluated for soot oxidation. These catalysts were prepared by co-precipitation and impregnation methods, and were characterized by X-ray diffraction, Raman spectroscopy, temperature programmed reduction and BET surface area techniques. Characterization results reveal formation of spinel phases in various samples, and Ce1−xCuxO2 solid solution in case of CuO–CoO/CeO2–ZrO2 sample. Among various catalysts investigated, the CuO–CoO/CeO2–ZrO2 combination exhibited a high activity and nearly 100% selectivity towards CO2.

Vapour phase selective hydrogenation of acetophenone has been performed over a series of Pt/CeO2–MOx (MOx = SiO2, Al2O3, TiO2, and ZrO2) catalysts. The controlled hydrogenation was carried out in the 453–533 K temperature range at normal atmospheric pressure. The ceria-based mixed oxides were prepared through a co-precipitation or deposition-precipitation route. Platinum was deposited by a wet impregnation method. The obtained catalysts were calcined at 773 K and characterized by means of X-ray diffraction, Raman spectroscopy, BET surface area, temperature programmed reduction, temperature programmed desorption, thermogravimetry, and scanning electron microscopy. XRD analyses suggest that CeO2–SiO2 and CeO2–Al2O3 primarily consist of CeO2 nanoparticles dispersed over the amorphous silica or alumina surface. In the case of CeO2–TiO2, presence of segregated nanocrystalline CeO2 and TiO2-anatase phase were noted. Formation of cubic Ce0.75Zr0.25O2 solid solution was observed in the case of CeO2–ZrO2. No peaks pertaining to platinum could be detected from XRD profiles. Formation of zirconia rich tetragonal phase (Ce0.4Zr0.6O2) was observed in the case of Pt/CeO2–ZrO2 sample. Raman measurements revealed the fluorite structure of ceria and presence of oxygen vacancies in all samples. TPR results suggest that the presence of Pt facilitates the reduction of ceria. The catalytic performance of Pt-based catalysts was found to depend strongly on the nature of the support oxide employed. Among various catalysts investigated, the Pt/CeO2–SiO2 catalyst exhibited better product yields.

Silica-supported CeO 2 and CeO 2 –ZrO 2 nanocomposite oxides were synthesized by a novel deposition–precipitation method and subjected to thermal treatments at 773–1073 K to study their sintering behavior and oxygen storage/release capacity (OSC). The prepared catalysts were characterized using thermogravimetry, BET surface area, X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy, high-resolution transmission electron microscopy and other techniques. BET measurements indicate that CeO 2 –ZrO 2 /SiO 2 (CZS) samples possess more specific surface area and substantial resistance towards thermal sintering relative to CeO 2 /SiO 2 (CS) samples. XRD profiles reveal only the broad diffraction lines due to CeO 2 in the case of CS while CZS discloses Ce 0.75 Zr 0.25 O 2 , Ce 0.6 Zr 0.4 O 2 and Ce 0.5 Zr 0.5 O 2 phases depending on the treatment temperature. Raman measurements of both series of samples indicate the presence of oxygen vacancies, lattice defects and displacement of oxygen ions from their ideal lattice positions. XPS studies indicate the presence of cerium at the surface in both 4+ and 3+ oxidation states. The HREM results reveal well dispersed CeO 2 (∼3–4 nm) and Ce–Zr oxide particles (∼5 nm) over the amorphous SiO 2 matrix in the case of CS and CZS samples, respectively. There was no significant increase in the size of the dispersed nano-oxides even after calcination at 1073 K. Both the samples exhibit reasonably high OSC values.

Alumina-supported ceria−terbia solid solution (CeO2−TbO2/Al2O3 = 80:20:100 mol % based on oxides) has been synthesized and analyzed by means of different complementary techniques, namely, X-ray diffraction (XRD), Raman spectroscopy (RS), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), ion scattering spectroscopy (ISS), temperature programmed reduction/oxidation (TPR−TPO), UV−vis diffuse reflectance spectroscopy (UV−vis DRS), BET surface area, and thermogravimetry (TG−DTA). The primary purpose of this investigation was to understand the structural and catalytic properties of ceria−terbia solid solutions dispersed over alumina support and their thermal stability. XRD studies revealed formation of ceria−terbia solid solutions without phase segregation up to the investigated temperature range of 1073 K. No specific inactive compounds were formed between the alumina support and cerium or terbium oxides. As revealed by TEM, the sizes of the Ce−Tb oxide are in the nanometer range ...

The aza-Michael addition reactions of amines with α,β-unsaturated carbonyl compounds were efficiently carried out at room temperature under solvent-free condition employing sulfated zirconia as a reusable heterogeneous catalyst. The desired products were formed in short reaction times and in high yields. The bulk and surface properties of the synthesized catalyst was examined by X-ray powder diffraction, BET surface area, temperature programmed desorption of ammonia, scanning electron microscopy and thermogravimetric techniques. Characterization results reveal the super acidic nature of the catalyst.