Search

The Ce0.7Bi0.3O2 catalyst exhibited superior catalytic activity in comparison to other cerium and bismuth based mixed oxides for styrene oxidation with 95% conversion and 85% selectivity to styrene epoxide.

Global warming has been a serious concern worldwide. Greenhouse gases like CO2 majorly contribute to the rise in average global temperature. Attempts have been made to reduce the CO2 in the atmosphere. However, carbon capture alone was not found to be commercially viable. Various other green and cost-effective methods to convert CO2 into more useful products have been researched. CO2 methanation was found to be one such vital reaction of converting CO2 to useful fuel, like methane, using different catalysts. In this paper, this vital reaction has been reviewed comprehensively. Studies conducted with respect to materials that have proven catalysts such as Ni, synthesised by impregnation, to be the most suitable, where use of promotors (like Si and Ce) and supports (like zeolites, ceria and MOFs), high pressures, low humidity and optimum temperatures have led to increased selectivity, have been presented. The different reactors/contactors that have been used in this process at various scales, their design parameters, process conditions, performance, and limitations have been discussed which have shown the use of annular fixed bed reactors to be the most favourable. The different mechanisms proposed for the reaction, involving various intermediates, mainly carbenes and formates, and problems incurred in low temperature operation and finding of an appropriate support and promotor have been presented. Thermo-kinetic modelling studies on this reaction have also been presented and discussed. Every section has been summarized in the form of a table. The recent advances as well as future challenges and prospects of the above-said aspects of CO2 methanation have also been cited. Recent advances suggest methods of electrocatalytic reduction potentially employing Cu based compounds and perovskite oxides as catalysts, bio-electrocatalytic reduction using microbes as catalysts, and photocatalytic reduction using noble or critical metals including Ni and TiO2 as catalysts and graphene as a support, for the conversion of carbon dioxide to methane.

This investigation focuses on the manipulation of the physicochemical properties and oxygen defect concentration of europium doped CeO2 by the introduction of a second dopant (co-dopant, M). Accordingly, in this study a series of Ce0.8Eu0.1M0.1O2−δ (M = Zr, Hf, La, and Sm) nano-oxides were prepared and tested for diesel soot oxidation catalysis. The systematic characterization studies indicated successful incorporation of both dopants in the cubic fluorite crystal structure of CeO2. A remarkable enhancement in the reduction properties and oxygen defect concentration was observed for the co-doped samples from structural and chemical analyses. The aliovalent co-doped materials exhibited better performance than the isovalent co-doped materials. The catalytic activity order of the prepared materials towards model soot oxidation was Ce0.8Eu0.1La0.1O2−δ > Ce0.8Eu0.1Sm0.1O2−δ > Ce0.8Eu0.1Hf0.1O2−δ > Ce0.8Eu0.1Zr0.1O2−δ > Ce0.9Eu0.1O2−δ > CeO2. The most favorable modification of the physicochemical properties of europium doped ceria was ascertained in the presence of La as a co-dopant compared to other combinations investigated. The correlation of the physicochemical properties with the catalytic activity has also been clearly demonstrated in the manuscript.

Forward osmosis as a water treatment option has been extensively studied in recent decades owing to its energy efficiency and enhanced performance. Even hybrid options of integrating forward osmosis with other separation technologies have been explored. In this article, forward osmosis has been comprehensively reviewed with reference to various process and engineering aspects viz., membranes, membrane fouling, contactors and their design, draw solutions, integration of forward osmosis with various other separation technologies and modeling, and simulation. Every aspect has been thoroughly reviewed and discussed in terms of development trends, in addition to presenting the future challenges and prospects.

The present work reports the synthesis and characterization of a ceria-based hybrid nano-catalyst composed of a Snx+ dopant incorporated in the CeO2 crystal lattice and a finely dispersed CoOx phase on its surface. Characterization studies showed that the Ce, Sn, and Co cations were present in their multivalent oxidation states. The CoOx was confirmed to be Co3O4. A HRTEM image depicted the presence of a stepped catalyst surface, which has a special importance in enhancing the heterogeneous catalytic reaction rate carried out on the solid catalyst surface. The prepared materials were subjected to diesel soot oxidation catalysis. Model soot was combusted in the presence of air under both tight and loose contact conditions of the catalyst and soot. The hybrid catalyst exhibited improved performance compared to the Sn-doped nano-CeO2 and nano-CeO2 supported CoOx catalysts. The improved catalytic activity was attributed to the existence of synergism among the multivalent cations and the stepped surface of the hybrid catalyst, which act as the potential active sites for oxidation catalysis.

The influence of an anatase-TiO2 support on the diesel soot oxidation catalytic activity of manganese doped ceria is investigated. The soot conversion light-off temperature is significantly lowered with the application of anatase-TiO2 as the support in comparison to the unsupported and γ-Al2O3 supported CeO2–MnOx catalysts. Additionally, considerable enhancement in bulk and surface defects is observed for CeO2–MnOx/TiO2, which is attributed to the promotional role of the CeO2/TiO2 interface in the formation and stabilization of defect sites. The temperature programmed desorption of oxygen (O2-TPD) study of CeO2–MnOx/TiO2 indicates a sharp increase in oxygen desorption after a temperature of 500 K. In good correlation, the diesel soot conversion substantially increases after 550 K, but below this temperature the TiO2 supported catalyst exhibits comparable activity to that of the γ-Al2O3 supported catalyst. Increased oxygen mobility at elevated temperatures might play a key role in the performance of the TiO2 supported catalyst. Moreover, its structural stability and appreciable catalytic activity were retained even after high temperature annealing treatment.

Herein we describe a novel strategy for noble-metal-free Mn3O4@POP (porous organic polymer) hybrid synthesis by encapsulation of Mn3O4-NP in the interior cavity of a porous organic polymer which exhibited enhanced catalytic activity and stability for oxidation of diverse activated and nonactivated alcohols relative to the conventional catalysts to demonstrate the benefits of such a nanoarchitecture in heterogeneous nanocatalysis. The use of a non precious catalyst, tremendous recyclability (upto 15 catalytic runs) and exceptional stability make our system innovative in nature, addressing all the profound challenges in the noble-metal-free heterogeneous catalysts development community.

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.

With the aim of efficiently degrading organic pollutants through an easily operated procedure, a series of MoO3–CeO2 and β-cyclodextrin supported MoO3–CeO2 nano-composite materials were synthesized by using a co-precipitation method. A surfactant such as Cetyl Trimethyl Ammonium Bromide (CTAB) was used during the synthesis of this nano-composite material. These prepared catalysts are thoroughly characterized by various techniques such as XRD, BET, FT-IR, pyridine adsorbed FT-IR, Raman spectroscopy, SEM and TEM. The XRD study results suggested the formation of nanocrystalline materials which is also clearly observed from the SEM and TEM analysis. Raman measurements disclosed the presence of oxygen vacancies and lattice defects in all synthesized nano-composite samples. The catalytic activities of the synthesized materials were successfully tested for the degradation of phenol by using hydrogen peroxide at room temperature. It is surprising that the phenol degradation efficiency of the β-cyclodextrin supported MoO3–CeO2 nano-composite material is exhibited higher than that of other materials, which has been mainly attributed to the promoting effect of β-cyclodextrin. The degradation reaction is carried out at room temperature with continuous stirring and without light irradiation. Therefore, this degradation reaction is different from conventional heterogeneous catalysis or photocatalysis, in which the pollutants cannot be degraded completely, but it may transform from one phase to another phase. The gradual decrease in COD value shows the degradation of phenol that leads to the conversion of organic compounds into harmless gaseous CO2 and inorganic ions. Thus, this reported phenol degradation reaction is a quite promising green technology, which could be widely applied in practice.

We have described herein the synthesis and characterization of a uniquely designed mesoporous silica shell@Pd nanoparticle tethered amine functionalized silica core catalyst and its catalytic properties in the hydrogenation of levulinic acid, a key platform molecule in many biorefinery schemes, into γ-valerolactone, using formic acid as a sustainable H2 source. Monodispersed silica core particles (∼300 nm in diameter) were prepared and further functionalized by amine groups and then the in situ loading of Pd nanoparticles was carried out. Pd0-NPs are sandwiched between the nonporous silica core and the mesoporous silica shell, leading to the exceptional stability of the catalyst. The nanostructured material was thoroughly characterised by means of powder XRD patterns, N2 sorption, FE-SEM, UHR-TEM, TG-DTA, and XPS analysis. Our core–shell nanostructure catalyst encapsulated with Pd nanoparticles exhibited a significant increase in catalytic activity and excellent selectivity towards γ-valerolactone (99%) compared with control catalysts for levulinic acid hydrogenation, including Pd@C and Pd@SiO2 (without a mesoporous SiO2 shell). Our results suggest that the core–shell silica based nanocatalyst offers tremendous recyclability (up to the 10th catalytic run with consistent conversion and selectivity of γ-valerolactone), stability (no leaching of Pd and structure collapsing) and no sign of deactivation.

In this work, alumina supported ceria–praseodymia (CP/A) samples were synthesized by a deposition coprecipitation method. The structural, textural, and redox properties of the prepared samples were characterized at different calcination temperatures from 773 to 1073 K and their catalytic activity was assessed in the CO oxidation reaction. In order to determine the promoting effect of the alumina support in the sample, the physicochemical and catalytic properties of CP/A were compared with unsupported ceria–praseodymia (CP) solid solutions. The X-ray diffraction results indicated the formation of ceria–praseodymia solid solutions over the alumina support. The nanocrystalline nature of the samples was confirmed by transmission electron microscopy. The CP/A sample showed an extremely high surface area which remained reasonably high even after calcination at 1073 K. The combined analyses revealed that the CP/A sample had more oxygen vacancies than CP. The H2-temperature programmed reduction results suggested that the active oxygens were significantly improved in CP/A over CP. The characterization results also highlighted the excellent thermal stability of CP/A. The CO oxidation profiles signified that the catalytic activity of CP/A calcined at 773 K was remarkably enhanced in comparison to that of CP. The fine dispersion of ceria–praseodymia solid solutions over the alumina support in the process of deposition coprecipitation and the synergistic effect between ceria–praseodymia and the support, which resulted in very high surface areas, oxygen vacancy concentrations, and active oxygen species, are believed to be responsible for the superior activity of the CP/A sample.

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).

A series of MnOx/CeO2 (Mn/Ce), MnOx/ZrO2 (Mn/Zr), and MnOx/Ce0.75Zr0.25O2 (Mn/CZ) catalysts prepared by an impregnation method were tested for their ability to catalyse the oxidation of Hg0 at relatively low temperature (423 K). Various characterization techniques, namely, Brunauer–Emmett–Teller (BET) surface area analysis, X-ray diffraction (XRD), Raman spectroscopy (RS), X-ray photoelectron spectroscopy (XPS), and H2-temperature programmed reduction (H2-TPR) were employed to understand the structural, surface, and redox properties of the prepared catalysts. Specific aspects of the catalysis of Hg0 oxidation that were investigated included the influence of MnOx loading (5, 15, and 25%) and the influence of HCl and O2. Among the catalysts tested, the 15Mn/CZ catalyst achieved the best Hg0 oxidation performance (~83% conversion of Hg0 to Hg2+) in the presence of HCl and O2. The higher activity of the 15Mn/CZ catalyst was most likely due to the presence of more oxygen vacancies, enhanced Mn4+/Mn4+ + Mn3+ + Mn2+ ratio and more surface adsorbed oxygen, which were proved by XRD, BET, Raman, and XPS. H2-TPR results also show that the strong interaction between the Ce0.75Zr0.25O2 support and MnOx improved the redox properties significantly as compared to pure CeO2 and ZrO2 supported MnOx catalysts.

To develop efficient materials for CO oxidation, a series of co-doped CeO2 ternary oxide solid solutions (Ce0.80M0.12Sn0.08O2−δ, M = Hf, Zr, Pr, and La) were prepared by a simple coprecipitation method. The fundamental characteristics of the co-doped CeO2 samples were studied by X-ray diffraction, Raman spectroscopy, UV-visible diffuse reflectance spectroscopy, transmission electron microscopy, Brunauer–Emmett–Teller surface area, H2-temperature programmed reduction, X-ray photoelectron spectroscopy, and O2-temperature programmed desorption. The oxidation of CO was chosen as a model reaction to evaluate the catalytic performance of these samples. The characterization results revealed that ternary oxide solid solutions had significantly enhanced surface area, improved reducibility, increased oxygen mobility and higher quantity of surface adsorbed oxygen species and oxygen vacancies, compared to undoped CeO2. The CO oxidation performance of CeO2 was greatly improved upon co-doping due to the modification in structural, textural, and redox properties. Especially, the Ce0.80Pr0.12Sn0.08O2−δ combination catalyst exhibited the highest oxidation activity among the investigated samples, which is attributed to its high specific surface area, better reducibility, superior surface active oxygen species, and oxygen vacancies 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.

Co3O4 promoted CeO2 nanocubes have been found to exhibit outstanding catalytic activity for the oxidation of diesel soot at low temperatures (50% soot conversion = 606 K). This remarkable performance is attributed to the superior reducible nature of cerium oxide and the preferential exposure of CeO2 (100) and Co3O4 (110) facets. A probable mechanism based on the cooperative effect of cerium- and cobalt-oxides has been proposed, offering new possibilities for the design of promising materials for catalytic soot oxidation.

Doping ceria with heterocations is a commonly applied strategy to alter its structural and chemical properties including its key feature oxygen storage capacity (OSC). Although a few papers have been published on the structural properties and chemical reactivity of Zn-doped ceria, one lacks a comprehensive investigation on the effect of zinc incorporation in the ceria lattice on its structural properties, and how it could be correlated to the changes in its chemical reactivity including OSC and catalytic activities. Here, we have established an interesting correlation between the structural properties of dual-phase Zn-modified ceria nanocrystals, their OSCs, and their catalytic performance for the reverse water-gas shift (RWGS) reaction and soot oxidation. Upon incorporation of zinc in the ceria lattice, the degree of crystallinity is decreased according to XRD. Raman spectroscopy reveals a concomitant increase of oxygen vacancy concentrations within the Zn-modified ceria samples in comparison to pure ceria. The incorporation of zinc increases the reducibility of ceria according to H2-TPR and doubles the OSC as revealed by thermogravimetric studies. When the variations of the degree of crystallinity, the oxygen vacancy concentrations and the OSCs within the Zn-modified ceria samples are compared, an excellent correlation is established. Catalytic testing shows that Zn-modified ceria exhibits higher activities for the RWGS reaction, especially at the lower temperatures of 400 °C and 600 °C, while at 800 °C the catalyst deactivates rapidly. Such deactivation at high temperature can be totally eliminated by impregnating additional cobalt oxide on the ceria support. Some improvement in the soot oxidation activity is achieved with Zn-modified ceria, attributed to enhanced OSCs of the materials. Within the set of Zn-modified ceria samples, the activities are essentially identical, which is again correlated to their nearly identical OSCs, irrespective of the zinc concentration. Upon impregnation of additional cobalt oxide, the materials' activities for soot oxidation are markedly enhanced, as observed with the RWGS reaction. Pure ceria and Zn-modified ceria samples perform significantly better for soot oxidation after being leached with citric acid. Such enhancement is more pronounced with CZ10 (10 mol% zinc) in comparison to pure ceria. This observation suggests that the removal of non-incorporated ZnO increases the activity for soot oxidation.

Some of our group recently demonstrated combining theory and a statistical survey of the Cambridge Structural Database (CSD) that the interaction between the π-holes of nitro groups and electron-rich atoms is somewhat directional (Chem. Commun., 2015, 51, 1491–1493). In this communication, we present a joint experimental and theoretical study on a novel cadmium(II) complex, [Cd(C7H3N2O6)2(C12H8N2)2]·H2O·DMF (1) [where C7H4N2O6 = 3,5-dinitrobenzoic acid and C12H8N2 = 1,10-phenanthroline] to unravel the important role of this π-hole interaction.

A nanostructured CeO2–MnOx catalyst was synthesized by a coprecipitation method and subjected to different calcination temperatures at 773 and 1073 K to understand the surface structure and the thermal stability. The structural and redox properties were deeply investigated by various techniques, namely, X-ray diffraction (XRD), inductively coupled plasma-optical emission spectroscopy (ICP-OES), Brunauer–Emmett–Teller (BET) surface area, transmission electron microscopy (TEM), Raman spectroscopy (RS), hydrogen-temperature programmed reduction (H2-TPR), and X-ray photoelectron spectroscopy (XPS). The CeO2–MnOx catalyst calcined at 773 K was tested towards elemental mercury (Hg0) oxidation and the achieved results are compared with the pure CeO2 and MnOx. The XRD and TEM results confirmed the incorporation of Mn ions into the ceria lattice and the formation of a nanostructured solid solution, respectively. The RS and TPR results showed that the CeO2–MnOx catalyst exhibits more oxygen vacancies with superior redox ability over CeO2 and MnOx. XPS analysis indicates that Ce and Mn existed in multiple oxidation states. Compared to pure CeO2 and MnOx, the CeO2–MnOx catalyst exhibited greater Hg0 oxidation efficiency (Eoxi) of 11.7, 33.5, and 89.6% in the presence of HCl, O2, and HCl/O2-mix conditions, respectively. The results clearly indicated that the HCl/O2-mix had a promotional effect on the catalytic Hg0 oxidation. This was most likely due to the presence of surface oxygen species and oxygen vacancies being generated by a synergetic effect between CeO2 and MnOx. In the presence of HCl, the CeO2–MnOx catalyst exhibited good adsorption efficiency (Eads) of 92.4% over pure CeO2 (46.5%) and MnOx (80.6%). It was found that increasing the operating temperature from 423 to 573 K resulted in considerable increase of Eoxi and a decrease in the sorption of Hg0 on the catalyst.

International audience; Oxide supported copper and gold catalysts are active for the selective hydrogenation of polyunsaturatedhydrocarbons but their low activity compared to palladium catalysts and the deactivation of copper catalystslimit their use. There are only a very limited number of studies concerned with the use of bimetallic Au–Cucatalysts for selective hydrogenation reactions and the aim of this work was to prepare TiO2-supported monometallicAu and Cu and bimetallic AuCu (Cu/Au atomic ratio of 1 and 3) catalysts and to evaluate their catalyticperformance in the selective hydrogenation of butadiene. Small gold, copper and gold–copper nanoparticles(average particle size o 2 nm) were obtained on TiO2 using the preparation method of deposition–precipitationwith urea followed by reduction under H2 at 300 1C. Very small clusters were observed for Cu/TiO2 (B1 nm)which might result from O2 induced copper redispersion, as also supported by the XPS analyses. The alloying ofcopper with gold was found to inhibit its redispersion and also limits its reoxidation, as attested by XPS. Thebimetallic character of the AuCu nanoparticles was confirmed by XPS and EDX-HAADF. Cu/TiO2 was initiallymore active than Au/TiO2 in the selective hydrogenation of butadiene at 75 1C but it deactivated rapidly duringthe first hours of reaction whereas the gold catalyst was very stable up to 20 hours of reaction. The bimetallicAuCu/TiO2 catalysts displayed an activation period during the first hours of the reaction, which was very pronouncedfor the sample containing a higher Cu/Au atomic ratio. This initial gain in activity was tentativelyassigned to copper segregation at the surface of the bimetallic nanoparticles, induced by the reactants. Whenthe AuCu/TiO2 catalysts were pre-exposed to air at 75 1C before butadiene hydrogenation, surfacecopper segregation occurred, leading to higher initial activity and the suppression of the activation period. Underthe same conditions, Cu/TiO2 totally lost its activity, probably due to irreversible copper oxidation.

A series of PBS-HPMO and Cu(II)-PBS-HPMO were synthesized from the self-assembly of 1,2-bis(triethoxysilyl)ethane and porphyrin-bridged silsesquioxane (PBS). These synthesized PBS-HPMO and Cu(II)-PBS-HPMO were characterized using different spectroscopic and non-spectroscopic techniques, namely, XRD, FT-IR spectroscopy, nitrogen adsorption–desorption isotherms, and UV-visible and EPR spectroscopies. Among these, the porphyrin-bridged PMOs, specifically Cu(II)-PBS-HPMO, were found to be proficient catalysts for the multicomponent reaction of benzyl halides with sodium azide and terminal alkynes. This catalyst allowed for the high regioselective synthesis of 1,4-disubstituted 1,2,3-triazoles through a one-step and atom economic tandem reaction with water as the solvent. Note that no additional base or ligand or reducing agent is required. Moreover, in addition to benzyl halides, hetero benzyl halides have also been achieved in remarkable yields and in a completely regioselective manner. A series of structurally diverse 1,2,3-triazoles were also prepared in good to excellent yields from easily accessible starting materials by employing this protocol. Furthermore, this process is purely heterogeneous and the cascade reactions were performed in water, and the efficient catalyst recyclability makes such a synthesis a truly green process.

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.

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.

An efficient and straightforward synthesis of 2H-indazoles is achieved from 2-bromobenzaldehydes, primary amines and sodium azide through consecutive condensation, C–N and N–N bond formations, catalyzed by a novel heterogeneous CuII–HT catalyst. The recoverable heterogeneous CuII–HT catalyst exhibited an impressive activity for the title reaction without any additives (expensive ligands, etc.). Heterocyclization proceeds through C–N and N–N bond formation, which is the key step to deliver the desired 2H-indazole scaffold. A series of structurally diverse 2H-indazoles were prepared in good to excellent yields from easily accessible starting materials by employing this protocol.

The present work has been undertaken with an aim to synthesize valuable bio-additive fuels from glycerol acetalization using SnO2-based solid acids. Various promoters, namely SO42−, MoO3 and WO3 were incorporated to the SnO2 using a wet-impregnation method. An extensive physicochemical characterization has been achieved by means of XRD, BET surface area, BJH analysis, FT-IR, pyridine adsorbed FT-IR, NH3-TPD, ICP-OES and XPS techniques. The BET surface area of SnO2 is significantly improved from 11 to 32, 56 and 41 m2 g−1 after the addition of the WO3, MoO3, and SO42− promoters, respectively. The XPS studies revealed that Sn is present in the +4 oxidation state, whereas Mo, W and S are in the +6 oxidation state in the prepared samples. In addition, the SO42−/SnO2 sample contained super acidic sites, along with strong- and medium-acidic sites. The amount of acidic sites was found to be 46.47, 61.81, 81.45 and 186.98 μmol g−1 for the SnO2, WO3/SnO2, MoO3/SnO2, and SO42−/SnO2 samples, respectively. The pyridine adsorbed FT-IR studies revealed the existence of a superior quantity of Bronsted acidic sites than Lewis acidic sites in the synthesized catalysts. Promoted SnO2 catalysts exhibited a promising catalytic performance for glycerol acetalization with acetone and furfural, and the activity of the catalysts was found to increase in the following order: SnO2 < WO3/SnO2 < MoO3/SnO2 < SO42−/SnO2. The outstanding performance of the SO42−/SnO2 catalyst is mainly due to the existence of a large amount of acidic sites associated with the super acidic sites. The achieved optimum glycerol conversions with acetone and furfural were ~98 and 99% over the SO42−/SnO2 catalyst, respectively.

The catalytic behavior of various CeO2-based solid solutions, namely, Ce1−xTMxO2−δ (TM = Mn, Fe, or Zr) and Ce1−xRExO2−δ (RE = Pr, La, or Sm) was studied for the removal of elemental mercury (Hg0) from coal-derived flue gas by catalytic oxidation (Hg0 → Hg2+). The investigated catalysts were synthesized by a coprecipitation method and characterized by various techniques, namely, X-ray diffraction (XRD), Raman spectroscopy (RS), high-resolution electron microscopy (HREM), Brunauer–Emmett–Teller (BET) surface area, X-ray photoelectron spectroscopy (XPS), temperature programmed reduction (TPR), and diffuse reflectance spectroscopy (UV-DRS). The XRD results confirmed the incorporation of Mn, Fe, Zr, La, Pr, and Sm cations into the CeO2 lattice and the formation of nanocrystalline solid solutions. The TEM measurements established the nanocrystalline nature of the solid solutions. The RS measurements suggested that the substitution process promotes the formation of oxygen vacancies, which hastens the diffusion rate of oxygen and improves the Hg oxidation. UV-vis DRS studies demonstrated the presence of the charge transfer transitions O2− → Ce3+ and O2− → Ce4+. The XPS and H2-TPR results suggested that the reduction of Ce4+ → Ce3+ is the foremost reason for the increase in oxygen vacancies, which are beneficial for Hg0 removal. The order of mercury oxidation activity over various doped catalysts is as follows: CM > CL > CZ > CF > CS > C > CP.

The intriguing research toward the exploitation of ceria-based materials for various applications has been growing significantly. In the present investigation, we describe the preparation, characterization and utilization of CeO2–La2O3 (CL) and CeO2–La2O3/SiO2 (CLS) solid solutions for the synthesis of two industrially useful chemicals namely 4-methylpent-1-ene and dehydroacetic acid. Coprecipitation and deposition coprecipitation from ultrahigh dilute solutions were used for the synthesis of CL and CLS catalysts, respectively. The physicochemical characterization has been achieved with the help of various techniques namely X-ray diffraction (XRD), BET surface area, transmission electron microscopy (TEM), UV-visible diffuse reflectance spectroscopy (UV-vis DRS), Raman spectroscopy (UV-RS and Vis-RS), X-ray photoelectron spectroscopy (XPS) and temperature programmed desorption (TPD) measurements. The structure–activity relationships helped to correlate different parameters that are necessary for obtaining desired products in good yields. The inclusion of silica support has an optimistic influence on the acid–base properties of the ceria–lanthana, in terms of both amount and strength of sites. The presence of silica not only manipulates the acid–base properties but also causes numerous benefits, for instance, it improves the dispersion, stabilizes the active component against sintering and enriches the oxygen vacancy concentration. The meticulous analysis of characterization and activity studies revealed the significant role of acid–base sites in directing the desired products. Interestingly, the CLS catalyst has shown better performance in the production of both 4-methylpent-1-ene and dehydroacetic acid compared to the unsupported CL sample due to well-balanced acid–base sites.

We report large-scale synthesis of high surface area nano-oxides of Ce0.8M0.2O2/Al2O3 (M = Tb and Hf) possessing cuboctahedral shape of 3–5 nm size, which exhibit excellent oxygen storage capacity (OSC) and superior CO oxidation activity in comparison to the most advanced ceria–zirconia/alumina catalyst supports employed in the existing three-way-catalytic converters (TWCs).

Titania supported ceria–lanthana solid solutions (CexLa1−xO2−δ/TiO2; CLT) have been synthesized by a facile and economical route. Existence of synergism between ceria–lanthana (CL) solid solutions and titania-anatase phase, which leads to decrease in the crystallite size, retarded titania phase transformation, and improved redox properties, has been thoroughly investigated by various techniques, namely, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), UV-visible diffuse reflectance spectroscopy (UV–vis DRS), Raman spectroscopy (UV–RS and Vis–RS), BET surface area analysis, and temperature programmed reduction (TPR). Two key observations made from the whole exercise were (i) mutual interaction of Ce and Ti ions could impose typical Ce–O–Ti modes at the interfacial region and (ii) the La3+ ion as a dopant provokes a large number of oxygen vacancies via a charge compensation mechanism. The promising role of these factors in the CO oxidation (one of the most formidable challenges) has been comprehensively described. The observed enhanced activity for the CLT sample is primarily attributed to an apparent specific orientation of the active component over the support, which is endorsed by the interfacial interaction. This specific mode could facilitate the CO adsorption with simultaneous bulk oxygen diffusion for more consumption and in turn better activity.

A novel copper (II) hydrotalcite catalyst has been investigated for its use in the cascade synthesis of β-hydroxy triazoles. It is found to be a dynamic catalyst for regioselective organic synthesis in water. The copper (II) hydrotalcite catalyst, in various Cu : Al molar ratios, was prepared by adopting a coprecipitation method and characterized using different techniques. The three component (epoxides, sodium azide and terminal alkynes) reactions under investigation were performed in water at ambient temperature without any additives. The formation of 2-azido alcohol, generated in situ, was observed to be the key step in the [3+2] cycloaddition of the click reaction. The optimized reaction procedures described herein are not only regioenriched and high yielding but also eco-friendly.

Alumina-supported nanosized ceria–lanthana solid solutions (CeO2−La2O3/Al2O3 (CLA) = 80 : 20 : 100 mol% based on oxides) were synthesized by a modified deposition coprecipitation method from ultra-high dilute aqueous solutions. The synthesized materials were subjected to various calcination temperatures from 773 to 1073 K to understand the surface structure and the thermal stability. Structural and redox properties were deeply investigated by different characterization techniques, namely, X-ray diffraction (XRD), Raman spectroscopy (RS), transmission electron microscopy (TEM), UV-visible diffuse reflectance spectroscopy (UV-vis DRS), X-ray photoelectron spectroscopy (XPS), temperature programmed reduction (H2-TPR), and Brunauer–Emmett–Teller (BET) surface area. The catalytic efficiency was evaluated for CO oxidation at normal atmospheric pressure. BET surface area measurements revealed that synthesized samples exhibit reasonably high specific surface area. As revealed by XRD measurements, samples maintain structural integrity up to 1073 K without any disproportionation of phases. XPS results suggested that there is no significant change in the Ce3+ amount during thermal treatments due to the absence of undesirable cerium aluminate formation. A significant number of oxygen vacancies were confirmed from Raman and UV-vis DRS measurements. The CLA 773 sample exhibited superior CO oxidation activity. The better activity of the catalyst was proved to be due to a high dispersion in the form of nanosized ceria–lanthana solid solutions over the alumina support, facile reduction, and a high oxygen storage capacity.

Selective synthesis of acetonitrile in one step from ethanol by ammoxidation is reported, for the first time, using alumina supported and antimony promoted vanadium phosphorus oxide catalyst.