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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.

The production of vanillin from lignin-derived vanillyl alcohol poses a great deal of research interest because of the availability of renewable lignin in abundant quantities. In the present study, a series of copper-doped ceria (CeO2) catalysts were prepared by a modified template-assisted method, characterized by various techniques, and explored for the oxidation of vanillyl alcohol to vanillin with molecular oxygen as the oxidant at normal atmospheric pressure. Interestingly, a 10% Cu-doped ceria (Cu0.1Ce0.9O2−δ) catalyst exhibited superior catalytic activity for the oxidation of vanillyl alcohol with 95% and 100% conversions at atmospheric and moderate pressures, respectively, with 100% vanillin selectivity in both cases. A thorough characterization (XRD, BET surface area, Raman spectroscopy, SEM, TEM, XPS, and H2-TPR) of the synthesized mesoporous oxides (CuO, CeO2, Cu0.05Ce0.95O2−δ, Cu0.1Ce0.9O2−δ, and Cu0.15Ce0.85O2−δ) revealed that mixed oxide catalysts exhibit more oxygen vacancies and better redox behavior in comparison to the single oxides, which lead to improved catalytic activity and selectivity. Reaction parameters, such as reaction temperature, reaction time, catalyst amount, and the solvent, were also optimized for the reaction.

WOx-promoted TiO2–ZrO2 solid acid catalyst was prepared and applied in the catalytic acetalization and ketalization of glycerol with carbonyl compounds to produce biofuel additives. The presence of WOx promoter and TiO2 remarkably improved the catalytic activity of ZrO2. Approximately, 100% glycerol conversion was evidenced with non-bulky aliphatic aldehydes and ketones like, propanol and cyclohexanone. The physical characterization of WOx-promoted TiO2–ZrO2, revealed a higher formation of tetragonal crystalline phase of ZrO2, over monoclinic. The total surface acidity and the ratio of Bronsted to Lewis acidic site concentrations were determined by NH3-TPD and pyridine-chemisorbed FTIR spectroscopy, respectively. A considerably higher concentration of Lewis acidic sites, ~ 213.29 μmol/gm, was evidenced on the WOx-promoted TiO2–ZrO2 catalyst surface. Catalytic activity study revealed a direct correlation between the surface Lewis acidic site concentration and the activity of catalyst. This significant observation indicated the key role of Lewis acidic sites in this catalytic process. The WOx-promoted TiO2–ZrO2 catalyst was also considerably stable and showed good performance in the acetalization/ketalization of glycerol with other substituted carbonyl compounds. The WOx-promoted TiO2–ZrO2 solid acid catalyst exhibits superior catalytic performance for acetalization and ketalization of glycerol with carbonyl compounds to produce biofuel additives.

Recent research in catalyst development for CO2 methanation has been focussing on the design of nanostructures with high porosity and better redox properties. Herein, nanostructured Ce0.8Zr0.2O2 mixed oxide support was prepared by a metal organic framework (MOF)-template approach and its properties were well compared with a similar catalyst prepared by a conventional coprecipitation (CP) method. The MOF-template approach resulted in the production of a nanoporous Ce0.8Zr0.2O2 support with improved redox properties compared to the coprecipitated Ce0.8Zr0.2O2. The prepared support was then decorated with Co3O4 nanoparticles and tested in CO2 methanation reaction. At 320 °C, 1.5 MPa and GHSV = 15,000 mL g˗1 h˗1, the Co/Ce0.8Zr0.2O2 catalyst prepared by MOF-template method achieved far better CO2 conversion (81.2%) and improved CH4 selectivity (99%) than the catalyst prepared by CP method (48.7% CO2 conversion and 97% CH4 selectivity). The long-time presence of the MOF-derived Co/Ce0.8Zr0.2O2 catalyst on the stream proved its resistance towards sintering, which may be ascribed to the fine dispersion of Co3O4 nanoparticles as well as their excellent integration in the network of nanoporous Ce0.8Zr0.2O2.

The fossil fuel run engines emit hazardous pollutants like CO, unburnt hydrocarbons, NOx, etc., due to partial burn of the fuel. These pollutants are converted to nontoxic elements like CO2, H2O and N2 by the catalytic convertor before releasing in the atmosphere. To carry out the redox conversion of the pollutants in the fluctuating O2 atmosphere of the real engine exhaust, CeO2-ZrO2 is used as an oxygen storage/release component of the catalytic convertor. High oxygen storage capacity (OSC) of the catalytic material usually ensures high conversion. The rare earth metal oxide CeO2 exhibits OSC property by virtue of its reversible redox capability. The redox conversion is carried out by the participation of the lattice oxygen and adsorbed active oxygen species present on the CeO2 surface. During the redox process, oxygen vacancies are generated on the catalyst surface, which consequently acts as the active centre for the next cycle of the catalytic reaction. Thus, the ease of oxygen vacancy formation along with other factors like the preparation/post-preparation treatment of the catalysts, presence of dopants, thermal treatment/ageing conditions, etc., strongly influences the OSC of CeO2. In the present article, these factors have been discussed in brief. Hopefully, this compendium will be helpful to gain a preliminary idea on this topic, especially for the student community.

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.

This work reports the synthesis of mesoporous Ce1-x-ZrxO2-δ (x = 0.5 and 0.8) mixed oxides with distinct Ce/Zr mole ratio by inverse micelle template method and their catalytic exploration for epoxidation of styrene in isopropanol solvent using TBHP as the oxidant. Among various catalysts investigated, the Ce0.8Zr0.2O2 combination catalyst exhibited best catalytic activity with ~ 98% conversion and ~ 90% selectivity to styrene epoxide. The synthesized Ce–Zr mixed oxide catalysts were characterized by various state-of-the-art techniques. Characterization studies revealed that Ce/Zr mole ratio has an imperative influence on the physicochemical properties such as surface area, oxygen vacancy concentration, and redox nature. Interestingly, catalytic efficiency was significantly improved with the increase of Ce and decrease of Zr content in the Ce–Zr mixed oxides. Catalytic efficiency and distribution of the products for styrene oxidation under various conditions such as reaction time, solvent, temperature, and styrene to TBHP mole ratio were also evaluated. Reusability of the highly active Ce0.8Zr0.2O2 mixed oxide catalyst was also demonstrated.

Shape-controlled metal nanomaterials are considered as a unique class of catalysts because of their synergistic size- and shape-dependent catalytic properties. This work reports the synthesis of a novel size- and shape-controlled catalyst, consisting of highly dispersed MnOx nanoparticles (average particle size of 4.5 nm) on shape-controlled SiO2 nanospheres (250–300 nm) for selective cyclohexene oxidation using air as the oxidant under solvent- and base-free conditions. The MnOx/SiO2 catalyst exhibited an excellent cyclohexene conversion (~ 92%) with a high selectivity (~ 96%) to the allylic products (2-cyclohexene-ol and 2-cyclohexene-one) under mild conditions, outperforming various SiO2 supported CoOx, FeOx, and CuOx catalysts. The better performance of shape-controlled MnOx/SiO2 nanocatalyst is due to high redox nature of Mn, uniform dispersion of smaller sized MnOx nanoparticles, and synergetic interaction between MnOx and SiO2 spheres, as evidenced by XPS and TEM studies. Further, the MnOx/SiO2 catalyst could be reused at least 5 times for selective cyclohexene oxidation with a negligible loss in its catalytic performance, indicating the excellent stability of shape-controlled metal nanocatalysts in organic synthesis under economically viable and mild conditions. Shape-controlled MnOx/SiO2 nanocatalyst shows an excellent catalytic activity and a high selectivity to allylic products in the oxidation of cyclohexene under mild conditions

ispartof: Acs Catalysis vol:11 issue:21 pages:13603-13648 status: published

The present work describes the role of oxide supports such as alumina (Al2O3), silica (SiO2), and titania (TiO2) on the structural and catalytic properties of europium ion-doped cerium oxide. In particular, the main motive of this study was to further improve the catalytic efficiency of Ce0.8Eu0.2O2-δ solid solutions for oxidation reactions. Diesel soot oxidation and oxidative coupling of benzylamine were examined as model reactions to assess the catalytic properties of the prepared materials. These were prepared by deposition coprecipitation method and characterized by various techniques namely, X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy, transmission electron microscopy, and BET/BJH surface area and pore-size distribution methods. The characterization studies reveal that Ce0.8Eu0.2O2-δ is well-dispersed without the formation of CeO2 or Eu2O3 crystalline compounds over the surface of various supports. The TEM studies confirm the nano-crystalline nature of the Ce0.8Eu0.2O2-δ and Raman studies indicate the formation of oxygen vacancies which are significant for oxidation reactions. As expected, the supported Ce0.8Eu0.2O2-δ mixed oxides exhibited better catalytic activity than pure ceria and unsupported oxides towards the soot and benzylamine oxidation reactions. Supported Ce0.8Eu0.2O2-δ(CE) catalysts are exhibiting better performance than unsupported CE and pure ceria for soot and benzylamine oxidation owing to metal oxide-support and metal oxide-metal oxide interactions.

Development of non-noble metal catalysts for oxidation of CO is an important subject for reducing the automotive emissions. Recently, shape-controlled synthesis of CeO2 has increasingly attracted the attention of researchers due to its size- and morphology-dependent unique properties. Following this line of thinking, herein, we successfully report the synthesis of Cr-doped CeO2 (Ce1−xCrxO2−δ; X = 0.05, 0.1, and 0.15) nanorods with various Cr contents by a facile hydrothermal method. Structural, surface, optical, and redox properties of the Cr-doped CeO2 nanorods were investigated by various techniques, namely, ICP-OES, TEM-HRTEM, FE-SEM/EDX/EDS, XRD, BET, Raman, UV–vis DRS, PL, XPS, H2-TPR, and O2-TPD. The catalytic performance was evaluated for CO oxidation. For comparison, the efficiency of Cr2O3 was also studied for CO oxidation under identical conditions. As revealed by various characterization results, the chromium ions were doped into the ceria lattice (formation of Ce–O–Cr solid solution), which enhanced the intrinsic properties such as oxygen vacancy concentration and surface area. It was found that the Cr-doped CeO2 nanorods show superior CO oxidation activity than the pristine counterparts (CeO2 nanorods and Cr2O3). The highest CO oxidation efficiency was achieved with the light-off temperature of T50 = 261 °C, when the Cr doping amount was 10% (Ce0.9Cr0.1O2−δ). A high specific surface area, more number of surface oxygen vacancies, a high concentration of Ce3+, and enhanced oxygen reducibility of Ce0.9Cr0.1O2−δ nanorods were found to be responsible for its superior catalytic performance. Further, the Ce0.9Cr0.1O2−δ nanorods exhibited a steady CO conversion over a period of 55 h investigated. The obtained results are expected to have a significant impact on the use of non-noble metal based Cr-doped CeO2 nanorods in environmental applications. The Cr-doped CeO2 nanorods with Ce0.9Cr0.1O2−δ composition showed enhanced CO oxidation performance at a lower temperature (~ 261 °C) than that of pristine CeO2 nanorods (338 °C) and Cr2O3 (361 °C) catalyst. This behaviour is a result of enhancement of oxygen vacancies, surface Ce3+ species, low-temperature reducibility, and high surface area.

Development of non-noble metal catalysts with improved structural, surface, and redox properties for catalytic soot oxidation has gained an enormous interest. Among practical alternatives, ceria-supported transition metal oxides have been proved to be the satisfactory catalysts for soot oxidation due to their outstanding redox properties and oxygen transfer capability promoted by the strong interaction between metal oxide and ceria interfaces. Following the above considerations, in the present work, CuO/Zn-CeO2 nanocomposite was prepared by a wet impregnation method and investigated for catalytic soot oxidation. To probe the significance of nanocomposites, pure counterparts, namely, CuO/CeO2, CuO/ZnO, and Zn-CeO2, were also synthesized. Various characterization techniques, namely, TEM-HRTEM, N2O chemisorption, XRD, ICP-OES, BET, Raman, XPS, and H2-TPR, were employed to investigate the structural, surface, and redox properties. Pure CuO/ZnO and CuO/CeO2 catalysts showed a soot oxidation activity with a T50 of 613 and 526 °C, respectively, under the practical conditions of NO concentration of 500 ppm and 20% O2. Interestingly, the CuO/Zn-CeO2 nanocomposite exhibited a remarkable higher soot oxidation activity with a T50 of 460 °C. The enhancement in the soot oxidation activity has been attributed to a strong interaction between the highly dispersed CuO and Zn-CeO2 support, which resulted in the desired textural properties and abundant surface defects (Ce3+ species as well as oxygen vacancies). In addition, the long-term stability test verifies an excellent reusability of the CuO/Zn-CeO2 nanocomposite towards soot oxidation without appreciable loss in the activity. The present study demonstrates the significance of ceria-based nanocomposite catalysts for environmental pollutant abatement.

Synergistic composite metal oxides are proven to be impressive materials due to their multi-functionalities across various catalytic applications. In a composite metal oxide, the interfacial chemistry between the components could provide exceptional redox and catalytic properties. In the present manuscript, the fundamental focus is devoted to investigating the interactions between active metal oxides at their interfaces and the catalytic activities towards diesel soot and CO oxidation. A series of flower-like microspheres namely, CeO2, 10%Mn3O4/CeO2, 20%Mn3O4/CeO2, and 40%Mn3O4/CeO2 catalysts were synthesized, where the effect of different Mn3O4 loadings towards soot combustion and CO oxidation were investigated. The characteristic 50% conversion temperature (T50) of catalytic soot oxidation under loose and tight contact conditions for CeO2 microspheres are 502 and 484 °C, respectively. After the integration of Mn3O4 and CeO2, the T50 values were decreased with the lowest values observed for the 20%Mn3O4/CeO2 microspheres (381 and 350 °C). Similarly, 20%Mn3O4/CeO2 microspheres showed T50 value at 103 °C for CO oxidation when compared to pure CeO2 microspheres (216 °C) and Mn3O4 nanoparticles (356 °C). Activation energy values were decreased when the Mn3O4/CeO2 composite used in soot and CO oxidation. The high catalytic activity can be attributed to the strong synergistic interactions between CeO2 and Mn3O4, variable oxidation states, the amount of readily available surface redox active sites and oxygen vacancies. The possible interfacial interaction between CeO2 and Mn3O4 can be exploited to exhibit enhanced surface structural, and redox properties when compared to the pure counterparts. Post-catalytic oxidation analysis confirms the high stability of the Mn3O4/CeO2 composite. The present study points out the vital role of interfacial interactions in composite metal oxides for improving the surface and redox properties, which are important for the development of highly efficient soot and CO oxidation catalysts.

A ceria (CeO2) promoted Cu-Ni bimetallic catalyst supported on SiO2 (Cu-Ni/CeO2-SiO2) was prepared and evaluated for catalytic hydrodeoxygenation (HDO) of vanillin. Silica supported monometallic Cu and Ni catalysts and bimetallic Cu-Ni catalyst (Cu/SiO2, Ni/SiO2, and Cu-Ni/SiO2), without a ceria promoter, were also synthesized and tested for the same application. The highest conversion of vanillin was achieved with the Cu-Ni/CeO2-SiO2 catalyst. Vanillyl alcohol was the sole product in the initial 2 h, followed by the formation of 2-methoxy-4-methylphenol, which was observed. Characterization of the synthesized catalysts revealed the presence of overlapping crystalline phases of CuO, NiO, and CeO2 on the Cu-Ni/CeO2-SiO2 surface. We extended our study to find out the results of using CeO2 as the support of the Cu-Ni bimetallic catalyst (Cu-Ni/CeO2). Partial incorporation of Cu and Ni cations into the ceria lattice took place, leading to the decrease of specific surface area and a concomitant compromise in the conversion. In the case of the Cu-Ni/CeO2-SiO2 catalyst, the higher conversion was accredited to the facile formation of Cu+ active centers by the synergistic interaction between Ce+4/Ce+3 and Cu+2/Cu+ redox couples and the incorporation of oxygen vacancies on the catalyst surface.

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

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.

TiO2 supported transition metal oxides were investigated for the direct decomposition of nitrogen oxides (NOx) at lower temperatures. The results showed that the catalytic performance strongly depends on the kind of transition metal oxide deposited on the TiO2. Among the various catalysts examined, Mn/TiO2 and Co/TiO2 exhibited relatively high NOx conversion at lower temperatures in the presence of 3 vol % O2. The oxygen in the reaction stream had a positive impact on the NOx decomposition over the Mn/TiO2 catalyst. We have not observed any TiO2 phase conversion from anatase to rutile in the Mn/TiO2 during the NOx decomposition reaction at different temperatures (100–350 °C). NOx decomposition activity was shown to be governed by the surface labile oxygen rather than the gas phase oxygen. The Mn/TiO2 catalyst exhibited a good resistance to 10 vol % H2O and 100 ppm of SO2.

This review article encompasses the progress and conventional overview of current research activities of porous organic polymers (POPs), especially in catalysis, as they have garnered colossal interest in the scientific fraternity due to their intriguing characteristic features. Various synthetic strategies with possible modification of functionality of POPs have been used to improve the catalytic efficiency towards value-added chemicals production. Accordingly, this review article is mainly focused on the design, development of various functionalized POPs by employing Friedel-Crafts alkylation, FeCl3 assisted oxidative polymerisation and polymerisation in nonaqueous medium, and a comprehensive understanding in potential catalytic applications namely, acetalization, hydrodeoxygenation (HDO), hydrogenation, coupling, photocatalytic hydrogen evolution and biomass conversion towards the production of value-added chemicals in biodiesel and chemical industries.

Hydrogen as a clean fuel is becoming vital in view of depleting fossil fuels and ever increasing energy demand. Hence hydrogen generation and storage gains immense importance. In this review article, different methods of hydrogen storage viz., physical, chemical and electrochemical in various forms like gas, liquid and solid have been discussed and compared in terms of their efficacy, capacity, operating conditions and other safety aspects. Modeling and simulation studies reported on various aspects of hydrogen storage have been presented and compared vis a vis governing equations, applications, assumptions, merits and demerits. These modeling studies would enable to understand the phenomenon better and to explore new avenues. Kinetic and thermodynamic aspects of hydrogen storage especially employing metal hydrides have been discussed too to understand the mechanism, rate controlling actors and energy aspects. Future challenges and prospects of all the aspects of the review were provided.

‘Three-way catalytic technology’ has been successfully implemented in automobile industries for cleaning of auto exhaust gases from 1980’s onward. Supported noble metal catalysts with ceria (CeO2) as the redox promoter have been employed for this technology. However, these catalytic materials have some drawbacks in terms of high light off temperature, catalyst poisoning and drop of activity, heavy metal pollution, etc. Hence, this technology is under active investigation throughout for the sake of better performance. Considerable research efforts have been devoted to develop new advanced materials. Noble metal-free CeO2-based mixed oxides, which can be deployed as potential substitutes, have been investigated at length with the goal to overcome the limitations like loss of stability and activity at elevated temperatures, improvement of oxygen storage/release capacity (OSC), and so on. However, the use of proper dopants at optimum concentration and tuning of the shapes, size and morphology of the nanoparticles via controlled synthesis is a challenging task, since it improves the features of CeO2. In this article, we have reviewed the influence of these factors on the properties of ceria-based materials and their catalytic efficiencies in CO and soot oxidation reactions.

Zeolite Cs-X is an acknowledged representative basic catalyst useful for side-chain alkylation of toluene with methanol. In spite of numerous investigations, still there has been long lasting challenge for achieving high selectivity for side-chain alkylated products rather than ring alkylated products. In an effort to improve the yields of side-chain alkylated products, CO2 was introduced during the toluene side-chain alkylation with methanol at 425 °C over Cs loaded faujasite catalyst. The CO2 addition facilitated in removing the formed hydrogen by reverse water-gas shift reaction and enhanced the product yield. Interestingly, CO2 addition helped in obtaining higher yields of side-chain alkylation products including styrene/ethylbenzene and α-methylstyrene/iso-propylbenzene. The CO2 introduction resulted in less H2 formation in the product stream during the reaction. Mesoporosity was also introduced to the zeolite X to improve the activity and product selectivity.

Selective allylic oxidation of cyclohexene was investigated over nanostructured CeO2/SiO2 and CeO2–Sm2O3/SiO2 catalysts synthesized by a feasible deposition precipitation method. The CeO2–Sm2O3/SiO2 catalyst showed excellent catalytic efficiency with ~89 % cyclohexene conversion and ~90 % selectivity for allylic products (i.e., 2-cyclohexen-1-ol and 2-cyclohexene-1-one), while only ~50 and ~35 % cyclohexene conversion was observed, respectively, over CeO2/SiO2 and CeO2 catalysts. Systematic characterization of the designed catalysts was undertaken to correlate their catalytic activity with the physicochemical properties using X-ray diffraction (XRD) analysis, Brunauer–Emmett–Teller (BET) surface area measurements, Raman spectroscopy, transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and NH3-temperature programmed desorption (TPD) techniques. The results revealed that doping of Sm3+ into the ceria lattice and simultaneous dispersion of resultant Ce–Sm mixed oxides on the silica surface led to improved structural, acidic, and catalytic properties. The better catalytic efficiency of CeO2–Sm2O3/SiO2 was due to high specific surface area, more structural defects, and high concentration of strong acid sites, stimulated by synergistic interaction between various oxides in the catalyst. The cyclohexene conversion and selectivity for allylic products depended on the reaction temperature, nature of solvent, molar ratio of cyclohexene to oxidant, and reaction time. Possible reaction pathways are proposed for selective allylic oxidation of cyclohexene towards 2-cyclohexen-1-ol and 2-cyclohexene-1-one products. SiO2-supported CeO2–Sm2O3 nanocatalyst exhibited outstanding catalytic performance with superior selectivity for allylic products in liquid-phase selective oxidation of cyclohexene under mild reaction conditions.

An efficient melamine-porous organic polymer (M-POP) as N-functionalized organic polymer catalyst was synthesized with melamine and terephthalaldehyde by a facile microwave-assisted method. The synthesized M-POP exhibited a high specific surface area with hierarchical pore structure of both mesoporosity and microporosity. The rich N-moieties namely, C N and N H from the melamine precursor were found to show hydrogen-bonding ability with various organic molecules such as carbonyl compounds. This was illustrated in the acetalization of aldehydes and ketones with methanol or ethylene glycol under mild conditions as a metal-free H-bonding catalyst with high product selectivity. The superior catalytic performance of M-POP was attributed to the availability of a large number of H-bonding sites both as H-donor and H-acceptor between the reactants and the catalyst.

A distinctive mesoporous titanium silicalite-1 (TS-1) was prepared by microwave-assisted postsynthetic treatment with H2O2 to generate hierarchical pore structure. For comparison, mesoporous TS-1 was also prepared with alkali or fluoride postsynthetic treatment. Synthesized catalysts were characterized by various techniques, namely, XRD, XPS, FTIR, UV–vis DRS, and others and evaluated for oxidation of cyclic olefins. The post-treated TS-1 with H2O2 and microwave irradiation exhibited a high catalytic activity in comparison to the parent TS-1. Both microwave irradiation time and temperature during postsynthetic treatment showed influence on the oxidation activity of the catalyst. The H2O2 coupled microwave irradiation generated mesoporosity in the microporous TS-1 crystals and improved its catalytic activity by the creation of external Ti species located on the TS-1 surface. Alkali or fluoride postsynthetic treated TS-1 catalysts also exhibited similar activity with that of H2O2 post-treated sample. In par...

The primary objective of this review was to illustrate the significance of ceria–zirconia (CZ) mixed oxides as catalysts and catalyst supports as employed for a wide variety of catalytic applicatio...

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.

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.

In this work, various transition and rare earth metal ions (M3+; M = Mn3+, Fe3+, La3+, and Pr3+) doped CeO2 solid solutions were prepared by a simple sol–gel method for the degradation of an organic dye, Rhodamine B (RhB) as a model pollutant. The as-prepared samples were thoroughly studied by various characterization techniques to understand the surface and optical properties. The XRD results suggested formation of solid solutions, and TEM studies confirmed the nanosized nature of the ceria particles. The Raman and XPS results revealed that the doping of metal ions enhanced the formation of Ce3+ ions associated with the oxygen vacancies. The doping of M3+ ions in the CeO2 lattice strongly influenced the band gap tuning of undoped CeO2 (3.01 eV) from the UV to Visible region (i.e., 2.45–2.90 eV). Photoluminescence studies suggested that doping of M3+ cations suppresses the recombination rate of photogenerated electron–hole pairs. The photocatalytic activity results indicated that the doped CeO2 samples exhibit substantially enhanced photocatalytic performance for the degradation of RhB compared to undoped CeO2. The better catalytic activity of doped CeO2 samples could be attributed to the presence of defects (Ce3+ ions and oxygen vacancies), which play a prominent role as trapping centres for excited electrons and inhibit the recombination process. The scavengers tests confirmed that the generation of highly reactive hydroxyl (·OH) and super oxide (·O2−) radicals are actively involved in the photodegradation process. This work rendered a new concept for rational design and development of doped CeO2-based materials as better photocatalysts.

The oxidation of cyclohexene was studied using nanostructured CeO2, CeO2/SiO2, CeO2-Sm2O3, and CeO2-Sm2O3/SiO2 catalysts. The CeO2-Sm2O3/SiO2 catalyst shows ~ 96% cyclohexene conversion and ~ 91% selectivity to allylic products, namely, 2-cyclohexen-1-one (~ 53%) and 2-cyclohexen-1-ol (~ 38%) owing to favorable redox (oxygen vacancies) and acid sites stimulated by synergistic interactions of dopant (Sm) and support (SiO2) with CeO2. In contrast, only ~ 40, ~ 55, and ~ 78% of cyclohexene conversions were observed, respectively, over CeO2, CeO2/SiO2, and CeO2-Sm2O3 catalysts. With the increase of reaction time, temperature, and molar ratio of cyclohexene/oxidant, the conversion of cyclohexene and the selectivity of 2-cyclohexen-1-one are increased considerably.

In the present work, nanowire morphologies of α-MnO2, cobalt monodoped α-MnO2, Cu and Co bidoped α-MnO2, and Ni and Co bidoped α-MnO2 samples were prepared by a facile hydrothermal synthesis. The structural, morphological, surface, and redox properties of all the as-prepared samples were investigated by various characterization techniques, namely, scanning electron microscopy (SEM), transmission and high resolution electron microscopy (TEM and HR-TEM), powder X-ray diffraction (XRD), N2 sorption surface area measurements, X-ray photoelectron spectroscopy (XPS), hydrogen-temperature-programmed reduction (H2-TPR), and oxygen-temperature-programmed desorption (O2-TPD). The soot oxidation performance was found to be significantly improved via metal mono- and bidoping. In particular, Cu and Co bidoped α-MnO2 nanowires showed a remarkable improvement in soot oxidation performance, with its T50 (50% soot conversion) values of 279 and 431 °C under tight and loose contact conditions, respectively. The soot combust...

In this work, a novel nanostructured TiO2 supported CeO2–Sm2O3 (CS/T) catalyst was prepared by deposition coprecipitation method and then evaluated for CO oxidation. The role of TiO2 support in the CS/T catalyst was studied by comparing its physicochemical and catalytic properties with the unsupported CeO2–Sm2O3 (CS) and CeO2. Under identical conditions, the CS/T catalyst showed better activity with lower light-off temperature (T50 = ~547 K) compared to the CS and CeO2. Characterization results revealed the constructive structural modifications in the CS/T catalyst owing to the strong synergistic effect between the CeO2–Sm2O3 and TiO2 support, which significantly influenced the catalytic performance for CO oxidation. The highly dispersed Ce–O–Sm solid solution over the TiO2 support leads to large specific surface area, more oxygen vacancies and active oxygen species, which are responsible for better activity of CS/T catalyst. Further, the CS/T catalyst exhibits high reusability (up to three runs) and good long-term stability (48 h) without appreciable loss of catalytic activity.

Carbon capture (CC) employing novel sorbents at high temperature is highly significant to address the serious concerns of global warming. In this work, thermodynamic and kinetic studies have been conducted on the carbonation using doped sorbents of CaO–MgO–CFA (coal fly ash). The thermodynamic estimations not only proved the feasibility and spontaneity of the reaction but also reinforced the positive role played by CFA in not only enhancing the CC but also reducing the regeneration temperatures. Regarding the kinetic studies, a model has been proposed for both the reaction and diffusion kinetic control regimes and has been validated with experimental data at optimal conditions. Various kinetic and Arrhenius parameters have been estimated and compared with the reported values. The rate constants at 650 °C and activation energies estimated for reaction and diffusion controlled regimes were 2.5 min−1, 23 kJ/mol and 0.8 min−1, 30 kJ/mol, respectively. Our values clearly indicate the enhanced rate achieved by ...

Robust nanoarchitectures based on surfactant-free ultrafine Pd nanoparticles (NPs) (2.7–8.2±0.5 nm) have been developed by using the incipient wetness impregnation method with subsequent reduction of PdII species encaged in the 1,3,5-triazine-functionalized nitrogen-rich porous organic polymer (POP) by employing NaBH4, HCHO, and H2 reduction routes. The Pd-POP materials prepared by the three different synthetic methods consist of virtually identical chemical compositions but have different physical and texture properties. Strong metal–support interactions, the nanoconfinement effect of POP, and the homogeneous distribution of Pd NPs have been investigated by performing 13C cross-polarization (CP) solid-state magic angle spinning (MAS) NMR, FTIR, and X-ray photoelectron spectroscopy (XPS), along with wide-angle powder XRD, N2 physisorption, high-resolution (HR)-TEM, high angle annular dark field scanning transmission electron microscopy (HAADF-STEM), and energy-dispersive X-ray (EDX) mapping spectroscopic studies. The resulting Pd-POP based materials exhibit highly efficient catalytic performance with superior stability in promoting biomass refining (hydrodeoxygenation of vanillin, a typical compound of lignin-derived bio-oil). Outstanding catalytic performance (≈98 % conversion of vanillin with exclusive selectivity for hydrogenolysis product 2-methoxy-4-methylphenol) has been achieved over the newly designed Pd-POP catalyst under the optimized reaction conditions (140 °C, 10 bar H2 pressure), affording a turnover frequency (TOF) value of 8.51 h−1 and no significant drop in catalytic activity with desired product selectivity has been noticed for ten successive catalytic cycles, demonstrating the excellent stability and reproducibility of this catalyst system. A size- and location-dependent catalytic performance for the Pd NPs with small size (1.31±0.36 and 2.71±0.25 nm) has been investigated in vanillin hydrodeoxygenation reaction with our newly designed Pd-POP catalysts. The presence of well-dispersed electron-rich metallic Pd sites and highly rigid cross-linked amine-functionalized POP framework with high surface area is thought to be responsible for the high catalytic activity and improvement in catalyst stability.