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Acetalization of glycerol into solketal, a potential fuel additive, is a promising approach to utilizing the large waste-stream of glycerol from the biodiesel industry. Herein, we report an efficient ultrasound-assisted room temperature synthesis of solketal by acetalization of glycerol with acetone using an easily recoverable sulfonic acid-functionalized, silica-coated Fe3O4 magnetic nanoparticle (Fe3O4@SiO2@SO3H MNP, FSS MNP) catalyst. The morphology, chemical composition and magnetic properties of the catalyst were elucidated. The acetalization of glycerol was carried out under ultrasonication at room temperature, resulting in 97% glycerol conversion after 15 minutes and 95% isolated yield of solketal with 100% selectivity for this acetal. The facile magnetic retrievability of the catalyst imparted operational simplicity to the solketal synthetic protocol, avoiding complicated catalyst separation and product purification processes. The FSS catalyst was magnetically recycled for up to five catalytic experiments, maintaining a glycerol conversion of 95% and without deterioration in its selectivity, composition, morphology or magnetic properties, thereby ameliorating the green aspects of the protocol.

A solvation-driven catalyst-free H2 generation system from water and various waste hydrosilanes at room temperature was developed, with good to quantitative H2 yields in minutes. Using a green solvent is found to promote the strong coordination of proton carriers with hydrosilane to liberate H2 based on molecular dynamics simulations. Theoretical calculations clarify that OH−in situ generated from H2O enabled by solvation is favorable for activating the Si–H species of hydrosilane, and the in situ formed Si–OH interacts more effectively with the adjacent remaining Si–H, both contributing to the overall enhanced H2 generation. Moreover, the overall life-cycle impacts of the developed system are less than those of industrial H2 production processes, especially in ozone layer depletion and abiotic depletion resources – fossil fuels. This protocol realizes the potential of efficiently producing H2 from waste and water, and opens a new avenue to alleviate petroleum consumption.

Lignin is a potential non-fossil resource of diverse functionalized phenolic units. The most important lignin-derived monomers are 4-alkylphenols, 4-hydroxybenzaldehydes, 4-hydroxybenzoic acids, and 4-hydroxycinnamic acids/esters. Efficient transformation of lignin and/or its monomers into valuable aromatics and their derivatives is crucial, not only for a sustainable lignocellulose biorefinery, but also to reduce our dependence on fossil feedstocks. This review provides a concise account of the recent advances in lignocellulose fractionation/lignin depolymerization processes towards lignin-derived monomers. Subsequently, numerous potential atom-efficient catalytic routes for upgrading lignin monomers into drop-in chemicals and new polymer building blocks are discussed.

Herein, we report the synthesis of carbon-supported palladium–nickel electrocatalysts (ECs) (Pd4–xNix/C ECs, x = 1–3) as an important class of non-platinum ECs, for both oxygen reduction reaction (...

Solid acid catalysts alone or in combination with redox metals play a pivotal role in biomass valorization to obtain alternative fuels and chemicals. In acid-catalyzed biomass conversions, water is...

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

With the depletion and increasing exploitation of fossil energy, it is necessary to develop renewable and alternative fuels. As the most abundant component of lignocellulosic biomass, cellulose can be converted into monosaccharides or other chemical platform molecules, which brings the potential for the sustainable production of chemicals and fuels. In the process of cellulose conversion, acid catalysts can promote hydrolytic degradation of cellulose into valuable platform compounds, which is of great significance in the development of chemicals and biofuels. Among the acid catalysts, heteropolyacid (HPA) as a green catalyst has extraordinary acidity, which is more conducive to the degradation of cellulose biomass. More importantly, HPAs can be designed in the heterogeneous systems that impel them to be easily separated from the products by some simple extraction processes. Compared with homogeneous catalysts, heterogeneous catalysts have some obvious advantages, such as easy separation and wide application. According to the unique properties of HPAs (e.g., strong acidity, high thermal stability, and good solubility), it has become one of the most significant processes of sustainable development in chemistry to use heteropolyacid-based catalysts to depolymerize cellulose and further convert it into high value-added chemicals and biofuels. In this chapter, the advantages, characteristics, and applications of HPAs in different categories for cellulose degradation, especially hydrolysis degradation, are summarized. Moreover, the mechanisms of heterogeneous HPA catalysts in the effective degradation of cellulosic biomass are discussed. This chapter provides more ways to develop new and high-performance heterogeneous HPA catalysts for cellulose degradation in the future.

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

According to the principles of green chemistry, the rapid recovery and reuse of catalysts after a catalytic reaction are important factors to realize the sustainable management of chemical production processes. The functionalization of magnetic nanoparticles is the basis for the efficient separation of heterogeneous catalysts from the reaction system by using the magnetic separation technology as well as for effectively bridging heterogeneous and homogeneous catalytic processes. This can considerably improve the production efficiency and reduce energy consumption as well. Owing to important applications as a potential biofuel or fuel additive, the synthesis of biodiesel mainly from low-cost biomass feedstocks has received considerable attention in the current biorefinery research. A simple synthesis process coupled with the application of functionalized magnetic catalysts can remarkably reduce the production cost and minimize waste generation, thereby promoting the potential development of green catalytic processes for the large-scale synthesis of biodiesel. In this review, the preparation methods, structural and performance control, and protection and functionalization of magnetic nanoparticles as well as the consequent catalytic effects in the synthesis of biodiesel (mainly long-chain fatty acid methyl esters) have been reported. In addition, various representative reaction mechanisms are discussed, emphasizing the existing challenges and prospects of industrialization.

Lignin (15–30 wt%) is a key component of lignocellulosic biomass, along with cellulose (30–50 wt%) and hemicellulose (20–35 wt%), which is largely obtained as a waste product from pulp/paper and biorefinery industries. Due to its aromatic polymer structure, lignin is an obvious non-fossil source for aromatics and their derivatives. Efficient lignin valorization can assist in achieving two essential energy goals, i.e., boosting the lignocellulosic biorefinery and reducing the utilization of fossil fuels for chemicals synthesis. Hence, developing efficient processes and technologies for transforming this waste lignin into value-added chemicals is of paramount interest in the current biorefinery research. Catalysis plays a crucial role in lignin valorization via efficient cleavage of C-O and C-C bonds, which is greatly dependent on the catalysts’ properties and the reaction conditions. In this mini review, we provided a concise account of the most important catalytic routes recently developed for the efficient cleavage of C-O and C-C linkages in lignin systems to produce desired aromatics and their derivatives. Strategies to control unwanted cracking of lignin and char formation especially during catalytic hydroprocessing of lignin are critically discussed. Special attention has been dedicated to understand the role of acid and redox properties of heterogeneous solid catalysts in the selective depolymerization/upgrading of lignin systems.

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.

Ceria cubes decorated with manganese oxide nanoparticles (Mn2O3/CeO2 nanocubes) were synthesized and used to modify a Au electrode for analysis of As(III) in aqueous solution. This modified electrode displayed improved sensitivity than either oxide on their own, indicating a synergistic effect due to the effect of Mn2O3 on the properties of CeO2. The improved sensitivity could be ascribed to the enhanced As (III) adsorption ability of Mn2O3/CeO2 nanocube during electrochemical pre‐concentration, combined with the well known As(III) sensing qualities of the gold substrate. The Mn2O3/CeO2 nanocube modified gold electrode behaved as a promising sensor with stable, repeatable square wave anodic stripping voltammetry (SWASV) peaks, separated from common interfering ions in natural water including Cu (II) under practical conditions. Repeatability and stability studies revealed the As (III) sensor to be robust and reliable, with a sensitivity of 0.0414 μA/ppb and a limit of detection (LoD) of 3.35 ppb under optimized conditions, indicating a possible general use of this class of heteronanostructures in electroanalytical chemistry for studies that rely upon adsorption of deposition of the analyte prior to stripping analysis.

This work reports the synthesis of heterostructured copper–ceria and iron–ceria nanorods and the role of their morphology, redox, and acid properties in catalytic diesel soot combustion. Microscopy images show the presence of nanocrystalline CuO (9.5 ± 0.5 nm) and Fe2O3 (7.3 ± 0.5 nm) particles on the surface of CeO2 nanorods (diameter is 8.5 ± 2 nm and length within 16–89 nm). In addition to diffraction peaks of CuO and Fe2O3 nanocrystallites, X-ray diffraction (XRD) studies reveal doping of Cu2+ and Fe3+ ions into the fluorite lattice of CeO2, hence abundant oxygen vacancies in the Cu/CeO2 and Fe/CeO2 nanorods, as evidenced by Raman spectroscopy studies. XRD and Raman spectroscopy studies further show substantial perturbations in Cu/CeO2 rods, resulting in an improved reducibility of bulk cerium oxide and formation of abundant Lewis acid sites, as investigated by H2-temperature-programmed reduction and pyridine-adsorbed Fourier transform infrared studies, respectively. The Cu/CeO2 rods catalyze the soot...

Efficient transformation of biomass to value-added chemicals and high-energy density fuels is pivotal for a more sustainable economy and carbon-neutral society. In this framework, developing potential cascade chemical processes using functionalised heterogeneous catalysts is essential because of their versatile roles towards viable biomass valorisation. Advances in materials science and catalysis have provided several innovative strategies for the design of new appealing catalytic materials with well-defined structures and special characteristics. Promising catalytic materials that have paved the way for exciting scientific breakthroughs in biomass upgrading are carbon materials, metal-organic frameworks, solid phase ionic liquids, and magnetic iron oxides. These fascinating catalysts offer unique possibilities to accommodate adequate amounts of acid-base and redox functional species, hence enabling various biomass conversion reactions in a one-pot way. This review therefore aims to provide a comprehensive account of the most significant advances in the development of functionalised heterogeneous catalysts for efficient biomass upgrading. In addition, this review highlights important progress ensued in tailoring the immobilisation of desirable functional groups on particular sites of the above-listed materials, while critically discussing the role of consequent properties on cascade reactions as well as on other vital processes within the bio-refinery. Current challenges and future opportunities towards a rational design of novel functionalised heterogeneous catalysts for sustainable biomass valorisation are also emphasized. ispartof: Chemical Society Reviews vol:47 issue:22 pages:8349-8402 ispartof: location:England status: published

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.

The design of novel, efficient supported bimetallic catalysts for the transformation of renewable lignin model compounds into valuable products is currently an emerging research topic. This study investigates the synthesis, characterization and the catalytic application of bimetallic Cu-Ni catalysts supported on pure MCM-41 and Ti incorporated MCM-41 porous materials for the valorization of a lignin model compound (i.e. guaiacol) into the transportation fuels via hydrodeoxygenation route (HDO). The investigated characterization results revealed that the Ti species are well-dispersed within the MCM-41 framework by a tetrahedral coordination. NH3-TPD studies show that the incorporation of Ti into the MCM-41 framework generates large amounts of acidic sites. It was also found that, the coordinated Ti species enhance the dispersion of CuO and NiO species on the surface of Ti-MCM-41 support. The CuNi/Ti-MCM-41 catalyst shows excellent reducible properties due to the co-operative effects of CuO and NiO with the Ti-MCM-41 support. The catalytic experiments revealed that the CuNi/Ti-MCM-41 catalyst exhibits a higher guaiacol conversion (~ 90.49%) and superior selectivity to cyclohexane (~ 50.09%) than the CuNi/MCM-41 catalyst which exhibits only ~ 10.57% cyclohexane selectivity with a guaiacol conversion of ~ 37.03%. The guaiacol conversion and cyclohexane selectivity were found to increase with the increase of reaction pressure from 40 to 100 bar for CuNi/Ti-MCM-41 catalyst. It has been demonstrated that the HDO of guaiacol proceeds via demethoxylation (CAR-OCH3 cleavage) over the CuNi/Ti-MCM-41 catalyst and both demethylation (CARO-CH3 cleavage) and demethoxylation (CAR-OCH3 cleavage) pathways are possible over the CuNi/MCM-41 catalyst in HDO of guaiacol.

Various Cu-Ni/Ti-MCM-41 catalysts by varying Ti amount (Ti/Si = 10, 20 and 30%) were synthesized for hydrodeoxygenation of guaiacol and characterized by XRD, N 2 adsorption-desorption, NH 3 -TPD, H 2 -TPR and Raman spectroscopy. The Ti loading shows an adverse effect on the catalyst surface area. But, more number of acidic sites (5173.55 μmol/g) were found for 20% Ti loaded Cu-Ni/Ti-MCM-41 catalyst. The 20% Ti loaded Cu-Ni/Ti-MCM-41 catalyst shows a high guaiacol conversion (74.2%) and cyclohexane selectivity (48.81%) which is due to abundant acid and redox sites: acid sites initiate removal of oxygen via dehydration, while hydrogenation of guaiacol to cyclohexane is promoted by redox sites.

In this work, a series of porous CeO2 stabilized PdCu nanoparticles are synthesized by a modified hydrothermal method and applied for catalytic reductive degradation of azo dyes. For the synthesis of CeO2 support a simple precipitation method is adopted using ammonium oxalate as precipitant. Synthesized support and nanoparticles are characterized by XRD, TGA, BET surface area, SEM/EDX, TEM, Raman, UV-visible DRS, FTIR and XPS analyses. Catalytic studies show that the synthesized nanoparticles can efficiently reduce model azo dyes, methyl orange (MO) and congo red (CR) with good recyclability. Among various PdCu compositions, Pd1Cu9/CeO2 exhibits superior catalytic activity towards reductive degradation of MO and CR at room temperature. Thus, PdCu/CeO2 nanoparticles can be accepted as potential component for the application in wastewater treatment.

Understanding the role of nanointerface structures in supported bimetallic nanoparticles is vital for the rational design of novel high-performance catalysts. This study reports the synthesis, characterization, and the catalytic application of Co–Mn oxide nanoparticles supported on CeO2 nanocubes with the specific aim of investigating the effect of nanointerfaces in tuning structure–activity properties. High-resolution transmission electron microscopy analysis reveals the formation of different types of Co–Mn nanoalloys with a range of 6 ± 0.5 to 14 ± 0.5 nm on the surface of CeO2 nanocubes, which are in the range of 15 ± 1.5 to 25 ± 1.5 nm. High concentration of Ce3+ species are found in Co–Mn/CeO2 (23.34%) compared with that in Mn/CeO2 (21.41%), Co/CeO2 (15.63%), and CeO2 (11.06%), as evidenced by X-ray photoelectron spectroscopy (XPS) analysis. Nanoscale electron energy loss spectroscopy analysis in combination with XPS studies shows the transformation of Co2+ to Co3+ and simultaneously Mn4+/3+ to Mn2+...

Heterogeneous catalysis is a promising technology for the valorization of renewable biomass to sustainable advanced fuels and fine chemicals. Porosity and nanostructure are the most versatile features of heterogeneous solid catalysts, which can greatly determine the accessibility of specific active sites, reaction mechanisms, and the selectivity of desirable products. Hence, the precise tuning of porosity and nanostructure has been a potential strategy towards developing novel solid catalysts with indispensable characteristics for efficient biomass valorization. Herein, we present a timely and comprehensive review of the recent advances in catalytic biomass conversions over microporous zeolites, mesoporous silicas, and nanostructured metals/metal oxides. This review covers the catalytic processing of both edible (lipids and starch) and non-edible (lignocellulose) biomass as well as their derived compounds, along with a systematic evaluation of catalyst reusability/kinetic/mechanistic aspects in the relevant processes. The key parameters essential for tailoring particle size, morphology, porosity, acid-base, and redox properties of solid catalysts are emphasized, while discussing the ensuing catalytic effects towards the selective conversion of biomass into desirable chemicals. Special attention has been drawn to understand the role of water in liquid phase biomass conversions as well as the hydrothermal stability and the deactivation of nanoporous catalysts. We believe this comprehensive review will provide new insights towards developing state-of-the-art solid catalysts with well-defined porosity and nanoscale properties for viable biomass conversion. ispartof: Chemical Society Reviews vol:48 issue:8 pages:2366-2421 ispartof: location:England status: published

The development of social productive forces leads to the increasing consumption of fossil fuels. However, the burning of traditional fossil fuels releases huge amounts of carbon emissions into the atmosphere, resulting in drastically increased global surface temperatures, and hence, global warming and abnormal climate change. Biodiesel, which can be produced by (trans)esterification of bio-oils using solid acid catalysts, is recognized as renewable and clean energy, alternative to fossil-derived diesel, and it can meet society's requirements. This review describes the catalytic conversion of bio-derived oils into biodiesel using various sulfonic acid-functionalized heterogeneous catalytic materials that show higher catalytic efficiency and superior recyclability. Besides, various methods of biodiesel preparation and the appropriate design and preparation of robust and efficient catalytic materials for biodiesel production were provided. Finally, the mechanisms of different catalytic esterification and transesterification reactions for biodiesel synthesis, the relevant reaction kinetic models, and techno-economic analysis of biodiesel production were critically discussed in this review.

Catalytic conversion of glycerol into value-added chemicals, particularly acrolein via acid-catalyzed dehydration route has received much attention due to the potential uses of acrolein. This work reports the synthesis of various alkaline metal substituted phosphotungstic acid (H3PW12O40, HPW) catalysts, namely M2.5H0.5PW12O40 (M = Cs, Rb and K) using a controlled precipitation method. A systematic structural, morphology, and chemical characterization were conducted using various analytical techniques. XRD studies revealed that the incorporation of alkaline metals in H3PW12O40 leads to decreased crystallite size and enhanced lattice strain. N2 adsorption–desorption studies show that the specific surface area of H3PW12O40 is significantly improved from 5 to 82 (K2.5H0.5PW12O40), 103 (Rb2.5H0.5PW12O40), and 94 m2/g (Cs2.5H0.5PW12O40). XRD, Raman, and FT-IR studies confirm the Keggin structure of all the alkaline metal substituted HPW catalysts. The acidity strengths estimated by NH3-TPD analysis were obtained in the following order: H3PW (2654.91 μmole/g) > K2.5H0.5PW (1060.10 μmole/g) > Rb2.5H0.5PW (762.08 μmole/g) > Cs2.5H0.5.5PW (461.81 μmole/g). Although alkaline metal substituted H3PW12O40 catalysts exhibit higher specific surface area and smaller crystallite size compared to parent H3PW12O40 low glycerol conversions were found for substituted H3PW12O40 catalysts. As well, the parent H3PW12O40 catalyst shows an excellent acrolein selectivity (95%) which is much higher than that of Cs2.5H0.5.5PW (81.9%) and very close to the selectivities obtained over Rb2.5H0.5PW (95.1%) and K2.5H0.5.5PW (95.6%) catalysts. The catalytic performance of H3PW12O40 and M2.5H0.5PW12O40 materials is directly proportional to their acidic strengths, indicating that the catalyst acidity is a key factor for achieving better results in glycerol dehydration.

This work investigates selective oxidation of glycerol with molecular oxygen, one of the viable routes to obtain value-added products from bio-glycerol, using nanosized Pd-based catalysts. For this, three types of 1 wt.% Pd catalysts supported on activated carbon (Ac), hydrotalcite (HTc), and activated carbon–hydrotalcite composite (Ac–HTc) were prepared. The physicochemical properties of the catalysts are characterized using various techniques, such as XRD, BET, XRF, H2-TPR, CO2-TPD, and TEM. The TEM images reveal the formation of Pd nanoparticles with an average diameter of 9.01, 9.10, and 11.16 nm on the surface of HTc, Ac, and Ac–HTc supports, respectively. The CO2-TPD results show that the Pd@HTc catalyst exhibits higher concentration of basic sites compared with that of Pd@HTc-Ac and Pd@Ac catalysts. The H2-TPR profiles show that the reducibility of Pd species is highly dependent on the nature of the supports. Catalytic activity results reveal that the conversion of glycerol over Pd catalysts increased in the following order: Pd/Ac

This work reports hydrodeoxygenation of dibenzofuran into bicyclic hydrocarbons over Cu-Ni catalysts supported on TiO2, ZrO2 and CeO2. The supported Cu-Ni catalysts were synthesized using a wet-impregnation method and calcined and reduced at 500 °C in accordance with TGA, DSC, and H2-TPR results. The catalyst properties were systematically examined using Raman, XRD, SEM, EDX and XPS techniques. XRD and Raman studies reveal the existence of cubic phase CeO2, monoclinic ZrO2, anatase TiO2, and cubic NiO in the synthesized catalysts. H2-TPR results show the simultaneous reduction of Cu2+ to Cu0 and Ni2+ to Ni0, forming bimetallic Cu-Ni alloy. Among the supports, a high dispersion of Cu-Ni particles was found on the CeO2 support, as evidenced by SEM studies. The reduced catalysts were investigated for hydrodeoxygenation of dibenzofuran at 250, 260 and 270 °C at 100 H2 bar for 6 h. The results show that the conversion of dibenzofuran increases with the increase of temperature: at 250 and 260 °C CuNi/TiO2 catalyst showed higher dibenzofuran conversions of 96% and 99% than the NiCu/CeO2 catalyst with relatively low conversions of 89% and 98%, respectively. In contrast, low conversions of 63% and 68% were found for the CuNi/ZrO2 catalyst under identical reaction conditions. In the case of selectivity to hydrocarbons, NiCu/TiO2 catalyst showed excellent selectivity to bicyclohexyl compared with that of NiCu/CeO2 and NiCu/ZrO2 catalysts at 260 °C. However, in terms of selectivity to bicyclohexyl-1-ene, NiCu/CeO2 catalyst showed the highest selectivity at 250 °C, while NiCu/ZrO2 catalyst exhibited the highest selectivity at 260 and 270 °C.

The structure-activity properties of MnO x /CeO 2 nanorods and MnO x /CeO 2 nanoparticles, with the importance of CeO 2 morphology have been investigated for the solvent-free oxidation of amines using oxygen as a green oxidant. The physicochemical properties of the samples have been investigated using HRTEM, XRD, Raman, BET, XPS, and FT-IR techniques. HRTEM studies reveal that CeO 2 nanorods preferentially expose {1 1 0} and {1 0 0} crystal planes, while CeO 2 nanoparticles expose {1 1 1} planes. The addition of manganese to CeO 2 supports leads to an enhancement in the concentration of Ce 3+ ions and oxygen vacancies, which are more pronounced for the MnO x /CeO 2 nanorods as evidenced by Raman and XPS studies. Another striking observation noticed from XPS studies is that MnO x /CeO 2 nanorods catalyst exhibits Mn 4+ , Mn 3+ , and Mn 2+ species, whereas only Mn 4+ and Mn 3+ are presented in MnO x /CeO 2 nanoparticles catalyst. It was found that MnO x /CeO 2 nanorods catalyst exhibit a two-fold higher activity for the oxidation of benzylamine with superior selectivity to dibenzylimine (∼99%) compared with that of MnO x /CeO 2 nanoparticles catalyst. The MnO x /CeO 2 nanorods catalyst was also found to be effective for the oxidation of various amines, and moderate to good product yields were obtained. Novel probable reaction pathways are proposed for solvent-free oxidation of primary and secondary benzylamines over MnO x /CeO 2 nanorods catalyst. The presence of surface-active Mn 4+ /Mn 2+ couple and the enhanced defect structure of CeO 2 nanorods (i.e., higher numbers of Ce 3+ ions and abundant O vacancies) are found to be key factors for the high catalytic efficiency of the MnO x /CeO 2 nanorods.

This work investigates the structure-activity properties of CuOx-decorated CeO2 nanocubes with a meticulous scrutiny on the role of the CuOx/CeO2 nanointerface in the catalytic oxidation of diesel soot, a critical environmental problem all over the world. For this, a systematic characterization of the materials has been undertaken using transmission electron microscopy (TEM), transmission electron microscopy-energy-dispersive X-ray spectroscopy (TEM-EDS), high-angle annular dark-field-scanning transmission electron microscopy (HAADF-STEM), scanning transmission electron microscopy-electron energy loss spectroscopy (STEM-EELS), X-ray diffraction (XRD), Raman, N2 adsorption-desorption, and X-ray photoelectron spectroscopy (XPS) techniques. The TEM images show the formation of nanosized CeO2 cubes (∼25 nm) and CuOx nanoparticles (∼8.5 nm). The TEM-EDS elemental mapping images reveal the uniform decoration of CuOx nanoparticles on CeO2 nanocubes. The XPS and Raman studies show that the decoration of CuOx on CeO2 nanocubes leads to improved structural defects, such as higher concentrations of Ce(3+) ions and abundant oxygen vacancies. It was found that CuOx-decorated CeO2 nanocubes efficiently catalyze soot oxidation at a much lower temperature (T50 = 646 K, temperature at which 50% soot conversion is achieved) compared to that of pristine CeO2 nanocubes (T50 = 725 K) under tight contact conditions. Similarly, a huge 91 K difference in the T50 values of CuOx/CeO2 (T50 = 744 K) and pristine CeO2 (T50 = 835 K) was found in the loose-contact soot oxidation studies. The superior catalytic performance of CuOx-decorated CeO2 nanocubes is mainly attributed to the improved redox efficiency of CeO2 at the nanointerface sites of CuOx-CeO2, as evidenced by Ce M5,4 EELS analysis, supported by XRD, Raman, and XPS studies, a clear proof for the role of nanointerfaces in the performance of heterostructured nanocatalysts.

Designing efficient and facile recoverable catalysts is desired for sustainable biomass valorization. This work reports the one-pot synthesis of a novel magnetic Fe(NiFe)O4–SiO2 nanocatalyst for hydrogenation of biomass-derived furfural into valuable furfuryl alcohol. Various techniques were used to systematically analyze the physicochemical properties of the Fe(NiFe)O4–SiO2 nanocatalyst. Vibrating sample magnetometer analysis reveals low coercivity of Fe(NiFe)O4–SiO2 (6.991 G) compared with that of Fe3O4–SiO2 (27.323 G), which is attributed to highly dispersed Ni species in the Fe(NiFe)O4–SiO2 catalyst. HRTEM images indicated the nanosized nature of the Fe(NiFe)O4–SiO2 catalyst with an average diameter of ∼14.32 nm. The Fe(NiFe)O4–SiO2 catalyst showed a superior BET surface area (259 m2/g), which is due to the formation of nanosized particles. The magnetic Fe(NiFe)O4–SiO2 nanocatalyst shows a remarkable performance with 94.3 and 93.5% conversions of furfural and ∼100% selectivity of furfuryl alcohol at 9...

Designing Au nanocatalysts supported on nanosized metal oxides has drawn much attention due to remarkable nanoscale influenced metal-support interactions and their favorable role in heterogeneous catalysis. This work reports development of Au nanocatalysts dispersed on nanosized CeO2 and CeO2-ZrO2 supports for solvent- and base-free oxidative coupling of benzylamines into N-benzylbenzaldimines using O2 as a green oxidant. The physicochemical characterization of nanocatalysts has been undertaken using HRTEM, UV–vis DRS, XRD, Raman, BET, TG-DTA, AAS, and XPS techniques. HRTEM images reveal the formation of nanosized CeO2 and CeO2-ZrO2 supports with an average diameter of ∼10 and 7 nm, respectively. HRTEM images also indicated that Au/CeO2-ZrO2 catalyst has smaller Au nanoparticles (∼2.1 nm) compared with that of Au/CeO2 catalyst (∼3.7 nm). Raman and XPS studies showed that the addition of ZrO2 to CeO2 leads to abundant oxygen vacancies and higher concentration of Ce3+, respectively. The Au/CeO2-ZrO2 catalyst exhibited a higher efficiency in benzylamine conversion (∼95%) followed by Au/CeO2 (∼78%), CeO2-ZrO2 (∼51%), and CeO2 (∼39%). The Au/CeO2-ZrO2 catalyst was also found to effective for oxidative coupling of various benzylamines, and moderate to good product yields were obtained. The presence of smaller Au particles (2.1 nm) and improved surface-defect properties of nanoscale CeO2-ZrO2 support are found to be key factors for high performance of Au/CeO2-ZrO2 catalyst. Additionally, the reaction temperature is one of the important factors for the performance of catalysts. Remarkably, ∼99.6–99.9% selectivity for N-benzylbenzaldimines was found in the amine oxidation, which highlights the significance of present work in the selective oxidation catalysis.

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

Developing one-pot reaction methodologies, which typically require multifunctional catalyst systems, is crucial for sustainable production of bio-derived fuels and chemicals. This work reports one-pot hydrogenation-esterification of furfural to furfuryl acetate using a bifunctional metal-based nanohybrid catalyst, composed of rice husk (RH) derived SiO2, Cu, Al, and Mg species (RHSiO2-Cu-Al-Mg). For comparison, the catalytic efficiency of RHSiO2-Cu and RHSiO2-Cu-Al were tested under similar reaction conditions. Various analytical techniques were used to elucidate the physicochemical, textural, and acid-redox properties of the catalysts. It was found that the RHSiO2-Cu-Al-Mg catalyst contains an optimum amount of acid and redox sites, as illustrated by NH3-TPD and H2-TPR studies, respectively. Especially, Mg addition played a vital role in tailoring acidity of the RHSiO2-Cu-Al catalyst to promote in-situ esterification of furfuryl alcohol with acetic acid to yield furfuryl acetate. As a result, the RHSiO2-Cu-Al-Mg catalyst exhibited the best performance in one-pot conversion of furfural to furfuryl acetate, outperforming various noble metal/silica based catalysts. This study offers potential opportunities for the rational design of novel, bifunctional heterogeneous catalysts for efficient production of bio-derived fuels and value added chemicals.

Heterogeneous solid catalysts have been largely developed for biodiesel production, because of their attractive acid-base properties, strong hydrothermal stability, and efficient recovery/reusability. In this framework, developing bio-waste derived heterogeneous catalysts has attracted immense attention for several catalytic applications, owing to their inexpensive, high abundance, non-toxic, and adequate acid-base properties. In the present work, we investigated the catalytic performance of a biomass-derived orange peel ash (OPA), which contains a porous structure, as a raw heterogeneous catalyst for the transesterification of soybean oil to biodiesel. About 98 % conversion of soybean oil to biodiesel was obtained under the optimized reaction conditions i.e., 6:1 methanol:oil ratio, 7 wt. % catalyst loading, 7 h reaction time at ambient reaction temperature, which ascribed to the presence of abundant basic sites in the developed OPA catalyst. The catalyst can be reused for five successive cycles and shows good stability towards the biodiesel production.