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Developing efficient and stable non-noble metal catalysts for the catalytic oxidation of volatile organic compounds (VOCs) has always been key for controlling air pollution. Chromium oxide nanoparticle catalysts act as a potential material for this purpose, and their morphology has a significant impact on the catalyst performance. Herein, two types of chromium oxides with different morphologies were prepared using two different precursors in a hydrothermal route: one that was synthesized using chromic acid and exhibited a strawberry micro-spindle type morphology consisting of innumerable nanoparticles in the range of ∼20–35 nm, and the other one that was synthesized using a nitrate precursor and consisted of thoroughly dispersed nanoparticles in the range of 30–40 nm. Both of them were successfully applied for the total oxidation of toluene. The former exhibited higher efficiency; for long-term stability of the catalyst, K+ ions were added during its synthesis. Importantly, the former catalyst was superior to the latter one because of the ease of activation and migration of lattice oxygen, which was comprehensively understood using H2-TPR, O2-TPD and XPS analyses. [ABSTRACT FROM AUTHOR]

Heterogeneous catalysts comprising silver nanoparticles supported on nanostructured tungsten oxide were applied for room temperature oxidative coupling of aniline to azoxybenzene, an important chemical intermediate and a chemical of industrial interest. The catalytic protocol features high activity and selectivity to the target product azoxybenzene with a turnover number of ∼368. The catalyst was characterized by XRD, XPS, ICP-AES, FT-IR, TGA, EXAFS, SEM and TEM. The silver-tungsten nanomaterial acts as an excellent catalyst for selective oxidation of aniline to azoxybenzene using H2O2 as an oxidant. An aniline conversion of 87% with 91% selectivity of azoxybenzene was achieved without the use of any external additives. Moreover, a high stability and recyclability of the catalyst is also observed under the investigated conditions. [ABSTRACT FROM AUTHOR]

We have developed a new synthesis strategy to prepare Pt nanoparticles with size between 2 and 5 nm supported on CeO2 nanoparticles with size between 30 and 60 nm by the hydrothermal method in the presence of the surfactant cetyltrimethyl ammonium bromide (CTAB) and a polymer (PVP). It was found that the catalyst is highly active for the chemoselective hydrogenation of nitro compounds in aqueous medium in the presence of molecular hydrogen at room temperature (25 °C). The catalyst was characterized by XRD, ICP-AES, XPS, BET-surface area measurements, SEM, TEM and EXAFS. Different reaction parameters like reaction time, catalyst ratio, Pt loading etc. were studied in detail. The investigation revealed that the site of Pt plays a crucial role in the activity by favouring the reduction of nitro-compounds. The catalyst shows ＞99.9% conversion of nitro-compounds with 99% selectivity of amino compounds. The reusability of the catalyst was tested by conducting the experiment with the same catalyst and it was found that the catalyst does not change its activity and selectivity even after five reuses. [ABSTRACT FROM AUTHOR]

Pt nanoparticle supported on nanocrystalline CeO2 was prepared, and it was found that the catalyst can selectively hydrogenate phenolic derivatives present in bio-oil. The catalyst was characterized by XRD, XPS, ICP-AES, EXAFS, SEM and TEM. TEM micrograms confirm the presence of very small Pt nanoparticles supported on nanocrystalline CeO2. The catalyst was found to be very effective in liquid phase hydrogenation of phenol and phenolic compounds present in bio-oil in the presence of molecular H2. The synergy between the surface and very small Pt particles on the nanocrystalline CeO2 plays the most vital role towards the extremely high catalytic activity of the catalyst. The reusability of the catalyst was tested, and it was found that the catalyst does not exhibit any significant change in its catalytic activity even after five reuses. The catalyst showed ∼100% conversion with very high selectivity after 3 h in phenol conversions of 100% with >98% cyclohexanol selectivity achieved after 3 h of reaction at 100 °C in aqueous medium. [ABSTRACT FROM AUTHOR]

A material consisting of highly dispersed Cu nanoclusters anchored on nanocrystalline SiO2-MnO2 has been prepared, and was found to act as a bifunctional catalyst for the one- step conversion of glycerol to acrylic acid using H2O2. Under optimized conditions a glycerol conversion of 77.1%, with 74.7% selectivity for acrylic acid, was achieved after 30 h reaction time. [ABSTRACT FROM AUTHOR]

Pt-nanoparticles, in the range of 2–5 nm, supported on hydrotalcite (HT), were used as a catalyst for the selective hydrogenolysis of glycerol to produce 1,2-propanediol by aqueous phase reforming in the absence of any added hydrogen. The catalyst was characterized by XRD, N2-sorption, pulse chemisorption, TPR, XPS, SEM, TEM, EXAFS. The influence of reaction parameters like reaction time, pressure, etc., were studied in detail. The study reveals that the Pt-nanoparticles are the active sites for the selective conversion of glycerol to 1,2-propanediol. The role of the support also plays an important role in the hydrogenolysis. The hydrogen required for the hydrogenolysis is derived from the reforming of H2O over the Pt-HT catalyst. The mechanism of the hydrogenolysis reaction is also proposed. A glycerol conversion of 98% with a 1,2-propanediol selectivity of 74% was achieved over 3 wt% Pt supported on HT. The reusability of the catalyst was tested by conducting four runs with the same catalyst and it was found that after four reuses, the conversion and selectivity was almost same. [ABSTRACT FROM AUTHOR]

Gold nanoparticles deposited on nanocrystalline magnesium oxide is a very efficient catalyst for the reduction of nitroarenes in aqueous medium at room temperature. Sodium borohydride is used as the source of hydrogen for the reduction of nitro groups. This catalytic system selectively reduces the nitro group even in the presence of other sensitive functional groups under very mild conditions in good to excellent yields without the requirement of any promoters. The reaction kinetics of reduction of 4-nitrophenol to 4-aminophenol has been studied by UV-visible spectrophotometry, and its apparent rate constant has been determined and compared with those of other supported gold catalysts. The spent heterogeneous catalyst is recovered by simple centrifugation, and reused for multiple cycles. [ABSTRACT FROM AUTHOR]

Cu-nanoclustures supported on nanocrystalline Cr2O3 were prepared by a hydrothermal synthesis method in the presence of surfactant, cetyltrimethylammonium bromide (CTAB). It was found that the catalyst is highly active for the selective oxidation of cyclohexane with H2O2 at room temperature. The catalyst was characterized by XRD, ICP-AES, XPS, TPR, BET-surface area, SEM, TEM and EXAFS. The effect of Cu loading and the influence of reaction parameters, such as the substrate to oxidant molar ratio and reaction time, were investigated in detail. The investigation revealed that the size of copper plays a crucial role towards the activity by favoring the oxidation of cyclohexane. The reusability of the catalyst was tested by conducting repeat experiments with the same catalyst, where it was found that the catalyst displays no changes in its activity and selectivity even after 4 reuses. The cyclohexane conversion of 86% with a cyclohexanone selectivity of 85%, and an overall C6 selectivity (cyclohexanol and cyclohexanone) of 100% was achieved after 3 h of reaction at room temperature, over 4.3 wt% Cu loaded on nanocrystalline Cr2O3. [ABSTRACT FROM AUTHOR]

Cu-nanoclustures supported on nanocrystalline Cr2O3 were prepared by a hydrothermal synthesis method in the presence of surfactant, cetyltrimethylammonium bromide (CTAB). It was found that the catalyst is highly active for the selective oxidation of cyclohexane with H2O2 at room temperature. The catalyst was characterized by XRD, ICP-AES, XPS, TPR, BET-surface area, SEM, TEM and EXAFS. The effect of Cu loading and the influence of reaction parameters, such as the substrate to oxidant molar ratio and reaction time, were investigated in detail. The investigation revealed that the size of copper plays a crucial role towards the activity by favoring the oxidation of cyclohexane. The reusability of the catalyst was tested by conducting repeat experiments with the same catalyst, where it was found that the catalyst displays no changes in its activity and selectivity even after 4 reuses. The cyclohexane conversion of 86% with a cyclohexanone selectivity of 85%, and an overall C6 selectivity (cyclohexanol and cyclohexanone) of 100% was achieved after 3 h of reaction at room temperature, over 4.3 wt% Cu loaded on nanocrystalline Cr2O3. [ABSTRACT FROM AUTHOR]

A material consisting of highly dispersed Cu nanoclusters anchored on nanocrystalline SiO2-MnO2 has been prepared, and was found to act as a bifunctional catalyst for the one-step conversion of glycerol to acrylic acid using H2O2. Under optimized conditions a glycerol conversion of 77.1%, with 74.7% selectivity for acrylic acid, was achieved after 30 h reaction time.

A novel oxide-supported Ir dimer, which was found to be active for transfer hydrogenation of aromatic ketones, was prepared on a γ-Al(2)O(3) surface from an Ir dimer complex [Ir(2){η(5)-C(5)(CH(3))(5)}(2)(μ-CH(2))(2)] (Ir(2)) with an Ir=Ir bond. Detailed characterization of the γ-Al(2)O(3)-supported Ir dimer (Ir(2)/γ-Al(2)O(3)) revealed that the structure of Ir(2) consisted of an Ir dimer with an Ir-Ir bond attached to the γ-Al(2)O(3) surface by two bridged Ir-(OAl)(2)-Ir bonds. The supported Ir(2)/γ-Al(2)O(3) dimer with bridged Ir-(OAl)(2)-Ir bonds acted as an efficient catalyst for transfer hydrogenation (turnover number of acetophenone = 699 (24 h)), while homogeneous Ir(2), SiO(2)- and MgO-supported Ir(2) were much less active. A structural transformation at the interface of the Ir dimer and the γ-Al(2)O(3) surface was suggested to assist the transfer hydrogenation catalysis via the formation of an Ir(2)-H(2) species on the γ-Al(2)O(3) surface (Ir(2)-H(2)/γ-Al(2)O(3)) as a key intermediate in the transfer hydrogenation. The present study deepened the understanding of the role and dynamic behaviour of the oxide surface in the hydrogen transfer catalysis on the supported Ir dimer.

Supported Pd-P and Pd-N complexes prepared by a selective reaction of Pd-monomer precursors with SiO2, Al2O3 and TiO2 surfaces and characterized by EXAFS, XPS, XRF and gas analysis exhibited oxide surface-promoted catalysis for the catalytic intrahydroamination of 3-amino propanol vinyl ether to produce a cyclic amine.

Zeolite-supported rhenium catalysts are active for selective oxidation of benzene with molecular oxygen, where coexisting ammonia is prerequisite to the direct phenol synthesis.