Rajaram Bal

Preparation of the CuCr2O4 spinel nanoparticles catalyst for selective oxidation of toluene to benzaldehyde

CuCr2O4 spinel nano.particles with size between 30 and 60 nm were prepared by a hydrothermal synthesis method in the presence of a surfactant, cetyltrimethylammonium bromide (CTAB). It was found that the catalyst is highly active in the selective oxidation of toluene with H2O2 at 75° C. The catalyst was characterized by XRD, ICP-AES, XPS, BET-surface area, SEM, TEM and EXAFS. Factors effecting reaction parameters, such as the substrate to oxidant molar ratio, weight of the catalyst, reaction time, etc., were investigated in detail. The investigation revealed that the size of the catalyst as well as the spinel phase plays a crucial role in the activity by favoring the oxidation of toluene. The reusability of the catalyst was examined by conducting repeat experiments with the same catalyst; it was observed that the catalyst displayed no significant changes in its activity even after 5 reuses. A toluene conversion of 57.5% with 84.4% selectivity towards benzaldehyde was observed after 10 hours over the CuCr2O4 spinel nanoparticles catalyst.

Nanocrystalline Pt-CeO2 as an efficient catalyst for a room temperature selective reduction of nitroarenes

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.

Room temperature selective oxidation of cyclohexane over Cu-nanoclusters supported on nanocrystalline Cr2O3

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.

Redox and catalytic chemistry of Ti in titanosilicate molecular sieves: an EPR investigation

An EPR study of Ti 3+ in titanosilicate molecular sieves, TS-1, TiMCM-41, ETS-10 and ETS-4 is reported. Ti 4+ is reduced to Ti 3+ by dry hydrogen above 673 K. Ti ions in TS-1 and TiMCM-41 are located in tetragonally elongated T d and those of ETS-10 and ETS-4 in a tetragonally compressed O h geometric positions. Reduction at 873 K revealed the presence of two non-equivalent Ti 3+ sites in TS-1 and TiMCM-41. Ti 4+ ions in a tetrahedral geometry are more difficult to reduce than in an octahedral symmetry. The effects of cation exchange and Pt impregnation, on the geometry and reducibility of titanium in ETS-10, are also examined. Interaction of a tetrahedrally coordinated Ti 3+ with O 2 or H 2 O 2 results in a diamagnetic titanium(IV) hydroperoxo species. Under the same conditions, an octahedrally coordinated Ti 3+ forms a paramagnetic titanium(IV) superoxo species. The higher catalytic activity of TS-1 and TiMCM-41 in selective oxidation reactions is probably a consequence of the formation of the hydroperoxy species on their surface during the catalytic reaction. The presence of Pt in the vicinity of Ti enables the use of H 2 and O 2 (instead of H 2 O 2 ) to generate the active hydroperoxy site. The absence of formation of titanium hydroperoxy species in ETS-4 and ETS-10 is the cause of their inactivity in selective oxidation reactions.

Room temperature selective oxidation of aniline to azoxybenzene over a silver supported tungsten oxide nanostructured catalyst

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.

Selective oxidation of cyclohexene to adipic acid over silver supported tungsten oxide nanostructured catalysts

We have developed a new synthesis strategy to prepare ∼5 nm metallic silver nanoparticles (AgNPs) supported on tungsten oxide (WO3) nanorods with diameters between 40 and 60 nm in the presence of a cationic surfactant, cetyltrimethylammonium bromide (CTAB). The catalyst was characterized by XRD, XPS, ICP-AES, FT-IR, Raman spectroscopy, EXAFS, SEM and TEM. The catalyst is very effective in liquid phase oxidation of cyclohexene to adipic acid with hydrogen peroxide as an oxidant. The synergy between the surface AgNPs and WO3 nanorods plays the most vital role towards this very high catalytic activity. The reusability of the catalyst which is a prerequisite for practical applications was analysed and it was found that the catalyst exhibits no significant changes in its catalytic activity even after five cycles of reuse. A cyclohexene conversion of >99.9% with an adipic acid selectivity of ∼94% was achieved over ∼5 nm AgNPs supported on the WO3 nanorod catalyst with a very high turnover frequency of ∼12 h−1.

Fabrication of three-dimensional (3D) raspberry-like copper chromite spinel catalyst in a facile hydrothermal route and its activity in selective hydroxylation of benzene to phenol.

Three-dimensional (3D) raspberry-like CuCr2O4 spinel nanoparticles were prepared hydrothermally in the presence of cationic surfactant, cetyltrimethylammonium bromide (CTAB). Detailed characterization of the material was carried out by X-ray diffraction (XRD), inductively coupled plasma-atomic emission spectroscopy (ICP-AES), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared (FTIR) spectroscopy, and thermogravimetric analysis (TGA). XRD revealed the formation of CuCr2O4 spinel phase, and SEM showed the formation of a 3D raspberry-like structure, composed of 20-50 nm nanoparticles. The raspberry-like particles exhibited excellent catalytic behavior for the hydroxylation of benzene to phenol with H2O2. The influence of reaction parameters were investigated in detail. A benzene conversion of 68.5% with 95% phenol selectivity was achieved at 80 °C. The catalyst did not show any leaching up to 10 reuses, showing the true heterogeneity of the catalyst. However, significant H2O2 decomposition occurs on the catalyst necessitating its use in 5-fold excess.

Preparation of silver–tungsten nanostructure materials for selective oxidation of toluene to benzaldehyde with hydrogen peroxide

We have developed a facile one-pot synthetic strategy to prepare Ag/WO3 nanostructure materials with different morphologies using a cationic surfactant, cetyltrimethylammonium bromide. These materials were employed as catalysts in the direct synthesis of toluene to benzaldehyde using H2O2. The morphology of the Ag/WO3 materials can be varied by changing the synthesis parameters. The size and shape of the Ag/WO3 nanostructure catalyst has direct influence on the toluene conversion and benzaldehyde selectivity. The effect of different reaction parameters like reaction temperature, H2O2 to toluene molar ratio, reaction time, and so forth have been studied in detail. The Ag/WO3 catalyst with ∼7 nm silver nanoparticles on the WO3 nanorod with a diameter ∼60 nm showed the best catalytic activity of 42% toluene conversion with 93% benzaldehyde selectivity. The catalyst did not show any leaching up to four reuses, showing the true heterogeneity of the catalyst.

Facile synthesis of CuCr2O4 spinel nanoparticles: a recyclable heterogeneous catalyst for the one pot hydroxylation of benzene

A facile hydrothermal synthesis method is developed to prepare CuCr2O4 spinel nanoparticle catalysts with sizes between 25–50 nm. A detailed characterization of the material was carried out by XRD, ICP-AES, XPS, EXAFS, SEM, TEM, and TGA. XRD revealed the formation of a CuCr2O4 spinel phase and TEM showed the that particles size was 20–50 nm. The catalyst was highly active for the selective oxidation of benzene to phenol with H2O2. The influence of reaction parameters such as temperature, solvent, substrate to oxidant molar ratio, reaction time, etc. were investigated in detail. The reusability of the catalyst was tested by conducting the same experiments with the spent catalyst and it was found that the catalyst did not show any significant activity loss, even after 5 reuses. A benzene conversion of 72.5% with 94% phenol selectivity was achieved over this catalyst at 80 °C. However, significant H2O2 decomposition occurs on the catalyst, necessitating its usage in five-fold excess.

Aqueous phase reforming of glycerol to 1,2-propanediol over Pt-nanoparticles supported on hydrotalcite in the absence of hydrogen

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.