Shankha S. Acharyya

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.

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.

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.

One-pot preparation of nanocrystalline Ag–WO3 catalyst for the selective oxidation of styrene

Cationic surfactant cetyltrimethylammonium bromide-mediated water-based preparation of nanocrystalline Ag–WO3 catalyst has been reported in a one-pot preparation method. This catalyst has been characterized by XRD, XPS, SEM, TEM, STEM-mapping, FTIR, Raman, TGA, and ICP-AES. SEM images displayed the formation of an aloevera-like structure. TEM-images revealed the formation of ultrasmall Ag (with average size 5 nm), anchored on monoclinic WO3 rods (with diameters in the range between 80 and 120 nm). It was found that the catalyst can effectively oxidize styrene with H2O2 as the oxidant. The effects of different reaction parameters have been studied in detail. A styrene conversion of 75% with a styrene-oxide selectivity of 55% and a styrene conversion of >99% with a benzaldehyde selectivity of 88% were accomplished over this catalyst, varying different reaction conditions. The catalyst did not show any leaching for up to five reuses, showing the true heterogeneity of the catalyst. However, significant H2O2 decomposition occurs on the catalyst necessitating its usage in four-fold excess.

Cetyl alcohol mediated synthesis of CuCr2O4 spinel nanoparticles: a green catalyst for selective oxidation of aromatic C–H bonds with hydrogen peroxide

We report here cetyl alcohol-promoted synthesis of spherical CuCr2O4 spinel nanoparticles with almost uniform morphology, prepared hydrothermally. Detailed characterization of the material was carried out by XRD, XPS, ICP-AES, SEM, TEM, and TGA. XRD revealed the exclusive formation of the CuCr2O4 spinel phase and TEM showed the formation of a 20–40 nm particle size. The catalyst was highly active for selective oxidation of benzene to phenol with H2O2. The influence of reaction parameters was investigated in detail. The catalyst was found to be selective for hydroxylation of other aromatic alkanes as well. The reusability of the catalyst was tested by conducting the same experiments with the spent catalyst and it was found that the catalyst does not show any significant activity loss even after 5 reuses. The benzene conversion of 67% with 94% phenol selectivity was achieved at 75 °C temperature.

Preparation of CeO2 nanoparticles supported on 1-D silica nanostructures for room temperature selective oxidation of styrene

CeO2 nanoparticles of 2–5 nm size supported on 1-D silica nanostructure with diameter of ∼25–40 nm and a length of ∼1–4 μm were synthesized hydrothermally and it was found that the catalyst is very active for selective oxidation of styrene to styrene oxide at room temperature.