L. N. Sivakumar Konathala

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.

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.

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.

Pt nanoparticle supported on nanocrystalline CeO2: highly selective catalyst for upgradation of phenolic derivatives present in bio-oil

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.

Oxidative coupling of aniline and desulfurization over nitrogen rich mesoporous carbon

Tungsten loaded mesoporous nitrogen rich carbon (WOxMCNx) materials were synthesized using SBA-15 as a hard template. With these new multifunctional materials, we performed a one-pot oxidative coupling of aniline to azo-benzene followed by desulfurization of dibenzothiophene (DBT) to dibenzothiophene sulfone (DBTSO). It was observed that the nature of the support for the catalyst has a strong influence on the activity of the WOx nanoparticle. Whilst WOx on MCNx proved to be a very active and selective catalyst for the formation of azo-benzene via oxidation of aniline as well as dibenzothiophene sulfone from dibenzothiophene, WOx on activated carbon or SBA-15 did not show comparable activity. These multifunctional hybrid catalysts retain their structural framework even after the reaction, and they were recovered easily from the reaction mixture through filtration and reused several times without a significant degradation in activity. Moreover, there was no contribution from leached active species in the activity and conversion was possible only in the presence of the multifunctional catalyst.

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.

Catalytic oxidation of aromatic amines to azoxy compounds over a Cu–CeO2 catalyst using H2O2 as an oxidant

We have prepared Cu-nanoparticles supported on nanocrystalline CeO2 by a one pot hydrothermal method using cetyltrimethylammonium bromide (CTAB) surfactant. The prepared catalyst was characterised by XRD, SEM, TEM, XPS, TPR, EXAFS, BET-surface area and UV-Vis spectroscopy. This prepared catalyst was highly active for the selective oxidation of aromatic amines to corresponding N-oxides with very high yield. It was observed that 5–10 nm Cu-nanoparticles supported on 20–40 nm CeO2 nanoparticles was formed when Cu loading was 3.8 wt%. 3.8 wt% Cu was the optimum loading to give maximum catalytic activity and above 3.8 wt% Cu loading due to the formation of agglomerated Cu species, catalytic activity decreases. The 3.8% Cu–CeO2 catalyst showed 95% aniline conversion and 92% selectivity towards azoxybenzene formation using H2O2 as an oxidising agent. The effect of different reaction parameters like temperature, reaction time, substrates and H2O2 mole ratio were investigated in detail.

Reaction and Mechanistic Studies of Heterogeneous Hydroamination over Support‐Stabilized Gold Nanoparticles

Highly stable gold nanoparticles (GNPs) around 5–6 nm have been prepared by in situ reduction of chloroauric acid on the surface of nitrogen‐rich mesoporous carbon (MCN) without adding any extra stabilizing agent. The synthesized materials have been efficiently utilized as a catalyst for the truly heterogeneous hydroamination of phenylacetylene with aniline. Large turnover numbers (42×106) were achieved by suitably adjusting the gold/support (w/w) ratio, time, temperature, and solvent, leading to 98 % selectivity towards the Markovnikov product. Density functional theory (DFT) studies have been performed to predict the mechanistic pathway of hydroamination with Au0 in GNP@MCN. To understand the structure–activity relationship, the catalyst was characterized by using different techniques such as X‐ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), nitrogen physisorption studies (BET), X‐ray photoelectron spectroscopy (XPS), and Fourier transform infrared (FTIR) spectroscopy.