Prabhas Jana

A green process for chlorine-free benzaldehyde from the solvent-free oxidation of benzyl alcohol with molecular oxygen over a supported nano-size gold catalyst

Benzyl alcohol is oxidized selectively to benzaldehyde with high yield, with a little formation of benzylbenzoate, by molecular oxygen over a reusable nano-size gold catalyst supported on U3O8, MgO, Al2O3 or ZrO2 in the absence of any solvent.

Solvent-free selective oxidation of benzyl alcohol by molecular oxygen over uranium oxide supported nano-gold catalyst for the production of chlorine-free benzaldehyde

A detailed investigation on the production of chlorine-free benzaldehyde in the solvent-free oxidation of benzyl alcohol by O2 over nano-gold supported on U3O8 has been carried out. Influence of different catalyst parameters (different methods of gold deposition on U3O8, gold loading and particle size, and catalyst calcination temperature) and reaction conditions (reaction period and temperature) on the process performance has been studied. The catalyst containing gold at higher concentration and with smaller gold particles showed the better process performance (higher benzyl alcohol conversion and benzaldehyde yield or selectivity). The benzyl alcohol conversion is largely increased but the selectivity for benzaldehyde is slightly decreased (while that of benzyl benzoate is increased) with increasing the reaction period or temperature. In the presence of solvent (viz. tolune, p-xylene, DMF or DMSO), the process performance was found to be inferior to that observed in the absence of any solvent. Substituted benzyl alcohols also can be oxidized by O2 to corresponding aldehydes with high yield and/or selectivity, using the catalyst in the absence of any solvent.

Epoxidation of styrene by TBHP to styrene oxide using barium oxide as a highly active/selective and reusable solid catalyst

Styrene can be oxidised by TBHP to styrene oxide with high selectivity/yield using barium oxide (with or without gallium oxide support) as a simple, inexpensive and reusable solid catalyst; compared to the other alkaline and rare earth metal oxides, barium oxide showed a much better performance in the styrene epoxidation.

Co-production of graphene sheets and hydrogen by decomposition of methane using cobalt based catalysts

The present study reports the simultaneous formation of graphene sheets and hydrogen by methane decomposition using cobalt catalysts. The production of graphene structures can be promoted by adjusting the method and conditions employed in the preparation of the metallic catalyst. The use of methane as a reducing agent seems to be an essential factor for the formation of graphene. The best performance in terms of graphene selectivity is shown by the catalyst obtained using Na2CO3 as a precipitating agent in ethylene glycol medium. Several characterization techniques viz.HRTEM, AFM and Raman spectroscopy have been used to identify the graphene sheets.

Mixed NaNbxTa1−xO3 perovskites as photocatalysts for H2 production

Mixed perovskites NaNbxTa1−xO3 were prepared by solid state reaction (SSR) as well as by hydrothermal (Hyd) methods, and their photocatalytic activity for hydrogen production was studied using the water–methanol system. The assessment of the NaNbxTa1−xO3 materials obtained by the SSR method reveals that the activity of the individual NaTaO3 and NaNbO3 perovskite semiconductors is largely improved in their combined form. Among several compositions employed, the 1 : 1 molar ratio (NaNb0.5Ta0.5O3 sample) shows the best performance for H2 production. On the other hand, using the Hyd method, which implies lower synthesis temperature, the photocatalytic activity of NaNb0.5Ta0.5O3 is enhanced compared to the material obtained by the high temperature SSR method. The characterization of the materials reveals that catalyst properties like high surface area, a larger proportion of the monoclinic crystalline phase and lower crystal defects for the NaNb0.5Ta0.5O3 photocatalyst synthesized by the hydrothermal route may be responsible for its superior activity. Further significant improvement in the activity of the NaNb0.5Ta0.5O3 semiconductor is achieved by the addition of Pt as the co-catalyst, showing that the loading amount has a great influence on the activity. The highest H2 production rate (37.8 μmol g−1 min−1) is obtained for the catalyst prepared by the hydrothermal method (Hyd-NaNb0.5Ta0.5O3) with 0.125 wt% of Pt loading. Moreover, the developed Hyd-NaNb0.5Ta0.5O3 sample shows a stable H2 evolution activity for several reuse cycles.

Ga-Promoted Photocatalytic H2 Production over Pt/ZnO Nanostructures

Photocatalytic H2 generation is investigated over a series of Ga-modified ZnO photocatalysts that were prepared by hydrothermal methods. It is found that the structural, textural, and optoelectronic properties remarkably depend on the Ga content. The photocatalytic activity is higher in samples with Ga content equal to or lower than 5.4 wt %, which are constituted by Zn1-xGaxO phases. Structural, textural, and optoelectronic characterization, combined with theoretical calculations, reveals the effect of Ga in the doped ZnO structures. Higher Ga incorporation leads to the formation of an additional ZnGa2O4 phase with spinel structure. The presence of such a phase is detrimental for the textural and optoelectronic properties of the photocatalysts, leading to a decrease in H2 production. When Pt is used as the cocatalyst, there is an increase of 1 order of magnitude in the activity with respect to the bare photocatalysts. This is a result of Pt acting as an electron scavenger, decreasing the electron-hole recombination rate and boosting the H2 evolution reaction.