Gangadhara Raju

Design of highly efficient Mo and W-promoted SnO2 solid acids for heterogeneous catalysis: acetalization of bio-glycerol

Development of highly promising solid acids is one of the key technologies to meet the essential challenges of economical and environmental concerns. Thus, novel molybdenum and tungsten promoted SnO2 solid acids (wet-impregnation) and pure SnO2 (fusion method) were prepared. The synthesized catalysts were systematically analyzed using various techniques, namely, XRD, BET surface area, pore size distribution, XPS, FTIR, FTIR of adsorbed pyridine, Raman, NH3-TPD, and H2-TPR. XRD results suggested formation of nanocrystalline SnO2 solid solutions due to the incorporation of molybdenum and tungsten cations into the SnO2 lattice. All the materials exhibited smaller crystallite size, remarkable porosity, and high specific surface area. Raman measurements suggested the formation of more oxygen vacancy defects in the doped catalysts, and the TPR results confirmed facile reduction of the doped SnO2. NH3-TPD studies revealed the beneficial role of molybdenum and tungsten oxides on the acidic properties of the SnO2. FTIR studies of adsorbed pyridine showed the existence of a larger number of Bronsted acidic sites compared to Lewis acidic sites in the prepared catalysts. The resulting catalysts are found to be efficient solid acids for acetalization of glycerol with acetone, furfural, and its derivatives under solvent-free and ambient temperature conditions. Particularly, the Mo6+-doped SnO2 catalyst exhibited excellent catalytic performance in terms of both glycerol conversion and selectivity of the products. The increased presence of acidic sites and enhanced specific surface area, accompanied by notable redox properties and superior lattice defects are found to be the decisive factors for better catalytic activity of the Mo6+-doped SnO2 sample. The investigated SnO2 solid acids represent a novel class of heterogeneous catalysts useful for the transformation of glycerol to value-added products in an eco-friendly manner.

One pot ‘click’ reaction: CuII–hydrotalcite catalyzed tandem synthesis of β-hydroxy triazoles via regioselective opening of epoxide followed by [3+2] cycloaddition

A novel copper (II) hydrotalcite catalyst has been investigated for its use in the cascade synthesis of β-hydroxy triazoles. It is found to be a dynamic catalyst for regioselective organic synthesis in water. The copper (II) hydrotalcite catalyst, in various Cu : Al molar ratios, was prepared by adopting a coprecipitation method and characterized using different techniques. The three component (epoxides, sodium azide and terminal alkynes) reactions under investigation were performed in water at ambient temperature without any additives. The formation of 2-azido alcohol, generated in situ, was observed to be the key step in the [3+2] cycloaddition of the click reaction. The optimized reaction procedures described herein are not only regioenriched and high yielding but also eco-friendly.

Catalytic decomposition of CH4 over Ni-Al2O3-SiO2 catalysts: Influence of pretreatment conditions for the production of H2

Abstract This article reports the production of CO x free hydrogen and carbon nanofibers by the catalytic decomposition of methane over Ni-Al 2 O 3 -SiO 2 catalysts. The influence of reaction temperature, pretreatment temperature, and effect of reductive pretreatment on the decomposition of methane activity is investigated. The physico-chemical characteristics of fresh and deactivated samples were characterized using BET-SA, XRD, TPR, SEM/TEM, CHNS analyses and correlated with the methane decomposition results obtained. The Ni-Al-Si (4:0.5:1.5) catalyst reduced with hydrazine hydrate produced better H 2 yields of ca . 1815 mol H 2 /mol Ni than the catalyst reduced with 5% H 2 /N 2 .

Solvent-free aerobic oxidation of ethylbenzene over supported Ni catalysts using molecular oxygen at atmospheric pressure

Abstract We investigated the aerobic oxidation of ethylbenzene in the absence of solvent or any additive carried out over Ni on different types of supports namely SiO2, hydroxyapatite, SBA-15, and USY Zeolites. The oxidation of ethylbenzene activities was measured in a round bottom flask immersed in oil bath at known reaction temperature. The physicochemical characteristics of the catalysts were examined by BET surface area, XRD, FT-IR and the oxidation activities were correlated with the acidities of the catalysts obtained by TPD of NH3. It was observed that both hydroxyapatite and USY (13% Na2O) supported Ni catalysts displayed higher ethylbenzene conversion and 80% selectivity towards acetophenone.

Selective Gas-Phase Conversion of Glycerol to Acetol Over Promoted Zirconia Solid Acid Catalysts

The vapour phase selective conversion of glycerol to acetol at normal atmospheric pressure in a fixed-bed micro reactor was investigated over SO4 2� and WOx promoted ZrO2 and M-ZrO2 (M = Al2O3 or TiO2) solid acid catalysts. The investigated sulfate and tungstate ion promoted zirconia-based catalysts were prepared by both coprecipitation and impregnation methods and calcined at 923 K. The synthesized catalysts were characterized by means of X-ray powder diffraction, X-ray photoelectron spectroscopy, BET surface area and ammonia temperature-programmed desorption methods. Characterization results suggest that SO4 2� promoter strongly influences the physicochemical properties of the support oxides than WOx. However, the WOx promoted catalysts exhibited better catalytic activity than SO4 2� promoted catalysts. Among various catalysts investigated, the WOx/Al2O3-ZrO2 catalyst exhibited stable catalytic activity with the highest glycerol conversion of 99% and acetol selectivity of 74%.

Hydrogenolysis of bioglycerol to 1,2-propanediol over Ru/CeO2 catalysts: influence of CeO2 characteristics on catalytic performance

Abstract Hydrogenolysis of glycerol to 1,2-propanediol is an alternative route for efficient utilization of biomass-derived glycerol to value-added chemicals. In this study, catalytic hydrogenolysis of glycerol was systematically investigated over various Ru/CeO2 catalysts. CeO2-support was prepared by different methods and Ru deposition by wet impregnation method. Synthesized catalysts were characterized by various techniques, namely, XRD, XPS, TPR, TPD, and other. Hydrothermally synthesized CeO2-supported Ru catalyst showed relatively more number of acid sites with mild acid strength and exhibited highest conversion and product selectivity. Effect of various parameters including Ru loading, reaction temperature, and hydrogen pressure was evaluated and addressed.