Influence of metal oxide and heteropoly tungstate location in mesoporous silica towards catalytic transfer hydrogenation of furfural to γ-valerolactone

Abstract

One pot conversion of furfural to γ-valerolactone by transfer hydrogenation has been achieved over bifunctional mesoporous silica catalysts containing Zr and tungstophosphoric acid (TPA). Different catalysts with TPA and ZrO₂ located inside and outside of SBA-15 pores were prepared and their activity was evaluated for transfer hydrogenation of furfural. Different characterization techniques such as N₂-sorption, FT-IR, pyridine/2-propanol adsorbed FT-IR, X-ray diffraction, temperature programmed desorption of NH₃/CO₂, electron spectroscopy for chemical analysis and TEM were used to evaluate the structural and surface aspects of the catalysts. The presence of ZrO₂ inside and outside the pore channels of SBA-15 was identified by XPS analysis as a higher binding energy value was observed for Zr 3d_5/2 of the catalyst with ZrO₂ present inside the pores of SBA-15 due to the formation of Si–O–Zr bonds. The catalyst with ZrO₂ present inside the SBA-15 pores and TPA dispersed on the support showed the highest activity with complete conversion of furfural and a GVL yield of 81%. The transfer hydrogenation activity depends on the interaction of the hydrogenating alcohol and the acid–base properties of the catalyst which are directed by the location of ZrO₂ or TPA in the support. All the reaction parameters were studied and the optimum conditions were established. The catalyst exhibited good recyclability without any variation in activity.