Mesoporous tin oxide-supported phosphomolybdic acid as high performance acid catalysts for the synthesis of hydroquinone diacetate

Abstract

Mesoporous SnO2 nanoparticles were prepared via surfactant-assisted sol-gel method and then modified with different amount (3–65) wt.% of phosphomolybdic acid (PMA) using the impregnation method. The prepared catalysts were characterized by thermal analysis (TGA and DTA), XRD, TEM, FTIR and N2 adsorption-desorption at −196 °C (BET and BJH). 25 %PMA/SnO2 nanoparticles were calcined at 400°, 450°, 550o, and 650 °C to study the effect of calcination temperature on the structural properties, surface acidity, catalytic activity and Keggin structure of the PMA. The surface acidity was measured by potentiometric titration and FTIR spectra of chemisorbed pyridine. It is observed that the crystallite size decreased with increasing the PMA content and increased with increasing the calcination temperature while the surface area (SBET) increased with increasing PMA loading to reach a maximum at 25 wt%. The surface acidity enhanced after addition of PMA and the catalysts shown both Brönsted and Lewis acid sites. The catalytic activity was tested by synthesis of hydroquinone diacetate. The sample with 55 wt.% PMA showed the highest acidity and catalytic activity.