The effect of calcination atmospheres of sol-gel TiO2 on the catalytic properties of Pt/TiO2 catalysts in selective hydrogenation of 3-nitrostyrene

Abstract

Nanocrystalline anatase TiO2 were synthesized by a sol-gel method and calcined under H2, air, N2, O2 and Ar atmosphere at 350 ̊C for 2 h and used as the supports for preparation of 0.5%Pt/TiO2 catalysts by incipient wetness impregnation (IW) method. The characteristics and catalytic properties of Pt (0.5wt% Pt) were analyzed by X-ray diffraction (XRD), N2-physisorption, X-ray photoelectron spectroscopy (XPS), H2-temperature programmed reduction (H2-TPR), infrared spectroscopy of adsorbed CO (CO-IR), CO-pulses chemisorption, electron spin resonance (ESR) and transmission electron microscopy (TEM). The 0.5%Pt supported on the TiO2 calcined under H2 and N2 atmosphere exhibited the best catalytic performances. High conversion of 3-NS (~70%) with high selectivity to 3-VA (>90%) could be obtained after 20 min reaction time upon reduction at 200 ̊C. The catalytic activities of Pt/TiO2 were correlated with Pt dispersion and the selectivity of 3-VA desired product was related to the presence of low coordinated Pt sites and the metal-support interaction, which were influenced by defects on the TiO2 support. Preparation by the strong electrostatic adsorption (SEA) method improved the conversion of 3-NS from 29% to 64% of the Pt/TiO2-air catalysts but for the Pt/TiO2-H2, preparation by SEA method did not improve both conversion of 3-NS and 3-VA selectivity, due probably to that the catalyst already had high Pt dispersion, comparing to the one prepared by the incipient wetness impregnation method.