THE EFFECT OF Pt PRECURSOR AND CALCINATION TEMPERATURE ON THE CATALYTIC PROPERTIES OF Pt/TiO2 CATALYSTS IN THE SELECTIVE HYDROGENATION OF 3-NITROSTYRENE

Abstract

In this research, selective hydrogenation of 3-nitrostyrene to 3-vinylaniline which is an important intermediate for the production of pharmaceuticals, dyes, and herbicides was studied over 0.5wt%Pt/TiO2 catalysts prepared by impregnation method with various Pt precursors including H2PtCl6•6H2O, Pt(C5H7O2)2, [Pt(NH3)4]Cl2, and [Pt(NH3)4](NO3)2. The catalyst samples were calcined at different temperatures between 250-400°C. The catalytic test results in the selective hydrogenation of 3-nitrostyrene at 50°C and 2 MPa hydrogen pressure show that the catalyst prepared from Pt(NH3)4Cl4 and calcined at 350 ºC exhibited the highest conversion of 3-nirtrostyrene and the highest 3-vinylaniline selectivity at 71 and 91%, respectively after 40 min reaction time. From the H2-TPR results, it suggested that calcination at 350 ºC led to autoreduction of Pt precursors into metallic Pt particles. However, due to low CO pulse chemisorption results, it is possible that these small Pt particles were in close contract with the TiO2 supports or some Pt particles could diffuse into the TiO2 lacttice, which in good agreement with the XPS results of Ti and Pt species. Such phenomena led to promotion of the hydrogenation of nitro group, hence the catalysts exhibited high performance in term of both 3-nitostyrene conversion and 3-vinylaniline selectivity.