Hydrogen adsorption sites studied by carbon monoxide adsorption to explain the hydrogenation activity of benzene on Pd and Pt catalysts

摘要

FT-IR of CO has been employed to study the relations between hydrogen adsorption and benzene hydrogenation on Pd/SiO_2 and Pt/SiO_2 catalysts.Three IR bands of CO stretching:2085 (L_1 band),1984 (B_1 band) and 1948 cm~(-1) (B_2 band),have been observed on Pd/SiO_2.Hydrogenation of benzene is dominated by hydrogen adsorption on B_1 sites (CO band at 1984 cm~(-1)) of Pd/SiO_2,because benzene and/or the benzene ring of acetophenone can preferentially cover on the B_1 sites to hinder hydrogen adsorption,leading to poor catalytic activity for hydrogenation of benzene.When hydrogen is pre-covered on Pd/SiO_2 to occupy the B_1 sites,it will cause intense benzene hydrogenation.Pre-adsorbed acetophenone on Pt/SiO_2 surface presents a surprising phenomenon that adsorbed acetophenone does not impede CO adsorption.We propose that adsorption of hydrogen is independent of the exposure of pre-adsorbed acetophenone,and therefore Pt/SiO_2 catalyst can offer high catalytic activity for hydrogenation of benzene.