Influence of oxidation/reduction pretreatment on hydrogen adsorption on Rh/TiO2 catalysts. An 1H nuclear magnetic resonance study

Abstract

Hydrogen adsorption on a Rh/TiO₂ catalyst previously subjected to different oxidation/reduction treatments has been studied by ¹H-n.m.r. spectroscopy. The detection of two lines in the n.m.r. spectra allows the differentiation of hydrogen adsorbed on Rh particles and that on TiO₂ support. In more oxidized samples, hydrogen is chemisorbed on both metal particles and metal support interface, while in less oxidized samples hydrogen is also adsorbed on the metal but spilt over, in a reversible way, to the support. Surface dehydroxylation decreases the amount of transferred hydrogen considerably and a new reversible hydrogen, ascribed to physisorbed H₂ molecules on the support, is detected at relatively high H₂ pressures.