Reactions of Glutaric Acid on the TiO2(001) Single Crystal. Effect of Surface Reduction on the Reaction Pathway

Abstract

The detailed reaction of glutaric acid (a C₅ dicarboxylic acid) has been studied by temperature programmed desorption (TPD) and X-ray photoelectron spectroscopy (XPS). Upon adsorption at 300 K, both carboxylic acid functions are deprotonated to give adsorbed glutarate species. The reaction of these species differs significantly on the oxidized surface from that on the reduced surface. On the oxidized surface, two competing reactions are seen: (i) decomposition to two molecules of CO and one molecule of propene and (ii) dehydration to ketene. Upon sputtering with hydrogen ions (reducing the surface states of Ti ions and implanting hydrogen atoms in the lattice), the main observed reaction is reduction to the dialdehyde and the dialcohol. The yield of these two products, not seen on the oxidized surface, reaches 80% on the highly reduced surface. Another compound is seen on the reduced surface with m/z = 70. The analysis of its fragmentation pattern tends to assign it to cyclopentane that is formed by an intramolecular reductive coupling reaction on the O-defect sites.