Carbon-oxygen bond strength as a control of reaction kinetics: Phenol on Mo(110)

Abstract

The reaction of phenol on Mo(110) has been studied using temperature programmed reaction and X-ray photoelectron spectroscopies. After desorption of multilayers and a weakly bound molecular species, decomposition produces the only reaction products observed: gaseous dihydrogen, surface carbon and surface oxygen. The O-H bond cleaves first at temperatures below 360 K to form surface phenoxide (C 6H 5O-), followed by C-H bond activation commencing at 370 K. C-O bonds are cleaved in the temperature range of 370 to 450 K. After annealing to 300 K, multiple species are detected on the surface by X-ray photoelectron spectroscopy. The cleavage of C-H bonds in the same temperature regime as C-O bonds is thought to lead to selective decomposition of phenol on Mo(110). The reaction of phenol is contrasted to that of a sulfur-containing analogue, benzenethiol, on the Mo(110) surface. The stability of the phenoxide intermediate with respect to carbon-heteroatom bond cleavage is greater than that of the corresponding phenyl thiolate formed from benzenethiol. Comparison of the reaction of phenol and benzenethiol demonstrates the importance of C- X ( X = O, S) bond strength in determining the reactivity and selectivity of these molecules.