Platinum metal surface chemistry of benzene and toluene

The coordination chemistry of benzene and toluene on Pt(lll) and pt 6(lll)x(lll) has been defined by thermal desorption spectrometry, isotopic labeling studies, and chemical displacement reactions.Benzene chemisorption was largely molecular (non-dissociatve) on Pt(lll) but less so on the stepped surface.At temperatures above 100°C, reversible benzene desorption and benzene decomposition were competing reactions.More than one differentiable benzene chemisorption state was present on both surfaces.Exchange experiments established that.therate of surface migration of chemisorbed benzene between states on these surfaces was very low.One sharp distinction in the benzene chemistry of the two platinum surfaces was that reversible C-H bond breaking occurred on the stepped surface but not an Pt(lll).Whereas toluene chemisorption on nickel surfaces is fully irreversible, toluene chemisorbed on Pt (111) was partially de sorbed as the toluene molecule at 70-ll0°C.Studies with c 6 H 5 cn 3 and c 6 n 5 cH 3 suggested that the faster low temperature C-H bond breaking process is centered on the methyl group C-H bonds. Chemisorption of mesitylene and m-xylene onPt -(lli) was partially reversible.••-:•