Conversion of regular and deuterated acetylene into benzene was studied on Pt(111) and two ordered surface alloys: Pt3Sn/Pt(111) and Pt2Sn/Pt(111) with HREELS and TPD at 90-1000 K. No benzene formation was detected on Pt(111). On alloys, formed benzene readily desorbs, and the amount of produced benzene is higher over the Pt2Sn alloy with a higher Sn concentration. DFT calculations were performed in order to assign experimental vibrational frequencies and develop a molecular reaction mechanism for benzene formation. The results suggest that acetylene forms a cyclic C4H4 dimer on the Pt-Sn alloys. This C4H4 intermediate is predicted to produce benzene by reacting with an additional surface acetylene. The destabilizing effect of Sn alloying is more significant for acetylene than for the C4H4 intermediate, and as a result, the reaction of C4H4 formation changes from being endothermic on pure Pt to being exothermic, i.e. energetically favorable, on the Pt-Sn alloys. 

Experimental spectroscopic and computational DFT studies of the mechanism of acetylene conversion to benzene on Pt-Sn alloys

243rd National Meeting (2012)

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