Mechanism of Dehydrocyclization of 1-Hexene to Benzene on Cu₃Pt(111): Identification of 1,3,5-Hexatriene as Reaction Intermediate

Abstract

We report here ultrahigh vacuum studies of the dehydrocyclization reaction of submonolayer coverages of 1-hexene to benzene on a Cu3Pt(111) single crystal surface, using reflection−absorption infrared spectroscopy (RAIRS), near edge X-ray absorption fine structure (NEXAFS) studies, and temperature-programmed reaction/desorption (TPR/D) spectrometry. As discussed in a previous TPR/D paper, at surface coverages up to 13% of monolayer saturation, 1-hexene forms benzene on a Cu3Pt(111) surface. Selectivity to benzene formation is 70 ± 10%, with the remaining 30 ± 10% of the adsorbed 1-hexene dehydrogenating irreversibly to surface carbon and H2. For higher coverages, molecular desorption commences. Spectroscopic identification of the intermediates of the reaction of 1-hexene and other model compounds, such as a 1,3,5-hexatriene, with a Cu3Pt(111) surface suggests that 1-hexene and 1,3,5-hexatriene have a common intermediate, and this intermediate has been identified as a rehybridized hexatriene species. Other model compounds, such as trans-3-hexene, have also been used to provide further understanding of the mechanism of the aromatization reaction.