Theoretical study of 1,3-cyclohexadiene dehydrogenation on Pt (1 1 1), Pt3Sn/Pt (1 1 1), and Pt2Sn/Pt (1 1 1) surfaces

The 1,3-cyclohexadiene dehydrogenation to phenyl on the Pt (1 1 1), Pt3Sn/Pt (1 1 1), and Pt2Sn/Pt (1 1 1) surfaces has been studied using density functional theory calculation. The results show that the adsorption energies of 1,3-cyclohexadiene and other intermediates decrease with the increasing concentration of Sn. The addition of Sn weakens the interaction between the adsorbate and the alloys. The barriers are 0.62, 0.72, and 0.75 eV for the first and 0.87, 0.51, and 0.32 eV for the second step on the Pt (1 1 1), Pt3Sn/Pt (1 1 1), and Pt2Sn/Pt (1 1 1), respectively, for the dehydrogenation of the 1,3-cyclohexadiene. The third dehydrogenation step is the rate determining step (rds) with the barriers of 1.49, 1.75, and 1.90 eV on the Pt (1 1 1), Pt3Sn/Pt (1 1 1), and Pt2Sn/Pt (1 1 1), respectively. The existence of the Sn facilitates the first two dehydrogenation steps that produce benzene and prohibits further dehydrogenation of benzene, thus increases the selectivity of the dehydrogenation of 1,3-cyclohexadiene to gas benzene.

Temperature dependence of the relative selectivity of gas benzene produced by the 1,3-cyclohexadiene dehydrogenation on Pt (1 1 1) and Pt2Sn/Pt (1 1 1) using the microkinetic modeling technique (PC6H8 = 7.4 × 10−5 Pa). The dashed line denotes a typical temperature at 500 K.Figure optionsDownload high-quality image (51 K)Download as PowerPoint slideHighlights
► Adsorption energies of species decrease with the increasing concentration of Sn.
► Rate-controlling step is the third dehydrogenation step on Pt (1 1 1) and Pt–Sn surfaces.
► Pt2Sn/Pt (1 1 1) presents high selectivity toward the formation of benzene.