The Positive Role of Hydrogen on the Dehydrogenation of Propane on Pt(111)

Propane dehydrogenation on a Pt-based catalyst can be accelerated by cofeeding hydrogen. An extensive reaction network for propane dehydrogenation on Pt(111), including side reactions and deep dehydrogenation reactions, is proposed to explain the effect of cofeeding hydrogen. Simulations at 873 K and 1 bar total pressure reproduce the experimental trends at increasing H-2/C3H8 inlet ratios and allow exploration of the origin of the positive effect of cofeeding hydrogen. Increasing hydrogen pressure leads to a lower coverage of deeply dehydrogenated coke precursors on the surface: in particular, CCH3 (ethylidyne) and CH (methylidyne). In addition, it increases hydrogen coverage, which decreases the propylene adsorption strength while the energy barriers for the further dehydrogenation of propylene increase. The combined effect of a decreasing coke precursor coverage, facilitated propylene desorption, and increasing deep dehydrogenation barriers explains the higher catalytic activity when hydrogen is cofed.