Insights into catalyst structure, kinetics and reaction mechanism during propane dehydrogenation on Pt-Ge bimetallic catalysts

In the present work, in-depth characterization techniques combined with kinetic analyses were used to develop a deep understanding of the remarkable catalytic performance observed during propane dehydrogenation (PDH) over Ge-promoted Pt/SiO2. Following our previous work on Pt-Ge/Al2O3, we found Ge to significantly affect Pt catalytic performance, reaction mechanism and kinetics, regardless of the nature of the support. The synthesized catalysts were characterized using XAS, XPS, TPR, TGA, C3H6/C3H8-TPD, HRTEM, CO-chemisorption, BET, and CO-DRIFT. Upon Ge promotion to Pt nanoparticles supported on a large, neutral, SiO2 surface area, the bimetallic samples showed higher activation energy, lower desorption energy of C3H6, lower coke formation rates, and higher C3H6 selectivity as compared to the results from using the unpromoted catalyst. Ruling out the neutral SiO2's support effect, the kinetic study indicates the C3H8 reaction order remains close to 1 for all the samples, while the H2 reaction order decreases from 0.04 to -0.52 with increasing Ge loading from 0 wt% to 5 wt%. According to the kinetic analysis, the first C-H bond cleavage seems to be the rate-determining step. The addition of Ge enhances the adsorption of hydrogen, which explains the change of the hydrogen reaction order and the apparent activation energy exhibited by the bimetallic samples.