Pt–Ag and Pt–Ag–Sn bimetallic and trimetallic catalysts supported on γ-Al2O3 for direct propane dehydrogenation

Abstract

The synthesis, characterization and catalytic performance assessment of Pt–Ag and Pt–Ag–Sn bimetallic and trimetallic catalysts supported on KOH-treated γ-Al₂O₃ for the direct propane dehydrogenation reaction have been carried out. The bimetallic catalysts contained 0.3 wt% Pt and 0.5 wt% K, with x = 0.1, 0.3, 0.5, 0.7, 0.9, and 1.1, corresponding to the amount of Ag (0.3Pt–xAg/0.5K–Al₂O₃). The trimetallic catalysts contained 0.3 wt% Pt, 0.7 wt% Sn and 0.5 wt% K, with the same x values for Ag (0.3Pt–xAg–0.7Sn/0.5K–Al₂O₃). The catalytic tests were run on real samples (1.8 mm spheres). The 0.3Pt–0.9Ag–0.7Sn/0.5K–Al₂O₃ composition resulted in the highest yield of propylene (31.4%), highest propylene selectivity (79.3%) and minimum deactivation after 200 min on stream at a gas hourly space velocity of 10 000 cm³ g per catalyst per h at a reaction temperature of 580 °C, comparable to the performance of a DeH-16 commercial catalyst under the same operating conditions. Based on X-ray diffraction, H₂-temperature-programmed reduction, X-ray photoelectron spectroscopy, NH₃-temperature-programmed desorption, electron microscopy, Raman spectroscopy and temperature-programmed oxidation analysis, the performance of the optimum sample was attributed to the synergetic electronic and geometrical effects induced by the formation of Pt–Ag and Pt–Sn alloys and partial coverage of support acidic sites by Ag and Sn clusters.