The influence of pore geometry of Pt containing ZSM-5, Beta and SBA-15 catalysts on dehydrogenation of propane

The influence of the pore geometry of the catalyst supports on dehydrogenation of propane (DHP) activity, selectivity to propylene and the degree of coke formation was evaluated over micro-(Pt-ZSM-5 and Pt-Beta) and meso-(Pt-SBA-15) porous materials in a tapered element oscillating microbalance (TEOM) reactor by analyzing reaction products and mass changes simultaneously. The catalysts were prepared by incipient wetness impregnation and were characterized by N-2-physisorption, X-ray diffraction (XRD) and H-2-chemisorption. The characterization results indicate that catalysts contain Pt within the pores and Pt nanoparticles of more or less similar sizes however stabilized on markedly different pore geometries (structure and size). This allowed to (i) largely marginalize the effect of the sizes of Pt particles on DHP and (ii) evaluate exclusively the vital role of pore geometry of the supports, where a fraction of Pt is located within the pores, on the catalytic performance. Pt-ZSM-5 presents the highest propane conversion followed by Pt-Beta and Pt-SBA-15 indicating that the activity decreases with increasing pore size (ZSM-5 < Beta < SBA-15) of the support. TEOM results evidence that the amount of coke formed during DHP is the highest on Pt-ZSM-5 and is the lowest on Pt-Beta thus, the latter exhibits better catalytic stability than the former and Pt-SBA-15. Among Pt-ZSM-5 and Pt-SBA-15, the former shows better selectivity and stability than the latter despite higher coke content. These observations demonstrate that the three dimensional microporous materials are better catalytic supports for DHP than the mesoporous SBA-15 because of their intrinsic nature that may induce optimum catalytic properties of Pt sites. (C) 2009 Elsevier Inc. All rights reserved.