Study On Properties Of Pt Catalysts And Its Reaction Mechanism In Propane Dehydrogenation

The flourishing development of the downstream industry of propylene lead to the sustainable growth of propylene demands. Propane dehydrogenation?PDH?, which is regarded as one of the main alternatives, attracts increased interest considering the economic development and environmental impacts. The Pt-based catalyst, which is one of the commercial catalysts for propane dehydrogenation, still suffers from the coke formation and unstable catalytic stability. Herein, it is of great importance to investigate Pt catalyst with higher catalytic activity and stability. This thesis describes the investigations of Pt-based catalysts on its catalytic performance and reaction mechanism for propane dehydrogenation to produce propylene.This thesis first describes an investigation on understanding catalytic performances of Pt nanoparticles supported on a TiO₂-Al₂O₃ binary oxide for propane dehydrogenation. The addition of appropriate amount of TiO₂ improves propylene selectivity and catalytic stability, which is ascribed to the electron transfer from partially reduced TiOx?x<2? to Pt atoms. The increased electron density of Pt could reduce the adsorption of propylene and facilitate the migration of coke precursors from the metal surface to the support. The addition of TiO₂, however, also increases the amount of strong acid centers on the supports and the excessive TiO₂ addition might lead to a significant amount of coke formation. The electron transfer effect and the acid sites effect of TiO₂ addition exert opposite influence on catalytic performance. The tradeoff between the electron transfer effect and the acid sites effect is studied by varying the amount of TiO₂ loading. An optimal loading content of TiO₂ is 10 wt%, which results in a higher propylene selectivity and a better stability.This thesis also describes the investigation on Pt/CeO₂-Al₂O₃ catalysts promoted with Ga species for propane dehydrogenation. The aim of doping the Pt/CeO₂-Al₂O₃ catalysts with the Ga species is to enhance the redox property of CeO₂ and modify the properties of Pt nanoparticles simultaneously, and hence to improve the catalytic performance of Pt catalysts in PDH. Ga³⁺ cations are incorporated into the cubic fluorite structure of CeO₂, which enhance both lattice oxygen storage capacity?OSC? and surface oxygen mobility?OM? of the catalysts. The enhanced reducibility of CeO₂ is indicative of higher capability to eliminate the coke deposition and thus is beneficial to the improvement of catalytic stability. Density functional theory?DFT? calculations confirm that the addition of Ga is prone to improving propylene desorption and highly suppressing deep dehydrogenation and the following coke formation. The content of Ga addition has a great influence on the catalytic performance. The optimal loading content of Ga is 3 wt%, which results in the maximal propylene selectivity together with the best catalytic stability against coke accumulation.