Study On Reaction Mechanism Of Propane Dehydrogenation Over Pt Catalysts

The blooming development of the downstream industry of propylene lead to thesustainable growth of propylene demands. Propane dehydrogenation, which isregarded as one of the main alternatives, attracts increased interest considering theeconomic development and environmental impacts. The Pt-based catalyst, which isone of the commercial catalysts for propane dehydrogenation, still suffers from thecatalytic deactivation and unstable catalytic stability. Herein, it is of great importanceto investigate Pt catalyst with higher catalytic activity and stability. This thesisdescribes the investigations of Pt-based catalysts on enhancing its catalyticperformance and revealing the mechanism, which can supply fundamental basis forfurther studies.This thesis first described an investigation regarding the influence of acid site ofsupport on coke formation. The high-temperature steam treatment can alter theamounts of acid sites, while bringing negligible change to active metal sites since thecatalytic performance as well as metal dispersion remains unchanged. The change inamounts of acid sites influences the ratio of coke that deposited on metal surface andsupports. Through NH3-TPD and TPO experimental analysis, the mechanism of cokeformation is believed that the coke precursor is first formed on metal surface viacondensation and polymerization of propylene and transfers to the supports, followedby further dehydrogenation and condensation, which eventually forms the type ofcoke that have higher C/H ratio and oxidation temperature.This thesis also describes the study of the promotional effect of Cu on thecatalytic performance of Pt/Al2O3catalysts for propane dehydrogenation. We haveshown that Pt/Al2O3catalysts possess higher propylene selectivity and lowerdeactivation rate as well as enhanced anti-coking ability upon Cu addition. Theoptimized loading content of Cu is0.5wt%, which increases the propylene selectivityto90.8%with a propylene yield of36.5%. The origin of the enhanced catalyticperformance and anti-coking ability of the Pt-Cu/Al2O3catalyst is ascribed to theintimate interaction between Pt and Cu, which is confirmed by the change of particlemorphology and atomic electronic environment of the catalyst. The Pt-Cu interactioninhibits the propylene adsorption and elevates the energy barrier of C-C bond rupture.The inhibited propylene adsorption diminishes the possibility of coke formation andsuppresses the cracking reaction towards the formation of lighter hydrocarbons on Pt-Cu/Al2O3, while a higher energy barrier for C-C bond cleavage suppresses themethane formation.Additionally, we have investigated in-situ characterization and TPDmeasurement to further confirm the promotional mechanism of copper addition. Viathe characterization of TPSR, the Cu addition can suppress the formation ofbyproducts and offers investigation regarding influence of copper on activation energy.Through the characterization of in-situ FTIR and C3H6-TPD measurements, the Cuaddition can lower the C3H6adsorption energy and facilitate C3H6desorption,therefore inhibiting the formation of coke precursors, which leads to the enhancementof catalytic stability and propylene yields.