Propane Dehydrogenation Over Pt/Al₂O₃ Catalysts

Propylene was widely used in chemical industry. The demand for propylene as industrial chemicals is growing fast. The catalytic dehydrogenation of propane is the main path to produce propylene. Reaction condition and catalysts greatly influenced the catalytic performance for propane dehydrogenation. In this thesis, the influence of reaction condition on catalytic performance for PDH was investigated by experiment and thermodynamic anaylsis. Moreover, three different alumina supports were used to synthesize Pt/Al2O3 catalysts with similar platinum partcle size by colloid method. The carrier effect on dehydrogenation of propane was evaluated over Pt/Al2O3 catalysts. Furthermore, carbon-covered aluminas (CCAs) were synthesized from alumina and a series of carbon source by different methods. Preparation process effect on the catalytic performance of Pt/CCA for propane dehydrogenation was investigated. The main results of this thesis are as follows:(1) Experimental studies on Pt/OX, combined with a thermodynamic analysis, indicate that reaction condition (including propane content, hydrogen content and velocity) greatly impact the PDH properties. When the velocity is relatively small, reaction properties are limited by thermodynamic equilibrium. Propane conversion increases with the decreas of propane content. Hydrogen in the raw gas can inhibit coke formation to some extent, but the increase of hydrogen content will lead to decrease of propane conversion. When velocity is high enough, reaction properties are mainly controlled by dynamics.(2) The carrier effect on dehydrogenation of propane activity, selectivity to propylene and the amount of coke was evaluated over Pt/Al2O3 in a fixed-bed reactor. The catalysts with similar platinum particle size were prepared by colloid method and were characterized by N2-physisorption, X-ray diffraction, NH3-TPD and so on. The influence of alumina supports physiochemical properties on the catalytic performance was investigated. The results evidenced that pore distribution and acidity of alumina supports have greatly impacted the catalytic performance of Pt for PDH while crystal structure has little to do with it. Small pore size and moderate acidity of alumina supports will increase propane conversion and propylene selectivity.(3) The large pore and acidic surface of alumina might cause a decrease in catalytic activity or selectivity. CVD, pyrolysis and physical blend method were used to synthesize carbon-covered alumina. After Pt loading, these novel composites were evaluated by propane dehydrogenation. The results showed that the activity and stability of catalysts were improved after carbon coverage on alumina by pyrolysis or physical blend. This is because this kind of carbon can inhibit cracking and coke formation markedly. However, propylene selectivity for Pt/CCA from CVD was obviously decreased.