Alkanes Dehydrogenation And Aromatics Hydrogenation Over S-1 Zeolite Supported Pt Catalysts

Hydrogen energy as one of the most promising clean energy sources is hopeful to change the life style of human society with its popularization and application.Commonly,hydrogen production and storage technologies are two important factors influencing the development of hydrogen energy era.The technology of propane dehydrogenation has great significance of developing hydrogen energy because it may combine both hydrogen production commission and chemical raw material production commission(propylene)together in the age of hydrogen energy,whereas the low hydrogen selectivity of the present catalysts is not suitable for hydrogen production.Considering that the reversible cycle consisted of methylcyclohexane dehydrogenation and toluene hydrogenation is expected to become a useful organic liquid hydrogen storage technology,the studies of this dissertation were focused on the preparations of catalysts with high selectivity and activity for propane dehydrogenation,methylcyclohexane dehydrogenation and toluene hydrogenation.Main contents and results were as follows:(1)Cu-Pt/S-1 catalysts with different Cu/Pt ratios were prepared by co-impregnation method using Cu as the second metal and zeolite S-1 as support.Catalytic performance of Cu-Pt/S-1 catalysts with different Cu/Pt ratios was studied in a fixed-bed reactor.Results showed that Cu-Pt/S-1 was a high selectivity and high activity propane dehydrogenation catalyst.Under the conditions of 610?,diluent gas-free and propane weight hourly space velocity(WHSV)of 1.3 h-1,the initial propane conversion rate of a Cu0.7Pt0.1/S-1 catalyst was nearly 50%,and the average selectivity of propylene and hydrogen(calculated)could reach 94.6%and 85%,respectively,during the 180 min reaction.By carrying out comparative studies with other second metal components(Sn,Zn)and supports(ZSM-5,?-Al2O3),it is concluded that the high activity and selectivity of Cu0.7Pt0.1/S-1 in propane dehydrogenation should be attributed to the cooperation of the second metal Cu and the S-1 zeolite support.While the rapid deactivation of Cu0.7Pt0.1/S-1 was found mainly owing to the sintering of metal nanoparticles dispersed on the S-1 zeolite support at high temperature,rather than the deposition of coke.Doping of Zn as the third metal during preparation of Cu-Pt/S-1 by co-impregnation method could solve the problem of deactivation and metal nanoparticles sintering in propane dehydrogenation effectively.(2)The catalytic performance of S-1 zeolite supported Cu-Pt bimetallic catalyst for methylcyclohexane dehydrogenation was studied in a fixed bed reactor.Cu-Pt/S-1 also exhibited high activity and selectivity in this dehydrogenation reaction.Under the conditions of 400? and methylcyclohexane WHSV of 4.6 h-1,the hydrogen release rate,toluene selectivity and hydrogen selectivity of Cu0.4Pt0.4/S-1 attained as high as 430 mmol/gPt/min,99.93%and 99.99%,respectively.Both the second metal Cu and the S-1 zeolite support made important contribution to the good performance of Cu0.4Pt0.4/S-1 catalyst.HAADF-STEM-EDX results indicated the formation of Cu-Pt alloy.And XPS analysis revealed that Cu accepted electron from Pt donor by alloying,resulting the proper adjustment on electronic state of Pt active center.Thus Cu0.4Pt0.4/S-1 could suppress the coke deposition,metal nanoparticles sintering,and side reactions such as ring opening of methylcyclohexane,dealkylation and transalkylation of methylcyclohexane and toluene.These results might provide important reference to the investigation of highly efficient hydrogen release catalyst(methylcyclohexane dehydrogenation)in methylcyclohexane-toluene-hydrogen cycle.(3)The catalytic performance of S-1 supported Pt catalyst(Pt0.6/S-1)prepared by different post-treatment methods was studied with a batch reactor for toluene hydrogenation.Results showed that Pt0.6/S-1-Air(O2)catalysts prepared by S-1 zeolite impregnated in[Pt(NH3)4](NO3)2 and calcinated in oxidizing atmosphere(the air,oxygen)exhibited good activity and sulfur poisoning resistance in toluene hydrogenation at low temperature.It is inferred that both the improved metal dispersion and the high ratio of oxidation state Pt(PtO and PtO2)should be helpful for increasing the hydrogen storage rate of Pt0.6/S-1-Air(O2)catalysts,while the enhancement of sulfur poisoning-resistant ability should be mainly attributed to high ratio of oxidation state Pt in the Pt0.6/S-1-Air(O2)catalysts.