PtSnNa/SUZ-4:An efficient catalyst for propane dehydrogenation

The structure and catalytic properties of PtSn catalysts supported on SUZ-4 and ZSM-5 zeolite have been studied by using various experimental techniques including XRD,nitrogen adsorption,NH3-TPD,TG,H2-TPR and TPO techniques combined with propane dehydrogenation tests.It has been shown that SUZ-4-supported PtSnNa（PtSnNa/SUZ-4） was determined to be a better catalyst for propane dehydrogenation than conventional catalysts supported on ZSM-5,owing to its higher catalytic activity and stability.Dibenzothiophene poisoning experiments were performed to investigate the detailed structures of the two supported catalysts.The characterization of the two catalysts indicates that the distribution of Pt on the porous support affects the activity.In contrast to ZSM-5-supported catalysts,Pt particles on the PtSnNa/SUZ-4 are primarily dispersed over the external surface and are not as readily deactivated by carbon deposition.This is because that the strong acid sites of the SUZ-4 zeolite evidently prevented the impregnation of the Pt precursor H_2PtCl_6 into the zeolite.In contrast,the weak acid sites of the ZSM-5 zeolite led to more of the precursor entering the zeolite tunnels,followed by transformation to highly dispersed Pt clusters during calcination.In the case of the PtSnNa/ZSM-5,the interactions between Sn oxides and the support were lessened,owing to the weaker acidity of the ZSM-5 zeolite.The dispersed Sn oxides were therefore easier to reduce to the metallic state,thus decreasing the catalytic activity for hydrocarbon dehydrogenation.

Effect of Mischmetal Addition on Catalytic Performance of PtSnNa/ZSM-5 for Propane Dehydrogenation

The influence of mischmetal addition on physicochcmical properties of PtSnNa/ZSM-5 catalyst was studied by means of XRF, H2 chemisorption, XRD, TPR, NH3-TPD and TPO techniques. The results showed that the presence of mischmetal had an obvious impact on the catalytic performance of the PtSnNa/ZSM-5 catalyst. A suitable content of mischmetal not only could enhance the interactions between Pt species and the support, but also inhibit the formation of coke during the reaction, thus improving the catalytic activity and stability. In our experiments, when the content of mischmetal was 3m%, the catalyst exhibited best catalytic performance. However, the continuous addition of mischmetal could promote the reduction of Sn species to metallic tin, which was disadvantageous to the reaction.

Propane Dehydrogenation on PtSnNa/AlSBA-15 Catalyst:Influence of Tin as a Promoter

PtSnNa/AlSBA-15 catalysts with different amounts of Sn were prepared for propane dehydrogenation.The catalysts were characterized by XRF,BET,H2 chemisorption,NH3-TPD,H2-TPR,and TPO techniques.Test results indicated that the presence of tin not only modified the acid function and the interfacial character between metal and support,but also reduced the coke deposition effectively.Among these catalysts investigated thereby,the PtSn(0.7%)Na/AlSBA-15 catalyst had the best catalytic performance in terms of propane conversion and stability.With the continuous addition of Sn,more amounts of Sn0 species appeared,which was unfavorable to the reaction.The PtSn(0.7%)Na/AlSBA-15 catalyst was parametrically characterized in order to obtain necessary information to integrate the process operating conditions.A weight hourly space velocity of 3 h-1,a reaction temperature of 610 ℃ and a H2/C3H8 molar ratio of 0.25 were found to be optimum conditions for achieving a higher dehydrogenation activity of the catalyst.

Effect of Impregnation Sequence on Propane Dehydrogenation Performance of PtSnNa/ZSM-5 Catalyst

The effects of the sequence for impregnation of metal precursors on the performance of PtSnNa/ZSM-5 catalyst for propane dehydrogenation to propene were studied in this paper.Some methods such as XRD,TPDA,BET,H2-TPR,XPS,ICP,TEM and hydrogen chemisorption were used to characterize the catalysts.The structure of ZSM-5 zeolite was not destroyed by the introduction of metal components.Meanwhile the different impregnation sequence of metal precursors could affect the behavior of Sn4+species entering the ZSM-5 channel,and the interaction between platinum and tin species,as well as the degree for reduction of Pt and Sn components.As a result,the prepared catalysts exhibited different reaction activity and selectivity.Compared with the co-impregnation treated catalyst,the catalysts prepared by the sequential impregnation method showed better catalytic activity in propane dehydrogenation,especially the one prepared through impregnation with tin precursor at first.Finally,a model for the effect of impregnation sequence on the distribution of Pt and Sn species in PtSnNa/ZSM-5 catalyst was proposed.