Sn additives can effectively improve the propylene selectivity of propane dehydrogenated Pt?based catalysts and inhibit the generation of carbon deposition,but the effect of Sn additives is still unclear.Therefore,in this paper,different PtSn action systems were constructed by co?impregnation method and sol?gel method to modulate the introduction of PtSn,and the effect of Sn introduction methods on the dehydrogenation performance of propane of Pt?based catalysts was systematically explored.XRD and BET were used to characterize the texture properties of the catalyst,H2?TPR,TEM and CO?IR were used to distinguish the Sn structure of the additives,and the propane dehydrogenation reaction evaluation and carbon deposition analysis of the catalysts were carried out.The results show that compared with the PtSn/γ?Al2O3 catalyst prepared by co?impregnation method,the Pt/Sn?γ?Al2O3 catalyst prepared by sol?gel method has a lower specific surface area and higher pore size,which can promote the interaction between PtSn clusters and carriers to achieve high metal dispersion.More active sites give the Pt/Sn?γ?Al2O3 catalyst higher propane conversion and propylene yield,and the larger pore size of the carrier also significantly reduces the carbon deposition of the catalyst.
Pt0.5?Snx/γ?Al2O3 catalysts with different Sn loads were prepared by constant volume sequential impregnation method and ultrasonic shock method to improve metal dispersion. The catalysts were characterized by XRD, BET, H2?TPR, CO?IR and TG, and the effects of Sn content on the active center structure and propane dehydrogenation performance of Pt0.5?Snx/γ?Al2O3 catalysts were investigated. The results showed that adjusting the n（Pt）/n（Sn） by changing the Sn content in the samples would lead to the difference in the spatial distribution of Pt and Sn species, and thus affect the mode of action between Pt and Sn. With the increase of Sn, the interaction between Pt?Sn helps to increase the dispersion of Pt, the number of active sites, the improvement of the reaction activity of the catalyst. However, when excessive Sn is introduced, a Pt?Sn alloy is formed, resulting in the coating of Pt, resulting in a decrease in the number of active sites and a decline in the reactivity.
The properties of alumina supports are the key factors affecting the propane dehydrogenation performance of Pt?Sn/γ?Al2O3 catalysts.In this paper,γ?Al2O3 supports were prepared at three calcination temperatures of 450,650,850 ℃,and the structures and properties of the supports and supported catalysts were systematically studied by XRD,XRF,NH3?TPD,Py?FTIR, CO?FTIR,OH?FTIR,and other characterization methods.The properties of the propane dehydrogenation reaction were evaluated by a fixed?bed micro?reaction evaluation device with online analysis,and the gas?phase product distribution and coking properties were analyzed.The results show that with the increase in calcination temperature,the surface acid content of γ?Al2O3 supports decreases,and calcination at 850 ℃ almost eliminates the weak L acid centers on the surface.This indicates that the number of coordinated unsaturated Al sites on the surface of γ?Al2O3 and surface hydroxyl groups decreases as the calcination temperature grows,which is not conducive to the high dispersion of metal active centers.Both CO?FTIR and TEM results confirm the formation of larger Pt clusters on Pt?Sn/γ?Al2O3?850,and more Pt active phase structure with saturated coordination can promote the occurrence of side reactions such as deep dehydrogenation and reduce the selectivity of propylene products.
