Study On The Titanium-modified PtSn/Ti-HMS Catalysts For The Dehydrogenation Of Propane To Propylene

China is rich in liquefied petroleum gas and natural gas.Propane is the main component of liquefied petroleum gas,accounting for about 60%of the total.In addition,the main component of natural gas is methane,and also includes some ethane,propane and butane.Considering the wide application of propylene,if propane can be directly dehydrogenated to propylene,the real problem of propylene scarcity can be solved,and the research in this area is of great significance.PtSn system is mostly used as the active component of catalysts for direct dehydrogenation of propane to propylene in industry,but there are still great improvements in the stability of the catalysts.In this paper,PtSn/HMS catalysts with different metal loadings and the carrier modified PtSn/Ti-HMS catalysts were firstly prepared by different methods.Then the effects of Ti modified catalysts on the activity and stability of propane dehydrogenation had been discussed by means of various characterization methods and reaction tests.The main conclusions are as follows:?1?PtSn/HMS catalysts were prepared by hydrothermal synthesis and incipient wetness method,and the effects of different metal loading catalysts on the dehydrogenation activity of propane were investigated.The activity tests found that all the PtSn/HMS molecular sieve catalysts had good initial activities.The initial propane conversion of Pt_0.1Sn_0.1/HMS molecular sieve catalysts reached 43.9%,and with the further increase of the metal loadings,the conversion increased.The initial propane conversion of Pt_0.3Sn_0.3/HMS molecular sieve catalysts were up to 58.0%.?2?A series of Ti-modified Ti-HMS carriers were synthesized by a simple one-pot method.PtSn/Ti-HMS molecular sieve catalysts were prepared by incipient wetness method and their propane dehydrogenation performances were tested.The results showed that the initial conversion of propane over Pt_0.3Sn_0.3/Ti-HMS?Ti/Si=0.02?zeolite catalysts were 55.5%,which decreased to 49.4%after 6 hours,showing good activity and optimal stability.However,with the further addition of Ti,the activity and stability of the catalysts decreased significantly.?3?Ultraviolet-visible diffuse reflectance and Fourier transform infrared absorption spectroscopy showed that Ti replaced Si atoms into the Ti-HMS molecular sieve frameworks,but excessive addition of Ti would produce small titanium oxide species on the surface of Ti-HMS zeolites,which are not conducive to dehydrogenation.Wide-angle XRD and TEM characterizations showed that Ti-HMS zeolite with low doping content was beneficial to the dispersion of Pt.However,as the doping amount of Ti increases,the active component of the catalysts agglomerated.H₂-TPR found that Ti doping could change the alloying degree of PtSn.Low-doping PtSn/Ti-HMS zeolite catalysts showed that the interaction between PtSn was enhanced,which made the catalysts showed high activity and good stability.