Effect Of Al Doped MCM-41 Supported Molybdenum On Self-disproportionation Of 1-butene

Due to the rapid increasing in the demand of propylene,the current propylene production capacity is insufficient,which can't meet the demand of market.The development of new technologies to increase propylene production has become an important issue for petrochemicals.Now,the production of propylene by a self-metathesis reaction of 1-butene is an important way to increase propylene.The key of this reaction is that 1-butene has to be isomerism to 2-butene in the process.So the catalyst of the reaction not only has metathesis actives center but also has acid centers.The key to improve the self-metathesis of 1-butene to produce propylene is to develop efficient and selective bifunctional catalysts.In this dissertation,based on the thermodynamic analysis of 1-butene self-metathesis reaction,MCM-41 was selected as the research object.Preparation of an Al-doped MCM-41 support with an acid center regulatable(xAl-MCM-41,where x represents the silica-alumina ratio of the aluminum-doped modified support),The bi-function supported molybdenum-based catalysts were synthesized by the impregnation method.The structure of the catalysts was characterized by modern analytical testing methods.The catalytic activity of these catalysts was evaluated in a fixed-bed reactor.The xAl-MCM-41(x=1-50)carriers with different Si/Al ratios were synthesized by hydrothermal synthesis.A double functional supported molybdenum-based catalyst was prepared by using an excess impregnation method with ammonium molybdate as a precursor and a xAl-MCM-41 support.The effect of aluminum-doped MCM-41 on the catalytic activity of the catalyst was studied such as XRD,N2-adsorption desorption,in-situ infrared(Py-IR),Raman spectroscopy,temperature-programmed reduction(H2-TPR),temperature-programmed desorption(NH3-TPD),UV-Vis diffuse reflectance spectroscopy(UV-Vis)and other characterizations of the catalyst analysis.The experimental results showed that the doping of aluminum into MCM-41 not only produced the acidic centers(L acidity increase and B acidity decrease),but also enhanced the interaction between the molybdenum oxide species and the support,and increased the dispersion of the molybdenum oxide species on the support surface.But the skeletal structure of MCM-41 was destroyed by the over doped aluminum when the ratio of silicon to aluminum was 1.When the loading of molybdenum oxide increases from 2%to 8%,the active component on the catalyst increases with the increase of the loading.But when the amount of loaded molybdenum oxide reached over 10%,the dispersion of molybdenum on the support was decreased,and the crystalline molybdenum oxide species appeared.When the aluminum doping amount is 5%and the molybdenum oxide loading is 8%,the prepared catalyst 8%Mo/5Al-MCM-41 has the highest dispersion of molybdenum oxide on the surface.In a fixed-bed reactor,the effects of the above synthesized catalysts on the self-metathesis reaction of 1-butene were investigated.The experimental results showed that both the acidity of the supports and the loaded amount of molybdenum oxide had the important influence on the activity of the catalysts.The Yield of propylene can be maximally increased to 30.9%while 1-butene self-metathesis react on 8%Mo/5Al-MCM-41.That was because the catalyst has a certain acidity and highly dispersed molybdenum oxide species on the support 5Al-MCM-41were,and also has little the crystalline molybdenum oxide particles,which is beneficial to the catalytic reaction.The influences of reaction temperature and space velocity on the self-metathesis of 1-butene were studied.When the WHSV of 1-butene was 0.6 h-1,the activity of the catalysts was stable after over 24 h of reaction.When the WHSV of 1-butene increased to 2.4 h-1,the activity of the catalysts was stable within 15 hours,however,after 20 hours of reaction,the conversion of 1-butene was reduced to 40 mol%,and the yield of propylene was less than 5 mol%.In the process of disproportionation of 1-butene,the yield of butene,the yield of ethylene,propylene,pentene,and hexene increase with the increase of temperature.When the reaction temperature reaches 393 K,it reaches the maximum and continues to increase the temperature.The yield is reduced instead.