The Synthesis Of Alumina Support And Its Application In Alkane Dehydrogenation

In recent years,with the change in energy consumption structure,the demand of light olefin is guadully increasing worldwidely.Compared to the traditionally steam cracking and fluid catalytic cracking（FCC）of crude oil-derived naphtha,direct catalytic dehydrogenation of light alkanes to light olefins is a more economical and environmentally friendly route,which has been an important way to solve the tension between the supply and demand of olefins.In commercialized dehydrogenation technologies,the Pt-based and CrOx-based catalysts have been widely used,owing to its outstanding performance.However,these catalysts suffer from fast deactivation by active component sintering and coke deposition.Alumina is one of the most widely used industrial materials with the desirable textual properties and thermal stability.As the catalyst support for alkane dehydrogenation,alumina not only serves as a scaffold but also provides a complexity microenvironment,which is a key factor in determining the catalytic property function.However,owing to the structural complexity and the diversity of phase transition,it is still challenging to precisely figure out the relation between the structure and preparation conditions.Herein,we have studied the alkane dehydrogenation catalysts starting with the control synthesis and adjustment structural of alumina.The alumina-supported Cr-based and Pt-based catalysts prepared by impregnation method,perform high activity and stability in alkane dehydrogenation reactions.This dissertation clarifies the structure-activity relationship between support structure and catalytic activity,and provide guidelines for the future design of new catalysts with high activity and stability.The specific research and content are as follows:（1）Alumina precursor was prepared by hydrothermal synthesis approach,and a series of rod-shaped porous alumina were abtained by a followed calcination step.Cr-Al-800 exhibited the optimal initial propane conversion of 33.2%,with 90.4%propylene selectivity,and the catalyst activity remained almost unchanged after five dehydrogenation-regeneration cycles.As-synthesized alumina as a support for chromium oxide possessed low acidity and exhibited excellent stability in propane dehydrogenation process.On the one hand,rod-shaped porous alumina offered an open structure for catalyst to allow easy access to reacting agents and prevented the blockage of the pore by coke.On the other hand,the low total acidity of alumina surface inhibited the side reactions and coke formation,which was beneficial for high activity and superior anti-coking ability（2）Alumina precursor was obtained by adjusting the molar ratio and concentration of reactants,and the surface-defective alumina was obtained by a calcination step.As-synthesized alumina as a support for platinum exhibited the isobutane conversion above 50%,with 99%isobutene selectivity.The deactivation rate constant for the PtSn-Al₂O₃-Sheet catalyst(0.014h^-1)was much lower than that for the reference catalyst.On the one hand,Al₂O₃ nanosheets rich in pentacoordinate Al³⁺,which could anchor the active component and inhibition of sintering.On the other hand,the catalyst with low acidity could inhibite the cracking and isomerization,which was beneficial for high selectivity and superior anti-coking ability.