Oxygen Exchange And Intrinsic Kinetic Study Of Bi₂MoO₆ Nanosheet Catalysts For Oxidative Dehydrogenation Of 1-butene

1,3-Butadiene is an essential raw material for manufacturing a large number of chemical products,such as polybutadiene rubber,styrene-butadiene rubber,polybutadiene and acrylonitrile-butadiene-styrene.Meanwhile,it can also be used to produce adiponitrile and hexamethylene diamine,as coatings,sealants and additives.Owing to its versatility,the global demand for 1,3-butadiene has been increasing consistently every year.Currently,there are two main routes for the production of 1,3-butadiene:a)extraction from mixed C4 hydrocarbons(byproducts of ethylene cracking);b)oxidative dehydrogenation of n-butane or n-butene.However,in recent years,the development of shale gas technology has led to the lightening of raw materials for ethylene cracking,which has caused a decline in the output of butadiene obtained by extraction,resulting in a shortage of market supply.In order to alleviate this trend,the technology of using butene as a raw material to produce butadiene by oxidative dehydrogenation has once again become a research hotspot.This technology can not only reduce the dependence on petroleum resources,but also increase the utilization rate of C4 resources and fill the supply gap in the butadiene market.The key factor of this process lies in the development of high activity and stability catalysts.This thesis aims to control the morphology of BiMo catalyst,establish structure-performance relationship during oxidative dehydrogenation reaction,identify oxygen exchange mechanism,and study its intrinsic kinetics.The main contents are as follows:1.Bi2MoO6 nanosheet catalysts with different thickness were controllably synthesized via hydrothermal method,and applied to ODH of 1-butene.The results revealed that the thickness of nanosheet had a significant effect on the catalytic performance.The catalyst with the thichness of 35.8 nm displayed the superior catalytic performance in this work,which were 87.2%for 1-butene conversion and 78.3%for BD yield,respectively.Based on XPS,TPRO and O2-pulse results,oxygen mobility and oxygen capacity were crucial factors that determined catalytic performance in ODH reaction.Results from the TPIE and IIE experiments indicated that the principal oxygen exchange mechanism for Bi2MoO6 nanosheet catalysts was simple heteroexchange and that the thickness of the nanosheet could affect the distance and rate of oxygen migration or replenishment between the bulk and the surface.2.The intrinsic kinetics was studied for oxidative dehydrogenation of 1-butene to 1,3-butadiene over Bi2MoO6 nanosheet and BiMoV0.15 catalysts in a fixed-bed reactor.The power-law model was used to fit the experimental data,and the model parameters were fitted by non-linear regression.Results showed the existence of two reaction temperature-dependent kinetic regimes as there was a break in the activation energy around 653 K for both catalysts.Regardless of the temperature range,the activation energy of the Bi2MoO6 nanosheet catalyst was lower than that of the BiMoV0.15 catalyst,indicating that the Bi2MoO6 nanosheet catalyst could effectively reduce the activation energy and make the reaction easier.Meanwhile,a series of mechanism-based derivations were made to reveal the relationship between the reaction order and oxygen coverage on the catalyst surface.