Preparation Of Li₃PO₄,Au/Li₃PO₄ And Isomerization Mechanism Of Propylene Oxide Catalyzed By Li₃PO₄

Allyl alcohol is an important raw material in the chemical industry and is widely used in the production of glycerin,pharmaceuticals,pesticides,and spices.In recent,the allyl alcohol is mainly derived from the isomerization of propylene oxide,and the isomerization catalyst is a phosphate catalyst.The experimental characterization methods to infer the catalytic mechanism is limited to the macroscopic phenomena.Therefore,the mechanism of isomerization of propylene oxide catalyzed by lithium phosphate was studied from theoretical calculations using density functional calculations.In this paper,hollow microspheres Li3PO4 catalysts were prepared by precipitation method.The morphology and structure of the catalysts were characterized by XRD,SEM,In-situ DRIFTS,BET,etc.The catalytic activity of its catalytic isomerization of propylene oxide to allyl alcohol was studied.It was found that the Li3PO4 is ?-Li3PO4 and has two strong basic positions.The Li3PO4 has a good activity of isomerization of propylene oxide to allyl alcohol.The conversion of propylene oxide can reach 70%,the allyl alcohol selectivity can reach 82%.In order to study the interaction of Li3PO4 catalyst and propylene oxide,Castep(Cambridge Sequential Total Energy Package)based on density functional theory(DFT)pseudopotential method was used to study the adsorption of propylene oxide,allyl alcohol,propionaldehyde and acetone on Li3PO4(001)surface.The charge transfer and interaction of propylene oxide and Li3PO4 were analyzed by the change of PDOS,Mulliken charge,structural parameters of propylene oxide before and after adsorption.Through further analysis and discussion,the mechanism of Lewis acid sites and Bronsted bases acting together to catalyze the isomerization of propylene oxide to form allyl alcohol was proposed.Complete LST-QST method was used to study the transition state of propylene oxide isomerization to propionaldehyde,acetone and allyl alcohol with or without Li3PO4.It was found that Li3PO4 can greatly reduce the isomerization energy barrier of propylene oxide.By reducing the energy barrier of each pathway,the selectivity of isomerization is changed,and Li3PO4 has a highly selective to allyl alcohol.In order to improve the activity of Li3PO4 catalyst,Au/Li3PO4 catalysts were prepared by Au deposition using traditional sedimentation method.Li3PO4 catalysts with different Au particle sizes were obtained by adjusting the pH value.The morphologies and structures of Au/Li3PO4 catalysts were investigated by SEM,XRD,TEM and other characterization methods.The catalytic activity of Au/Li3PO4 with different Au particles to catalytic isomerization of propylene oxide to allyl alcohol was tested.It was found that as the pH becomes smaller,the particle size of Au becomes smaller,and the activity of catalyzing propylene oxide isomerization is better.The adsorption of Au clusters on the(001)plane of Li3PO4 was studied by DFT.It was demonstrated that the Au loading increased the alkali strength of the Li3PO4 catalyst.