Cost-effective Synthesis Of TS-1 And Its Catalytic Performance For Gas-phase Propene Epoxidation

As a typical MFI structure zeolite,TS-1 as a support or catalyst has exhibited attractive catalytic activity and selectivity in a series of selective oxidation reactions,for instance,epoxidation of alkenes,oxidation of sulfide,ammoximation of ketone and aromatic hydroxylation.However,the expensive TPAOH template significantly increases the synthetic cost,hindering the extensive application of TS-1 in industrial processes.Therefore,it is necessary to reduce the synthetic cost of TS-1.In this work,the method of steam-assisted crystallization combined with adding seeds and the template free method were used to synthesize the low-priced,small-sized mesoporous TS-1.Firstly,this work used the inexpensive tetrapropylammonium bromide(TPABr)as organic template.However,the as-synthesized TS-1 shows a large particle size over 10 μm.The large zeolite crystals could impose significant diffusion limitations,impeding the transport of reactants and products inside the porous channels and leading to reduced activity,selectivity and catalytic lifetime.Therefore,in order to overcome the above defects,the low-cost and small-sized mesoporous TS-1 was synthesized by steam-assisted crystallization method with adding seeds in this work.On one hand,adding seeds can effectively reduce the particle size because adding seeds can promote the formation of a large number of crystal nucleus at the early stage of the synthesis process.Moreover,adding seeds is not only helpful to reduce the concentration of TPABr template,but also useful to promote the titanium into the framework of TS-1.On the other hand,a large number of crystal nucleus are formed at the early stage of the synthesis process and the slow growth of crystals after nucleation should be the main reason for the smaller particle size of STS-1 crystals prepared by the steam-assisted crystallization method.Furthermore,mesoporous are present on the STS-1 sample and the formation of the pore structure is probably attributed to the desilication by alkaline steam during the steamassisted crystallization process.Notably,it is found that STS-1 supported Au catalyst exhibits good catalytic performance for direct propene epoxidation with H2 and O2 which is comparable to the reported conventional expensive Au/TS-1 catalyst with the same Si/Ti molar ratio.This work of synthesize the low-priced and efficient TS-1 with high catalytic performance is of prime industrial and scientific importance.Secondly,the nano-level mesoporous UTS-1 was successful synthesized by controlling the species of seeds and the roasting conditions of the seeds without adding the organic template agent.This organic template free method with the accompany of adding the uncalcined S-1 zeolite as seeds can not only promote the titanium into the framework of TS-1,but also reduce the particle size of TS-1.It provides a larger surface area and more active position,shortens the length of the channel,and effectively improves the mass transfer and heat transfer capacity of the TS-1.Furthermore,it is found that the Au/UTS-1 catalyst exhibits good catalytic performance for direct propene epoxidation with H2 and O2.This work will be of referential importance to the rational design of efficient and cost-effective industrial TS-1 catalysts for epoxidation reactions.