The Synthesis Of Heteroatom-molecular Sieves And The Catalytic Performance Of Styrene Oxide Isomerization

The catalytic performance of isomerization of styrene oxide tophenylacetaldehyde was studied over a series of boron containing MFI zeolites, TS-1zeolites with different pore structure and modified beta zeolites. The catalysts werecharacterized by XRD, ICP-OES, N2adsorption, SEM, TEM, XPS,27Al,11B,29SiMAS NMR and NH3-TPD, etc.The weakly acidic B-ZSM-5zeolites could facilitate the reaction at highconversion and selectivity to phenylacetaldehyde. The stability of the catalystsdepends largely on the concentration of weak acid sties and the coordination state ofboron. The presence of [BO3] is unfavorable. As for Al-ZSM-5and B-Al-ZSM-5which contained strong acid sites, the stability relied heavily on the concentration ofweak acid sites and the properties of strong acid sites. Coke deposition was the mainreason for the deactivation of the catalysts, the coking rate of Al-ZSM-5was very fastand the formed coke blocked the micropores and thus of the acid sites, leading to thedeactivation of it. The coking rate of B-Al-ZSM-5is relatively slower, although partof the acid sites (especially the strong acid sites) were poisoned, the micropores or theentrances were not blocked, so there were still large amount of pore volume and acidsites available for the proceeding of the reaction.The catalytic performance of TS-1was mainly affected by the pore structure. Themicropores of TS-1-P constrained the diffusion of phenylacetaldehyde whichsuccessively reacted to large amount of dimer. The diffusion path of TS-1-nano wasshortened which benefited the diffusion of phenylacetaldehyde in the micropores andrestrained the formation of dimer. The mesopores produced after alkalinemodification was helpful for the diffusion of phenylacetaldehyde, but the amount ofmesopores over TS-1-N was overmuch and their diameter was too large, leading tothe formation of an oligomer and accelerating the deactivation of the catalyst. As forTS-1-O, the micropores which favored the formation of phenylacetaldehyde werewell preserved, in the meanwhile, the suitable mesopores system were helpful for thediffusion of phenylacetaldehyde. The balanced pore distribution of TS-O-1wasfavorable for the selectivity to phenylacetaldehyde and the stability of the catalyst.The weakly acidic boron-beta could catalyze the reaction at high conversion andselectivity to phenylacetaldehyde, but it deactivated only after6h TOS. The conversion over M-beta was very high, a large amount of trimer formed and theselectivity to phenylacetaldehyde was only76%. The deactivation of M-beta wascaused by dealumination and coke deposition. The stability of P-beta was similar toM-beta and its deactivation was mainly due to block of pore by aluminum phosphorusspecies. However, owing to the reduction of the acid site density, the selectivity tophenylacetaldehyde over P-beta was much higher than that of M-beta. The poresystem of B-beta was not blocked after modification and the lower acid site density ofit prevented the formation of trimer. In addition, the large amount of weak acid sitewas helpful for the reaction. Hence, B-beta showed the best performance.