Silica chemical vapor deposition (Si-CVD) technique was applied in the silylation of ZSM-5 zeolite to enhance para isomer product selectivity in the disproportionation of toluene (TDP) and ethylbenzene (EBDP). A threshold value in Si-CVD deposition for enhancement in para isomer selectivity in TDP and EBDP was determined. Beyond the threshold value, the para selectivity increased with increasing silica deposition amount. Upon Si-CVD modification, while the micropore size of the MFI zeolite stayed the same with the parent MFI zeolite, the enhancement in para selectivity could be due to the passivation of external active sites. The p-diethylbenzene isomer selectivity of>99 % was demonstrated at EB conversion up to 35 %. Nevertheless, p-xylene isomer product selectivity of around 83 % was obtained only at a reasonable conversion level of 20 %. The difference in selectivation efficiency between TDP and EBTDP reactions could be attributed to the difference in the relative ratio of reaction kinetics rate to the diffusion rate in associated with different reaction temperature range.
