Influence of crystal size of HZSM-5 on activity and shape selectivity in xylene isomerization

Contribution of particle size and aluminium distribution to the para-selectivity of ZSM-5 type zeolites

“…The increase of crystal size alone results in the decrease of external surface, lower activity and higher selectivity for the para-isomer [7][8]. Decreasing the aluminium content during zeolite crystallization is another way to reduce the number of acid sites on the external surface of crystals and consequently improve their para-selectivity [9].…”

The effect of ZSM-5 zeolite crystal size on p-xylene selectivity in toluene disproportionation

“…Although it is anticipated that p-xylene is a primary product leaving the pore mouth of ZSM-5 zeolite, it isomerizes on the external surface which leads to the production of xylene isomers in their thermodynamic equilibrium values. To obtain higher p-xylene selectivity than the thermodynamic equilibrium value, it was suggested that deactivating the external acid sites of the catalyst and increasing the diffusion pathway by increasing the crystal size are crucial factors [4,[7][8][9][10][11][12][13][14][15][16]. A unique relationship between o-xylene diffusion time, by adsorption measurements, and p-xylene selectivity was found by Olson and Haag.…”

“…Thus, increasing the crystal size will lead to obtaining more p-xylene in the product stream as the other isomers will have to isomerize to the much faster diffusing isomer (p-xylene) in order to diffuse out of the channels [21,22]. Ratnasamy et al [10] performed xylene isomerization reaction over ZSM-5 zeolites with different crystal size to investigate the effects of diffusion path length on the activity and selectivity towards p-xylene. ZSM-5 catalysts with 8, 13 and 16 µm were tested and it was clearly shown that the activity was decrease decreased by a factor of 3 as a result of increasing the crystal size from 8 to 16 µm.…”

Influence of crystallization times on the synthesis of nanosized ZSM-5

“…In recent years, many efforts and increasing attention have been devoted to understand the mechanisms, which govern the different synthesis procedures. Most of these investigations are summarized and/or discussed in some recent review articles [3][4][5][6][7][8][9][10][11][12].…”