Effects of Surface Modification on Product Shape-Selectivity during Catalytic Reactions of Aromatics over ZSM-5 Zeolites

• Main Authors: Tsai, Chung Ta, 蔡忠達
• Other Authors: Lee, Huang Kuei
• Format: Others
• Language: zh-TW
• Published: 1999
• Online Access: http://ndltd.ncl.edu.tw/handle/53821579229797924370

碩士 === 中國文化大學 === 材料科學與製造研究所 === 87 === Alkylbenzene disproportionation reaction is an important process in petrochemical industry for the production of benzene and xylene. Zeolitic catalyst, such as H-ZSM-5 zeolite, which possesses a higher acidity are commonly used. The effects of surface modification on the para-selectivity of H-ZSM-5 zeolites during catalytic reactions hence provoke interest in both academic research and industrial applications. The objectives of this work are two-folds; first, to investigate the effects of aluminum content and catalyst surface modification by silicon chemical vapor deposition (Si-CVD) on the product selectivity during ethylbenzene disproportionation over different H-ZSM-5 zeolites. The surface acid properties of the modified catalysts, which differed with the aluminum content of the zeolites, were carefully monitored by Infrared spectroscopy. It was found that silica is deposited mostly on the external surface of the zeolites and effectively shielded the surface silanols and Bronsted acid sites. The presence of surface silica served to inhibit secondary isomerization reactions on the external surface of the zeolite crystallites thus resulted in a marked enhancement in para-selectivity during the disproportionation reaction. Secondly, the effect of Si-CVD surface modification on an H-ZSM-5 zeolite on product para-selectivity was investigated for different catalytic reactions, namely during disproportionation of ethylbenzene and toluene, and during isomerization of o-xylene. It was also found that the deposition of silica on the catalyst surface provokes enhancement of para-selectivity in spite of the type of the reactions. The results obtained from this comprehensive study not only invoke further understanding toward the effect of catalyst surface modification on product selectivity but also provide valuable information in the enhancement of product selectivity and market value for future industrial applications.