Mesoporosity and Acidity Manipulation in ZSM-23 and their n-Hexadecane Hydroisomerization Performance

Graphical Alkali treatment and acid treatment were conducted on ZSM-23 zeolite, which achieved the acidity manipulation and improved the mesoporosity of the zeolite. The modification of the support was conducive to catalysts when used for n -hexadecane hydroisomerization, which enhanced the selectivity of isomers significantly and inhibited the cracking processes. The enhanced mesoporosity in the networks is expected to offer a potential route to surmount mass-transport constraints within one-dimensional microporous structural zeolites. Highly crystalized ZSM-23 zeolite was synthesized and subsequently post-treated with alkali-etching and acid-etching, the effects of post-treatments on the physical and chemical properties of the parent zeolite were investigated via XRD, N 2 physical adsorption, FE-SEM, TEM, 27 Al MAS NMR, Py-IR and NH 3 -TPD. The catalytic activity of various Pt supported bifunctional catalysts was investigated via n -hexadecane hydroisomerization. The post-treated process not only increased the pore volume as well as the specific surface area, which efficiently improved the diffusion efficiency, but also changed the acidity and acid distribution of zeolite: alkali treatment could increase the content of total Brönsted acid while acid treatment exhibited an opposite trend. Acid treatment effectively promoted the density of weak Brönsted acid sites and suppressed the med-strong Brönsted acid sites. With the manipulation of acidity and development of mesoporosity in zeolite, the formation of isomers and the suppression of cracked products in the n -hexadecane hydroisomerization were accomplished. The catalytic performance of catalysts showed that acid treatment could effectually promote the formation of isomeric products and inhibit cracking reactions. Especially, Pt/Z(1.0 HN) catalyst with suitable distribution of acid sites and textural properties, exhibited an outstanding n -C 16 hydroisomerization performance with the highest i -C 16 yield of 64 wt.% at 340 °C.