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

Abstract

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 medstrong 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 nhexadecane 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.

Hydroisomerization Principles of Acenaphthene to Alkyladamantanes over Modified USY-Supported Pt Catalysts

“…It was widely accepted that different temperatures correspond to different acid site strengths. Therefore, NH 3 desorption peaks observed at 150–300 °C, 300–450 °C, and 450–550 °C correspond to weak, moderate, and strong acid sites, respectively . The concentration values of Brønsted and Lewis acid sites (BAS and LAS) were determined through the integration of NH 3 -TPD curved in combination with the integrated absorbance of the bands at 1546 and 1455 cm –1 in the FT-IR pyridine adsorption experiments .…”

“…Therefore, NH 3 desorption peaks observed at 150−300 °C, 300−450 °C, and 450−550 °C correspond to weak, moderate, and strong acid sites, respectively. 45 The concentration values of Brønsted and Lewis acid sites (BAS and LAS) were determined through the integration of NH 3 -TPD curved in combination with the integrated absorbance of the bands at 1546 and 1455 cm −1 in the FT-IR pyridine adsorption experiments. 46 The ratios of Brønsted acid to Lewis acid relative to the total acid sites of USY zeolites were determined and calculated, as shown in Table 3.…”