晶种诱导合成ZSM-5多晶聚集体及其在甲醇制碳氢化合物中的催化性能
Polycrystalline ZSM-5 Aggregates Induced by Seed and Catalytic Performance in Methanol to Hydrocarbon
王旭昌 1焦楚钰 1季卓 1焦其瑞 1秦波 2杜艳泽 2郑家军 1李瑞丰1
作者信息
- 1. 太原理工大学 能源化工与催化研究中心,太原 030024
- 2. 中国石油化工集团 大连石油化工研究院,大连 116045
- 折叠
摘要
合成ZSM-5沸石通常以小分子多元胺或季铵盐作为有机结构导向剂(OSDA).无OSDA的水热合成体系避免了使用有机模板和随后的煅烧步骤,这不仅可以降低合成成本,而且避免因有机模板燃烧造成环境污染,是一种环境友善的合成方法.然而,已有的研究显示,某些有机物如乙醇,会或多或少地参与所谓的无模板合成系统.为确保合成体系中不带入有机模板,本研究以煅烧的商用 ZSM-5 沸石为晶种,铝酸钠为铝源,硅溶胶为硅源,在无OSDA的体系中成功制备了一种由棒状纳米晶组成的多晶 ZSM-5 聚集体.详细研究了 ZSM-5 晶种的硅/铝比、加入量和晶化条件(如晶化温度以及晶化时间)等对ZSM-5 沸石合成的影响.研究结果表明:以含质量分数 5.6%MFI拓扑结构晶种的凝胶前驱体为原料,经水热处理 48 h,可制得由尺寸小于 100 nm的初级纳米晶粒组成的高结晶度ZSM-5 多晶聚集体;ZSM-5 晶种的硅/铝比不影响样品的拓扑结构、孔结构,但低硅/铝比的晶种更有利于目标沸石快速结晶,并更有利于获得高酸量尤其是较强酸量的ZSM-5.采用甲醇脱水考察合成的多晶ZSM-5的催化性能,并与商用参比ZSM-5r催化剂进行比较.结果表明,与参比催化剂相比,合成的样品因疏松聚集的纳米初级晶粒堆积形成多级孔而具有较长的催化寿命(16 h vs 8 h),且合成的多晶聚集体催化剂具有较高的芳烃选择性(28.1%～29.8%vs 26.5%).
Abstract
Synthesis of ZSM-5 zeolite typically utilizes small molecule polyamines or quaternary ammonium salts as organic structure guiding agent(OSDA).By contrast,the OSDA-free hydrothermal synthesis system eliminates the use of organic templates and the subsequent calcination procedure.This not only reduces the cost of synthesis,but also prevents environmental pollution from the combustion of organic templates,representing an eco-friendly approach.Despite this,literature suggests that even so-called template-free synthesis systems often involve trace amount of organic substances like alcohol.In the present work,a calcined commercial ZSM-5 zeolite was served as seed,with sodium aluminate as aluminum source and silica sol as silicon source,ensuring an entirely template-free synthesis system.Polycrystalline ZSM-5 aggregates consisted of rod-like nanocrystals were successfully prepared in the completely OSDA-free system.Effects of the Si/Al ratio in ZSM-5 seed,dosage and crystallization conditions such as crystallization temperature and crystallization time on ZSM-5 synthesis were investigated.The results show that a highly crystallinity ZSM-5 aggregate consisting of primary nano-sized crystals less than 100 nm is produced from a gel precursor with 5.6%(in mass)seed after hydrothermal treatment for 48 h.Furthermore,the Si/Al ratio in ZSM-5 seed has little effect on the topological structure and pore structure of the synthesized samples.However,the seeds with a low Si/Al ratio facilitate faster crystallization of zeolite and enhance the acidity,especially the strong acid centers,of the catalyst.The catalytic performance of the synthesized polycrystalline ZSM-5 was evaluated during dehydration of methanol and compared with a commercial reference ZSM-5r.The results exhibit that as compared with the reference catalyst,the fabricated sample has a longer catalytic lifetime(16 h vs 8 h)attributed to its hierarchical pores derived from the loosely packed primary nanoparticles.Additionally,the prepared polycrystalline catalyst also exhibits a higher aromatics selectivity(28.1%-29.8%vs 26.5%).
关键词
ZSM-5/多晶聚集体/晶种/结构导向剂Key words
ZSM-5/polycrystalline aggregate/crystal seed/structure guiding agent引用本文复制引用
基金项目
国家自然科学基金(U19B2003)
国家自然科学基金(21706177)
国家自然科学基金(21975174)
Foundation Supported by China Petroleum&Chemical Corporation(121014-2)
出版年
2024
国家科技期刊平台
NSTL
万方数据