Tailoring mesoscopically structured H-ZSM5 zeolites for toluene methylation
Tailoring mesoscopically structured H-ZSM5 zeolites for toluene methylation
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DOI：
10.1016/j.jcat.2013.12.003
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发表时间：
2014-03
影响因子：
7.3
通讯作者：
Johng‐Hwa Ahn;R. Kolvenbach;C. Neudeck;S. Al-Khattaf;A. Jentys;J. Lercher
中科院分区：
文献类型：
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作者：
Johng‐Hwa Ahn;R. Kolvenbach;C. Neudeck;S. Al-Khattaf;A. Jentys;J. Lercher
通过调节催化剂的扩散和酸中心浓度，设计并合成了具有介观结构的H-ZSM5分子筛，作为甲苯甲基化反应的高效择形催化剂。这是通过结合脱硅、随后的脱铝和化学沉积几纳米厚度的介孔二氧化硅覆盖层来实现的。脱硅和脱铝使沸石晶体中的有效扩散长度减小，从而有利于甲醇的活化和生成的二甲苯的脱附，从而提高了甲苯的周转率，但对二甲苯的选择性有所下降。SiO_2覆盖层的存在增加了沸石的曲折性，无规地堵塞了表面的孔洞，增加了有效扩散路径长度，从而提高了对二甲苯的选择性。最终的材料结合了更高的催化剂利用率和更高的选择性，从而使反应速度与母体沸石相当，但选择性明显更高。
Mesoscopically structured zeolites based on H-ZSM5 were designed and synthesized as highly active and shape selective catalysts for methylation of toluene by tuning diffusion and acid site concentration of the catalysts. This was achieved by combining desilication, subsequent dealumination and chemical deposition of a mesoporous SiO2overlayer of several nanometer thickness. The decreasing effective diffusion length in zeolite crystals achieved by desilication and dealumination increased the turnover rate of toluene by favoring activation of methanol and facilitating desorption of the produced xylenes, albeit with some loss in p-xylene selectivity. The presence of the SiO2overlayer increased the p-xylene selectivity by enhancing the tortuosity of the zeolite, randomly blocking pore openings at the surface, and increasing the effective diffusion path length. The final material combines the higher catalyst utilization with enhanced selectivity leading to rates comparable to the parent zeolite, but at significantly higher selectivity.