Catalytic Transformation Conditions of Ethanol on Dealuminated BEA Zeolites

Catalysis is an important tool in obtaining a range of derivative products from renewable sources, such as ethanol. Solid-state dealumination using ammonium hexafluorosilicate on the BEA zeolite under the treatment at temperature of 190 °C, 70 mol% dealumination in the presence of humidity and washing with buffer solution at 25 °C generated larger pores. The absence of washing procedure for the same sample resulted in pore blockage. Ethanol dehydration reactions showed conversion of 72% (64% ethylene and 8% diethyl ether) for this sample at 300 °C and high weight hourly space velocity (WHSV, 3247 h-1), whereas, at the same temperature but at a low WHSV (57 h-1), the conversion was 88% (49% ethylene and 39% diethyl ether). Dealuminated BEA zeolite presented better diffusion conditions, higher hydrophobicity and generated larger pores. Impregnation with H3PW12O40, H4SiW12O40 and Nb2O5 explained the selectivity, showing that Lewis acid sites from Nb2O5 favored the diethyl ether production.

催化是从可再生资源（如乙醇）制备一系列衍生产物的关键技术手段。以六氟硅酸铵为试剂，对BEA分子筛（BEA zeolite）进行固态脱铝（solid-state dealumination），在190℃下处理，配合湿度环境中70摩尔百分比的脱铝率，并经25℃缓冲溶液洗涤后，可得到孔道更大的分子筛。若对同一样品省略洗涤步骤，则会引发孔道堵塞。乙醇脱水反应测试结果显示，在300℃、高空速（重量时空速度，weight hourly space velocity, WHSV，3247 h⁻¹）条件下，该样品的转化率为72%（产物组成为64%乙烯与8%二乙基醚）；而在相同温度、低空速（WHSV=57 h⁻¹）下，转化率提升至88%（产物组成为49%乙烯与39%二乙基醚）。经脱铝处理的BEA分子筛具备更优异的扩散性能、更高的疏水性且孔道尺寸更大。采用磷钨酸（H3PW12O40）、硅钨酸（H4SiW12O40）与五氧化二铌（Nb2O5）进行浸渍改性可调控反应选择性，研究表明五氧化二铌上的路易斯酸位点（Lewis acid sites）更有利于二乙基醚的生成。