The purification of clay minerals prior to their use as catalysts can escalate processing costs so methods are needed whereby less purification is necessary. One such potential method is acid treatment of the unpurified clay minerals. The main objectives of the present study were to develop the optimal acid-treatment conditions and to determine how the acidic properties of the modified clay samples influenced their catalytic capability toward the dehydration of ethanol and methanol. Clay mineral samples – allophane, palygorskite, and sepiolite, without purification – were acid treated (0.8 M HNO 3 ; 95°C; 2, 8, or 24 h) and after calcination (500°C; 6 h) tested as catalysts for the conversion of methanol to dimethyl ether and of ethanol to diethyl ether and ethene. The changes in chemical and structural compositions as well as surface acidity of the mineral samples were analyzed and correlated with their catalytic performance. Among the samples studied, allophane was the most catalytically active in the dehydration of methanol to dimethyl ether. Acid treatment of this mineral sample decreased methanol conversion slightly. An opposite effect was found for ethanol dehydration to diethyl ether, where acid treatment increased catalytic activity of allophane. The differences in catalytic performance of the mineral samples were discussed with respect to the nature and concentration of acid sites.

中文翻译：

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酸处理粘土矿物作为甲醇和乙醇脱水的催化剂

在将粘土矿物用作催化剂之前对其进行纯化会增加加工成本，因此需要减少纯化的方法。一种可能的方法是对未纯化的粘土矿物进行酸处理。本研究的主要目标是开发最佳酸处理条件，并确定改性粘土样品的酸性特性如何影响其对乙醇和甲醇脱水的催化能力。粘土矿物样品——水铝石、坡缕石和海泡石，未经纯化——经过酸处理（0.8 M HNO 3 ；95°C；2、8 或 24 小时）并在煅烧（500°C；6 小时）后作为催化剂进行测试甲醇转化为二甲醚，乙醇转化为乙醚和乙烯。分析了矿物样品的化学和结构组成以及表面酸度的变化，并将其与其催化性能相关联。在所研究的样品中，水铝烷在甲醇脱水生成二甲醚过程中的催化活性最高。该矿物样品的酸处理略微降低了甲醇转化率。发现乙醇脱水为乙醚的相反效果，其中酸处理增加了水铝烷的催化活性。根据酸性位点的性质和浓度，讨论了矿物样品催化性能的差异。该矿物样品的酸处理略微降低了甲醇转化率。发现乙醇脱水为乙醚的相反效果，其中酸处理增加了水铝烷的催化活性。就酸性位点的性质和浓度而言，讨论了矿物样品催化性能的差异。该矿物样品的酸处理略微降低了甲醇转化率。发现乙醇脱水为乙醚的相反效果，其中酸处理增加了水铝烷的催化活性。就酸性位点的性质和浓度而言，讨论了矿物样品催化性能的差异。