Abstract

The samples of alumina of different origin exhibit different activity in the reaction of methanol dehydration to dimethyl ether (DME). To elucidate reasons for differences in their activity, a comparative study of the structural (XRD analysis, specific surface area, and porosity) and surface (Brønsted and Lewis acidity and hydroxyl coverage) properties of alumina samples was carried out. The presence of formates, aldehyde complexes, and bridging and terminal methoxy groups in different ratios on the surface of aluminum oxide samples under the reaction conditions of methanol conversion was detected using in situ IR spectroscopy. The reactivity of the detected surface compounds was compared for all of the samples. It was found that the activity of the samples in the formation of DME correlated with the rate of conversion of bridging methoxy groups. In turn, the rate of conversion of the bridging methoxy groups was determined by the acidity of bridging hydroxyl groups. An increase in acidity led to an increase in the bond strength of the methoxy group with the surface and a decrease in the rate of its conversion into DME. Linear methoxy groups underwent oxidative conversion into formate and aldehyde surface complexes. The nature of the oxidizing ability of an alumina surface is discussed.

中文翻译：

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根据原位红外光谱数据，γ-Al2 O 3的表面性质对甲醇转化为二甲醚的影响

摘要

不同来源的氧化铝样品在甲醇脱水成二甲醚（DME）的反应中表现出不同的活性。为了阐明其活性差异的原因，对氧化铝样品的结构（XRD分析，比表面积和孔隙率）和表面（布朗斯台德和路易斯酸度和羟基覆盖率）性能进行了比较研究。使用原位红外光谱法检测了在甲醇转化反应条件下，氧化铝样品表面上存在不同比例的甲酸酯，醛配合物，桥连和末端甲氧基。比较所有样品的检测到的表面化合物的反应性。发现样品在DME形成中的活性与桥连甲氧基的转化率相关。反过来，桥连甲氧基的转化率由桥连羟基的酸度确定。酸度的增加导致甲氧基与表面的结合强度增加，并且其转化成DME的速率降低。线性甲氧基经过氧化转化为甲酸和醛表面配合物。讨论了氧化铝表面氧化能力的性质。