Abstract:

Utilizing the ammonia-evaporation method and employing silica (SiO₂) as a support, we synthesized Cu/SiO₂ catalysts with varying loadings. The influence of Cu catalyst particle size on the performance of methanol nonoxidative dehydrogenation for formaldehyde production was investigated. Characterization results revealed an increase in Cu particle size with Cu loading. The experimental results showed that the rate of methanol dehydrogenation increased with the increase in Cu particle size when the Cu particle size was less than 2.8nm. Accordingly, it was inferred that the active sites for methanol dehydrogenation to formaldehyde might reside on the planar surfaces of the Cu catalyst. Theoretical calculations unveiled that on the Cu (111) plane, the predominant pathways for formaldehyde generation involved the cleavage of O－H and C－H bonds, with the former as the rate-determining step. Furthermore, kinetic experiments were conducted on the 15%Cu/SiO₂ catalyst, which exhibited superior formaldehyde yield. The obtained reaction order and activation energy for methanol conversion were 0.42 and 32.42kJ/mol, respectively, while those for formaldehyde production were 0.45 and 30.23kJ/mol, respectively. These findings could provide valuable insights for the development of highly active and selective catalysts for methanol nonoxidative dehydrogenation.

Key words: methanol, formaldehyde, catalyst, kinetics, silica

摘要：

采用蒸氨法，以二氧化硅（SiO₂）为载体，制备了不同负载量的Cu/SiO₂催化剂，并考察了Cu催化剂粒径对甲醇非氧化脱氢制备甲醛性能的影响。表征结果显示，Cu的粒径随Cu负载量增加而增大。结合实验结果发现，当Cu粒径小于2.8nm时，甲醇脱氢生成甲醛的速率随Cu粒径增大而增大。据此，推测甲醇脱氢生成甲醛的活性位点可能存在于Cu催化剂表面的平板位点上。理论计算揭示在Cu(111)平板位上，甲醛生成途径主要涉及O—H键和C—H键的断裂，其中O－H键断裂是速率决定步骤。进一步，对具有较好甲醛产率的质量分数15%Cu/SiO₂催化剂进行动力学实验，得到甲醇转化的反应级数和活化能分别为0.42和32.42kJ/mol，甲醛生成的反应级数和活化能分别为0.45和30.23kJ/mol。上述研究发现为开发高活性和高选择性的甲醇无氧脱氢制甲醛催化剂提供了指导。

关键词: 甲醇, 甲醛, 催化剂, 动力学, 二氧化硅