甲醇羰化Cu-HMOR催化剂中铜落位控制与活性价态研究

Acetic acid (HAc), which is currently manufactured from homogeneous carbonylation of methanol via noble metal catalysts, is one of the most important coal chemical products. However, these homogeneous carbonylation processes suffer obvious disadvantages: halide-contained system causes serious equipment corrosion because of the existence of HI in this catalytic cycle; homogeneous system requires excessive energy to separate the products and catalysts. Gas-phased carbonylation of methanol over H-mordenite zeolites, which is a greener process to synthesize HAc, will be potential to overcome these problems. Cu modified H-mordenites by ion-exchange (Cu-HMOR) exhibit improved carbonylation performances and have caused the extensive concern. However, catalytic performances of Cu-HMOR prepared by routine procedures are still not satisfied because the location of Cu species is difficult to control. Furthermore, identification of the active valence of Cu species in the Cu-HMOR for methanol carbonylation is controversial so far. In this application, location of Cu species in 8-MR or 12-MR channels will be controlled by pre-adsorption of cyclic organic amines in 12-MR channels or designing Cu coordination ions with size between 8-MR or 12-MR channels, respectively. Then, their carbonylation performances will be studied in various reductive or oxidative atmospheres. Finally, the influence of location and valence of Cu species in the mordenites to methanol carbonylation will be exploded by using operando methods under real reactive conditions. The implement of this project is not only helpful to understand the nature of the improving carbonylation performances for H-mordenite by Cu modification, but also promising to develop an efficient carbonylation catalyst for applications.

乙酸是一种重要的煤化工产品，目前主要通过基于贵金属的甲醇均相羰化法生产，反应过程生成强腐蚀性HI，催化剂与产物分离能耗大。基于酸性丝光沸石的甲醇气相羰化过程可以有效解决这些问题，有望成为一条“绿色合成乙酸”新路线。Cu离子交换改性酸性丝光沸石有利于提高羰化性能，引起了广泛的关注。然而常规制备方法不能有效控制Cu的落位，导致性能提升不够显著，另外Cu的羰化活性价态也一直存在争议。本项目拟发展控制Cu落位的方法，利用环状有机胺预吸附12-元环孔道B-酸后再交换或构建尺度介于8和12-元孔道之间的Cu配位离子，使Cu选择性落位于丝光沸石的8或12-元环孔道中；随后考察不同氧化还原气氛下的甲醇羰化性能；结合落位情况，利用operando方法揭示真实反应条件下甲醇羰化的活性价态。本项目的顺利实施，将揭示Cu改性酸性丝光沸石提高甲醇羰化性能的本质原因，还有望开发出高效实用的催化剂。

乙酸是一种重要的煤化工产品，目前主要通过基于贵金属的甲醇均相羰化法生产，反应过程生成强腐蚀性HI，催化剂与产物分离能耗大。基于酸性丝光沸石的甲醇气相羰化过程可以有效解决这些问题，有望成为一条“绿色合成乙酸”新路线。然而，常规丝光沸石催化剂稳定性差，容易积碳失活，开发高稳定性、高选择性的分子筛羰化催化剂挑战很大。我们制备了一种吡啶改性丝光沸石催化剂Py-MOR，在甲醇羰化反应中具有高效、稳定的性能，反应145小时，乙酸选择性能保持90%以上，乙酸与乙酸甲酯选择性可达到98%。本过程不需要使用铑、铱等贵金属催化剂，不需要使用强腐蚀性卤素，反应产物与催化剂容易分离，具有潜在的应用前景。结构表征与理论计算表明，吡啶分子选择性吸附在丝光沸石的12元孔道，导致生成大尺寸积碳物质的空间位阻增大，从而抑制了积碳的生成，表现出较高的稳定性。8元环孔道酸性是主要的羰化反应活性中心，吡啶分子因尺寸大于8元环孔道直径，几乎不影响其羰化性能。反应机理研究表明，甲醇先在丝光沸石上形成表面甲氧基，引入一氧化碳后形成表面乙酰基，再通入甲醇表面乙酰基消失并重新生成表面甲氧基。基于本研究对催化剂结构与反应机理的认识，我们进一步发现与本项目相关的两种新反应过程—甲酸甲酯异构化制乙酸和甲醇与一氧化碳羰化耦合制芳烃。