限域超临界CO2中制备铜单原子的吸附脱附调控机制及其反应性能研究

利用催化手段将CO2加氢合成大宗化学品甲醇，是“一举两得、变废为宝”的技术路线，其至今尚未实现商业化应用的关键在于缺乏高效催化剂。单原子催化剂兼具均相催化剂活性中心均一和多相催化剂结构稳定易分离等优点。因金属原子极易团聚，其制备极具挑战性，目前报道的制备方法较少且存在局限性。为此，本项目提出利用超临界CO2优越的传质能力和溶剂能力，将金属前驱物携带进入纳米级孔道，通过调节共溶剂调控纳米相吸附，通过精细梯度泄压耦合超声能，干预前驱物在限域孔道内的聚集和结晶过程制备单原子催化剂。将重点研究：（1）超临界法制备单原子催化剂分散度、担载量、配位环境、电子价态等的基本调控规律和优化；（2）超临界CO2氛围下限域空间内两步成核理论的实验研究和分子模拟；（3）所制备催化剂用于CO2加氢制备甲醇的活性、选择性和稳定性评价；旨在为制备高分散、高担载量、高稳定的Cu基单原子催化剂提供新的途径。

Selective hydrogenation of CO2 to ethanol over catalysts is a useful technical routes, which can realize the CO2 capture and solve the lack of energy resources. However, this technique was not available in commercialization for the lack of highly active catalysts.Single atom catalysts combine the advantages of uniform active site in homogeneous catalysts, and the stability as well as easy separation in heterogeneous catalysts. However, the preparation of single atom catalysts is still challenging because the single atoms are prone to aggregation. There are several reported methods of preparing such catalysts and most of them have limitations.Herein, supercritical fluid deposition (SCFD) method is proposed to synthesize these catalysts instead. Environmental benign supercritical CO2(scCO2) is used as solvent for its near zero surface tension and excellent transport property. The precursors are first dissolved in scCO2 and are then brought to the nanochannels of the substrates. After that, the adsorption of precursors onto the substrates is adjusted by using different co-solvents and the desorption of precursors is controlled by gradient depressurization and the ultrasonication. The single atom catalysts are then formed by interfering the aggregation and crystallization of the precursors confined in the nanochannels in scCO2.The aim of this project was to prepare highly active Cu single atom catalysts with highly dispersed active components, high metal loading and high stability. Based on this aim, three contents were emphasized as follows: (1) The influence of the operating parameters on the metal loading, dispersity, coordination environment and valence state of the single atoms and the optimization of the parameters; (2) The experimental study and molecular simulation of the two-step nucleation theory in confined nanochannels in scCO2; (3) The activity, selectivity and the stability of the prepared catalysts.