多孔核壳CuOx@CeO2纳米催化剂构建及其组分界面对氨选择催化氧化净化作用机制的研究

The ammonia emission from waste stream, particularly in synthetic ammonia industry, and the slip ammonia from deNOx process can cause acidification of the environment and form secondary inorganic aerosols that contribute significantly to PM2.5, and it has been regarded as a more sensitive air pollutant than NOx. Thus the treatment of ammonia is becoming an important issue due to ever increasing environmental concerns. In this project, the selective catalytic oxidation (SCO) of NH3 to nitrogen at low temperatures under the effect of the transition metal oxides with specieal structure is used for the ammonia abatement. The fablication of porous CuOx@CeO2 core-shell nanocatalyst will be helpful for the stability of copper active species and the formation of the stronger component interfacial effect and the multi-reaction path, and thus the activity at low temperatures (<200oC) and the selectivity(>90%) will be strongly enhanced. Herein we will pay more attention on the component interfacial effect between copper and ceria by adjusting the crystal structure and the morphology of nanocatalyst, on the structure and the electron performance of the active species in the core-shell catalysts by the in situ ESR, EXAFS, MS and FTIR techniques. The relationship of the component interfacial effect with the catalytic performance for NH3 selcective oxidation and the activation and the transfer pathway of reactants species on the surface and at the interface of CuOx@CeO2 are stressed. And the reaction mechanism for NH3 selcective oxidation to N2 on CuOx@CeO2 core-shell nanocatalysts is also suggested in this project. The obtained results will show critical effects to understand the metal oxide interfacial effect on the NH3 selective catalytic oxidation and the synergetic catalytic effect in CuOx@CeO2 core-shell nanocatalyst, and consequently to be very significant for the development of the novel environmentally friendly transition metal oxide and their practical application.

合成氨工业驰放气的排放以及脱硝工艺中氨的泄漏严重污染了空气质量，造成了大量PM2.5二次粒子的产生，对人体健康产生了严重影响。本项目采用环境友好的选择催化氧化技术(SCO)，利用氧化物特定结构，在较低温度下高效选择性地将氨气转化为氮气和水。通过制备多孔核壳CuOx@CeO2纳米催化剂，有效提高铜活性组分的稳定性以及氧化铜和氧化铈组分间的界面作用，实现同一体系下的多条反应路径的发生，从而提高催化剂对氨净化的低温(<200oC)活性和选择性（>90%）。研究中结合顺磁、XAFS、质谱和红外等原位技术，深入研究催化剂不同结构和形貌对组分间界面作用以及活性组分的结构和电子性质的影响，重点探讨组分界面与活性间的构效关系，明确氨和氧在多孔核壳CuOx@CeO2纳米催化剂上的活化过程及反应历程，为新型环境友好廉价催化剂构建以及选择催化氧化技术在实际氨净化中的应用奠定坚实的研究基础。

项目中通过构建Cu-Ce-Zr，CuO-CeO2(核壳、不同形貌界面)和Cu2O-CuO组分递减的催化体系，系统研究活性组分与助剂、活性组分与活性组分间的协同及界面作用与催化剂结构关系，并通过调节协同（界面，价态等）作用，实现提高Cu基催化剂对NH3-SCO催化性能。溶胶凝胶法制备的Cu-Ce-Zr-SOL催化剂中组分间协同作用促进了CuO的高分散和Cu-Ce-Zr固溶体的形成，NH3在Lewis酸性位的吸附和氨物种氧化中间态(NOx)的积累促进了催化活性的提升；采用牺牲模板法构建出的拥有多孔道结构、清晰CuO-CeO2界面的CuO@CeO2核壳结构催化剂中存在的良好组分间界面大大促进了催化剂内部的SCR (iSCR)反应；相对于立方CeO2，棒状CeO2与CuO形成更强的相互作用，产生更多的氧空穴；结合液相原位法及反应气预处理过程构建单组分双活性位Cu2O-CuO立方核壳结构催化剂，两组分间的界面协同作用使NH3在210°C完全转化；结合原位实验与DFT计算，获得了重构后催化剂表面氧与氨物种的活化过程及催化剂表面氨氧化中间物种的反应路径。形成的立方Cu2O-CuO核壳催化剂可快速将O2分子解离成O原子，形成的双齿配位硝酸根物种(bi-NOx)有效促进了低温区间的iSCR反应路径，从而提高催化剂的低温活性和N2选择性。