柴油车用高效Ce基氧化物NH3-SCR催化剂的改进及机理研究

Selective catalytic reduction of NOx with NH3 (NH3-SCR) is one of the most promising after-treatment technologies for the NOx abatement from diesel vehicles. Due to some inevitable problems of the traditional vanadium-based catalysts, development of environmentally-benign catalysts with high efficiency and stability is very important for the application of NH3-SCR technology on diesel vehicles. In our previous study, we have developed several ceria-based catalysts with excellent activity, high N2 selectivity and good resistance to poisoning, under high space velocity conditions. In this study, based on the systemically investigation of hydrothermal effects and clearly understanding of the tungsten function, we will remarkably improve the hydrothermal stability of the ceria-based catalysts and decrease the preparation cost of the catalysts by reducing the use of tungsten. In addition, some characterization methods will be used for establishing the structure-activity relationships of the catalysts in NH3-SCR reaction and clarifying the reaction mechanism on the catalysts, which will be helpful for the improvement of the catalysts. The washcoating technology of the improved ceria-based catalysts will also be studied for the application. This study will be meaningful and helpful for both of the application of light rare earth Element Ce in environmental catalysis and the NOx abatement from diesel vehicles.

NH3选择性催化还原NOx（NH3-SCR）广泛应用于柴油车尾气NOx去除已是大势所趋。由于传统的钒基催化剂仍存在诸多问题，开发高效、稳定、环境友好的新型催化剂对NH3-SCR技术的实际应用具有重要意义。本项目以前期开发的适用于高空速环境，并具有优异NH3-SCR活性、N2选择性及抗中毒能力的Ce基氧化物催化剂为基础，以不影响催化性能为前提，系统研究催化剂的高温水热失活原因，大幅改善其水热稳定性；在充分理解W对Ce基氧化物催化剂NH3-SCR催化性能促进机理的基础上，实现对W的替代，以降低催化剂的生产成本。另外，将采用多种表征手段，建立催化剂在NH3-SCR反应中的构效关系，阐明反应机理，指导催化剂的改进；开展涂覆成型研究，为所开发高效Ce基氧化物催化剂的实际应用奠定基础。本项目对于开发高丰度轻稀土元素Ce在环境催化领域的新用途以及解决柴油车尾气NOx催化净化所面临的困境具有重要意义。

我国柴油车尾气NOx控制是环境催化和大气污染控制领域亟待解决的问题。NH3选择性催化还原NOx（NH3-SCR）是目前最有效的柴油车尾气NOx后处理技术之一，该技术的关键核心是催化剂。开发高效、稳定、环境友好的新型催化剂来替代传统钒基催化剂用于柴油车尾气NOx净化，是NH3-SCR技术发展的一个重要趋势。本项目以高丰度轻稀土元素Ce为主活性组分的氧化物催化剂为起点，开发和改进了一系列具有优异催化性能和稳定性的Ce基氧化物催化剂，降低了催化剂生产成本，建立了催化剂在NH3-SCR反应中的构效关系，阐明了反应机理，开展了催化剂涂覆成型研究，并且在发动机台架上考察了所制备整体催化剂去除真实柴油发动机尾气NOx的能力。研究表明，Ce物种在NH3-SCR反应中主要起氧化-还原作用，需要催化剂中有提供酸性位的组分（如W和Ti）协同作用，才能使NH3-SCR反应高效发生。活性物种Ce的高度分散以及与酸性组分的紧密结合是催化剂具有优异NH3-SCR催化活性的关键因素。以此理论为指导，所开发的Ce基氧化物催化剂都表现出了优异的催化性能，发动机台架的ESC测试结果显示，在不使用其他后处理装置的情况下，基于本项目所开发催化剂的NH3-SCR后处理系统可使国产重型柴油车NOx排放达到国五（欧V）标准的要求，表明所开发的Ce基氧化物催化剂具有非常好的应用前景。