富氧条件下Co/ZSM-5催化剂对C3H8选择还原NOx的性能

采用多种物理化学手段研究了在模拟的轻型柴油车尾气中不同Co担载量及Cu掺杂的Co/ZSM-5催化剂的Co组分分散状态、可还原性、NO吸附脱附性质对C₃H₈选择性催化还原NO_x性能的影响。结果表明，浸渍法制备的Co/ZSM-5催化剂上既有外表面上的Co³⁺和Co²⁺物种，也有孔内的Co²⁺离子。富氧条件下Co/ZSM-5催化剂上C₃H₈选择性催化还原NO_x的活性主要与ZSM-5载体孔外表面分散的CoO_x物种中的钴离子可还原能力和NO吸附脱附性能密切相关。Co/ZSM-5催化剂上适宜的Co担载量约为4.0wt%，低担载量时随Co担载量增加，表面CoO_x物种中钴离子可还原能力增强，C₃H₈选择性催化还原NO_x的低温转化活性增加；高担载量时，随Co担载量增加，单位Co离子的NO吸附量的减少以及催化剂表面活性中心数的减少，导致了Co/ZSM-5催化剂NO_x的转化率和催化剂比速率（k）的下降。孔外表面Co₃O₄晶体的存在使催化剂表面产生较强的NO吸附，并在高温时有利于C₃H₈的氧化燃烧，使C₃H₈选择性催化还原NO_x的活性降低。

Performance of Selective Catalytic Reduction of NOx by C3H8 over Co/ZSM-5 Catalysts under Excess Oxygen

Under the simulated conditions of light-duty diesel vehicles exhaust, the effect of the dispersion state and surface property of supported cobalt on the selective catalytic reduction of NO_x by C₃H₈ (C₃H₈-SCR) over Co/ZSM-5 and Co-Cu/ZSM-5 catalysts was studied by various experimental techniques. The cobalt existed and dispersed on the catalyst external surface in the form of Co³⁺ and Co²⁺ species, and located in the zeolite channels in the form of Co²⁺ cations. The C₃H₈-SCR activity of the Co/ZSM-5 catalysts was related to the reducibility, NO adsorption-desorption performance of the cobalt ions in external CoO_x species dispersed on the catalyst surface. When Co loading was below 4.0wt%, the increase of Co loading would enhance the reducibility of the cobalt ions of CoO_x species and NO_x low-temperature conversion; when Co loading was above 4.0wt%, further increase of the Co loading led to the decrease of the ratio of exposed active centers on the surface of catalysts and the decrease of NO adsorption performance per cobalt ion, thus resulting in a decrease of NO_x conversion and specific reaction rate at higher temperature. The optimum Co loading for the Co/ZSM-5 catalyst was about 4.0wt%. The formation of external Co₃O₄ bulk crystallites generated the strong NO adsorption on the Co/ZSM-5 catalyst and promoted C₃H₈ oxidizing combustion, and reduced the C₃H₈-SCR activity at high reaction temperature.