不同方法制备的Cu/HZSM-5催化剂上NO的催化分解反应

采用离子交换法、固相分散法和微波固相法等不同方法制备了Cu/HZSM-5催化剂，以BET、XRD和XPS等手段对催化剂样品进行了表征。结果表明，不同方法制备的Cu/HZSM-5催化剂上Cu物种的落位分布状态不同，离子交换法制备的催化剂Cu物种更多地落位于分子筛孔道内，微波固相法和固相分散法制备的催化剂Cu物种较多地落位分布在分子筛外表面。固相分散法制备的样品未能使铜物种完全分散于分子筛表面，在13.1°、16.8°、35.5°和38.0°等处仍存在CuO的晶相衍射峰。催化分解NO反应的活性考察结果表明，用微波固相法制备的催化剂催化分解NO的活性及稳定性明显超过另两种方法所制备的催化剂，在无氧条件下NO最初转化率高达89.2%，经反应25h后，转化率仍维持在70%以上；在富氧气氛下催化分解NO活性降低速率低于由离子交换法制备的催化剂。结合表征结果可以得出，落位于分子筛外表面以离子交换态形式存在的Cu物种对催化分解NO反应更为有利，而且催化稳定性更好。

Catalytic decomposition of nitrogen oxide over Cu/HZSM-5 catalysts prepared by different methods

Cu/HZSM-5 catalysts were prepared by different methods of ion exchange, solid-state dispersion and solid-state microwave irradiation. The obtained Cu/HZSM-5 catalysts were characterized by means of BET, XRD and XPS. Experimental results exhibited that the location of Cu species was strongly dependent on the preparation method. Cu species on the external surface of the zeolite prepared by solid-state microwave irradiation and solid-state dispersion are more than ion exchange. And the crystalline diffraction peaks of CuO species can be found in the samples prepared by solid-state dispersion. In addition, the catalytic performance of the catalyst for NO catalytic decomposition was investigated. Compared with the other two methods, the catalysts prepared by solide-state microwave irradiation showed higher catalytic activity and stability for NO catalytic decomposition. Under anaerobic conditions, the NO conversion was up to 89.2% and could remain at 70%, after 25h. Under the condition of excess oxygen, the deactivation rate of the catalyst was lower than that of the catalysts prepared by ion exchange. Corresponding with the characterization results, we can draw a conclusion that the Cu species, which exist as ion exchange state on the external surface of zeolite, are helpful to the decomposition of NO reaction and its catalytic stability is better.