铜改性分子筛的低温NH_3-SCR性能研究

NH_3-SCR performance over different types of Cu modified zeolites at low temperature

采用浸渍法制备了Cu-ZSM-5、Cu-beta、Cu-USY和Cu-SAPO-34四种铜改性分子筛催化剂,并评价了各个催化剂的NH3选择性催化还原（NH3-SCR）性能,同时通过X射线衍射（XRD）、H2程序升温还原（H2-TPR）、CO吸附红外（CO-DRIFTS）、原位红外（In-situ FTIR）等实验技术研究了不同Cu-zeolite催化剂的物理化学性质及其对NH3-SCR性能的影响.结果表明,Cu-ZSM-5和Cu-beta在150℃时NO转化率可达到80%左右,表现出优异的低温活性,并且催化剂的温度窗口很宽,在170~400℃内都能够将NO完全转化.这很可能与这2种催化剂拥有较低的起始还原温度和较高的Cu＋物种含量有关.原位红外研究表明,NH3先吸附在催化剂表面的Lewis酸位（Cun＋位）和Brnsted酸位上,进而参与SCR反应,且吸附在Lewis酸位上的NH3物种有更高的低温NH3-SCR活性.

In this work, four different Cu-zeolite catalysts named Cu-ZSM-5, Cu-beta, Cu-USY and Cu-SAPO-34 were prepared by an incipient wetness impregnation method. These catalysts are evaluated for the selective catalytic reduction （SCR） of NOx to NHa. Furthermore, all the catalysts are characterized in detail by various techniques （XRD, H2-TPR,CO-DRIFTS,In-situ FTIR）, in order to study the physieoehemieal properties of the catalysts and their effects on the NH3-SCR performance. The results indicate that Cu-ZSM-5 and Cu-beta exhibite excellent low temperature activity, reaching about 80~ NO conversion at 150 ~C, and the temperature window was rather wide within the range of 170-400 ℃, probably due to the lower initial reduction temperature and higher Cu＋ content for the two catalysts. The results of in-situ FTIR studies show that ammonia can strongly adsorb onto both Lewis and Eronsted sites, thus participating in the SCR reaction, and Lewis acid site-adsorbed ammonia species are much more active than Bronsted sites bound NH3 at low temperature.