Studies of Ti_(0.5)Zr_(0.5)O_2 supported CuO catalysts for NO + CO reaction

摘要

The activities of CuO supported on Ti_(0.5)Zr_(0.5)O_2 have been examined with a microreactor-GC NO+CO reaction system and the catalysts characterized by BET,TPR.TG-DTA,XRD and NO-TPD.Experimental results show that the CuO/Ti_(0.5)Zr_(0.5)O_2 activities increase with increase in CuO loading.To obtain 99% NO conversion,the reaction temperature needed to be 350 deg C in air but only 200 deg C in H_2 atmosphere.TPR analysis shows two peaks (a and p peaks) at CuO loading of <=12%,while a third peak (y peak) occurs with higher CuO loading at 300 deg C.The a peak is attributed to highly dispersed CuO,the p peak to isolated CuO and the gamma peak to crystal CuO.TG-DTA also shows endothermic peak at low temperature (120 deg C) and exothermic peak at high temperature (725 deg C),indicating the completion of ZrTiO4 crystallization.From the XRD analysis,it has been found that there is no CuO crystal diffraction peaks at 12% CuO loading,but two CuO crystal diffraction peaks at 20 35.5 deg and 38.7 deg are present at 18% CuO loading.With increase in CuO loading,the intensity of CuO diffraction peaks is increased.In addition,NO-TPD analysis shows that NO adsorption and desorption by Ti_(0.5)Zr_(0.5)O_2 in air are similar to those in H_2 atmosphere.In air atmosphere,both CuO/Ti_(0.5)Zr_(0.5)O_2 and Ti_(0.5)Zr_(0.5)O_2 have two adsorption peaks,but the former has lower desorption peak temperature than the latter,suggesting that the activity of NO decomposition by CuO/Ti_(0.5)Zr_(0.5)O_2 is higher than that by Ti_(0.5)Zr_(0.5)O_2.In H_2 atmosphere,the high temperature desorption peak disappears and there only exists one low temperature desorption peak at 150°C,inferring that the high temperature adsorption site is probably Cu~(2+) and the low temperature adsorption site is Cu deg.