反应条件对Pd/Ce-Ti催化剂CO低温氧化性能的影响

Effect of Reaction Condition on the Low-Temperature Oxidation of CO over Pd/Ce-Ti Catalyst

对溶胶-凝胶法制备的CeO2 TiO2复合氧化物载体负载Pd催化剂进行了表观动力学研究,在pCO==1×10-3～4×10-3MPa,CO和O2的反应级数分别为-1.0和1.0级.在温度范5×10-4～3×10-3MPa,pO2/pCO接近化学计量比的条件下,CO氧化反应的平均表观活化能为67.2kJ·mol-1.考察了气围303～343K,pO2体组成对CO低温氧化反应的影响和催化剂的稳定性.x(O2)/x(CO)=0.5时,CO氧化反应的起燃温度为345K,提高x(O2)/x(CO),可以降低起燃温度,在较低的CO浓度(0.5%)和较高的x(O2)/x(CO)(6.3)下,催化剂在室温下就有氧化活性,起燃温度仅为308K.在φ(CO)=1.0%的空气中,空速39000mL·h-1·g-1的条件下,CO反应在室温(293～303K)就可以实现完全转化,其反应稳定性与反应温度相关,313K下催化剂寿命可达15.5h.

The kinetics of the reaction between CO and O2 over Pd(1%)/CeO2(20%)TiO2 catalyst was studied. The CeO2TiO2 mixed oxide support was prepared by solgel method. The influence of the partial pressures of CO and O2 upon the reaction rate was investigated at 303 K. The corresponding kinetic orders are -1.0 for CO and 1.0 for O2 when CO and O2 partial pressures were in the range 5×10-4 MPa to 3×10-3 MPa and 1×10-3 MPa to 4×10-4 MPa, respectively. The effect of temperature on the reaction rate over the catalyst was examined between 303 K and 343 K under stoichiometric pO2/pCO condition. The average apparent energy of activation for the CO+O2 reaction is equal to 67.2 kJ·mol-1. The influence of the O2/CO ratio (x(O2)/x(CO)) on the lightoff performance was investigated. At the stoichiometric x(O2)/x(CO) (0.5), the lightoff temperature of CO oxidation was 345 K. The lightoff temperature was decreased with the increase of x(O2)/x(CO). At low CO concentration (0.5 %) and high x(O2)/x(CO) (6.3), the reaction of CO oxidation occurred even at room temperature and the lightoff temperature was only 308 K. With 1.0% CO in air at space velocity of 39 000 mL·h-1·g-1, the overall conversion of CO was achieved at ambient temperature (293303 K). The reaction stability was correlated with the reaction temperature, and the catalyst life lasted for 15.5 h at 313 K.