La-Cu氧化物催化剂的催化性质和表征

CATALYTIC PROPERTIES AND CHARACTERIZATION OF La-Cu OXIDE CATALYSTS

研究了三个La-Cu氧化物催化剂对CO-O_2和NO-CO反应的催化活性。No.1样品的La/Cu原子比为1.0。No.1附品经H_2还原为No.2样品。No.1样品浸渍50ppmPt后,用H_2还原得样品No.3。对CO-O_2和NO-CO反应活性的次序均为NO.3>NO.2>NO.1。NO.1样品的主要组成为La_2CuO_4+CuO。No.2,No.3样品是Cu_2O,CuO,La_2O_3的混台物,并含少量Cu。NO.1,2,3的平均表面铜的氧化数分别为1.7,1.5和1.3。测定了O_2不可逆吸附量、在125℃表面“晶格”氧的反应百分数(A_L)以及“晶格”氧开始参与氧化反应的温度(T_L),讨论了活性氧的反应和补充以及氧化反应时可能存在的CU^+-CU^(2+)氧化还原循环。从TPR等实验结果,提出了微量Pt可能高度分散在表面上,削弱了CU^(2+)-O的键能,而使Cu^(2+)在氧化反应中更易被还原的设想。

The catalytic activities for the reaction of CO + O2 and NO + CO over three mixed oxide catalysts, La-Cu oxide (La/Cu = 1 atomic ratio, sample No.1), sample No.1 treated with H2 for 2 h at 500癈 (sample No.2) and La-Cu-Pt-O (doping with 50 ppm Pt and treated by H2, sample No.3), were studied. The order of activity for both CO + O2 and NO + CO was found to be No.3>No.2>No.1. It was identified that No.l sample was mainly composed of La2CuO4 + CuO. After treatment with H, or doping with 50 ppm Pt and reduced by H2 ,the La2CuO4 phase (K2NiF4-type) was destroyed, CuO phase was partially reduced and mixed phases of Cu2O, CuO. La2O3 with small amount of Cu were formed. The average surface oxidation number of copper for No.1, No.2 and No.3 was 1.7, 1.5 and 1.3 respectively. The amount of irreversible O, adsorption, the reaction percentage of surface 'lattice' oxygen (AL) at 125℃ and the initial reaction temperature of 'lattice' oxygen (TL) were measured, the reaction and replenishment of active oxygen were discussed, and the possible redox cycle of Cu+-Cu2+ d.uring oxidation was suggested. In the light of TPR spectra of La-Cu-Pt-O, it was supposed that trace amount of Pt was highly dispersed on the surface, and thus it weakened the bond energy of Cu2+-O and made Cu2+ ions easily to bo reduced.