Catalytic Activities of Metallic Oxides Clusters in Pore Structures of a Zeolite

用氧焙烧、氢还原和氧再氧化三步R-O处理法在Y型沸石的孔结构中制备了活性氧化钯簇。考察了Pd簇合物催化剂在CH_4部分氧化为CO和H_2以及C_3H_8还原NO为N_2和CO_2反应中的催化性能。通过程序升温和瞬态模式研究了反应机理。在前一反应的主要过程中，气相中的CH_4与氧化Pd表面的氧物种反应。在后一反应的速率控制过程中，CH_4还原表面上的含碳物种与气相中的NO反应。EXAFS分析证实，在操作条件下，两种Pd物种（Pd和PdO）共存于孔中，它们可以通过可逆的氧化还原机制作为催化中心。

Active clusters of palladium oxide has been prepared in the pore structures of Y-zeolite by the R-O treatment consisted of three steps, calcination with O_2, reduction with H_2 and reoxydation with O_2. The catalytic behaviors of the cluster catalyst have been investigated in the partial oxidation of CH_4 into CO and H_2 and in the reduction of NO with C_3H_8 into N_2 and CO_2.The Pd clusters catalyst showed high activities and excellent selectivities for both reactions. The mechanism of the reactions was investigated by temperature-programd and transient modes. In the main process of the former reaction, CH_4 in the gas phase reacts with oxygen species on the oxidized Pd surface. In the rate determining process of the latter reaction, on the other hand, carbonaceous species on the reduced surface from CH_4 reacts with NO in the gas phase. It was confirmed by EXAFS analyzes, furthermore, that under the operating conditions two kinds of Pd species (Pd and PdO) coexist in the pores and that they can function as catalytic centers via a reversible redox mechanism.