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

通过O_2焙烧、H_2还原、O_2再氧化三步处理，在y型沸石的孔结构中制备了活性氧化钯簇。研究了该簇催化剂在CH_4部分氧化成CO和H_2以及C_3H_8将NO还原成N_2和CO_2过程中的催化行为。钯簇催化剂在两种反应中均表现出较高的活性和良好的选择性。采用程序升温和瞬态模式对反应机理进行了研究。在前一反应的主要过程中，气相CH_4与氧化Pd表面的氧发生反应。另一方面，在后一反应的速率决定过程中，CH_4还原表面上的碳质物质在气相中与NO发生反应。此外，EXAFS分析证实，在操作条件下，两种钯（Pd和PdO）在孔隙中共存，并通过可逆氧化还原机制作为催化中心发挥作用。

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.