Silica-encapsulated palladium clusters for methane combustion catalysis

Methane is the most abundant constituent of natural gas and it is difficult to fully oxidize without effective catalysts. Pd is recognized as the most efficient catalyst for the methane combustion reaction. However, few routes are available for the preparation of near-monodisperse Pd clusters for catalysis. Here we focused on the synthesis and activation of mercaptoundecanoic acid-protected Pd clusters (1.1 +/- 0.3 nm) and encapsulated them in a silica matrix using sol-gel chemistry. EXAFS analysis revealed that nearly complete removal of thiolate ligands at 250 degrees C in air leads to the partial oxidation of Pd clusters and that the clusters are completely oxidized to PdO at 650 degrees C. TEM and CO chemisorption studies suggest that silica coated Pd clusters are much more resistant to sintering than the control sample of Pd clusters deposited on silica spheres. The activity studies over silica-coated and non-coated catalysts for the methane combustion reaction indicate the presence of the silica shell on the Pd clusters significantly improves the catalytic activity.