KINETICS OF THE METHANATION REACTION OVER RU, RU-NI, RU-CU, AND NI CLUSTERS IN ZEOLITE-Y

Clusters of Ru, Ni, and a series of RuNi and RuCu bimetallics in a Y-type zeolite were investigated as catalysts for the reaction of CO with H2 to form CH4. Although the particle size of the Ru clusters indicates that they remained in the large cavities of the zeolite, the turnover numbers for several samples were in agreement with those observed for Ru Al2O3. By contrast, the nickel clusters were located on the external surface of the zeolite, and the turnover number was more than an order of magnitude less than that observed for Ni Al2O3. The presence of ruthenium in bimetallic clusters caused the average particle size to decrease significantly, relative to the values which were observed for pure nickel or pure copper. The turnover numbers for the RuNi zeolites decreased linearly with respect to the addition of Ni, but the decrease in initial activity was much more severe upon addition of Cu to the RuY zeolite. The supported ruthenium catalysts exhibited a marked decline in activity during the reaction, but the addition of excess nickel (1:7 atomic ratio) brought about a stabilization in activity which even exceeded the stability of the supported Ni catalysts. The decrease in activity is attributed to the build-up of excess carbon which results from the dissociation of CO. The presence of Ni is believed to moderate the activity of ruthenium for this reaction, thus providing more sites for dissociative chemisorption of H2. © 1979.