3D charged grid induces a high performance catalyst: ruthenium clusters enclosed in X-zeolite for hydrogenation of phenol to cyclohexanone

Abstract

The hydrogenation of phenol to cyclohexanone is an important industrial reaction and supported palladium catalysts are the most popular catalysts applied nowadays. Hitherto, there has been no success in using ruthenium catalysts for this reaction because of their poor catalytic performance, in spite of the fact that ruthenium is a frequently used metallic component in hydrogenation catalysts. Herein, we report our effort in creating a meso-structured catalyst composed of ruthenium clusters enclosed in the super cages of X-zeolite, which is prepared by mixing precursors of ruthenium and X-zeolite at the beginning stage of preparation, i.e., before the crystallization of the zeolite. This well-defined Ru catalyst exhibits excellent catalytic performance for the selective hydrogenation of phenol, similar to palladium catalysts. The results demonstrate that the joint effects of the 3D negatively charged grid of X-zeolite and the enclosed electron-deficient ruthenium clusters enhance the activity of metallic ruthenium and suppress the further hydrogenation of the valuable product cyclohexanone, which is not possible with traditional Ru catalysts. This investigation reveals the fact that although catalytic reactions are always initiated on the active centers of the catalyst at dimensions on the atomic scale, the effect of the neighboring environment surrounding the active species might extend it to the meso-scale, which should not be ignored as it might induce electronic and structural changes in the active species as well as possibly dramatic changes in the performance of the catalyst. The meso-structured catalyst integrated active species and the neighboring environment as a whole should be considered in discussing the performance of catalysts.