Nanowire network catalysts embedded in the mesopore network of zeolite

Abstract

Loading a large amount of catalyst on a support is desirable in order to obtain a high catalytic activity, but but in general at high loading, the increased amount of catalyst is dissipated by the decrease of catalyst dispersion due to agglomeration. This thesis demonstrates that this problem is remarkably diminished if we support metals or metal oxide catalysts in zeolites that possess mesopores and micropores in a hierarchical manner. Under this purpose, two hierarchically nanoporous zeolites, beta and MFI, were synthesized using surfactants which were functionalized with the corresponding zeolite structure-directing agents. These zeolites were supported with Co up to 50 wt% using a proper impregnation method. The Co-supporting zeolites exhibited the formation of Co nanowire networks inside the zeolite mesopore network. Although most of the Co surfaces were inaccessible through the mesopores, the zeolitic micropore windows on the mesopore walls allowed access to surfaces of the Co nanowires. As a result, the hierarchically nanoporous zeolites with high Co loading exhibited far superior catalytic activities for Fischer-Tropsch synthesis to other porous materials supporting Co such as bulk zeolites (i.e., solely microporous zeolites), mesoporous silica MCM-41, MCM-48, and γ-alumina. Further, the present concept of catalyst loading on hierarchically porous zeolites have been expanded to the hydrogenation of benzene using supported Ni catalyst, and the transfer hydrogenation of furfural over zeolite-supported $TiO_2$ catalyst.