(387b) Metal Cation-Exchanged Zeolites with the Location, State and Size of Metal Species Controlled

We have studied a new class of metal cation-exchanged zeolite with controlling the location, state, and size of metal species. Controlling the environment of the active sites in the solid catalyst is a hot topic because it is a very important factor to improve the catalytic activity. In zeolite chemistry, many researchers have been investigated the framework Al distribution to control the location of Brønsted acid sites. Even though the metal-cation exchanged zeolites have attracted much attention due to their oxidation-reduction ability, controlling the location, state, and size of metal species in the metal cation-exchanged zeolites has not been achieved so far. Therefore, we tried controlling the location, state, and size of metal species in the metal cation-exchanged zeolites in this study.

Our strategy for this study is based on the framework Al distribution because the introduced metal cation should exist around Al³⁺ species to balance the negative charge of the zeolite framework. Previously, our group reported the synthesis of MFI-type aluminosilicate zeolites with the different framework Al distributions by a rational selection of the cations. It is noted that the location of the exchanged metal-cations depends on the framework Al distribution. Moreover, the zeolite-supported Rh sub-nano cluster was obtained by the ion-exchange method in the previous work. In this case, the size of the Rh cluster might be affected by the space size of the ion-exchange sites (Al³⁺ sites). Accordingly, we applied the MFI-type aluminosilicate with the different framework Al distributions to Rh ion-exchanged zeolites.

Consequently, the synthesized Rh ion-exchanged MFI-type aluminosilicate zeolites with the different framework Al distributions showed the different catalytic activity for the oxidative reforming of methane. The MFI-type aluminosilicate zeolite with the framework Al atoms mainly located in the channel intersections gave the formation of relatively large Rh species, which were confirmed by UV-vis and in-situ CO adsorption IR techniques. In addition, it showed remarkably high catalytic activity for the reaction. These results revealed that the location of the framework Al species is one of the important factors for controlling the location, size, and state of the metal species in the metal cation-exchanged zeolites. Thus, we succeed in the synthesis of a new class metal cation-exchanged zeolite.