Nickel silicate CHA-type zeolite prepared by interzeolite transformation and its catalytic activity in dry reforming of methane

We newly synthesized the nickel silicate CHA-type zeolitic material (Ni-CHA) through the interzeolite transformation of the parent nickel silicate MWW-type zeolite (Ni-MWW) using the structure-directing ability of N,N, N-trimethyl-1-adamantammonium hydroxide. With increasing crystallization time under hydrothermal conditions, the parent Ni-MWW was decomposed into an X-ray amorphized nickel silicate, which was then consecutively reassembled into Ni-CHA. Furthermore, as the crystallization progressed, the framework Ni species gradually transformed from intermediate Ni to isolated Ni species, achieving a more thermodynamically stable chemical state. The metallic Ni clusters can be formed by exsolving from the CHA framework during the hightemperature reduction treatment, which were mainly distributed on the external surface. A series of in-situ reduced Ni-CHA-x catalysts obtained after different crystallization times (x = 0-72 h) were applied to the dry reforming of methane to evaluate their catalytic activity corresponding to the differences in crystallinity and chemical state. As a result, the interzeolite transformed Ni-CHA-72 h catalyst exhibited the highest catalytic performance even compared to the Ni-impregnated commercial SSZ-13.