Interzeolite Transformation of Borosilicate MWW to Metallosilicate BEA-Type Zeolites: Separated Kinetics of Structural Transformation and Metal Substitution

Abstract

The synthesis of cobalt-, nickel-, and zincosilicate β zeolites (Co-BEA, Ni-BEA, and Zn-BEA, respectively) via a single-step hydrothermal interzeolite transformation of borosilicate MWW (B-MWW) with each metal precursor solution was systematically investigated. While all three metallosilicates exhibited distinct BEA structures with stable framework metal species, their structural transformation and metal substitution kinetics differed depending on the type of metal. The crystallization of Co-BEA and Ni-BEA was completed within two days, while that of Zn-BEA continued even after seven days. Apart from the crystallization kinetics, the incorporation rate of Co into the framework of the BEA structure was slower than that of the other two metals. The characteristics of the BEA structure according to the type of framework heteroatom were further demonstrated using density functional theory calculations. Despite having a comparable metal content (ca. 3 wt %), the Lewis acidities of fully crystallized Co-, Ni-, and Zn-BEA were different corresponding to the types of framework metals. These three metallosilicates showed good catalytic activity for Lewis acid-catalyzed glucose conversion, and the catalytic results were attributed to the intrinsic properties of the catalysts determined from their synthesis stage.