In-situ construction and catalytic property of highly exposed Lewis acidity on hierarchical Zr-zeolite assisted by K+ cation

Herein, highly exposed Lewis acidity on hierarchical Zr-HSZ zeolite (Hollownest-Structured Zr-zeolite) have been firstly constructed by one-step rotating hydrothermal synthesis with the assistance of K+, which are characterized by various techniques. The addition of small amount of K+ ions (K/Si molar ratio of 0.07) into the synthetic reaction gel is found to be highly efficient for the crystallization of Zr-doping HSZ zeolite, in which K+ ions play important roles for the charge balance of reaction gel, promoting the formation of Zr-O-Si bonds and accelerating the crystallization process consequently. Thus-prepared materials own distinct weak acid property and contain purely Lewis acid sites, which are proven by ammonia-TPD and pyridine-FT-IR. Two types of zirconium species are detected by UV–vis and XPS characterizations, one of which is the isolated >Zr=Ospecies (Zr4+open) in high dispersion on the surface of zeolite, the other is the tetrahedral species in the zeolite framework (Zr4+closed). The unique hollownest morphology of HSZ material with hierarchically porous structure constructed by intergrown MWW nanosheet crystals has no hindrance on the mass transfer and diffusion of substrate molecules, and provides enough reaction spaces for reactant molecules. Also, the high dispersion of Zr4+open species on the surface of HSZ material has endowed it with highly exposed Lewis acid sites, beneficial to the acid-catalyzed transformation. As expected, Zr-HSZ-K catalyst shows highly catalytic performance for the acid-catalyzed Prins condensation to nopol from β-pinene and paraformaldehyde, which achieved high conversion (93.2%) and selectivity (96.0%) with TON of 163.6, and exhibited highly recyclable stability. This work has highlighted one-step rota-construction of metal-doping HSZ zeolite with highly exposed catalytic active sites for the catalytic conversion of bulky organic molecules.