Tuning the location of Pd on HY zeolite by a dual-solvent method for efficient deep hydrogenation saturation of naphthalene

Abstract

Tuning the location of metal on the support is of great importance for catalyst performance optimization, which is hardly realized by the traditional impregnation method. Herein, a dual-solvent method using dichloromethane and water has been developed for the preparation of Pd/HY catalysts via evaporation-induced aggregation of Pd(OAc)2. The state and location of Pd nanoparticles on HY can be effectively tuned by the water content in the dual-solvent system. Due to the filling of partial micropore channels by certain amount of water, hydrophobic Pd(OAc)2 is selectively deposited on the un-occupied surface of HY, which is verified by the changes in textural and acid properties of the Pd/HY catalysts. FT-IR spectra illustrate the reconstruction of tridimensional Pd3(CH3COO)6 trimer in solution to the planar bidentate Pd(II) acetate species on HY surface, which guarantees the stable loading of active Pd nanoparticles on HY. Pd nanoparticles selectively loaded around the junctions of micropores and mesopores of HY zeolite by moderate amount of water have been demonstrated to be highly active for the deep hydrogenation saturation of naphthalene. Due to the selective locating of Pd nanoparticles in the properly open space of HY, the B acid sites are well maintained and efficiently utilized for the enhanced anchoring of Pd nanoparticles and facilitated diffusion of the reactants. Therefore, the optimum Pd/HY catalyst possesses highly dispersed and electron-deficient Pd nanoparticles, and exhibited superior performance of hydrogenation saturation. The dual-solvent strategy can be applied to other zeolite systems to selectively loading of Pd nanoparticles for various catalytic applications.