Hydroisomerization of n-heptane on a new kind of bifunctional catalysts with palladium nanoparticles encapsulating inside zeolites

Abstract

The bifunctional catalysts capable of regulating the metal dispersion and location through encapsulating palladium (Pd) nanoparticles inside Beta and mordenite (MOR) zeolites were used for n-heptane hydroisomerization. Several characterizations such as X-ray powder diffraction (XRD), scanning electron microscope (SEM), N2-adsorption and so on suggested that the difference in the phase, textural property, morphology, and acidity of zeolites between the catalysts with encapsulation structure and prepared by impregnation method was negligible whether Beta- or MOR-series catalysts. Nevertheless, the higher Pd dispersion, smaller Pd particle size, and higher aggregation resistance can be achieved on the encapsulation catalysts as determined by H2-pulse and transmission electron microscopy (TEM). Compared to the palladium-loading catalyst prepared by conventional impregnation method, the encapsulation structure guaranteed the higher selectivity and yield in n-heptane isomerization due to the significantly improved balance and intimacy. Furthermore, the catalyst with the complete encapsulation structure for the Beta-series catalysts and the catalyst with partial encapsulation structure for the MOR-series catalysts respectively exhibited the highest isomer selectivity and yield. All results may be resulted from that the zeolite topology and crystal size acted a significant role in determining the intimacy of the bifunctional catalysts with encapsulation structure, due to the different diffusion hurdles of the channels structure.