Abstract:

The hexaammineplatinum chloride（［Pt（NH₃）₆］Cl₄） was synthesized from sponge platinum，and the geometrical structure of ［Pt（NH₃）₆］Cl₄ was determined by thermogravimetric analysis（TG），scanning electron microscopy energy spectrum（SEM-EDS），ultraviolet visible spectrophotometer（UV Vis），mass spectrometry（MS），X-ray photoelectron spectroscopy（XPS），etc.Pt/Beta catalysts were prepared by impregnation method using H₂PtCl₆，Pt（NH₃）₄Cl₂ and ［Pt（NH₃）₆］Cl₄ as precursors.The physicochemical properties of these catalysts were characterized by X-ray diffraction（XRD），X-ray fluorescence spectrum（XRF），ammonia temperature programmed desorption（NH₃-TPD），hydrogen oxygen titration（H₂-O₂），transmission electron microscope（TEM），hydrogen temperature programmed desorption（H₂-TPD），and their performance on selective ring opening of polycyclic aromatics was investigated.The results showed that ［Pt（NH₃）₆］Cl₄ had higher“anti self reduction”ability，which could reduce the self reduction phenomenon of platinum ammonia precursor during thermal decomposition.The precursor structure had great influence on the geometric size and distribution of Pt nanoparticles.On the one hand，the valence state of the complex significantly affected the electrostatic interaction between the precursor and the molecular sieve，and then affected the location and size of Pt nanoparticles.On the other hand，the spatial structure of the complex affected the distribution of precursors in the micropores of molecular sieve and the Ostwald ripening rate of Pt nanoparticles.The structure of precursor could adjust the bifunctional matching relationship of Pt/Beta catalyst，which significantly affected the activity and stability of Pt/Beta catalyst for the conversion of methylnaphthalene.The Pt/Beta catalyst prepared by ［Pt（NH₃）₆］Cl₄ precursor had better activity and long?term stability.

Key words: noble metal catalyst, platinum precursors, self reduction phenomenon, polycyclic aromatics, selective ring opening