PVP-Pt nanoclusters supported zeolite catalysts for converting methane to higher hydrocarbon at low temperature

摘要

Macromolecule polyvinylpyrrolidone (PVP)-immobilized Pt nanoclusters supported on HBeta, HY, NaY and SiO_2 catalysts (signed as PVP-Pt/S) prepared by the alcohol-water reduction method are examined for their catalytic performance in the two step conversion of methane to higher hydrocarbons and compared with corresponding supported Pt catalysts (noted as Pt/S) prepared by the general incipient wetness impregnation method. The nature of the support affects the formation of ofdistributions of C_(2+)hydrocarbons, by influencing the electronic state of Pt in catalysts Pt/S. The C_2~+ hydrocarbon amounts of methane conversion on PVP-Pt/S catalysts do not depend greatly on the supports and but binding energy of supported Pt clusters. Compared with the Pt/S catalysts, PVP-Pt/S catalysts have such characteristics as: (1) a well-dispersed and uniform particle size which can be controlled by adjusting the added amount of PVP; (2) a diminished interaction between the metal particle and support. This class of catalyst, therefore, may be expected to study the effect of particle size upon the catalytic activity and selectivity. The catalytic results combined with TEM over PVP-Pt/HBeta with various ratios of PVP to platinum show that the activity of catalysts increases for methane conversion with decrease of particle size, and the distributions of C_(2+) 　 products vary in favour of the heavier hydrocarbons as the particle size increase.