Polymer-stablized Pt Nanoclusters: Preparation, Characterization And Catalysis For Methane Conversion

Well-dispersed and stable polymer-protected nanoclusters supported on Beta have been easily prepared by refluxing solutions of hexachloroplatinic(IV) acid in methanol/water (l/l,v/v) in the presence of poly vinyl pyrrolidone(PVP). In this paper, the preparation and characterization of these novel PVP-stablized nanoclusters and their catalysis for low temperature catalytic homologation of methane on this catalyst have been investigated.Size and shape of Pt particles in as-prepared catalysts were found to strongly depend on many factors, such as the relative amount of PVP to Pt, Pt loading, et al. The results of experimentssuggested:1. The PVP-protected nanoclusters were highly-dispersed inside and outside the zeolite with a narrow particle size distribution.2. Under mild condition (low temperature alcohol-water reduction method), the nanoclusters can be easily prepared.3. Pt particle size and distribution are affected by Pt: PVP and Pt loading. And the particle size can be controlled by the relative amount of PVP.4. To prepare well-dispersed platinum particles, the dispersion effect on the Pt(NH3)42+ precursor by PVP is nessessary.5. Due to the high surface area of Beta zeolite, Pt particles can be prepared with very high dispersion on zeolite supports.6. The presence of PVP in the sample weakens the interaction between metal and support. This class of catalyst, therefore, may be expected to study the effect of particle size upon the catalytic activity and selectivity.In addition, the PVP-protected nanoclusters prepared by thealcohol-water reduction method have been examined for catalyticperformance in the two step conversion of methane to higher hydrocarbons. The catalytic results showed that compared with the corresponding supported Pt catalyst prepared by the general incipient wetness impregnation method, on supported Pt-PVP catalysts the amounts of €2+ hydrocarbons from methane conversion did not depend greatly on the supports whatever were used in the case of addition of proper PVP. The catalytic results over Pt-PVP/HBeta in various ratio of PVP to Pt have shown that the activity per gram of metal increased with decrease of particle size, and distributions of C2+ products varied in favor of the heavier hydrocarbons as the particle size decreased.From above research, the alcohol-water reduction preparation method in the presence of PVP proved to be a novel preparation method, and the as-prepared nanoclusters exhibited some novelcatalytic properties compared to other methods.