Preparation And Study Of Supported Pt Catalyst Based On Dendrimer Template

Pt-based supported catalysts are widely applied in different reactions due to high catalytic performances, such as dehydrogenation of low carbon alkanes, CO oxidation, selective oxidation of alcohols reactions, and so on. It is generally believed that the catalytic performance of the catalyst is closed related to the distribution of Pt particles and structure of supports. For the synthesis of supported catalyst, traditional impregnation methods hardly control the size and distribution of Pt particles, causing the rapid catalyst deactivation. Consequently, it becomes a key to improve the performance of catalysts how to control the dispersion of metallic particles and improve the structure of supports. In this paper, based on improving the dispersion and reaction properties of Pt particles, poly(amidoamine)(PAMAM) dendrimer were employed as the template to prepare homodisperse Pt nanoparticles, which were immobilized on mesoporous Al2O3, CeO2, and Co3O4-CeO2 supports. The Pt catalysts on diflferent carriers were achieved after decomposition of dendrimer via specific treatments. The prepared materials were characterized by various technologies. The reduction of 4-nitrophenol was chosen as the probe reaction, and the intrinsic structure-activity relations of the catalysts were investigated combing with different characterization results of catalysts.Hydroxyl-terminated poly(amidoamine) dendrimer were employed as the template to encapsulate Pt2+ via coordination reaction, and uniform dispersed dendrimer-templated Pt nanoparticles with small size were obtained after reduction by NaBHU. After Pt nanoparticles were loaded on mesoporous alumina (MA), Pt/MA catalyst was obtained. It was investigated that the effect of different calcination atmosphere and temperatures on Pt nanoparticles. Results revealed that the aggregation of Pt nanoparticles could be controlled effectively in nitrogen due to the slow decomposition of dendrimer. Moreover, the calcination at 550℃ in nitrogen could decompose completely and suatain the small size of Pt nanoparticles. For the reduction of 4-nitrophenol, the catalyst calcined at 550℃ in nitrogen exhibited the best catalytic activity compared with catalyst with other calcination condition. Besides, the catalyst was easily recycled without a marked decrease of the catalytic performance.Mesoporous silica KIT-6 prepared with hydrothermal method, was used as the hard template, and was immersed with Ce(NO3)3.6H2O solution. After calcination and etching, ordered mesoporous ceria (meso-CeO2) with high crystallinity was obtained. The special surface area of meso-CeO2 was 115.3 m2/g。Meanwhile, ceria nanoparticles (nano-CeO2) with non-ordered mesoporous were also prepared via a sol-gel method. Then, PAMAM dendrimer-templated Pt nanoparticles were immobilized on meso-CeO2 and nano-CeO2, resulting in Pt/meso-CeO2 and Pt/nano-CeO2 catalysts. The results showed that high area surface of meso-CeO2 facilitate the dispersion of Pt nanoparticles, and its regular channels can restrict the aggregation of Pt nanoparticles to sustain the size of Pt particles. Besides, compared with the Pt/nano-CeO2 catalyst, Pt/meso-CeO2 has the better catalytic activity for the reduction of 4-nitrophenol, and exhibites good reusability.The mixture of Ce(NO3)3.6H2O and Co(NO3)3.6H2O solution were immersed into the channels of KIT-6 template. After thermal treatment in air and etching, ordered mesoporous Co3O4-CeO2 metal composite oxide was obtained. After PAMAM dendrimer-templated Pt nanoparticles were immobilized on mesoporous Co3O4CeO2 oxides, Pt/meso-Co3O4-CeO2 catalyst was obtained after removal of dendrimer. It was found that the support still maintained relatively regular structure and Pt nanoparticles have relatively small size and good dispersion after loading on supports. When Pt/meso-Co3O4-CeO2 was used to catalyze the reduction of 4-nitrophen, the reaction was nearly complete in 6 min and the conversion rate of 4-nitrophenol got 97.3%. Obviously, the catalytic performance of Pt catalyst based on composites is superior to Pt supported on sole ceria.