Synthesis And Application Of Porous Oxide Confined Pt-based Catalytic Materials

Noble metal catalysts are widely used in fine chemical synthesis,automobile exhaust purification,and other processes in the petroleum and chemical industry because of their incompletely filled d electron orbitals,ease in the formation of a reactive intermediate,as well as excellent catalytic activity,selectivity,and stability.Resource scarcity and high costs are their disadvantages,thus,improving the usage of the precious metal has drawn wide research interest and has been a challenge.To address this problem,current research have been directed toward the confinement effects and the preparation of bi-metallic catalysts materials.The first involves the preparation of highly dispersed and stable noble metal nanoparticles;the second involves the fabrication high-performance bimetallic catalysts to reduce the usage of noble metals.Now is generally believed that there is strong interaction between metal oxide and noble metals,exactly highly active sites locate in the interface between metal oxide and noble metal,which is considered to be the interface catalysis.In this paper,the noble metal Pt are used as the research object,the porous oxide confined Pt-based catalytic materials with high dispersion and small particle size are prepared based on the strategy of the core-shell confinement and interfacial catalysis.And we studied the CO catalytic oxidation performance and toluene catalytic oxidation performance.The structure properties of the catalyst and its effect on the reaction performance were discussed.The main results are summarized here:In the first part,we demonstrated a facile strategy to design and synthesis a stable ultrafine bimetallic NPs with dual interfaces（Pt-Ni（O）@SiO₂）.Relevant characterizations confirmed that the Pt-Ni（O）@SiO₂ nano-catalyst consisted of Pt-Ni（O）heterojunction cores and microporous silica shells.The catalytic performances of the Pt-Ni（O）@SiO₂ catalyst was markedly higher than that of the Pt@SiO₂ catalyst,although the former（1%wt.）only had half the Pt content of the latter（2%wt.）.Moreover,the Pt-Ni（O）@SiO₂ showed high thermal and cycle stability,which indicates that adding small amounts of Ni to form the Pt-Ni（O）interfaces can improve the catalytic performance of the Pt@SiO₂ catalyst and effectively decrease the using amount of Pt.The catalytic performance enhancement over Pt-Ni（O）@SiO₂is attributed to their distinct architectures in which the Pt-Ni-NiO dual interface structures enhanced the catalytic activity for CO oxidation and the microporous shell enhanced the accessibility of reactants.Pt-Ni（O）@SiO₂ catalyst also exhibited high catalytic performance for toluene（one of the main VOCs）total combustion.In addition,we explored different reduction temperatures over Pt-Ni（O）@SiO₂ to evaluate the effect of the interface on catalytic performances for CO oxidation.From various characterizations results,it can be concluded that the activities of the Pt-Ni（O）interface decreased in the following order:Pt-NiO≈Pt-Ni-NiO≈Pt-Ni>Pt?Ni.In the second part,self-assembled Pt-CeO₂ nanowires confined within a thermally robust microporous silica shell（Pt-CeO₂ NW@SiO₂）was prepared via a facile in situ strategy for the first time.The formation mechanism of Pt-CeO₂NW@SiO₂ with well-defined metal-oxide interfaces and stable architecture was investigated in detail.We deduced that Pt-CeO₂ nanowires formed by a self-assembly process,and then in situ embedded in microporous silica shell.Pt-CeO₂ NW@SiO₂showed superior catalytic performance for CO oxidation,the superior catalytic properties are attributed to the strong synergistic effect between Pt and CeO₂ and the Pt-CeO₂ interfaces and also the confinement effect of the porous silica shell.The relationship between the special catalyst structure and its catalytic performance was also studied detailedly.We treated the catalyst with concentrated nitric acid to dissolve the CeO₂ species in the core-shell structure and its catalytic activity decreased evidently,which signifies the importance of the stronger synergistic effect between Pt and CeO₂,Pt-CeO₂ nanowire offer Pt-CeO₂ interface and active sites accessible to reactants in the final structure.The special core-shell structure also shows excellent sintering resistance due to the confinement effect of porous silica shell,the catalyst keep the morphology and structure of catalyst unchanged after reacting for 100 h at 700 ^oC.The microporous silica shell can effectively prevent the sintering of precious metals under high temperature.