Synthesis Of Flexible Noble Metal/Graphene Aerogels For CO Oxidation

Graphene aerogel has a low density, high porosity, a large surface area, good flexibility, impressive mechanical strength and excellent electrical conductivity, making it an ideal substrate for multifunctional materials. Many simple methods for preparing graphene aerogel have been reported, but among them various additives should be used, and the self-assembly process of graphite oxide has not been deeply understood. In addition, CO oxidation has been a hot topic in the field, and graphene-based aerogels as catalysts for the oxidation of CO is still relatively limited..Macroscopic 3D flexible Ru/graphene aerogel (RuGA) and PtRu/graphene aerogel (PtRuGA) were prepared by a unique polyol-mediated solvothermal method, where ethylene glycol (EG) served as both solvent and reducing agent. In addition, the RuGA with improved methanical properties was prepared by adding CNTs as a mechanical reinforcement agent. With abundant macroporous structures and fully exposed noble metal active sites, RuGA and PtRuGA could be used as flexible heterogenous catalysts to provide multiple transfer and diffusion pathways for molecules, leading to high activity and excellent stability for low-temperature CO oxidation.The major conclusions are summarized as follows.1) Preparation and characterization of RuGA and RuGACNT by a solvothemal method with EG as the solvent and reducing agent. During the solvothermal process, the key to the synthesis is relied on the ethylene glycol as the solvent and reducing agent, which could simultaneously reduce GO and Ru3+ ions and further self-assemble into the 3D aerogel network. The resultant RuGA has a low density (<30 mg/cm3), a high surface area (207 m2/g), large pore sturctures (10-50 μm) and excellent electrical conductivity (333 S/m). Additionally, as a mechanical reinforcement agent, CNTs may act as a scaffold in the aerogels to resist compressive stress, leading the flexible RuGA became a rigid aerogel and the compress modulus increased from 0.12 MPa to 0.45 MPa.2) The catalytic avtivity of RuGA before and after treatment with different atmospheres. The surface chemistry of Ru could be easily switched by pretreated at different atmospheres (< 200℃). The results showed that RuGA with mild air pretreatment could deliver 100% CO conversion with long durability (>72 h) at room temperature. It was demonstrated from H2-TPR, O2-TPD and XPS results that RuOx had a better ability for O2 desorption and more active oxygen-vacancies than RuO2, leading to a higher catalytic activity. However, excessive oxidation or partial reduction would decrease the content of RuOx and was not benefical to improve the catalytic activity. Although a detailed reaction mechanism has not been reached, strong graphene-support interaction may also play a significant role since Ru-based catalyst itself cannot completely convert CO at room temperature so far.3) Preparation of PtRuGA with different Pt/Ru mole ratio for CO oxidation.Without any pretreatment, PtRuGA exhibited a high catalytic activity at room temperature with a CO conversion of over 60% at 25℃ and a 100% conversion at 80℃. The high activity should be due to the strong adsorption of Pt for CO and O2, as well as the presence of RuOx. With mild air pretreatment, PtRuGA showed an improved catalytic activity with 100% CO conversion at room temperature, profiting from the increased content of RuOx. In addition, PtRuGA also possessed an outstanding long-term catalytic stability (>72h).