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Stabilization of metal surfaces by formation of bimetallic compositions

This project aims to prepare core-shell, bimetallic catalysts with higher thermal and chemical stability by using computational guidance. The surface of the bimetal will be enriched with the metal with the lowest surface free energy (SFE). By choosing the core metal strategically, stronger metal-support interactions can be achieved. The project also explores the use of strong electrostatic adsorption (SEA) to prepare evenly-distributed core metal particles on the support. The industrial relevance of the project includes applications in sulfur-based thermochemical cycles, direct hydrochlorination of acetylene, and dry reforming of methane using CO2.

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Stabilization of metal surfaces by formation of bimetallic compositions

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  1. Stabilization of metal surfaces by formation of bimetallic compositions J.R. Monnier1, S. Khanna2, and J.R. Regalbuto1 1Department of Chemical Engineering, USC 2Department of Physics, VCU Center for Rational Catalyst Synthesis University of South Carolina, Columbia, SC June 16, 2014

  2. Project Title • Research team: Monnier (USC), Regalbuto (USC, and Khanna (VCU). • Overview: Use computational guidance to prepare core-shell, bimetallic catalysts with higher thermal and chemical stability. Project • to include shell metal-core metal-support interactions. • Creation of surface requires work and positive free energy change. • Surface of bimetal enriched with lowest surface free energy (SFE) metal. • If concentration of the lower SFE metal is high enough, core-shell • bimetallic particle is favored. • Choice of core metal may give stronger metal-support interaction, e.g.,oxophilic or base metal surfaces as core metals. • Strong electrostatic adsorption (SEA) to prepare small, evenly-distributed • core metal particles on support.

  3. Industrial relevance • Many reactions conducted at extreme conditions—three examples. • Sulfur-based thermochemical cycle to produce H2 and O2 from H2O. --key reaction is Pt-catalyzed SO3 SO2 + 1/2O2 at T > 700 – 800oC. --rapid Pt sintering has restricted commercialization. • Direct hydrochlorination of acetylene to vinyl chloride. --Au-catalyzed reaction of HC≡CH + HCl  CH2=CHCl at high selectivity and activity. --Rapid sintering of Au at < 200oC in HCl has prevented potential commercialization. --VCM production is 60 – 80 Blbs/yr. Current method is oxychlorination of CH2=CH2. • Dry reforming of methane using CO2. --Ni, Pt, and Ni-Pt catalysts used for CH4 + CO2  2CO + 2H2 --T > 700oC typically required and sintering becomes key issue. Ginosar, Cat. Today, 139 (2009) 291. Monnier, Appl. Catal. A: General, 475 (2014) 292. Navarro, Green Energy Tech. (2013) 45.

  4. Goals of the proposal • Use combination of SEA and ED to prepare core-shell bimetallic particles on different supports. • Determine stability of particle size and surface composition at extreme conditions of temperature and/or gas phase composition. • Use computational analysis to correlate particle size and composition. energetics of catalyst support-metal core-metal shell interactions. • Use above information to prepare ultra-stable catalyst surfaces.

  5. Hypothesis for high stability bimetallic particles • Shell composition of lower SFE metal will be deposited by ED. • Migration of shell metal onto low SFE support not favored since maintenance on high SFE core metal lowers overall SFE of system. ED of Au on Ni ED of Pt on Ru

  6. Preparation of core-shell compositions Core metal particles prepared by SEA. Metal on right hand side deposited on metal to the left.

  7. Outcomes/deliverables – Year 1 • Synthesize several families of bimetallic catalysts with core-shell structures exhibiting greater resistance against sintering. • Characterization using STEM, XRD, XPS, and chemisorption. • Generation of initial computational model correlating interaction of catalyst support - core metal - shell metal.

  8. Duration of project and proposed budget • Minimum of two years. • $60,000/yr. • In second year, materials will be supplied to facilities conducting reactions at extreme conditions of temperature and gas composition for real testing. • Additional length dependent on support.

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