1. Stabilization of metal surfaces by formation of bimetallic compositions J.R. Monnier 1, S. Khanna 2, and J.R. Regalbuto 1 1 Department of Chemical Engineering, USC 2 Department 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.  Many reactions conducted at extreme conditions—three examples.  Sulfur-based thermochemical cycle to produce H 2 and O 2 from H 2 O. --key reaction is Pt-catalyzed SO 3  SO 2 + 1/2O 2 at T > 700 – 800 o C. --rapid Pt sintering has restricted commercialization.  Direct hydrochlorination of acetylene to vinyl chloride. --Au-catalyzed reaction of HC≡CH + HCl  CH 2 =CHCl at high selectivity and activity. --Rapid sintering of Au at < 200 o C in HCl has prevented potential commercialization. --VCM production is 60 – 80 Blbs/yr. Current method is oxychlorination of CH 2 =CH 2.  Dry reforming of methane using CO 2. --Ni, Pt, and Ni-Pt catalysts used for CH 4 + CO 2  2CO + 2H 2 --T > 700 o C 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. Industrial relevance

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. MetalTemp (°K)SFE (ergs/cm 2 )Temp (°K)SFE (ergs/cm 2 ) Ag2981.30213231.046 Au2981.6269041.345 Cu2981.93413571.576 Pd2982.04318251.376 Ni2982.36417261.773 Pt2982.69120452.055 Co2982.70917682.003 Ir2983.23126382.352 Ru2983.40925832.348 SupportTemp (°K)SFE (ergs/cm 2 )Temp (°K)SFE (ergs/cm 2 ) C (graphite)2980.50638230.344 Al 2 O 3 23230.69 - 0.84 SiO 2 2980.60520630.390 TiO 2 2980.67221250.355 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.