Stabilization of metal surfaces by formation

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
  conditionsthree examples.
• Sulfur-based thermochemical cycle to produce H2
  and O2 from H2O.
• --key reaction is Pt-catalyzed SO3 ? SO2
  1/2O2 at T gt 700 800oC.
• --rapid Pt sintering has restricted
  commercialization.
• Direct hydrochlorination of acetylene to vinyl
  chloride.
• --Au-catalyzed reaction of HCCH HCl ?
  CH2CHCl at high selectivity and activity.
• --Rapid sintering of Au at lt 200oC in HCl has
  prevented potential commercialization.
• --VCM production is 60 80 Blbs/yr. Current
  method is oxychlorination of CH2CH2.
• Dry reforming of methane using CO2.
• --Ni, Pt, and Ni-Pt catalysts used for CH4 CO2
  ? 2CO 2H2
• --T gt 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.

Metal Temp (K) SFE (ergs/cm2) Temp (K) SFE (ergs/cm2)
Ag 298 1.302 1323 1.046
Au 298 1.626 904 1.345
Cu 298 1.934 1357 1.576
Pd 298 2.043 1825 1.376
Ni 298 2.364 1726 1.773
Pt 298 2.691 2045 2.055
Co 298 2.709 1768 2.003
Ir 298 3.231 2638 2.352
Ru 298 3.409 2583 2.348
ED of Au on Ni
ED of Pt on Ru
Support Temp (K) SFE (ergs/cm2) Temp (K) SFE (ergs/cm2)
C (graphite) 298 0.506 3823 0.344
Al2O3     2323 0.69 - 0.84
SiO2 298 0.605 2063 0.390
TiO2 298 0.672 2125 0.355
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.