Jeffrey T. Miller
- PhD, Chemistry, Oregon State University (1980)
- MS, Chemistry, University of New Mexico (1973)
- BS, Chemistry, Memphis State University (1971)
Research Synopsis
Supported metal catalysts are used in a large number of commercially
important processes, and it is known that the method of preparation, support
interaction, particle size and alloy compositions influence the catalytic
properties of the reduced metal particles.
The preparation steps of several synthesis methods for supported metal
nanoparticle catalysts have been studied by EXAFS and XANES spectroscopies
including adsorption and impregnation of metal salts in aqueous solution,
adsorption of single-site organometallic compounds, and synthesis and deposition
of colloidal nanoparticles on oxide supports. As the size of the metal
nanoparticles decreases to less than about 3 nm, there is a decrease in the
metal-metal bond distance and a decrease in the LIII and LII XANES intensities
consistent with an increase in the number of d electrons. These changes lead to
altered catalytic activity. Adsorption of CO leads to an increase in the LIII
and LII XANES intensity and can be used to determine the influence of the
support on the number of d electrons.
Bimetallic nanoparticles have higher activity than that of single metals and
several structures are possible. Promotion of Pd for the water gas shift (WGS)
reaction with Zn leads to a 1:1 alloy, while promotion by Fe leads to a Fe
surface layer covering a metallic Pd core. Pt WGS catalysts promoted with Mo
give mixed metal catalysts. During the WGS reaction, IR and EXAFS spectroscopies
indicate that the nanoparticle surface composition in the Pd-Zn alloy catalyst,
for example, changes with the composition of the reactants. A plug-flow
fixed-bed EXAFS reaction cell capable of measuring accurate kinetics has been
constructed and can be used to follow the changes in structure that occur under
reaction conditions.
phone: 630/252-1928, millerjt@anl.gov |
