Theoretical insight into heterogeneous catalysis

Ping Liu
Brookhaven National Laboratory

Density functional theory has reached a level where it can be used to describe complete catalytic reactions on both surfaces and nanoparticles. This gives a basic insight into these processes, and it allows us to pinpoint the origin of the catalytic activity of the material. Here, the water-gas shift (WGS, CO + H2O ? CO2 + H2) reaction on metal/oxide catalysts will be used to exemplify this approach.
The WGS reaction is primarily used to increase the H2 content as well as reducing the CO concentration in synthesis gas and is an essential part of a hydrogen plant. However, current industrial catalysts (Fe-Cr or Zn-Al-Cu oxides) are pyrophoric and require complex activation steps before usage. Recent studies show that the disadvantages of the industrial catalysts can be overcome by the use of metal (Au, Cu, Pt)-oxide (CeO2, TiO2, MoO2) composite materials. However, the promoting effect of the oxide on the WGS activity of the metals has not been well-understood. Here we present our DFT-based studies of the WGS reaction on various metal-oxide composite catalysts. In strong interaction with the experiments on model catalysts, our DFT calculations provide more insight into the reaction and catalysts in various ways: (i) determining the reaction mechanism, key intermediates and active sites; (ii) estimating the reaction rate comparable to experiments in combination with kinetic modeling . (iii) identifying the key parameter that controls the overall conversion, which aids in theoretical screening of better WGS catalysts.

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