“The paper in question involved a methodical study of the effect of catalytic metal on water-gas-shift activity with ceria-based catalysts.”

The water-gas-shift (WGS) reaction (CO + H₂O = CO₂ + H₂) is a crucial part of fuel reforming to produce hydrogen. Because it is desirable to carry this reaction out at low temperatures, WGS catalysts can take up the largest volume in fuel processors to produce hydrogen. The catalysts that are usually used for this reaction in industrial-scale hydrogen production cannot be used for fuel-cell fuel processors because they are very sensitive to air exposure and other pretreatments.

It has been known from automotive emissions control that the three-way catalysts used in that application are good WGS catalysts. We had been exploring the mechanism how oxygen-storage in three-way catalysts functions. It became apparent that the activity of these catalysts was sufficient to be interesting. The paper in question involved a methodical study of the effect of catalytic metal on water-gas-shift activity with ceria-based catalysts.

We had initially been studying Oxygen Storage Capacitance (OSC) in automotive, emissions-control catalysis. Automotive catalysts work well only when the engine operates at the stoichiometric, air-fuel ratio (just enough air to completely burn the fuel, but no extra). Because the engine cycles between lean and rich, it is necessary to include ceria (CeO₂) in the catalytic converter to release oxygen when there is not enough to burn excess CO and unburned hydrocarbons (2CeO₂ --> Ce₂O₃ + 1/2 O₂) and to take up oxygen when there is too much, so as to allow NO to react with CO. The conventional view of OSC is that it is simply a capacitor.

The WGS reaction involves the reduction of H₂O to H₂, using CO as the oxidant (producing CO₂.). We hypothesized that, given the amount of water present in automotive exhausts; the WGS reaction is really the crucial part of OSC, since H₂ is a much better reductant for NO than either CO or unburned hydrocarbons. The paper in question involved a study of the mechanism of water-gas shift on ceria-supported metals. The results showed that a series of ceria-supported metal catalysts showed similar rates. Based on this and other data, we suggested that the metals simply play the role of holding CO on the surface, while oxygen from the ceria was transferred to the metal, oxidizing CO to CO₂. Since water is a good oxidant for taking Ce₂O₃ to CeO₂, one can complete the cycle. The fact that the reaction rates are almost independent of metal, so long as the metal can be reduced, suggests that the crucial steps in the reaction are associated with either the oxidation of ceria or the transfer of oxygen from ceria to the metal.

We were investigating the mechanism of how oxygen storage works in emissions control. We hypothesized that the water-gas-shift activity was a crucial part of this.