Standard Article

PROX catalysts

Fuel Cell Technology and Applications

Hydrogen storage and hydrogen generation

Fuel processing from hydrocarbons to hydrogen

  1. L. Shore,
  2. R. J. Farrauto

Published Online: 15 DEC 2010

DOI: 10.1002/9780470974001.f302019

Handbook of Fuel Cells

Handbook of Fuel Cells

How to Cite

Shore, L. and Farrauto, R. J. 2010. PROX catalysts. Handbook of Fuel Cells. .

Author Information

  1. Engelhard Corporation, Iselin, NJ, USA

Publication History

  1. Published Online: 15 DEC 2010


The proton exchange membrane fuel cell uses a Pt-based catalytic anode and operates at about 80 °C. The hydrogen that is oxidized at the fuel cell anode can be obtained from reforming a hydrocarbon fuel. Depending on the reforming model, the hydrogen stream may initially contain almost 10% CO (dry basis). Since carbon monoxide adsorbs strongly on precious metals, one of the most important requirements for successful operation of this fuel cell is that the CO concentration be reduced to <10 ppm (99.99% conversion) to protect the Pt anode from CO poisoning and deactivation.

The task of CO removal is a multi-stage process within the fuel reformer. The primary CO converter is a water gas shift (WGS) reactor, where the CO is reacted with water to yield equimolar concentrations of CO2 and H2. Because of both thermodynamic and kinetic limitations, WGS normally yields a stream with 0.2–0.5% CO. The most effective mechanism for further CO removal is oxidation with air injection. Because of the very high ratio of hydrogen to carbon monoxide (>100 : 1), the catalyst needs to be highly selective. Therefore, the process is called selective oxidation or preferential oxidation (PROX).

The objective of the PROX reaction is high CO conversion to CO2 without excessive hydrogen oxidation (to water). This article discusses the details of the PROX reaction, catalytic materials currently being investigated and alternative approaches to CO removal.


  • carbon monoxide;
  • carbon dioxide;
  • catalyst;
  • heat exchanger;
  • methanation;
  • monolith;
  • precious metal;
  • platinum group metal;
  • poisoning;
  • preferential oxidation;
  • reverse water gas shift;
  • selectivity (catalytic);
  • space velocity;
  • water gas shift