Performance of water gas shift reaction catalysts: A review

Human beings have been using fossil fuels for their energy needs since long. Reducing availability of these non-renewable energy sources due to increasing consumption and resultant adverse effects on the environment has led researchers to focus on renewable and cleaner energy alternatives. Hydrogen is one such promising option which can serve as a renewable and cleaner alternative to conventional fossil fuels. Water-gas shift (WGS) reaction is currently widely employed to produce hydrogen from fossil carbonaceous as well as renewable biomass feed-stocks. WGS reaction involves reaction between CO and water over a suitable catalyst to enrich the gaseous mixture with H-2. Traditionally, iron-chromium (Fe-Cr) and copper-zinc (Cu-Zn) catalysts have been used to facilitate the reaction at high and low temperatures, respectively. But over the years, WGS reaction catalyst technology has advanced dramatically and has been suitably modified to assist the reaction even in the medium temperature range and achieve higher CO conversion. Most of the current research is focused on ceria (CeO2) based WGS catalysts because of their unique favorable properties. Furthermore, there have been an ever-increasing number of recent studies which deal with fabricating nano-structured catalysts for WGS reaction because of the advantages offered by nano-materials over conventional materials. This review gives a progressive account of the evolution of WGS catalysts over the years with focus on those that are currently being investigated for better performances.