Abstract

CO hydrogenation and oxidation were conducted over Ir supported on TiO2 and ZrO2 catalysts using a feed mimicking the water–gas shift reformate stream. The influence of the support interaction with Ir and the catalysts’ redox and CO chemisorption properties on activity and selectivity were evaluated. Both catalysts oxidised CO to CO2 in the absence of H2, and a conversion of 70% was obtained at 200 °C. For the CO oxidation in the presence of H2 over these catalysts, the oxidation of H2 was favoured over CO due to H2 spillover occurring at the active metal and support interface, resulting in the formation of interstitials catalysed by Ir. However, both catalysts showed promising activity for CO hydrogenation. Ir-ZrO2 was more active, giving 99.9% CO conversions from 350 to 370 °C, with high selectivity towards CH4 using minimal H2 from the feed. Furthermore, results for the Ir-ZrO2 catalyst showed that the superior activity compared to the Ir-TiO2 catalyst was mainly due to the reducibility of the support and its interaction with the active metal. Controlling the isoelectric point during the synthesis allowed for a stronger interaction between Ir and the ZrO2 support, which resulted in higher catalytic activity due to better metal dispersions, and higher CO chemisorption capacities than obtained for the Ir-TiO2 catalyst.

Highlights

  • In the transition to the hydrogen economy from current power sources, proton exchange membrane fuel cells (PEMFC) are considered good candidates for portable power generation [1,2]

  • During onboard reforming of hydrogen for these fuel cells, trace amounts of CO are still present in the reformate feed following the water–gas shift (WGS) reaction

  • Co supported on non-reducible oxides [5,9,10,11,12,13,14,15,16]. Among these catalytic formulations, supported Ir catalysts have not been widely explored for the Preferential oxidation (PROX) reaction [13,17,18]

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Summary

Introduction

In the transition to the hydrogen economy from current power sources, proton exchange membrane fuel cells (PEMFC) are considered good candidates for portable power generation [1,2]. Preferential oxidation (PROX) and methanation (MET) of CO are viable processes employed to reduce the CO concentration to acceptable levels, feeding onboard PEMFCs with pure hydrogen, and avoiding unwanted poisoning by CO of the Pt anode [3,4,5,6,7,8]. These reactions have been widely studied using Au, Pt, Ru, Rh, Pd, Ir, Ni, Cu, and. The stability of the ceria supported Ir, compared to Rh and Ru, was much higher above 200 ◦ C, since Rh and Ru, encouraging CO dissociation, followed the methanation pathway

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