Abstract
The preferential oxidation of CO (CO-PrOx) to CO2 is an effective catalytic process for purifying the H2 utilized in proton-exchange membrane fuel cells for power generation. Our current work reports on the synthesis, characterization and CO-PrOx performance evaluation of unsubstituted and magnesium-substituted iron- and cobalt-based oxide catalysts (i.e., Fe3O4, Co3O4, MgFe2O4 and MgCo2O4). More specifically, the ability of Mg to stabilize the MgFe2O4 and MgCo2O4 structures, as well as suppress CH4 formation during CO-PrOx was of great importance in this study. The cobalt-based oxide catalysts achieved higher CO2 yields than the iron-based oxide catalysts below 225 °C. The highest CO2 yield (100%) was achieved over Co3O4 between 150 and 175 °C, however, undesired CH4 formation was only observed over this catalyst due to the formation of bulk fcc and hcp Co0 between 200 and 250 °C. The presence of Mg in MgCo2O4 suppressed CH4 formation, with the catalyst only reducing to a CoO-type phase (possibly containing Mg). The iron-based oxide catalysts did not undergo bulk reduction and did not produce CH4 under reaction conditions. In conclusion, our study has demonstrated the beneficial effect of Mg in stabilizing the active iron- and cobalt-based oxide structures, and in suppressing CH4 formation during CO-PrOx.
Highlights
Goal number seven in the United Nations Sustainable Development Goals is to “ensure access to affordable, reliable, sustainable and modern energy for all” [1]
This study aimed at determining the effect of Mg on the physicochemical properties and catalytic performance of Fe- and Co-based oxide catalysts during carbon monoxide (CO)-PrOx under model reaction conditions
Our results showed that Mg was successfully doped into the Fe- and Co-based oxides since only the reflexes of the targeted spinel structures were observed in the acquired powder X-ray diffraction (PXRD) patterns
Summary
Goal number seven in the United Nations Sustainable Development Goals is to “ensure access to affordable, reliable, sustainable and modern energy for all” [1]. The sustainability part of this goal is of great importance due to the challenges associated with the depleting fossil fuels and the negative impact that these have on the environment. H2 is produced from hydrocarbons via a reforming and/or partial oxidation process, followed by a high- and a low-temperature water-gas shift (HTWGS and LTWGS) reaction. The main challenge associated with the use of fuel cells, in particular, proton-exchange membrane fuel cells (PEMFCs), is the carbon monoxide (CO) present (0.5–2 vol.%) in the H2-rich reformate gas, which poisons the platinum (Pt)-based anode catalyst of the PEMFC [2]. The preferential oxidation of carbon monoxide (CO-PrOx) is considered as an effective and affordable H2 purification process, where CO is oxidized by oxygen (O2) to form carbon dioxide (CO2), while minimizing/preventing the concurrent oxidation of H2 to water (H2O) [3]
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