Support and gas environment effects on the preferential oxidation of carbon monoxide over Co3O4 catalysts studied in situ

Nyathi, Thulani M.; Fadlalla, Mohamed I.; Fischer, Nico; York, Andrew P. E.; Olivier, E.J.; Gibson, Emma K.; Wells, Peter P.; Claeys, Michael

doi:10.1016/j.apcatb.2021.120450

Cited by 29 publications

(31 citation statements)

References 61 publications

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“…In the case of the Co3O4 catalyst, the crystallite size decreased upon formation of the CoO and the hcp Co phases, while the crystallite size of the fcc Co phase was comparable with that of the starting Co3O4 phase, indicating a possible cleavage of the particles during CO-PrOx. This is in agreement with the findings reported by Nyathi et al from their in situ PXRD-based CO-PrOx studies [16]. SEM-EDS analysis of the spent catalysts (Figure 4) shows a uniform distribution of the cations (i.e., Mg and Fe or Co), indicating that the cations remain in close proximity even after partial reduction (in the case of MgCo2O4).…”

Section: Spent Catalyst Characterisationsupporting

confidence: 91%

“…Assuming the Mars-van Krevelen (MvK) mechanism for CO oxidation, which requires the catalyst surface to be easily reduced (and re-oxidised) [45][46][47][48], it is possible that the low CO oxidation activity of the Fe-based oxides was caused by their less reducible nature. This has also been proposed for other less reducible catalysts that displayed low CO oxidation activity during CO-PrOx [11,16,49]. It can also be observed that the addition of Mg in the Fe-and Co-based oxide structure (i.e., MgFe 2 O 4 and MgCo 2 O 4 ) decreased the CO and O 2 conversions, as well as CO 2 yields below 250 • C. This decrease in the CO oxidation activity is consistent with the effect that Mg has on the reducibility of the catalysts (see H 2 -TPR profiles in Figure 3), i.e., the addition of Mg makes the Fe-and Co-based oxide less reducible.…”

Section: Co-prox Performance Evaluationsupporting

confidence: 55%

“…In the case of Co3O4, the H2-TPR profile (Figure 3) shows two convoluted reduction peaks having temperature maxima (Tmax) at ca. 260 °C and 340 °C, corresponding to the reduction of Co3O4 to CoO and then from CoO to Co 0 , respectively [16]. The addition of Mg to the Co-based oxide structure resulted in two resolved reduction peaks, with the first one observed between 190 and 220 °C, corresponding to the reduction of MgCo2O4 to a CoO-type phase containing Mg (possibly in the form Mg0.32Co0.68O).…”

Section: Catalystmentioning

confidence: 99%

“…The CO-PrOx reaction is carried out under a reducing environment due to the high concentration of H 2 (typically between 40 and 75 vol.%) [5,6,40,41]. Nyathi et al [16,17] showed that the performance of Co-based catalysts is phase dependent, i.e., the phases Co 3 O 4 , CoO and Co 0 kinetically favor different reactions during CO-PrOx. For example, the authors showed the onset of CH 4 formation to coincide with the onset formation of Co 0 from Co 3 O 4 .…”

Section: Catalystmentioning

confidence: 99%

“…Iron (Fe) [7,8], nickel (Ni) [2,7,9], cobalt (Co) [7,8,[10][11][12][13] and copper (Cu) [7,14,15] have been investigated for this purpose. The main challenge associated with using base metals is the phase dependency of their activity and selectivity, i.e., the metal oxide phase typically favors the oxidation of CO, while the metallic phase often favors CO hydrogenation to produce methane (CH 4 ) [11,16,17]. CO hydrogenation is not a desired CO-consuming route as it results in the consumption of the valuable H 2 that is required in the PEMFC [14,17].…”

Section: Introductionmentioning

confidence: 99%

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Magnesium as a Methanation Suppressor for Iron- and Cobalt-Based Oxide Catalysts during the Preferential Oxidation of Carbon Monoxide

2022

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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.

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Section: Spent Catalyst Characterisationsupporting

confidence: 91%

Section: Co-prox Performance Evaluationsupporting

confidence: 55%

Section: Catalystmentioning

confidence: 99%

Section: Catalystmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Magnesium as a Methanation Suppressor for Iron- and Cobalt-Based Oxide Catalysts during the Preferential Oxidation of Carbon Monoxide

2022

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Insight into the Structural Evolution of the Cobalt Oxides Nanoparticles upon Reduction Process: An In Situ Transmission Electron Microscopy Study

Yun²,

Zhang

et al. 2021

ChemCatChem

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As a prerequisite elementary step, the reduction of cobalt (Co) oxides to form metallic Co is essential to display activity in heterogeneous catalysis. Nevertheless, the intrinsic principle of phase and morphology evolution for Co oxides and formation mechanism of the active Co site remains unclear. Here, we resolve this decades-long question by using a state-of-the-art in situ transmission electron microscopy (TEM) to elucidate the multi-role of initial crystalline phase and size of Co oxides in modulation of reduction rate, phase and morphology evolution under H 2 atmosphere, by excluding the possible interference from promoter and support. We anticipate that this study enriches current understanding on the surface structure and morphology evolution of Co oxides, and provides reference for rational design of Co-based catalytic material as well as its pretreatment protocol.

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In situ and Operando Characterisation in the Preferential Oxidation of Carbon Monoxide over Base Metal Oxide Catalysts: A Review

Nyathi,

Fadlalla,

Claeys

2024

ChemCatChem

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Polymer electrolyte membrane fuel cells (PEMFCs) are the core technology of the steadily growing hydrogen (H2) economy as they can convert chemical energy, in the form of H2, to electrical energy. If the H2 is derived from (green) hydrocarbons, via steam reforming and the water‐gas‐shift reaction, then it would contain small amounts of carbon monoxide (CO, 0.5 – 2%), among other gases. CO poisons the platinum‐based anode catalyst in the PEMFC, and the current recommendation is to decrease its concentration to below 0.01% (or 100 ppm) in the H2‐rich PEMFC feed. The preferential oxidation of CO (CO‐PrOx) is a promising strategy for decreasing the CO concentration, and base metal oxide catalysts have shown great potential in this regard. However, such catalysts tend to undergo physicochemical changes that cause undesirable catalytic activity and selectivity changes. This review discusses the different base metal oxide catalysts that have been evaluated in CO‐PrOx, while paying special attention to the various in situ and operando techniques that have been used to monitor the physicochemical changes of such catalysts during operation. We conclude the review by highlighting the recent and possible future attempts of circumventing the undesired physicochemical changes of base metal oxides during CO‐PrOx.

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Support and gas environment effects on the preferential oxidation of carbon monoxide over Co3O4 catalysts studied in situ

Cited by 29 publications

References 61 publications

Magnesium as a Methanation Suppressor for Iron- and Cobalt-Based Oxide Catalysts during the Preferential Oxidation of Carbon Monoxide

Magnesium as a Methanation Suppressor for Iron- and Cobalt-Based Oxide Catalysts during the Preferential Oxidation of Carbon Monoxide

Insight into the Structural Evolution of the Cobalt Oxides Nanoparticles upon Reduction Process: An In Situ Transmission Electron Microscopy Study

In situ and Operando Characterisation in the Preferential Oxidation of Carbon Monoxide over Base Metal Oxide Catalysts: A Review

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