Uncovering the reaction mechanism behind CoO as active phase for CO2 hydrogenation

Abstract

Transforming carbon dioxide into valuable chemicals and fuels, is a promising tool for environmental and industrial purposes. Here, we present catalysts comprising of cobalt (oxide) nanoparticles stabilized on various support oxides for hydrocarbon production from carbon dioxide. We demonstrate that the activity and selectivity can be tuned by selection of the support oxide and cobalt oxidation state. Modulated excitation (ME) diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) reveals that cobalt oxide catalysts follows the hydrogen-assisted pathway, whereas metallic cobalt catalysts mainly follows the direct dissociation pathway. Contrary to the commonly considered metallic active phase of cobalt-based catalysts, cobalt oxide on titania support is the most active catalyst in this study and produces 11% C2+ hydrocarbons. The C2+ selectivity increases to 39% (yielding 104 mmol h−1 gcat−1 C2+ hydrocarbons) upon co-feeding CO and CO2 at a ratio of 1:2 at 250 °C and 20 bar, thus outperforming the majority of typical cobalt-based catalysts.

RETRACTED: Hydrogenolysis of Polyethylene and Polypropylene into Propane over Cobalt-Based Catalysts

“…Interestingly, Have et al demonstrated that H 2 activation routes differ depending on the cobalt oxidation state in CO 2 -based Fischer–Tropsch synthesis. In particular, they showed that while H 2 is adsorbed dissociatively over metallic cobalt, cobalt oxide follows a H 2 -assisted pathway . In addition to the potential influence of acidity as previously discussed, the observed shift from mainly terminal to close-to-terminal C–C bond cleavage in polyolefin hydrogenolysis over Co/ZSM-5 might stem from the preferential stabilization of oxidized cobalt phases by the zeolite that are different from those observed for bulk Co 3 O 4 or other supports under reductive conditions.…”

On the link between CO surface coverage and selectivity to CH4 during CO2 hydrogenation over supported cobalt catalysts

“…While our data show that the state of the surface of metallic cobalt is not modified by varying feed composition in terms of CO/CO 2 proportions, we need to stress that some CoOx phases may still have been present under reaction conditions. Those were shown to lead mostly to methane formation 12 . These authors proposed that two reaction pathways occurred, one through CO(ads) on metallic cobalt and one through carbonate/formate on CoOx.…”

“…Metallic cobalt is often considered as the most active phase during CO and CO 2 hydrogenations over Co-based materials 7,8,10,11 . However, it was recently shown that cobalt oxides could be the main phases responsible for the formation of hydrocarbons (mostly CH 4 ) over Co-based catalysts used for CO 2 hydrogenation 12 . The oxidation of a fraction of metallic cobalt could thus potentially be a major cause for the increased selectivity to methane when increasing the CO 2 proportions in CO-CO 2 -H 2 mixtures.…”

Controlled Oxidation of Cobalt Nanoparticles to Obtain Co/CoO/Co3O4 Composites with Different Co Content

“…CoO is successfully used in catalytic processes of CO 2 hydrogenation [ 12 ], as photo- and electrocatalytic materials [ 13 , 14 ].…”