Ambient pressure CO2 hydrogenation over a cobalt/manganese-oxide nanostructured interface: A combined in situ and ex situ study.

• MnCo 2 O 4 has high activity & superior methane selectivity compared to published data. • MnCo 2 O 4 structure is stable and can be reactived. • Co/MnO interphase are responsible for methane production even at high temperatures. We report on a cobalt/manganese-oxide interface catalyst with outstanding activity and selectivity towards methane even at high temperatures and ambient pressure in CO 2 hydrogenation. The catalyst was formed from a MnCo 2 O 4 -based spinel structure during the oxidative-reductive pretreatment process just before the catalytic tests. Several Mn-, Fe- and Ni-containing cobaltite spinel and reverse spinel structures were tested to find the best overall performer. The reusable MnCo 2 O 4 -based structure featured a CO 2 consumption rate of ~8500 nmol*g−1*s−1. Even though methane is not the thermodynamically favoured product, it was produced with ~80% and ~50% selectivity at ambient pressure at 673 K and 823 K, respectively. This unexpected finding is linked to the presence of a unique nanostructured Co/Mn(II)O catalyst with a surface composition of Mn 3.3 Co 2.0 O 4.7 formed after the pretreatment activation step. Over this phase, the reduction of CO 2 progresses through bridge bonded formate located at the Co/Mn2+ interface and this is mostly responsible for high temperature methane formation. This hypothesis is proven here by the reported combination of ex-situ XRD, TPR, HRTEM-ED, HAADF-EDX and in-situ NAP-XPS and DRIFTS techniques. [ABSTRACT FROM AUTHOR]