CO₂ methanation over Rh/CeO₂ and Ni/CeO₂ highlighting the different surface speciation during reaction as deduced from our study.

Intermediate species formed during CO₂ methanation over Rh/Al₂O₃ and Rh/SiO₂ catalysts.

Methane is a well-established fuel molecule whose production from CO ${}_2$ through methanation garners increasing interest as an energy storage solution. While often produced with Ni based catalysts, other metals are of interest thanks to higher robustness and activity-selectivity numbers. The Rh/CeO ${}_2$ catalyst has shown appreciable properties for CO ${}_2$ methanation and its structural dynamics has been studied in situ. However, the reaction pathway is unknown. Here, we present infrared modulation excitation spectroscopy measurements with phase sensitive detection of a Rh/CeO ${}_2$ catalyst adsorbate composition during H ${}_2$ pulsing (0–2 vol.%) to a constant CO ${}_2$ (0.5 vol.%) feed. Various carbonyl (CO) and carbonate (b-CO ${}_3$ /p-CO ${}_3$ ) ad-species clearly respond to the hydrogen stimulus, making them potential reaction intermediates. The different CO ad-species are likely intermediates for product CO and CH ${}_4$ but their individual contributions to the respective formations are not unambiguously ascertained. As for the carbonate dynamics, it might be linked to the reduction/oxidation of the CeO ${}_2$ surface upon H ${}_2$ pulsing. Formate (HCOO) ad-species are clearly visible but appear to be, if not spectators, linked to slow side reactions possibly also affected by CeO ${}_2$ redox processes.

Boron silicate (BS) with a chabazite framework structure was synthesised using a direct route and rigorously characterized before it was ion-exchanged with copper to form Cu-BS. Employing in situ infrared spectroscopy, we show that Cu-BS is capable of oxidising methane to methoxy species and methanol interacts with the boron sites without deprotonation.