CO2 hydrogenation: Selectivity control of CO versus CH4 achieved using Na doping over Ru/m-ZrO2 at low pressure

By doping 1%Ru/m-ZrO2 with sodium, selectivity tuning between CO and CH4 during CO2 hydrogenation was achieved by controlling the relative rates of reverse water-gas shift and CO methanation. By increasing basicity through Na loading: (1) the formate C-H bond is weakened in DRIFTS of adsorbed CO, accelerating C-H bond formation of formate and promoting CO formation at the Ru/m-ZrO2 interface; and (2) the coverage of Na increases on ensembles of Ru atoms responsible for methanation. Increasing Na content shifts selectivity from CH4 (useful for synthetic natural gas) to CO, which can be used for Fischer-Tropsch synthesis or methanol-to-gasoline. Electronic modification of formate is likely due to enhanced basicity (strengthening bonding between catalyst and the -CO2 function of formate and weakening C-H). No electron transfer from Na to Ru was detected in XANES. DRIFTS as a function of time and XPS results showed that Na exacerbates site blocking and deactivation. [Display omitted] •As with Pt/ZrO2, Na doping promotes the water-gas shift reaction for Ru/ZrO2.•Na doping weakens the formate C-H bond in WGS, the scission of which is the proposed RLS.•In reverse WGS, Na doping weakens the formate C-H bond and partially suppresses Ru sites.•These aspects promote the relative rate of RWGS and hinders methanation.•Na doping allows fine tuning of the selectivity of Ru/ZrO2 between CO and CH4 at low P.