Catalysis Science & Engineering, Short talk
CE-015

Unveiling the promotional effect of nickel in indium-catalyzed CO2 hydrogenation to methanol

M. S. Frei1, C. Mondelli1, R. García-Muelas2, N. López2, O. V. Safonova3, D. Curulla-Ferré4, J. A. Stewart4, J. Pérez-Ramírez1*
1ETH Zürich, 2Institute of Chemical Research of Catalonia, 3Paul Scherrer Institute, 4Total Research & Technology Feluy

The thermocatalytic hydrogenation of CO2 with renewable hydrogen stands as a sustainable route to produce the commodity and potential fuel methanol. In2O3 emerged as a promising catalyst for this reaction owing to superior selectivity and stability1 and can be effectively promoted by anchoring tiny palladium clusters to its surface via a coprecipitation synthesis.2 Herein, here we gather comprehensive molecular-level understanding on nickel as an alternative activity booster, which could better fulfil economic requirements of a practical process. Following the more easily scalable impregnation method, no methane formation was detected even at 10 wt.% nickel loading, despite the high stand-alone CO2 methanation activity of nickel nanoparticles. Altering the amount of indium in In-Al mixed oxide supports (0‑100 mol% In) while keeping the nickel content constant corroborated that only very small indium quantities are sufficient to produce the unexpected selectivity switch on nickel. In-depth characterization revealed a highly dispersed two-dimensional nickel phase onto In2O3 in low-loading samples, which is accompanied by nanoparticles at high promoter contents. Upon reaction, nickel alloyed with indium atoms from the oxide surface forming indium- or nickel-rich intermetallic compounds depending on the promoter loading (Fig. 1). DFT simulations elucidated that indium-modulated nickel species are intrinsically active in the reverse water-gas shift reaction rather than in methanation, while simultaneously providing activated hydrogen to In2O3 that enhances the methanol formation rate. This explains why 5 wt.% nickel on the oxide offers an optimal balance between metals’ alloying and In2O3 surface coverage and hence, between suppression of methanation and fostering of CO2-to-methanol. Overall, this study identified key structural and electronic phenomena controlling the behavior of the classical hydrogenation metal nickel in contact with indium oxide, relevant to attain a stable promoted system for an emerging application.

Fig. 1. Catalyst selectivity in CO2 hydrogenation as a function of nickel loading in Ni/In2O3 catalysts. Relevant structures formed under reaction conditions and the dominant hydrogenation mechanisms are depicted for indium- (orange atoms) and nickel- (blue atoms) rich systems to the left and right, respectively.

[1] O. Martin, A.J. Martín, C. Mondelli, S. Mitchell, T.F. Segawa, R. Hauert, C. Drouilly, D. Curulla-Ferré, J. Pérez-Ramírez, Angew. Chem. Int. Ed., 2016, 55, 6261-6265.
[2] M. S. Frei, C. Mondelli, R. García-Muelas, K. S. Kley, B. Puértolas, N. López, O. V. Safonova, J. A. Stewart, D. Curulla-Ferré, J. Pérez-Ramírez. Nat. Commun. 2019, 10, 3377.