Mechanistic Insights into CO₂ Activation via Reverse Water–Gas Shift on Metal Surfaces

Abstract

By the means of density functional theory calculations, we find that CO 2 activation via reverse water−gas shift (r-WGS) follows different elementary steps on different metals (Pt, Rh, Ni, Cu, Ag, and Pd). We relate these differences to the interactions between the adsorbed oxygen and the metals, which strongly affect the dissociation activation energy. In particular, CO 2 dissociation is favored on metals that present high affinity toward oxygen. As the O interaction with the metals weakens, CO 2 hydrogenation becomes more favored at the expenses of the dissociation. We found that the binding energy of oxygen scales almost linearly with the difference between the activation energy of the two competing paths, and therefore this quantity can be used as a simple descriptor to discriminate which of the two mechanisms is dominant on different metals. Such findings allow rationalization of the different catalytic cycles reported in the literature for the r-WGS reaction on metal surfaces.

Catalytic behavior of metal catalysts in high-temperature RWGS reaction: In-situ FT-IR experiments and first-principles calculations

“…Figure 6(a) presents the overall energetics of different metal catalysts for each reaction pathway, a total of 5 elementary reaction steps (including 3 intermediate adsorbed states): (1) H 2 (g) + CO 2 (g) ↔ (2) CO 2 *  + 2H *  ↔ (3) HCOO *  + H *  ↔ (4) CO *  + OH *  + H *  ↔ (5) CO(g) + H 2 O(g), where the asterisks (*) denote adsorbed species. Most reaction energies are in general agreement with the previous (R)WGS results323334, favourable CO 2 hydrogenation, and (temperature-dependent endothermic) limited process. Considering the difficulty of adsorbing a non-polar linear CO 2 molecule, surprisingly, all three metals except Ag showed favourable energetics in the reaction step (1) to (2).…”

Product selectivity in plasmonic photocatalysis for carbon dioxide hydrogenation

“…A high E ads,O partially compensates the energy cost for C–O bond cleavage in the CHO intermediates and increases the selectivity towards CH 4 . Although the reaction on the Au catalysts has been reported to involve additional reaction intermediates225960, the selectivity observed here is consistent with the corresponding E ads,O of Rh (5.22 eV) and Au (3.25 eV)61: the Rh catalyst had a slight preference towards CH 4 production under dark conditions, whereas the Au catalyst exclusively produced CO.…”

Intrinsic reactivity of Ni, Pd and Pt surfaces in dry reforming and competitive reactions: Insights from first principles calculations and microkinetic modeling simulations

“…These results indicate that both C-O activation routes are energetically equivalent for Pd and Pt, but the direct CO 2 dissociation is preferred on Ni. Indeed, recent DFT calculations showed that CO 2 hydrogenation to COOH ⁄ is preferred over its cleavage on metal surfaces that interact less with the O ⁄ species, whose adsorption energy magnitude was found to decrease in the order Ni > Rh > Cu > Pd > Ag > Pt [47], in agreement with our results.…”