(9e) Mechanistic Insights into r-WGS Reaction on Rh and Pt Via a Combined Experimental and Structure-Dependent Microkinetic Analysis

The Reverse-WGS reaction is a critical process in CO2 upgrading strategies, primarily because it generates CO, an essential building block in the chemical industry. Nevertheless, considerable debate persists regarding the exact mechanism of this reaction¹. Previous theoretical investigations² showed that the activation of CO₂ depends on the oxyphilic nature of the catalyst material. Here, we combined both theoretical and experimental methodologies to investigate how the reaction mechanism changes according to the oxygen-affinity of the surface on Rh and Pt materials.

The reaction rate exhibited a direct proportionality on CO₂ concentrations for both catalysts but showed a significant dependency on H₂ only on Pt. As suggested in [2], oxophilic surfaces activate CO₂ via dissociation into CO^* and O^*, while surfaces with lower oxophilicity facilitate a hydrogen-mediated pathway. Therefore, we proposed that, on Rh, CO₂ is activated through dissociation into CO^* and O^* (Fig.1a), while, on Pt, CO₂ activation occurs via a hydrogen-mediated route forming a COOH^* intermediate (Fig.1b).

To shed light on this mechanistic understanding, we performed a DFT-based structure-dependent microkinetic analysis on both catalysts³. Our findings indicate that CO2 activation is the rate-limiting step for both materials, occurring through dissociation into CO* and O* on Rh, whereas it follows a hydrogen-mediated pathway on Pt, aligning with experimental observations. The microkinetic model incorporates the activity and prevalence of various active sites presented by the catalyst nanoparticles, a crucial step for pinpointing the kinetically predominant active sites, specifically Rh(100) and Pt(111). This inclusion of structure dependency is vital for developing fundamental rate equations essential for catalyst design and optimization.

Project funded under PNRR-NextGenerationEU “Network 4 Energy Sustainable Transition – NEST”.

[1] Alam et al., Catal, Sci. Technol, 2021, 11, 6601.

[2] Dietz et al., J. Phys. Chem. 2015, 119, 4959.

[3] Cheula et al., Catalysis Today, 2022, 387, 159.