Operando XAS and DFT Uncover Structure-Performance Relationships in Re/TiO₂ for Selective CO₂ Hydrogenation to...

Area of Science:

• Catalysis
• Renewable Energy
• Chemical Engineering

Background:

• CO2 conversion to value-added chemicals like methanol is a promising renewable energy strategy.
• Precisely controlling kinetics and catalyst selectivity is vital to favor methanol over methane during CO2 hydrogenation.
• Rhenium-based catalysts, specifically Re/TiO2, exhibit high activity and selectivity for methanol synthesis under elevated pressures.

Purpose of the Study:

• To investigate the impact of rhenium (Re) cluster size on the performance of Re/TiO2 catalysts for CO2 hydrogenation to methanol.
• To understand the structure-activity relationship governing methanol selectivity and conversion.
• To provide insights for designing efficient catalysts for sustainable methanol production.

Main Methods:

• Synthesis and characterization of Re/TiO2 catalysts with varying Re loadings (1 wt% and 5 wt%).
• High-pressure catalytic testing for CO2 hydrogenation to methanol.
• X-ray absorption spectroscopy (XAS) to analyze active site structure.
• Density functional theory (DFT) calculations to explore reaction mechanisms and energy barriers.

Main Results:

• Re/TiO2 catalysts achieved high methanol selectivity (97-99%) at 100 bar and 200 °C.
• At 250 °C, 1 wt% Re/TiO2 showed 97% selectivity at 23% conversion, while 5 wt% Re/TiO2 yielded 74% selectivity at 40% conversion.
• Smaller Re clusters (1 wt%) led to higher selectivity but lower conversion compared to larger clusters (5 wt%), impacting space-time yield.

Conclusions:

• Optimizing rhenium cluster size is critical for balancing conversion and selectivity in CO2 hydrogenation to methanol.
• Catalyst structure, particularly cluster size, significantly influences H2 activation, methanol dissociation, and desorption pathways.
• These findings are essential for the rational design of advanced catalysts for efficient and selective renewable methanol synthesis.