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

TL;DR

Scientists used advanced techniques to understand how rhenium catalysts convert CO2 to methanol efficiently, finding that smaller catalyst clusters work better.

Contribution

The study reveals how cluster size affects catalytic performance in CO2 hydrogenation to methanol using operando XAS and DFT.

Findings

1 wt% Re/TiO2 achieves 97% methanol selectivity at 23% conversion, while 5 wt% Re/TiO2 achieves 74% selectivity at 40% conversion.

XAS and DFT show that cluster size influences energy barriers for H2 activation, CH3OH dissociation, and desorption.

Balancing cluster size is crucial for optimal catalyst performance in methanol production from CO2.

Abstract

The conversion of
CO2 into value-added chemicals, such
as methanol, offers a promising pathway toward a renewable energy
future. However, a precise kinetic control and a highly selective
catalyst are necessary to overcome the thermodynamic preference for
CO2 hydrogenation to methane. Rhenium-based catalysts,
particularly Re/TiO2, demonstrate high activity and selectivity
for methanol under high-pressure conditions. For example, at 100 bar
and 200 °C, a methanol selectivity of 97–99% was obtained.
Catalysts with 1 wt % Re and 5 wt % Re/TiO2 were used to
study the effect of cluster sizes. At 250 °C, the 1 wt % catalyst
achieves 97% selectivity at 23% conversion, whereas 5 wt % Re/TiO2 achieves 74% selectivity at 40% conversion, corresponding
to a drop in space-time yield from 65 to 16 gCH3OH·gRe
–1·h–1, respectively. X-ray absorption spectroscopy provided insights into
the structure of the active sites, while density functional theory
calculations revealed the effects of cluster size on the energy barriers
for H2 activation, CH3OH dissociation, and CH3OH desorption, all of which directly influence conversion
and selectivity. These results underscore the importance of balancing
cluster size for optimal catalyst performance and provide insights
into the design of efficient and selective catalysts for renewable
methanol production.

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