How Does the Ni-Ga Alloy Structure Tune Methanol Productivity and Selectivity?

Area of Science:

• Heterogeneous catalysis
• Materials science
• Chemical engineering

Background:

• Catalyst structure-activity relationships are crucial for optimizing chemical reactions.
• Nickel-gallium (Ni-Ga) alloys are investigated for CO2 hydrogenation.
• Understanding the role of alloy phases and support interactions is key.

Purpose of the Study:

• To investigate the influence of Ni-Ga alloy phase structure on CO2 hydrogenation to methanol.
• To correlate catalyst structure with activity and selectivity.
• To elucidate the mechanism of methanol formation over different Ni-Ga phases.

Main Methods:

• Synthesis of SiO2-supported Ni-Ga catalysts with distinct phases (α-Ni, α-Ni9Ga, α'-Ni3Ga, δ-Ni5Ga3) via hydrothermal deposition-precipitation.
• Characterization using operando X-ray pair distribution function analysis and X-ray absorption spectroscopy.
• Activity and selectivity measurements for CO2 hydrogenation; Density Functional Theory (DFT) calculations.

Main Results:

• Catalysts α'-Ni3Ga/SiO2 and δ-Ni5Ga3/SiO2 exhibited significantly higher methanol formation rates (27x) compared to α-Ni9Ga/SiO2 and α-Ni/SiO2.
• α'-Ni3Ga/SiO2 demonstrated the highest methanol selectivity (71%), challenging previous assumptions about its catalytic performance.
• DFT calculations revealed that Ni-rich step sites in α'-Ni3Ga stabilize key intermediates (HCOO*, CH3O*), while GaOx species mitigate CO* adsorption, promoting methanol formation.

Conclusions:

• The specific Ni-Ga alloy phase structure is critical for high methanol productivity and selectivity in CO2 hydrogenation.
• The presence of GaOx species plays a vital role in modulating catalyst electronic properties and stabilizing reaction intermediates.
• This work provides insights into designing advanced catalysts for selective methanol synthesis by controlling metallic and oxidic species.