Ni5Ga3 Catalysts for CO2 Reduction to Methanol: Exploring the Role of Ga Surface Oxidation/reductions on Catalytic Activity

Journal Article · Mon Jun 15 00:00:00 EDT 2020 · Applied Catalysis B: Environmental

DOI:https://doi.org/10.1016/j.apcatb.2019.118369· OSTI ID:1755168

Gallo, Alessandro ^[1]; Snider, Jonathan L. ^[2]; Sokaras, Dimosthenis ^[2]; Nordlund, Dennis ^[3]; Kroll, Thomas ^[3]; Ogasawara, Hirohito ^[4]; Kovarik, Libor ^[5]; Duyar, Melis S. ^[2]; Jaramillo, Thomas F. ^[2]

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1. University of California, Santa Barbara
2. Stanford University
3. SLAC National Accelerator Laboratory
4. Stanford Synchrotron Radiation Laboratory
5. BATTELLE (PACIFIC NW LAB)

Ad-Ni5Ga3/SiO2 catalyst, which is highly active and stable for thermal CO2 hydrogenation to methanol, was investigated to understand its surface dynamics during reaction conditions. The catalyst was prepared, tested and characterized using a multitude of techniques, including ex-situ XRD, TEM, H2-TPR, CO chemisorption and in-situ ETEM and APXPS. The formation of Ga2O3 upon air exposure was observed and the consequences on catalytic activity were investigated. Results revealed that upon air exposure Ga migrates from the subsurface region to the surface of the nanoparticles forming a Ga-oxide shell surrounding a metallic core. The oxide shell can be reduced completely at high temperatures and the temperature of the reduction activation treatment plays a crucial role on the catalytic activity. This air exposure-reduction procedure results in a redistribution of the Ga species in the surface/subsurface region, promoted by a higher Ga affinity for oxygen. XRD analysis of the post-reaction samples provide evidence for the partial transformation of a Ni5Ga3 intermetallic phase into a Ni-rich Ni3Ga phase. APXPS data indicate that the Ni-rich phase forms in the subsurface region. A Ga-rich phase exists on the surface, where the Ni/Ga ratio reaches 2/3 upon activation in hydrogen. At low reduction temperatures an amorphous Ga2O3 shell remains, indicating a promotion effect on methanol synthesis activity.

• Research Organization: Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
• Sponsoring Organization: USDOE
• DOE Contract Number: AC05-76RL01830
• OSTI ID: 1755168
• Report Number(s): PNNL-SA-146889
• Journal Information: Applied Catalysis B: Environmental, Vol. 267
• Country of Publication: United States
• Language: English

Related Subjects

Ni-Ga
intermetallic
methanol synthesis
in-situ characterization
Ga2O3
utilization