Promotion versus Poisoning in Copper–Gallium-Based CO2-to-Methanol Hydrogenation Catalysts

Cu–Ga-based CO2-to-methanol hydrogenation catalysts display a range of catalytic performance, depending on their preparation. In a previous study, we successfully prepared a highly active and selective Cu–Ga catalyst using surface organometallic chemistry. However, the specific location of active Ga has remained unknown because Ga was present as GaIII sites dispersed on silica and Ga alloyed with copper in bimetallic nanoparticles. Here, we investigated how the Ga/Cu ratio and Ga speciation affect the catalytic activity. Using surface organometallic chemistry, we prepared a series of silica-supported 3–6 nm Cu1–xGaxOy nanoparticles with a range of xGa. In these nanoparticles, Cu is always fully metallic, while Ga is partially alloyed with Cu in the core and partially oxidized on the surface. By minimizing the fraction of GaIII species dispersed on silica, we could focus on the reactivity of the bimetallic nanoparticles. The thus-developed materials display a volcano-type activity behavior, where methanol formation is promoted when xGa < 0.13–0.18 and is suppressed at higher values, indicating a poisoning of the catalysts. Alternative materials containing bimetallic nanoparticles coexisting with Ga species dispersed on silica follow a similar trend when considering only the fraction of Ga in the nanoparticles. In situ X-ray absorption spectroscopy shows that GaOx species over the promoted Cu0.93Ga0.07–SiO2 catalyst are much more redox active than those over the poisoned Cu0.77Ga0.23–SiO2. In situ infrared spectroscopy detected methoxy groups over the promoted Cu0.93Ga0.07–SiO2 catalyst, while no formate or methoxy species could be observed over poisoned Cu0.77Ga0.23–SiO2. The absence of formate and methoxy surface species and irreversible oxidation of GaOx over poisoned catalysts suggest encapsulation of Cu by the GaOx shell resulting in low activity.


Dr Olga Safonova
Operando spectroscopy group
Swiss Light Source, Paul Scherrer Institute
5232 Villigen-PSI, Switzerland
Telephone: +41 56 310 58 05

Original Publication

Boundary Conditions for Promotion versus Poisoning in Copper–Gallium-Based CO2-to-Methanol Hydrogenation Catalysts

Jan L. Alfke, María Tejeda-Serrano, Sumant Phadke, Andrei Tereshchenko, Terry Z. H. Gani, Lukas Rochlitz, Seraphine B. X. Y. Zhang, Lin Lin, Christophe Copéret*, and Olga V. Safonova*

ACS Catalysis,  31 May 2024