Cu-based bimetallic catalysts are highly efficient in converting CO2 to methanol.cu catalyst However, the exact mechanism remains a mystery.cu catalyst The morphology of the active Cu surface, the presence or absence of second metal components and the interactions between the two elements are the major factors that determine the performance of the catalysts.cu catalyst A comprehensive understanding of these mechanisms is important for improving the efficiency and reducing the cost of the process. In this article, we investigate the underlying principles that govern the formation of the Cu-Zn/Al foam catalyst and its exceptional performance in CO2 reduction, focusing on the role of secondary metals and the interaction between them with the host copper surface.
The Cu-Zn/Al foam catalyst is a bimetallic catalyst that was prepared by co-precipitation of copper and zinc precursors in alkaline media.cu catalyst The bimetallic complex was characterized using various techniques, including infrared (IR) and X-ray photoelectron spectroscopy.cu catalyst The results showed that the morphology and the structure of the Cu-Zn bimetallic complex have a significant impact on the performance of the catalyst in CO2 reduction.cu catalyst The IR and X-ray photos reveal that the bimetallic complex contains multiple tetrahedral and octahedral Cu atoms. The tetrahedral Cu atoms have a higher binding energy with methanol than the octahedral atoms.
In addition, the co-precipitation process significantly affects the catalytic activity.cu catalyst The catalyst has a morphology similar to that of a needle with a very high surface area and is able to reduce CO2 to methanol efficiently.cu catalyst Moreover, the catalyst has superior selectivity in comparison with conventional bimetallic catalysts.
The CO2 reductive hydrogenation to methanol typically proceeds via the RWGS and formate pathways.cu catalyst The RWGS pathway involves a CO intermediate that is reduced to methanol via the hydrogenation of water, while the formate pathway proceeds through reductive insertion of methanol into the d-sites of Cu and Zn.cu catalyst
Recently, researchers from Weizmann and the Center for Functional Nanomaterials (CFN), a DOE Office of Science User Facility at Brookhaven, have compared three different morphological aspects of a commercially-active Cu-Zn bimetallic catalyst with respect to their effect on CO2RR performance.cu catalyst Infrared and X-ray characterizations revealed that the compressive strain of the Cu surfaces promotes a stronger interaction between methanol and the d-sites of Cu, leading to more methanol adhesion.cu catalyst
The authors have also shown that the octahedral structure of the active Cu surface increases the strength of the electric field between the d-sites and improves the selectivity for CO2 conversion.cu catalyst The octahedral structure is attributed to the formation of sharp needle structures with high curvature on the Cu-Zn surface.cu catalyst These structures are induced by a combination of the reactivity of the octahedral Cu-Zn interface and the interaction between the octahedral sites with methanol. In contrast, the tetrahedral structures on the other hand are less active and exhibit weaker electric fields. The results suggest that a mixture of the two types of morphologies could be optimal for promoting CO2 reduction in bimetallic catalysts. The octahedral structures may also contribute to the low activation energy of the Cu-Zn bimetallic catalyst and its ability to generate methanol with high methanol selectivity.
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