Enhanced Methanol Synthesis from CO2 Hydrogenation Achieved by Tuning the Cu–ZnO Interaction in ZnO/Cu2O Nanocube Catalysts Supported on ZrO2 and SiO2

TL;DR

Researchers improved methanol production from CO2 by optimizing the interaction between copper and zinc oxide in a catalyst.

Contribution

They showed that a stable ZnO shell on Cu2O nanocubes enhances methanol synthesis and prevents catalyst deactivation.

Findings

High Zn loadings with stable ZnO shells increase methanol production compared to Zn-free particles.

Low Zn loadings result in metallic Zn species and no significant catalytic improvement.

ZnO overlayer thickness determines catalyst stability and performance during CO2 hydrogenation.

Abstract

The nature of the
Cu–Zn interaction and especially the role
of Zn in Cu/ZnO catalysts used for methanol synthesis from CO2 hydrogenation are still debated. Migration of Zn onto the
Cu surface during reaction results in a Cu–ZnO interface, which
is crucial for the catalytic activity. However, whether a Cu–Zn
alloy or a Cu–ZnO structure is formed and the transformation
of this interface under working conditions demand further investigation.
Here, ZnO/Cu2O core–shell cubic nanoparticles with
various ZnO shell thicknesses, supported on SiO2 or ZrO2 were prepared to create an intimate contact between Cu and
ZnO. The evolution of the catalyst’s structure and composition
during and after the CO2 hydrogenation reaction were investigated
by means of operando spectroscopy, diffraction, and ex situ microscopy methods. The Zn loading has a direct
effect on the oxidation state of Zn, which, in turn, affects the catalytic
performance. High Zn loadings, resulting in a stable ZnO catalyst
shell, lead to increased methanol production when compared to Zn-free
particles. Low Zn loadings, in contrast, leading to the presence of
metallic Zn species during reaction, showed no significant improvement
over the bare Cu particles. Therefore, our work highlights that there
is a minimum content of Zn (or optimum ZnO shell thickness) needed
to activate the Cu catalyst. Furthermore, in order to minimize catalyst
deactivation, the Zn species must be present as ZnOx and not metallic Zn or Cu–Zn alloy, which is undesirably
formed during the reaction when the precatalyst ZnO overlayer is too
thin.

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