Ambient Pressure Oxidation-Reduction Dynamics of Cu/ZnO Model Catalysts for Methanol Synthesis

14 September 2022, Version 1

Abstract

We investigated Cu/ZnO model catalysts for methanol synthesis to obtain an atomistic picture of activation and deactivation processes under in situ oxidizing and reducing conditions. We have investigated Cu nanoparticles with different shapes and aspect ratios grown epitaxially on basal and vicinal ZnO surfaces at elevated gas pressures by high energy grazing incidence X-ray diffraction and ambient pressure X-ray photoelectron spectroscopy (AP-XPS). We find that the Cu nanoparticles are fully oxidized to Cu2O under atmospheric conditions at room temperature. During oxidation, they maintain their epitaxy on basal ZnO (000-1) surfaces, whereas on the vicinal ZnO (10-14) surface, the nanoparticles undergo a coherent tilt. We find that the oxidation process is fully reversible under H2 flow at 500 K, resulting in predominantly well-aligned nanoparticles on the basal surfaces, whereas a random orientation is preferred for the (10-14) surface. Under CO2 flow, no diffraction signal from the nanoparticles is detected, pointing to their completely disordered state. The AP-XPS results are in line with the formation of CuO. The analysis of the substrate crystal truncation rods evidences the stability of basal ZnO surfaces under all gas conditions. No proof for Cu-Zn alloy formation is found. Scanning electron microscopy images show that massive mass transport has set in, leading to the formation of larger agglomerates, which is detrimental to the catalyst’s performance.

Keywords

Cu/ZnO
methanol
model catalyst
vicinal
active sites
in situ
ambient pressure

Supplementary materials

Title
Description
Actions
Title
Supporting Information: Ambient Pressure Oxidation-Reduction Dynamics of Cu/ZnO Model Catalysts for Methanol Synthesis
Description
SI contains: - further HE-GIXRD H-L maps - fitting of the XRR data and parameter tables - Cu2O/vZnO interface models - conversions of ZnO Bragg peaks from bulk coordinates to (10-14) surface coordinates - SEM images - UHV-XPS data - HE-GIXRD data of CTR's obtained for Zn-bZnO and O-bZnO
Actions

Comments

Comments are not moderated before they are posted, but they can be removed by the site moderators if they are found to be in contravention of our Commenting Policy [opens in a new tab] - please read this policy before you post. Comments should be used for scholarly discussion of the content in question. You can find more information about how to use the commenting feature here [opens in a new tab] .
This site is protected by reCAPTCHA and the Google Privacy Policy [opens in a new tab] and Terms of Service [opens in a new tab] apply.