Activating a Cu/ZnO : Al Catalyst – Much More than Reduction: Decomposition, Self‐Doping and Polymorphism

Abstract

ature, time) might yield to a maximum of kinetically stabilized high energy surfaces without phase separation and the most active catalyst.

Mechanistic Study of Carbon Dioxide Hydrogenation over Pd/ZnO‐Based Catalysts: The Role of Palladium–Zinc Alloy in Selective Methanol Synthesis

“…9658 eV.T his feature we may associate with the formation of either,r educed zinc (Zn 0 ), and therefore the presence of palladium-zinc alloys, and/or the presence of zinc oxygen vacancies. [34] Thed ouble peak structure of the derivative spectra (Figure 3e)could be indicative of the presence of both Zn 0 and Zn II containing phases in each of the catalyst systems.Wemight further intuit, from the relative magnitudes of the pre-edge feature (Figure 3d), that the proportions of the two zinc states are markedly different across the samples,w ith significantly higher levels of reduced zinc being indicated for PdZn/SiO 2 and PdZn/Al 2 O 3 compared to PdZn/ZnO/SiO 2 .…”

Cu−Zn Alloy Formation as Unfavored State for Efficient Methanol Catalysts

“…The manifold character of the synergism between Cu and ZnO focusses generally on surface alloying, surface ZnO species and the interfacial contact . We could recently show that this intimate metal/oxide contact is already developed during the multi‐event nature of the activation process . Within this study, we report on the impact of the activation temperature on the performance of a Cu/ZnO : Al (in atom‐% 69Cu/29Zn/2Al, XRF Table S1) catalyst in CH 3 OH formation (8CO 2 /6CO/59H 2 /27He, 30 bar, 230 °C).…”

“…Heating the sample in reductive atmosphere leads to a decrease in whiteline intensity at 9669 eV, indicating a slightly reduced character of Zn (II‐x). Between 250 °C and 350 °C, the differences in the Zn K‐edge XANES spectra seem to be negligible, however, the corresponding derivative spectra shown in Figure (b) reveal further details: The decrease in the whiteline intensity and its shift towards lower energies at ∼9662.5 eV (1 s –4 p transition) in the derivative spectra is interpreted as a change in the coordination environment of a small fraction of Zn 2+ (octahedral→tetrahedral) . This is coupled to an increase in covalence and loss of ionicity (ZnCO 3 →ZnO), respectively, and stays stable up to 350 °C (complete decomposition of residual carbonate already at 250 °C).…”

“…The activation of a Cu/ZnO : Al catalyst itself is a complex process, involving HT‐CO 3 decomposition, Cu reduction, ZnO polymorphism, self‐doping and charge transfer. This intriguing interplay leads to the formation of an intimate interfacial Cu−ZnO contact and was subject of a separate, recently published study . Here, we focus on structural changes upon exceeding 250 °C under reductive atmosphere (5 % H 2 in He).…”

Mechanistic Study of Carbon Dioxide Hydrogenation over Pd/ZnO‐Based Catalysts: The Role of Palladium–Zinc Alloy in Selective Methanol Synthesis

“…9658 eV. This feature we may associate with the formation of either, reduced zinc (Zn 0 ), and therefore the presence of palladium–zinc alloys, and/or the presence of zinc oxygen vacancies [34] . The double peak structure of the derivative spectra (Figure 3 e) could be indicative of the presence of both Zn 0 and Zn II containing phases in each of the catalyst systems.…”