期刊
ACS APPLIED MATERIALS & INTERFACES
卷 13, 期 29, 页码 35113-35123出版社
AMER CHEMICAL SOC
DOI: 10.1021/acsami.1c07510
关键词
strong metal-support interaction; ZnOx/Pd(111); irreducible oxide; hydroxylation; Pd-Zn alloy; scanning tunneling microscopy; density functional calculations
资金
- National Science Foundation [1804712]
- U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences [DE-AC02-06CH11357]
- Div Of Chem, Bioeng, Env, & Transp Sys
- Directorate For Engineering [1804712] Funding Source: National Science Foundation
The study investigated the interfacial interaction of well-defined ultrathin ZnOxHy films on Pd(111) under varying gas-phase conditions, revealing that zinc oxide, as an irreducible oxide, can spread on metal surfaces and show an SMSI-like behavior in the presence of hydrogen. A mixed canonical-grand canonical phase diagram was developed to bridge the gap between UHV conditions and true SMSI environments, revealing that certain ZnOxHy films with stoichiometries that do not exist in bulk are stabilized by Pd in the presence of hydrogen. This study proposes that SMSI metal nanoparticle encapsulation for irreducible oxide supports such as ZnO involves both surface (hydroxy)oxide and surface alloy formation, depending on the environmental conditions.
Structural and chemical transformations of ultrathin oxide films on transition metals lie at the heart of many complex phenomena in heterogeneous catalysis, such as the strong metal-support interaction (SMSI). However, there is limited atomic-scale understanding of these transformations, especially for irreducible oxides such as ZnO. Here, by combining density functional theory calculations and surface science techniques, including scanning tunneling microscopy, X-ray photoelectron spectroscopy, high-resolution electron energy loss spectroscopy, andlow-energy electron diffraction, we investigated the interfacial interaction of well-defined ultrathin ZnOxHy films on Pd(111) under varying gas-phase conditions[ultrahigh vacuum (UHV), 5 x 10(-7) mbar of O-2, and a D-2/O-2 mixture] to shed light on the SMSI effect of irreducible oxides. Sequential treatment of submonolayer zinc oxide films in a D-2/O-2 mixture (1:4) at 550 K evoked reversible structural transformations from a bilayer to a monolayer and further to a Pd-Zn near-surface alloy, demonstrating that zinc oxide, as an irreducible oxide, can spread on metal surfaces and show an SMSI-like behavior in the presence of hydrogen. A mixed canonical-grand canonical phase diagram was developed to bridge the gap between UHV conditions and true SMSI environments, revealing that, in addition to surface alloy formation, certain ZnOxHy films with stoichiometries that do not exist in bulk are stabilized by Pd in the presence of hydrogen. Based on the combined theoretical and experimental observations, we propose that SMSI metal nanoparticle encapsulation for irreducible oxide supports such as ZnO involves both surface (hydroxy)oxide and surface alloy formation, depending on the environmental conditions.
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