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Abstract: Co nanoislands were grown on (332) vicinal surface of Au in UHV using the e-beam evaporation technique. Scanning tunneling microscopy results reveal that Co deposition occurs following an islanding mode for θCo ranging from 0.17 to 0.64 ML. At low coverage nanoislands show a monolayer height, while at higher Co loadings, islands have a maximum bilayer height. XPS measurements rule out the possibility of alloy formation provided that binding energy of Co2p core lines remains unchanged as cobalt loading increases. Also, XPS data reveals that, when subjected to thermal annealing, Co atoms diffuse into Au crystal retaining its chemical nature as before the annealing. Finally, NO adsorption experiments show that Co nanostructures are partially oxidized upon adsorption, as evidenced by changes in core photoemission lineshapes of the Co2p lines. Also, NO adsorption seems to inhibit Co atom diffusion into Au crystal during moderate thermal treatment. [Copyright &y& Elsevier]

Exsolution is one of the most successful functionalization techniques to improve the catalytic activity of electrodes in solid oxide fuel and electrolyzer cells (SOFC/SOEC). The objective of this technique is to produce the highest possible number of metallic nanoparticles on the surface of a host-oxide, without significantly altering its structure. In this work, we compare three similar SOFC electrodes: STF (SrTi 0.3 Fe 0.7 O 3), STFN (Sr 0.93 Ti 0.3 Fe 0.63 Ni 0.07 O 3), and STFNC (Sr 0.93 Ti 0.3 Fe 0.56 Ni 0.07 Co 0.07 O 3), revealing that there is a significant difference between Ni–Fe/Ni–Co–Fe nanoparticle formation in STFN/STFNC and pure Fe0 particle formation in STF, which is evidenced by the size and amount of produced nanoparticles, but also by their anchoring to the host-oxide. The terms exsolution and particle segregation will be used, respectively, to distinguish these phenomena. Next, we explore two different reduction methods and observe that the characteristics of exsolution do not only depend on temperature, atmosphere and reduction times, but also on the reduction path taken to reach such conditions. [Display omitted] • Exsolution differs from particle segregation in the NP distribution, density, size and anchorage. • The characteristics of exsolved NPs are influenced by the hydrogen reduction path. • In-situ absorption spectroscopy is used to determine the exsolution temperature threshold. [ABSTRACT FROM AUTHOR]

Kohlenstoff‐gesättigte Pd0‐Nanopartikel mit ausgedehnter Phasengrenze zu ZrO2 bilden sich unter CH4‐Trockenreformierbedingungen aus einem intermetallischen Pd0Zr0‐Präkatalysator. Der resultierende, hochaktive Katalysatorzustand arbeitet bifunktionell: CO2 wird an oxidischen Phasengrenzplätzen effizient aktiviert, und PdxC gewährleistet die rasche Versorgung der Phasengrenze mit reaktiven C‐Atomen. ZrO2‐geförderte Methan‐Trockenreformierung auf PdxC: Kohlenstoff‐gesättigte Pd0‐Nanopartikel mit ausgedehnter Phasengrenze zu ZrO2 entstehen unter CH4‐Trockenreformierbedingungen aus einem intermetallischen Pd0Zr0‐Präkatalysator. Der so gebildete hochaktive Katalysatorzustand arbeitet bifunktionell: CO2 wird an oxidischen Phasengrenzplätzen effizient aktiviert, und PdxC gewährleistet die rasche Versorgung der Phasengrenze mit reaktiven C‐Atomen. [ABSTRACT FROM AUTHOR]

C‐saturated Pd0 nanoparticles with an extended phase boundary to ZrO2 evolve from a Pd0Zr0 precatalyst under CH4 dry reforming conditions. This highly active catalyst state fosters bifunctional action: CO2 is efficiently activated at oxidic phase boundary sites and PdxC provides fast supply of C‐atoms toward the latter. ZrO2‐promoted methane dry reforming on PdxC: C‐saturated Pd0 nanoparticles with extended phase boundary to ZrO2 evolve from a Pd0Zr0 precatalyst under CH4 dry reforming conditions. This highly active catalyst state fosters bifunctional action: CO2 is efficiently activated at oxidic phase boundary sites and PdxC provides fast supply of C‐atoms toward the latter. [ABSTRACT FROM AUTHOR]

We report on theoretical and experimental studies of the reactivity of ethylene with oxygen in two well-known oxygen induced surface reconstructions on silver, the p(2 × 1) reconstruction on the Ag(110) surface and the p(4 × 4) reconstruction on the Ag(111) surface. Density functional theory calculations demonstrate that ethylene can react with oxygen on both surfaces to form an oxametallacycle that can decompose into either ethylene oxide or a CO2 precursor, acetaldehyde. The activation energy associated with acetaldehyde formation is predicted to be 0.4 eV lower than that associated with epoxide formation on both surfaces, though we find lower barriers for all elementary steps on the p(4 × 4) reconstruction due to its unique structural dynamics. Our calculations predict these dynamics make the p(4 × 4) reconstruction active in acetaldehyde formation at room temperature. Experiments performed by exposing the p(4 × 4) reconstruction to ethylene at room temperature support this finding with CO2, the only carbonaceous product formed during temperature-programmed desorption. Our results unambiguously demonstrate that, alone, these oxygen reconstructions are not selective in ethylene epoxidation on silver. [ABSTRACT FROM AUTHOR]

Starting from subsurface Zr0-doped "inverse" Pd and bulk-intermetallic Pd0Zr0 model catalyst precursors, we investigated the dry reforming reaction of methane (DRM) using synchrotron-based near ambient pressure in-situ X-ray photoelectron spectroscopy (NAP-XPS), in-situ X-ray diffraction and catalytic testing in an ultrahigh-vacuum-compatible recirculating batch reactor cell. Both intermetallic precursors develop a Pd0–ZrO2 phase boundary under realistic DRM conditions, whereby the oxidative segregation of ZrO2 from bulk intermetallic PdxZry leads to a highly active composite layer of carbide-modified Pd0 metal nanoparticles in contact with tetragonal ZrO2. This active state exhibits reaction rates exceeding those of a conventional supported Pd–ZrO2 reference catalyst and its high activity is unambiguously linked to the fast conversion of the highly reactive carbidic/dissolved C-species inside Pd0 toward CO at the Pd/ZrO2 phase boundary, which serves the role of providing efficient CO2 activation sites. In contrast, the near-surface intermetallic precursor decomposes toward ZrO2 islands at the surface of a quasi-infinite Pd0 metal bulk. Strongly delayed Pd carbide accumulation and thus carbon resegregation under reaction conditions leads to a much less active interfacial ZrO2–Pd0 state. [ABSTRACT FROM AUTHOR]