High-pressure X-ray photoelectron spectroscopy of palladium model hydrogenation catalysts.Part 1: Effect of gas ambient and temperature

Abstract

In light of accumulating evidences highlighting the major role of operational conditions (gas composition, pressure, temperature) on the surface/bulk structure of catalytic materials, their characterization should involve more and more in-situ methods. We constructed a synchrotronbased high-pressure XPS (X-ray photoelectron spectroscopic) instrument, allowing us to investigate the surface and near-surface state of a catalyst in the mbar pressure range. We discuss here the surface characteristics of palladium samples as a function of gas-phase (hydrogen, oxygen) and temperature. We demonstrate that the surface region of catalytic materials behaves dynamically in its composition, always reflecting on its environment. For example, surface oxide can be formed on Pd(111) in oxygen which decomposes rapidly as the gas supply is switched off. The chemical nature of carbonaceous deposits depends also strongly on the operational conditions (gas-phase hydrogen, temperature). It is the first time that XPS investigation on palladium β-hydride was performed at RT. The possible drawbacks of using non-UHV setup e.g. fast carbon accumulation are also discussed.

Evolution of surface of Pd-Rh bimetallic nanocubes and its correlation with CO oxidation

“…This shift was likely due to the formation of Pd hydride when the catalyst was exposed to H 2 at an elevated temperature. The 0.3 eV upshift of binding energy of Pd 3d 5/2 for Pd hydride agreed well with literatures [45,46]. After H 2 treatment, the catalyst was cooled down to room temperature in H 2 .…”

On the Surface Chemistry of Iron Oxides in Reactive Gas Atmospheres

“…This contribution at 282.7 eV is assigned to atomically dispersed surface or subsurface carbon, similar to species observed in Pd cata- lysts. [20] At 350 8C, there is also an additional contribution to the O 1s spectrum at 529.0 eV, assigned to subsurface or atomically dispersed adsorbed oxygen species. [6] The morphology and texture of both samples were analyzed after treatment by N 2 physisorption and TEM ( Figure S1, Supporting Information).…”

“…[20] At 350 8C, there is also an additional contribution to the O 1s spectrum at 529.0 eV, assigned to subsurface or atomically dispersed adsorbed oxygen species. The carbonate species formed during CO/H 2 treatment slowly desorb at higher temperatures.…”

In situ synchrotron based x-ray techniques as monitoring tools for atomic layer deposition

“…37,38,[42][43][44][45] However, the development of high pressure XPS and ambient pressure XPS systems, as are currently pioneered for in situ studies during catalysis, could make in situ XPS possible under ALD conditions. 73 …”