Surface X-ray studies of catalytic clean technologies

Abstract

The rational design of new heterogeneous catalysts for clean chemical technologies can be accelerated by molecular level insight into surface chemical processes. In situ methodologies, able to provide time-resolved and/or pressure dependent information on the evolution of reacting adsorbed layers over catalytically relevant surfaces, are therefore of especial interest. Here we discuss recent applications of surface X-ray techniques to surface-catalysed oxidations, (de)hydrogenations, C-C coupling, dehalogenation and associated catalyst restructuring, and explore how these may help to shape future sustainable chemistry.

Creating and mastering nano-objects to design advanced catalytic materials

“…There is increasing evidence by advanced in situ studies [135][136][137][138] that a dynamic surface reconstruction of the active sites occurs in many industrial relevant reactions. Although these observations were mainly made for supported metal particles, it is reasonably expected that also occurs in metal oxides.…”

Shining light on the solid–liquid interface:in situ/operandomonitoring of surface catalysis

“…5-20 keV) under real-world environments, in contrast to e.g. X-ray photoelectron spectroscopy (XPS), wherein vacuum or low pressures are necessary, 57 due to the relatively weak attenuation of X-rays versus low energy electrons. However, although the penetrating nature of (particularly hard) X-rays is beneficial for investigating catalysts within fluids, and active sites at buried interfaces or within porous architectures, a caveat is that transmission and fluorescence XAS detection are not surface sensitive, indeed spectral contributions may be a summation over several thousand nanometers of material.…”

“…XPS is an inherently surface sensitive technique due to the relatively short inelastic mean free path (λ) of emitted photoelectrons, which usually span 0.1 to 2 nm, and hence has found routine application in heterogeneous catalysis where surface phenomena dominate. 57,128 2.4.1 Applications and limitations. Since XPS requires detection of an emitted photoelectron, it was historically performed under ultra-high vaccum (UHV) conditions, rendering it inefficient as a probe of solid-liquid interfaces where vapour pressures would compromise the necessary vacuum.…”

Mechanistic Studies of Alcohol Selective Oxidation

“…X-ray-based methods in particular can provide detailed insight into chemical composition and environment of active components and reacting adsorbates [140][141][142]. Quick and dispersive XAS have the capability to monitor dynamic changes in catalyst structure under reaction conditions (so-called operando spectroscopy) and have been applied to alcohol selox over Pd [96,[143][144][145][146], Pt [67,147], and Ru [147] nanoparticles.…”