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

Abstract

Many industrially important chemical transformations occur at the interface between a solid catalyst and liquid reactants. In situ and operando spectroscopies offer unique insight into the reactivity of such catalytically active solid–liquid interfaces.

Hydrogenolysis of Lignin-Derived Aromatic Ethers over Heterogeneous Catalysts

“…Mechanistic studies of catalysis at the solid–liquid–gas interface are challenging due to the low concentration of intermediate species and limited number of analytical techniques able to probe the interface . Attenuated total reflection infrared (ATR-IR) spectroscopy is one such powerful tool for probing the chemistry of both soluble and adsorbed reactants, products, and surface intermediates on a immobilized catalyst film.…”

“…Such problems may be partially mitigated by using bimetallic formulations to weaken adsorbed poisons and an improved understanding of deactivation pathways arising from different phenolic intermediates. Operando ATR-IR studies, performed using reaction cells capable of elevated pressure and temperature under flowing gas/liquid mixtures, will enable the nature/concentration of adsorbed reactive intermediates to be decoupled from spectator species, aided by the application of pulse modulation experiments …”

Challenges and Opportunities of Tip-Enhanced Raman Spectroscopy in Liquids

“…Biomolecules in particular could reveal their true nature in an aqueous environment. Additionally, heterogeneous catalytic reactions at the solid–liquid interface can be investigated in a new way to gain a deeper insight into electrochemical processes. ,,, Second, the heat from the laser source required for Raman spectroscopy is dissipated much better in water than in air . This reduces the degradation of heat-sensitive analytic compounds.…”

“…To get a localized electric field enhancement at the tip apex, the wavelength of the localized surface plasmon, which depends on the radius, the roughness, and the material of the tip, must match the wavelength of the excitation laser. , This results in a locally confined and enhanced electromagnetic field. , The intensity of the Raman spectra from a sample is proportional to the electric field. This means that if the tip apex is closer to the sample, the Raman signal will be significantly enhanced by a factor of 10 5 −10 12 . ,,− The chemical enhancement also contributes to the improved TERS, which is based on the interaction of the metallic particle on the tip apex and the molecular sample in the ground state, resonance contributions (resulting from the excited state of the sample in the electric field near the excitation wavelength), and charge transfer. ,, Through the lightning-rod effects and the LSPR (localized surface plasmon resonance), TERS provides a detection sensitivity down to the subnanometer length scale. , The substrate for TERS can be dielectric (e.g., Al 2 O 3 or SiO 2 , no plasmonic properties) or a noble metal (e.g., Au, Ag or Cu, plasmonic properties, gap-mode) . For example, the electronic and catalytic properties of bimetallic (Pd/Pt on Au (111)) surfaces with phenyl isocyanide were studied with a 3 nm resolution .…”

Short-Lived Interfaces in Energy Materials

“…Other analysis techniques utilize photons to circumvent the challenges associated with electrons (e.g., X-ray absorption spectroscopy, de Groot, 2001;Newton and Dent, 2013;Nachtegaal et al, 2017). An established optical technique is diffusive reflectance infrared Fourier transform spectroscopy (DRIFTS Terreni et al, 2020;Negahdar et al, 2020). In general, operando investigations using probes with small mean free path lengths are usually limited to changes of the surface of materials, or adsorbates on it (Li and Gong, 2020).…”