9 September 2023
acetylene hydrochlorination active sites

Evidence of bifunctionality of carbons and metal atoms in catalyzed acetylene hydrochlorination

Carbon supports are ubiquitous components of heterogeneous catalysts for acetylene hydrochlorination to vinyl chloride, from commercial mercury-based systems to more sustainable metal single-atom alternatives. Their potential co-catalytic role has long been postulated but never unequivocally demonstrated. Herein, combining operando X-ray absorption spectroscopy with other spectroscopic and kinetic analyses, we evidence the bifunctionality of carbons and metal sites (Pt, Au, Ru) in the acetylene hydrochlorination catalytic cycle.

Read more
12 May 2023

Deciphering the Mechanism of Crystallization of UiO-66 Metal-Organic Framework

Zirconium-containing metal-organic framework (MOF) with UiO-66 topology is an extremely versatile material, which finds applications beyond gas separation and catalysis.  By means of in situ time-resolved high-resolution mass spectrometry, Zr K-edge X-ray absorption spectroscopy, magic-angle spinning nuclear magnetic resonance spectroscopy, and X-ray diffraction it is showed that the nucleation of UiO-66 occurs via a solution-mediated hydrolysis of zirconium chloroterephthalates, whose formation appears to be autocatalytic.

Read more
1 March 2023

Activity Trend Origin of Ethanol Oxidative Dehydrogenation over VOx/CeO2

Using operando time-resolved X-ray absorption spectroscopy, we investigated the origin of volcano-shaped ethanol oxidative dehydrogenation activity trend of VOx/CeO2 catalysts as a function of VOx surface coverage. Vanadium and cerium synergistically change their oxidation states during the catalytic cycle. The catalytic activity correlates with the concentration of reversible Ce4+/3+species.

Read more
21 February 2023
Pd Hydrides on Pd/Al2O3 in Liquid Environment

Preparation, Quantification, and Reaction of Pd Hydrides on Pd/Al2O3 in Liquid Environment

The ability to study in situ the formation and consumption of Pd hydrides (PdH) in liquid environments is a significant challenge hampering a deeper understanding of catalyzed liquid-phase hydrogenation reactions. Here, using quick scanning X-ray absorption spectroscopy (QEXAFS), we present a detailed kinetic study of Pd hydride formation and reactivity on Pd/Al2O3 in 2-propanol solvent. 

Read more
7 February 2023
Catalyst Layer Thickness Effects on Operando/In Situ Measurements

Spectroscopy vs. Electrochemistry: Catalyst Layer Thickness Effects on Operando/In Situ Measurements

Operando/in situ spectro-electrochemical studies often require high loadings and thick catalyst layers (CLs) leading to large ion- and mass-transport limitations. In this study we investigate PdH-formation in two Pd-catalysts with similar surface areas but drastically different morphologies. Our results unveil that the CL-thickness largely determines the PdH formation trends calling for the minimization of the CL-thickness in such experiments.

Read more
9 November 2022

Platinum-Iron(II) Oxide Sites Directly Responsible for Preferential Carbon Monoxide Oxidation at Ambient Temperature: An Operando X-ray Absorption Spectroscopy Study

Operando X-ray absorption spectroscopy revealed a linear correlation between the amount of oxidic Fe2+ and the ambient temperature activity of Pt−FeOx preferential carbon monoxide oxidation catalysts. The hydrogen prereduction temperature and pressure determines the amount of active Fe2+ sites for alumina- and silica-supported Pt−Fe catalysts. Catalyst deactivation is linked with the oxidation of these sites.

Read more
21 April 2022

Quantifying Photoinduced Polaronic and Thermal Distortions in Inorganic Lead Halide Perovskite Nanocrystals

The development of next-generation perovskite-based optoelectronic devices relies critically on the understanding of the interaction between charge carriers and the polar lattice in out-of-equilibrium conditions. While it has become increasingly evident for CsPbBr3 perovskites that the Pb–Br framework flexibility plays a key role in their light-activated functionality, the corresponding local structural rearrangement has not yet been unambiguously identified. In this work the photoinduced lattice changes were investigated using combination of time-resolved and temperature-dependent studies at Br K and Pb L3 X-ray absorption edges and ab initio simulations.

Read more
14 March 2022

Redox Dynamics of Active VOx Sites Promoted by TiOx during Oxidative Dehydrogenation of Ethanol Detected by Operando Quick XAS

Operando time-resolved V and Ti K-edge X-ray absorption near-edge spectroscopy, coupled with a transient experimental strategy, quantitatively showed that the formation of acetaldehyde over 5% V2O5/15% TiO2/SiO2 is kinetically coupled to the formation of a V4+ intermediate, while the formation of V3+ is delayed and 10–70 times slower. The low-coordinated nature of various redox states of VOx species (V5+, V4+, and V3+) in the 5% V2O5/15% TiO2/SiO2 catalyst is confirmed using the extensive database of V K-edge XANES spectra of standards and specially synthesized molecular crystals.

Read more
1 February 2022
4 and 5 coordinated Cu complexes

Exploring the role of structural distortions to obtain Cu photosensitizer with thousand times longer excited state lifetime

Cu diimine complexes present a noble metal free alternative to classical Ru, Re, Ir and Pt based photosensitizers in solution photochemistry, photoelectrochemical or dye-sensitized solar cells. Optimization of these dyes requires an understanding of factors governing the key photochemical properties: excited state lifetime and emission quantum yield. Using pump-probe XAS and DFT calculations we have explored the involvement of exciplex formation in the deactivation of the photoexcited state.

Read more