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We employ UV/Vis Diffuse Reflectance spectroscopy directly coupled with a packed bed flow reactor to extract quantitative kinetic information. We use as a show-case the Cu II /Cu I redox dynamics during the reduction half cycle of the NH 3 -Selective Catalytic Reduction (SCR) on Cu-CHA catalysts. Our measurements enable quantification of the fraction of oxidized Cu, reconstructed by Multivariate Curve Resolution (MCR) together with monitoring of the gas-phase evolution during the reaction. These data both on the dynamics of the gas-phase and of the active site oxidation state have been used to assess the reduction half cycle rate equation and estimate the rate constant. Our results in terms of reaction orders and kinetic constant are in line with previous findings in the literature. Overall, our results demonstrate that the combined analysis of the UV spectra and of the gas-phase dynamics provides converging and unparalleled kinetic insight: this approach effectively resolves ambiguities concerning RHC kinetics and mechanism. More in general, this work provides evidence that operando spectroscopy can be used to extract quantitative kinetic information on catalytic cycles., (© 2024 Wiley-VCH GmbH.)

A mechanism for carbon deposition and its impact on the reaction kinetics of Methane Dry Reforming (MDR) using Rhodium-based catalysts is presented. By integrating Raman spectroscopy with kinetic analysis in an operando-annular chemical reactor under strict chemical conditions, we discovered that carbon deposition on a Rh/α-Al 2 O 3 catalyst follows a nucleation-growth mechanism. The dynamics of carbon aggregates at the surface is found to be ruled by the CO 2 /CH 4 ratio and the inlet CH 4 concentration. The findings elucidate the spatiotemporal development of carbon aggregates on the catalyst surface and their effects on catalytic performance. Furthermore, the proposed mechanism for carbon formation shows that the influence of CO 2 on MDR kinetics is an indirect result of carbon accumulation over time frames exceeding the turnover frequency, thus reconciling conflicting reports in the literature regarding CO 2 's kinetic role in MDR., (© 2024 Wiley-VCH GmbH.)

Given the strong influence of surface structure on the reactivity of heterogeneous catalysts, understanding the mechanisms that control crystal morphology is an important component of designing catalytic materials with targeted shape and functionality. Herein, we employ density functional theory to examine the impact of growth media on NiO crystal faceting in line with experimental findings, showing that molten-salt synthesis in alkali chlorides (KCl, LiCl, and NaCl) imposes shape selectivity on NiO particles. We find that the production of NiO octahedra is attributed to the dissociative adsorption of H 2 O, whereas the formation of trapezohedral particles is associated with the control of the growth kinetics exerted by ordered salt structures on high-index facets. To our knowledge, this is the first observation that growth inhibition of metal-oxide facets occurs by a localized ordering of molten salts at the crystal-solvent interface. These findings provide new molecular-level insight on kinetics and thermodynamics of molten-salt synthesis as a predictive route to shape-engineer metal-oxide crystals., (© 2021 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH.)

Though largely influencing the efficiency of a reaction, the molecular-scale details of the local environment of the reactants are experimentally inaccessible hindering an in-depth understanding of a catalyst's reactivity, a prerequisite to maximizing its efficiency. We introduce a method to follow individual molecules and their largely changing environment during a photochemical reaction. The method is illustrated for a rate-limiting step in a photolytic reaction, the dissociation of CO 2 on two catalytically relevant surfaces, Ag(100) and Cu(111). We reveal with a single-molecule resolution how the reactant's surroundings evolve with progressing laser illumination and with it their propensity for dissociation. Counteracting processes lead to a volcano-like reactivity. Our unprecedented local view during a photoinduced reaction opens the avenue for understanding the influence of the products on reaction yields on the nanoscale., (© 2021 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH.)