This work studies the effects of microscopic shape, crystallinity, and purity for the chemical reaction of CuO nanoparticles with hydrogen sulfide (H 2 S) to form copper sulfide. Several CuO nanomaterials were prepared via various synthesis techniques, including sol-gel, precipitation, hydrothermal synthesis in the presence of a polymer/surfactant, hydrolysis, and electrospinning, using different copper precursors (nitrate and acetate) and thermal treatment conditions (623 to 1023 K). The synthesized materials, which had different morphologies (flower-like, nanobelt-like, petal-like, spherical, and nanofibers) and physiochemical chemical properties (e.g., crystallite size, surface area and pore volume), were tested for their performance as low-temperature H 2 S sorbents in fixed-bed experiments at 294 K and 1 atm. Despite ostensible differences between the various properties of the tested sorbents, a strong linear relationship was recognized between the sorbents' sulfur removal capacity and crystallite size, independent of changes in the materials' microscopic shape and porosity. Specifically, it was observed that CuO materials with crystallite sizes larger than 26 nm exhibited low sulfur uptake capacities (less than 0.5 wt%) whereas capacity increased linearly (from 0.5 wt% to 12 wt%) with decreasing crystallite sizes for materials with CuO crystallites from 26 nm to 5 nm. In addition, the effect of residual carbon on CuO surfaces was also probed in this study, for the first time, showing that amorphous carbon inherently imparted by the use of a polymer, Polyvinylpyrrolidone (PVP) or poly(ethylene oxide) (PEO), or a surfactant, Poly(ethylene glycol)-block-poly(propylene glycol)-block-poly(ethylene glycol) (P123), in the synthesis procedure inhibits reaction and deleteriously impacts the H 2 S uptake capacity. This trend demonstrates that sorption capacity is strongly influenced by crystallite size and is independent of microscopic shape, surface area and mesopore structure. First principles atomistic simulations explain which surface O anions are most reactive and supportive to the observations.

The adsorption and activation of iodo-, bromo-, and chlorobenzene over gold catalysts of different size, including an extended Au(111) surface; three-dimensional Au 38 and Au 13 nanoparticles; and planar Au 7 , Au 6 , and Au 3 clusters has been systematically investigated by means of periodic density functional theory calculations. Several adsorption modes have been explored for each molecule, and the relative stability of such modes and the degree of C−X or C−C bond activation has been rationalized in terms of their molecular orbital distribution. Analysis of the electronic properties of the gold catalyst models allows the explanation of the influence of particle size on adsorption and activation energies in the subnanometer regime, while inclusion of dispersion interaction corrections becomes crucial for describing the reactivity of larger nanoparticles.

An understanding of the fundamentals of the reaction between CuO with trace amounts of H 2 S to form CuS products is critical for the optimal utilization of this process in sulfur removal applications. Unfortunately, CuS is a complex material, featuring various Cu 2-x S compounds (with 0 ≤ x ≤ 1), distorted crystal phases, and varying electronic structures and coordination environments of Cu and S ions. In this work, we combine ex situ and in situ X-ray absorption spectroscopy (XAS) at S and Cu K edges, fixed bed sorption experiments, DFT simulations, and other characterization techniques to speciate the CuS products formed at different temperatures (298−383 K) and from CuO sorbents with different crystallite sizes (2.8−40 nm). The results of our analysis identify the formation of a distorted CuS layer at the surface of CuO crystals with disulfide groups with shorter Cu−S bonds and higher delocalization of the positive charge of the Cu center into (S 1− ) 2 . This distorted CuS layer dominates the XAS signal at lower temperatures (298−323 K) and at the initial stages of sulfidation at higher temperatures (353 and 383 K) where conversion is low (<40%). First-principles atomistic simulations confirm the thermodynamic favorability of the formation of surface (S 1− ) 2 on both CuO (111) and (1̅ 11) surfaces, providing further support for our experimental observations. Furthermore, these simulations reveal that the presence of disulfide bonds stabilized surface hydroxyl groups, leading to lower Gibbs Free Energies of their surface migration.