Using model catalysts with well-defined particle sizes and morphologies to elucidate questions regarding catalytic activity and stability has gained more interest, particularly utilizing colloidally prepared metal(oxide) particles. Here, colloidally synthesized iron oxide nanoparticles (FexOy-NPs, size ∼7 nm) on either a titania (FexOy/TiO2) or a silica (FexOy/SiO2) support were studied. These model catalyst systems showed excellent activity in the Fischer-Tropsch to olefin (FTO) reaction at high pressure. However, the FexOy/TiO2 catalyst deactivated more than the FexOy/SiO2 catalyst. After analyzing the used catalysts, it was evident that the FexOy-NP on titania had grown to 48 nm, while the FexOy-NP on silica was still 7 nm in size. STEM-EDX revealed that the growth of FexOy/TiO2 originated mainly from the hydrogen reduction step and only to a limited extent from catalysis. Quantitative STEM-EDX measurements indicated that at a reduction temperature of 350 °C, 80% of the initial iron had dispersed over and into the titania as iron species below imaging resolution. The Fe/Ti surface atomic ratios from XPS measurements indicated that the iron particles first spread over the support after a reduction temperature of 300 °C followed by iron oxide particle growth at 350 °C. Mössbauer spectroscopy showed that 70% of iron was present as Fe2+, specifically as amorphous iron titanates (FeTiO3), after reduction at 350 °C. The growth of iron nanoparticles on titania is hypothesized as an Ostwald ripening process where Fe2+ species diffuse over and through the titania support. Presynthesized nanoparticles on SiO2 displayed structural stability, as only ∼10% iron silicates were formed and particles kept the same size during in situ reduction, carburization, and FTO catalysis.

Au-Cu bimetallic thin films with controlled composition were fabricated by magnetron sputtering co-deposition, and their performance for the electrocatalytic reduction of CO ₂ was investigated. The uniform planar morphology served as a platform to evaluate the electronic effect isolated from morphological effects while minimizing geometric contributions. The catalytic selectivity and activity of Au-Cu alloys was found to be correlated with the variation of electronic structure that was varied with tunable composition. Notably, the d-band center gradually shifted away from the Fermi level with increasing Au atomic ratio, leading to a weakened binding energy ofCO, which is consistent with low CO coverage observed in CO stripping experiments. The decrease in theCO binding strength results in the enhanced catalytic activity for CO formation with the increase in Au content. In addition, it was observed that copper oxide/hydroxide species are less stable on Au-Cu surfaces compared to those on the pure Cu surface, where the surface oxophilicity could be critical to tuning the binding strength ofOCHO. These results imply that the altered electronic structure could explain the decreased formation of HCOO ^- on the Au-Cu alloys. In general, the formation of CO and HCOO ^- as main CO ₂ reduction products on planar Au-Cu alloys followed the shift of the d-band center, which indicates that the electronic effect is the major governing factor for the electrocatalytic activity of CO ₂ reduction on Au-Cu bimetallic thin films.

ZnS shelling of I-III-VI₂ nanocrystals (NCs) invariably leads to blue-shifts in both the absorption and photoluminescence spectra. These observations imply that the outcome of ZnS shelling reactions on I-III-VI₂ colloidal NCs results from a complex interplay between several processes taking place in solution, at the surface of, and within the seed NC. However, a fundamental understanding of the factors determining the balance between these different processes is still lacking. In this work, we address this need by investigating the impact of precursor reactivity, reaction temperature, and surface chemistry (due to the washing procedure) on the outcome of ZnS shelling reactions on CuInS₂ NCs using a seeded growth approach. We demonstrate that low reaction temperatures (150 °C) favor etching, cation exchange, and alloying regardless of the precursors used. Heteroepitaxial shell overgrowth becomes the dominant process only if reactive S- and Zn-precursors (S-ODE/OLAM and ZnI₂) and high reaction temperatures (210 °C) are used, although a certain degree of heterointerfacial alloying still occurs. Remarkably, the presence of residual acetate at the surface of CIS seed NCs washed with ethanol is shown to facilitate heteroepitaxial shell overgrowth, yielding for the first time CIS/ZnS core/shell NCs displaying red-shifted absorption spectra, in agreement with the spectral shifts expected for a type-I band alignment. The insights provided by this work pave the way toward the design of improved synthesis strategies to CIS/ZnS core/shell and alloy NCs with tailored elemental distribution profiles, allowing precise tuning of the optoelectronic properties of the resulting materials.

A simple amphiphilic surfactant containing a mono-quaternary ammonium head group (N -methylpiperidine) is effective in imparting substantial mesoporosity during synthesis of SSZ-13 and ZSM-5 zeolites. Highly mesoporous SSZ-13 prepared in this manner shows greatly improved catalytic performance in the methanol-to-olefins reaction compared to bulk SSZ-13.