Search

The computational complexity required to find the low energy structures for large oligomers of supported metal oxides remains a barrier to understanding their reactivity at intermediate to high coverages. To circumvent this challenge, we use machine learning potentials (MLP) to perform high throughput screening of vanadium oxide clusters supported on titanium dioxide for intermediate coverages up to a monolayer. The most stable structures obtained from an MLP are then optimized with density functional theory to examine their electronic properties. We find that even at coverages up to 3/4 of a monolayer, it is possible to form highly active monomeric species when there is a vacancy in the TiO2support and an oxygen atom adsorbed on the surface. The extent of dissociation of supported oligomeric vanadia and hence the concentration of monomeric vanadium oxide species depend on the concentration of oxygen vacancy–oxygen adatom pairs.

PtSn bimetallic catalysts are among the best-performing propane dehydrogenation (PDH) catalysts. However, understanding these catalysts remains limited due to the intricate nature of bimetallic systems and their dynamic structural evolution under reaction conditions. To address this challenge, we employ various in situ/operandotechniques, including UV-vis, CO diffuse reflective infrared Fourier transform spectroscopy (CO-DRIFTS), near ambient pressure X-ray photoelectron spectroscopy (NAP-XPS), and operandoX-ray absorption spectroscopy (XAS), to elucidate the structural dynamics of PtSn/SiO2catalysts under reduction and working conditions. Our investigation reveals that the interactions between Pt, Sn, and SiO2support are strongly influenced by the synthesis procedures and the initial catalyst structure. Exposure to H2causes a reversible Sn–OH formation observed by modulation excitation spectroscopy (MES). A sequentially impregnated catalyst with a nominal Pt : Sn ratio of 1 : 3 and a co-impregnated catalyst with a ratio of 1 : 2 exhibit optimal performance for PDH. Despite distinct synthesis procedures and bulk structures, these two catalysts exhibit comparable surface properties and PDH performance, attributed to the dynamic migration of Sn species and formation of a Pt-rich metal surface under reductive atmospheres.

A comprehensive framework is developed for the study of the molecular configuration of (MoOx)nspecies supported on pure anatase-TiO2as well as on mixed CeO2–TiO2. The framework first employs the equilibrium deposition filtration method to molecularly control the nature of the active molybdenum sites on the surface of the supports while ensuring loadings below monolayer coverage. Next, we deploy in situ Raman spectroscopic characterization in combination with the isotope 18O2/16O2exchange technique for the molecular-level identification of (MoOx)nsurface configurations. Results show that the distribution of (MoOx)nspecies depends strongly on the pH of the precursor solution and that on both the TiO2and CeO2–TiO2supports, the dominant configuration pertains to a mono-oxo arrangement. Distinctive spectral behaviors of a multicomponent band in the vicinity of the ∼900 cm–1band for supported (MoOx)non CeO2–TiO2are assigned to two separate vibrational modes that involve different anchoring Mo-O-Supportbonds. The framework also extends to the coupling of pulse experimentation with operando Raman spectroscopy (transient operando spectroscopy) to distinguish the reactivity among oxygen sites. From the rationalization of combined results, we show that upon H2exposure, the initial removal of surface oxygen predominantly happens at the terminal (Mo═O) site, which is then followed by the breaking of some Mo-O-Supportbonds. This mechanism allows for oxygen swapping between different Mo–O bonds during reoxidation.

Metal-metal oxide inverse catalysts are valuable in diverse applications, but selecting pairs is challenging. Here, we investigate the role of metal cores (Pt, Ru, Rh, Pd, and Ni) in the formation and dynamics of Brønsted acid sites on the WOxoverlayer on carbon. By in situand ex situcharacterizations, probe chemistry kinetics, and density functional theory (DFT) calculations, we demonstrate that metals with varying work functions promote WOxdispersion and modulate the Brønsted acidity of submonolayer WOxon metal surfaces by tuning the deprotonation energy (DPE) and oxidation state of WOx. The metal core affects the water splitting and hydroxylation of WOx. Water splitting on Ru-WOxis more thermodynamically favorable and has a higher dehydration rate than that on Ni-WOx, leading to an activity enhancement as a result of an increased H2pulsing frequency. This study provides insights into optimizing inverse catalysts.

The structure of supported MoOx/Al2O3catalysts is investigated using ab initio molecular dynamics (AIMD) and density-functional theory (DFT). Phase diagrams were computed to understand the hydroxylation coverage as a function of the temperature, H2O partial pressure, and MoOxloading. We relate the shifts in experimental Raman vibrational frequencies under hydrated conditions to hydrogen bonding interactions and the MoOxanchoring location. We showcase that the use of AIMD as a benchmark for DFT can provide insight into how, under certain hydrated conditions, DFT excels as an inexpensive method for computing vibrational frequencies, while, under dehydrated conditions, it is susceptible to the largest errors. Additionally, to facilitate the analysis of the hydroxyl region of experimental infrared spectra, we compute the power spectra of individual hydroxyls and see a strong relationship between OH stretching frequencies and the surrounding coordination environment, which are also impacted by anchored MoOx. We compare computational and experimental IR and Raman spectra of catalysts synthesized herein under the same conditions.