Ye Xu

Understanding coordination-driven bond activation at metal oxide interfaces is essential for predicting the chemical stability of complex organic molecules. Here, we demonstrate that nanoceria efficiently drives the spontaneous, dark hydrolysis of sulfonylureas (amidosulfuron, metsulfuron-methyl, and nicosulfuron) via surface acid–base chemistry under ambient conditions. By combining liquid chromatography–mass spectrometry (LC-HRMS) with density functional theory (DFT) calculations, we show that the degradation proceeds through urea N–C bond cleavage. While the experimental identification of the degradation products confirms the overall hydrolytic pathway, DFT calculations are used to provide unique insights into the specific mechanism, proposing that the reaction is initiated by lattice-oxygen nucleophilic attack leading preferentially to sulfonyl-side N–C bond cleavage. Crucially, solid-state 31P MAS NMR spectroscopy using a trimethylphosphine oxide probe explicitly mapped the distribution and strength of surface Lewis and Brønsted acidic sites (oxygen vacancies and bridging hydroxyls). This provides a molecular-level link between ceria defect structures and their unique interfacial reactivity, highlighting the potential of tailored ceria surfaces to drive spontaneous chemical transformations without external energy inputs.

An empirical approach based on density functional theory (DFT)+U is proposed to provide adsorption energies for atoms of transition metals adsorbed on ceria that are more accurate than those found in the existing DFT literature. It involves applying an intermediate Hubbard U value to the Ce 4f states and another U value to the d states of the metal adatom that is optimized for each metal to match its calculated bulk cohesive energy with the experimental value. The results compare favorably with Campbell’s calorimetric measurements of metal adsorption heats on CeO2(111). Thus, this approach produces metal adsorption energies on ceria that are more accurate in both the single-atom and the bulk limits. Furthermore, it preserves a common reference for Ce so that calculations involving different metals adsorbed on ceria, e.g., bimetallic and multimetallic clusters, can be analyzed on the same footing.

This paper reports on a study of the adsorption and thermal stability of phenylphosphonic acid (PPA) adsorbed by physical vapor deposition on the surfaces of epitaxial cerium oxide films of different structure, stoichiometry and composition. Advanced analytical methods based on photoelectron spectroscopy combined with DFT calculations showed that the binding of PPA to cerium oxide is through the phosphonate group, while the decomposition temperature is defined by the nature of the oxide. Tridentate PPA species are present on all substrates (CeO₂, CeO_1.7, Ce₂O₃, and Ce₆WO₁₂), indicating a strong affinity of PPA for cerium oxide. The presence of vacancies in the oxide influences the molecular orientation. The phenyl ring of the PPA tilts about 10° more toward the surface plane of the reduced cerium oxides compared to CeO₂, which is attributed to the adsorption of phosphonate groups on Ce⁴⁺ and Ce³⁺ cations. The PPA adlayer is more stable on the surfaces with higher concentrations of oxygen vacancies and/or Ce³⁺ cations, increasing the temperature to initiate cleavage of the P-C bond from 225 °C for PPA/CeO₂ to 350 °C for the other systems. The PPA decomposition is signaled by the desorption of carbonaceous species above a critical temperature, while the phosphorus species remain stable even after annealing at 450 °C for all the cerium oxides. Overall, the results provide a comprehensive understanding of the binding of PPA to cerium oxides, allowing further development of functionalization strategies for inorganic materials by phosphonic acids.

The adsorption of 1,3-butadiene (BD, C₄H₆) on Cu(111) was studied experimentally with reflection absorption infrared spectroscopy (RAIRS) and temperature programmed desorption (TPD) and computationally with density functional theory (DFT).

Co nanoparticles (NPs) dispersed on ceria have been widely studied as active catalytic materials for many industrially relevant reactions. The detailed nature of such particles and the factors affecting their interaction with ceria remain to be better understood. In this study, a very low coverage (∼0.02 ML) of Co is deposited on a model CeO₂(111) thin-film surface and is examined using scanning tunneling microscopy (STM) and X-ray photoelectron spectroscopy (XPS). The Co NPs that nucleate on terrace sites grow with coverage in this range to a maximum size of ca. 40 Co atoms, with an average diameter and height of 16.1 and 1.1 Å, respectively. Global minimization of the structures of Co NPs consisting of up to 23 Co atoms on CeO₂(111) is performed based on the minima hopping algorithm and density functional theory (DFT) calculations, and the energetic and chemical properties of the resulting NPs are analyzed. While the theoretical findings are consistent with the STM observations on the strong Co-ceria interactions and the prevalence of oxidic Co species, some notable discrepancies are identified, including inconsistent aspect ratios and the existence of a low oxidation state Co^δ+ species. The combined experimental and theoretical findings provide new insights into Co NPs formed on ceria and identify areas requiring further investigation.

The vibrational properties of CO, O-2, and H-2 molecularly or dissociatively adsorbed on a CoCrFeNi(110) surface have been probed using high-resolution energy loss spectroscopy (HREELS) and modeled using density functional theory (DFT) calculations. Large (similar to 20 mm(3)) single-crystal, quaternary face-centered cubic CoCrFeNi was synthesized via a modified Czochralski technique. We show strong evidence that CO adsorbs primarily on bridge and on-top sites in compositionally varied local environments, which reflect the random, multielemental surface composition inherent in a high entropy alloy. A variation of adsorption sites is also found with oxygen, which exhibits two broad groups of modes. Comparison to previous photoemission and theoretical studies suggests that the higher energy modes consist primarily of local CrOx species, while the lower energy modes are due to oxygen atoms adsorbed on other metal sites. Unlike CO and O-2, HREELS upon H-2 adsorption shows only two much narrower modes and is consistent with atomic adsorption on 3-fold hollow sites. The hypothesized adsorption sites for all three species are directly corroborated by our DFT calculations.