Cerium dioxide (CeO2, ceria) is becoming an ubiquitous constituent in catalytic systems for a variety of applications. 2016 sees the 40th anniversary since ceria was first employed by Ford Motor Company as an oxygen storage component in car converters, to become in the years since its inception an irreplaceable component in three-way catalysts (TWCs). Apart from this well-established use, ceria is looming as a catalyst component for a wide range of catalytic applications. For some of these, such as fuel cells, CeO2-based materials have almost reached the market stage, while for some other catalytic reactions, such as reforming processes, photocatalysis, water-gas shift reaction, thermochemical water splitting, and organic reactions, ceria is emerging as a unique material, holding great promise for future market breakthroughs. While much knowledge about the fundamental characteristics of CeO2-based materials has already been acquired, new characterization techniques and powerful theoretical methods are dee...

Fundamentals and Catalytic Applications of CeO2-Based Materials

Copper–ceria as one of the very active catalysts for oxidation reactions has been widely investigated in heterogeneous catalysis. In this work, copper oxide (1 wt % Cu loading) deposited on both ceria nanospheres with a {111}/{100}-terminated surface (1CuCe-NS) and with nanorod exposed {110}/{100} faces (1CuCe-NR) have been prepared for the investigation of crystal plane effects on CO oxidation. Various structural characterizations, especially including aberration-corrected scanning transmission electron microscopy (Cs-STEM), X-ray absorption fine structure (XAFS) technique, and in situ diffuse reflectance infrared Fourier transform spectroscopy (in situ DRIFTS), were used to precisely determine the structure and status of the catalysts. It is found that the copper oxides were formed as subnanometer clusters and were uniformly dispersed on the surface of the ceria support. The results from XAFS combined with the temperature-programmed reduction technique (H2-TPR) reveal that more reducible CuOx clusters w...

Crystal Plane Effect of Ceria on Supported Copper Oxide Cluster Catalyst for CO Oxidation: Importance of Metal–Support Interaction

Metal ions play significant roles in numerous fields including chemistry, geochemistry, biochemistry, and materials science. With computational tools increasingly becoming important in chemical research, methods have emerged to effectively face the challenge of modeling metal ions in the gas, aqueous, and solid phases. Herein, we review both quantum and classical modeling strategies for metal ion-containing systems that have been developed over the past few decades. This Review focuses on classical metal ion modeling based on unpolarized models (including the nonbonded, bonded, cationic dummy atom, and combined models), polarizable models (e.g., the fluctuating charge, Drude oscillator, and the induced dipole models), the angular overlap model, and valence bond-based models. Quantum mechanical studies of metal ion-containing systems at the semiempirical, ab initio, and density functional levels of theory are reviewed as well with a particular focus on how these methods inform classical modeling efforts. F...

Metal Ion Modeling Using Classical Mechanics

Copper-containing cerium oxide materials have received considerable attention both in catalysis and electro-catalysis fields due to their unique physicochemical characteristics in conjunction to their lower cost compared to noble metals (NMs)-based catalysts. Nowadays, it is well documented that the complex Copper–Ceria interactions (either geometric or electronic) have a key role on the catalytic performance. Hence, considerable efforts have been devoted on the understanding and the fine-tuning of metal–oxide interactions. Despite the growing progress in the field, several crucial issues related to the influence of: i) particle’s shape and size, ii) active site’s chemical state, iii) charge transfer between interfacial sites, and iv) intrinsic defects (e.g., surface oxygen vacancies) on the interfacial activity are still under investigation. This survey summarizes the recent advances in the last 10 years on the fundamental origin of Copper–Ceria interactions and their implications on the catalytic activity. The insights lately obtained by means of: i) ex situ advanced characterization techniques, ii) in situ sophisticated studies (e.g., operando techniques), iii) theoretical analysis (e.g., DFT calculations), and iv) innovative probing approaches (such as the inverse CeO2/CuO model system) are provided. The state-of-the-art catalytic applications of CuO/CeO2 binary oxides (water gas shift (WGS) reaction, preferential oxidation (PROX) of CO, CO2 hydrogenation, selective catalytic reduction (SCR), N2O decomposition, etc.) in relation to the aforementioned aspects are discussed. Some guidelines towards the fine-tuning of the surface chemistry of CuO/CeO2 catalysts for real life energy and environmental application are provided.

The role of Copper–Ceria interactions in catalysis science: Recent theoretical and experimental advances

This year marks the 350th anniversary of the discovery of phosphorus by the alchemist Hennig Brand. However, this element was not included in the p-block of the periodic table until more recently. 2019 also marks the 150th anniversary of the preliminary tabular arrangement of the elements into the periodic system by Mendeleev. Of the 63 elements known in 1869, almost one-third of them belonged to what ultimately became the p-block, and Mendeleev predicted the existence of both gallium and germanium as well. The elements of the p-block have a disparate and varied history. Their chemical structure, reactivity, and properties vary widely. Nevertheless, in recent years, a better understanding of trends in p-block reactivity, particularly the behavior of those elements not typically found in biological systems, has led to a promising array of emerging applications, highlighted herein.

https://science.sciencemag.org/content/sci/363/6426/479.full.pdf

Frontiers in molecular p-block chemistry: From structure to reactivity.

Copper-ceria is one of the very active catalysts for the preferential oxidation of carbon monoxide (CO-PROX) reaction, which is also a typical system in which the complexity of copper chemistry is clearly exhibited. In the present manuscript, copper–ceria catalysts with different Cu contents up to 20 wt % supported on CeO2 nanorods were synthesized by a deposition–precipitation (DP) method. The as-prepared samples were characterized by various structural and textural detections including X-ray diffraction (XRD), Vis-Raman, transmission electron microscopy (TEM), ex situ/in situ X-ray absorption fine structure (XAFS), and temperature-programmed reduction by hydrogen (H2-TPR). It has been confirmed that the highly dispersed copper oxide (CuOx) clusters, as well as the strong interaction of Cu-[Ox]-Ce structure, were the main copper species deposited onto the ceria surface. No separated copper phase was detected for both preoxidized and prereduced samples with the Cu contents up to 10 wt %. The fresh copper–...

Highly Dispersed Copper Oxide Clusters as Active Species in Copper-Ceria Catalyst for Preferential Oxidation of Carbon Monoxide

Electrostatic Catalyst Generated from Diazadiborinine for Carbonyl Reduction

We present a new protocol for deriving force constant parameters that are used in molecular mechanics (MM) force fields to describe the bond-stretching, angle-bending, and dihedral terms. A 3 × 3 partial matrix is chosen from the MM Hessian matrix in Cartesian coordinates according to a simple rule and made as close as possible to the corresponding partial Hessian matrix computed using quantum mechanics (QM). This partial Hessian fitting (PHF) is done analytically and thus rapidly in a least-squares sense, yielding force constant parameters as the output. We herein apply this approach to derive force constant parameters for the AMBER-type energy expression. Test calculations on several different molecules show good performance of the PHF parameter sets in terms of how well they can reproduce QM-calculated frequencies. When soft bonds are involved in the target molecule as in the case of secondary building units of metal-organic frameworks, the MM-optimized geometry sometimes deviates significantly from the QM-optimized one. We show that this problem is rectified effectively by use of a simple procedure called Katachi that modifies the equilibrium bond distances and angles in bond-stretching and angle-bending terms. © 2016 Wiley Periodicals, Inc.

Partial hessian fitting for determining force constant parameters in molecular mechanics.

Building upon our recently developed partial Hessian fitting (PHF) method (Wang et al., J. Comput. Chem. 2016, 37, 2349), we formulated and implemented two other rapid force-field parameterization schemes called full Hessian fitting (FHF) and internal Hessian fitting (IHF), and comparisons were made among these three parameterization schemes to assess their performance. FHF minimizes deviation between the Hessian matrices in Cartesian coordinates computed by quantum mechanics (QM) and molecular mechanics (MM), to determine the best possible MM force-constant parameters. While PHF requires step-by-step fittings of 3 × 3 partial Hessian matrices, FHF compares the lower triangular part of the QM and MM Hessian matrices, which allows simultaneous determination of all force-constant parameters. In addition to this simple FHF scheme, IHF was developed such that it considers the Hessian matrices in redundant internal coordinates, where all possible internal coordinates that arise from the user-defined interatomic connectivity are utilized. The results show that IHF performs best overall, followed by PHF and then FHF. Python-based programing codes were developed to automate various tedious steps involved in the parameterization processes. © 2017 Wiley Periodicals, Inc.

Ruixing Wang

Papers

Highly Dispersed Copper Oxide Clusters as Active Species in Copper-Ceria Catalyst for Preferential Oxidation of Carbon Monoxide

Electrostatic Catalyst Generated from Diazadiborinine for Carbonyl Reduction

Partial hessian fitting for determining force constant parameters in molecular mechanics.

Analytical hessian fitting schemes for efficient determination of force‐constant parameters in molecular mechanics