Mechanism of Ethylene Oxychlorination on Ceria

Atomic Cu-N-P-C Active Complex with Integrated Oxidation and Chlorination for Improved Ethylene Oxychlorination

Fine constructing the chemical environment of the central metal is vital in developing efficient single-atom catalysts (SACs). Herein, the atomically dispersed Cu on the N-doped carbon is modulated by introducing CuP moiety to CuNC SAC. Through fine-tuning with another heteroatom P, the Cu SAC shows the superior performance of ethylene oxychlorination. The Cu site activity of Cu-NPC is four times higher than the P-free Cu-NC catalyst and 25 times higher than the Ce-promoted CuCl₂ /Al₂ O₃ catalyst in the long-term test (>200 h). The selectivity of ethylene dichloride can be splendidly kept at ≈99%. Combined experimental and simulation studies provide a theoretical framework for the coordination of Cu, N, and P in the complex active center and its role in effectively catalyzing ethylene oxychlorination. It integrates the oxidation and chlorination reactions with superior catalytic performance and unrivaled ability of corrosive-HCl resistance. The concept of fine constructing with another heteroatom is anticipated to provide with inspiration for rational catalyst design and expand the applications of carbon-based SACs in heterogeneous catalysis.

Vinyl chloride catalytic combustion on Pt/CeO2: Tuning Pt chemical state to promote Cl removing

Supported Pt catalysts usually produce chlorinated byproducts during chlorinated volatile organic compounds (CVOCs) combustion, the removal of formed surface chlorine species is the key to improve the activity, selectivity and stability. In this paper, the Pt chemical state is adjusted by the interaction between Pt and CeO₂ through controlling the morphology of CeO₂, which further affects the catalytic performance of VC combustion. For Pt/CeO₂-octahedron, the weak interaction between Pt and CeO₂ results in the formation of PtO₂, facilities VC adsorption and C-Cl bonds cleavage and becomes a key active site to accommodate the dissociated Cl species. While the strong interaction leads to the formation of Pt_xCe_1-xO_2-σ solid solution on Pt/CeO₂-rod has relative lower ability in Cl species removal compared with PtO₂. Density functional theory (DFT) calculations also confirms that the introduced Pt species reduces the concentration of Cl species on the surface as well as the chlorinated-byproducts. Hence, Pt/CeO₂-octahedron outperformed Pt/CeO₂-rod and Pt/CeO₂-cube with 90% VC conversion at 280 °C. Furthermore, under the same VC conversion (90%), the concentration of chlorinated byproducts on Pt/CeO₂-octahedron was only 4% than that of Pt/CeO₂-rod.

Nanocomposite antimicrobials prevent bacterial growth through the enzyme-like activity of Bi-doped cerium dioxide (Ce1-xBixO2-δ)

Preventing bacterial adhesion on materials surfaces is an important problem in marine, industrial, medical and environmental fields and a topic of major medical and societal importance. A defense strategy of marine organisms against bacterial colonization relies on the biohalogenation of signaling compounds that interfere with bacterial communication. These reactions are catalyzed by haloperoxidases, a class of metal-dependent enzymes, whose activity can be emulated by ceria nanoparticles. The enzyme-like activity of ceria was enhanced by a factor of 3 through bismuth substitution (Ce1-xBixO2-δ). The solubility of Bi3+ in CeO2 is confined to the range 0 < x < 0.25 under quasi-hydrothermal conditions. The Bi3+ cations are located close to the nanoparticle surface because their ionic radii are larger than those of the tetravalent Ce4+ ions. The synthesis of Ce1-xBixO2-δ (0 < x < 0.25) nanoparticles was upscaled to yields of ∼50 g. The halogenation activity of Ce1-xBixO2-δ was demonstrated with phenol red assays. The maximum activity for x ≈ 0.2 is related to the interplay of the ζ-potential of surface-engineered Ce1-xBixO2-δ nanoparticles and their BET surface area. Ce0.80Bi0.20O1.9 nanoparticles with optimized activity were incorporated in polyethersulfone beads, which are typical constituents of water filter membrane supports. Although Ce1-xBixO2-δ nanoparticles are not bactericidal on their own, naked Ce1-xBixO2-δ nanoparticles and polyethersulfone/Ce1-xBixO2-δ nanocomposites showed a strongly reduced bacterial coverage. We attribute the decreased adhesion of the Gram-negative soil bacterium Pseudomonas aeruginosa and of Phaeobacter gallaeciensis, a primary bacterial colonizer in marine biofilms, to the formation of halogenated signaling compounds. No biocides are needed, H2O2 (formed in daylight) and halide are the only substrates required. The haloperoxidase-like activity of Ce1-xBixO2-δ may be a promising starting point for the development of environmentally friendly, "green" nanocomposites, when the use of conventional biocides is prohibited.

Quasi-degenerate states and their dynamics in oxygen deficient reducible metal oxides

The physical and chemical properties of oxides are defined by the presence of oxygen vacancies. Experimentally, non-defective structures are almost impossible to achieve due to synthetic constraints. Therefore, it is crucial to account for vacancies when evaluating the characteristics of these materials. The electronic structure of oxygen-depleted oxides deeply differs from that of the native forms, in particular, of reducible metal oxides, where excess electrons can localize in various distinct positions. In this perspective, we present recent developments from our group describing the complexity of these defective materials that highlight the need for an accurate description of (i) intrinsic vacancies in polar terminations, (ii) multiple geometries and complex electronic structures with several states attainable at typical working conditions, and (iii) the associated dynamics for both vacancy diffusion and the coexistence of more than one electronic structure. All these aspects widen our current understanding of defects in oxides and need to be adequately introduced in emerging high-throughput screening methodologies.

Dual catalyst system for selective vinyl chloride production via ethene oxychlorination

A dual system featuring ZrO₂-supported CeO₂ and Ca-doped Al₂O₃ catalysts enables the direct production of vinyl chloride via ethene oxychlorination.