Conversion of Isobutene and Formaldehyde to Diol using Praseodymium-Doped CeO2 Catalyst

Advanced Biological Applications of Cerium Oxide Nanozymes in Disease Related to Oxidative Damage

Due to their excellent catalytic activities, cerium oxide nanoparticles have promise as biological nanoenzymes. A redox reaction occurs between Ce3+ ions and Ce4+ ions during which they undergo conversion by acquiring or losing electrons as well as forming oxygen vacancies (or defects) in the lattice structure, which can act as antioxidant enzymes and simulate various enzyme activities. A number of cerium oxide nanoparticles have been engineered with multienzyme activities, including catalase, superoxide oxidase, peroxidase, and oxidase mimetic properties. Cerium oxide nanoparticles have nitric oxide radical clearing and radical scavenging properties and have been widely used in a number of fields of biology, including biomedicine, disease diagnosis, and treatment. This review provides a comprehensive introduction to the catalytic mechanisms and multiple enzyme activities of cerium oxide nanoparticles, along with their potential applications in the treatment of diseases of the brain, bones, nerves, and blood vessels.

Boosting the ammonia synthesis activity of ceria-supported Ru catalysts achieved through trace Pr addition

The amount of dopant used in conventional cases for improving catalytic performance is higher than 5%. In this work, a strategy to enhance the ammonia synthesis performance of a Ru/CeO2 catalyst by using trace Pr (0.1 mol%) is reported. Owing to the improvement of oxygen defects, Ce3+ concentration and interfaced Ru species, the hydrogen adsorption was enhanced, and the desorption of hydrogen species would be promoted. As a result, Ru/CeO2 with 0.1 mol% Pr shows 1.4 times higher ammonia synthesis rate and excellent stability compared to Ru/CeO2 or the sample with high Pr loading (50 mol% Pr). This study provides a new idea for the design of high-efficiency ammonia synthesis catalysts.

Regulated Li2 S Deposition toward Rapid Kinetics Li-S Batteries by a Separator Modified by CeO2 -Decorated Porous Carbon Nanostructure

Although the high-energy-density lithium sulfur (Li-S) battery has been considered one of the most promising next-generation energy storage technology, the practical applications have been plagued by the sluggish reaction kinetics and the shuttle effect of lithium polysulfides intermediates. Here, to address the above issues, the authors report a novel separator modified by CeO₂ -decorated porous carbon nanostructure (CeO₂ /KB/PP). Benefiting from the strong polar surface and large specific surface area, (CeO₂ -doped Ketjen Black) delivers efficient chemical adsorption toward lithium polysulfides. Moreover, rich oxygen vacancies of CeO₂ provide abundant active sites to expedite lithium polysulfides conversion and regulate deposition and nucleation of Li₂ S. Taking advantage of these merits, the battery with the CeO₂ /KB/PP separator exhibits remarkable electrochemical performance, including low-capacity decay of only 0.06% per cycle over 1000 cycles at 2 C and superior rate capability of 627 mAh g^-1 at 3 C. Even with a high sulfur loading of 6.6 mg cm^-2 , the battery can achieve a high areal capacity of 3.6 mAh cm^-2 after 100 cycles. This work provides a new application of rare-earth-based materials to facilitate Li-S batteries.

Green Synthesis of 3-Hydroxybutyraldehyde from Acetaldehyde Catalyzed by La-Ca-Modified MgO/Al2O3

3-hydroxybutyraldehyde (3-HBA) is mainly employed to synthesize 1,3-BDO (1,3-butanediol), which is one of the most important components in cosmetics moisturizers. In this study, a series of composite oxide catalysts were prepared by bringing alkaline earth metal Ca and rare earth metal La to the composite oxide MgO/Al2O3, which were made through the co-precipitation method. These catalysts were applied in the synthesis of 3-HBA through acetaldehyde (AcH) condensation. The structure, texture, and acidic properties of these catalysts were characterized using various characterization methods, and the effects of catalyst composition, reaction temperature, reaction pressure, and residence time on the conversion of AcH were investigated as well. The results showed that the introduction of Ca and La weakened the acidic property and enhanced the basic property, which favored the AcH condensation to synthesize 3-HBA. At a temperature of 20 °C, pressure of 200 kPa, and residence time of 70 min, 0.5%La-2.3%Ca-2MgO/Al2O3 exhibited a better catalytic activity, and the conversion of AcH reached 95.89%. The selectivity and yield of 3-HBA were 92.08% and 88.30%, respectively. The stability test indicated that the high AcH conversion could be maintained for 5 h.

Enhanced catalytic performance of atomically dispersed Pd on Pr-doped CeO2 nanorod in CO oxidation

Single-atom noble metal catalysts have been widely studied for catalytic oxidation of CO. Regulating the coordination environment of single metal atom site is an effective strategy to improve the intrinsic catalytic activity of single atom catalyst. In this work, single atom Pd catalyst supported on Pr-doped CeO₂ nanorods was prepared, and the performance and nature of Pr-coordinated atomic Pd site in CO catalytic oxidation are systematically investigated. The structure characterization using AC-HAADF-STEM, EXAFS, XRD and Raman spectroscopy demonstrate the formation of single atom Pd site and abundant surface oxygen vacancies on the surface of Pr-doped CeO₂ nanorod. With the combination of the XPS characterization and DFT calculations, the oxidation state of Pd on Pr-doped CeO₂ nanorod is determined lower than that on CeO₂ nanorod. The turnover frequency of CO oxidation is markedly increased from 8.4 × 10^-3 to 31.9 × 10^-3 s with Pr-doping at 130 ºC and GHSV of 70,000 h^-1. Combined with kinetic studies, DRIFT and DFT calculations, the doped-Pr atoms reduced the formation energy of oxygen vacancies and generate more oxygen vacancies around the atomically dispersed Pd sites on the surface of cerium oxide, which reduces the dissociation energy of oxygen, thereby accelerating the reaction rate of CO oxidation.

Effective conversion of CO2 into light olefins over a bifunctional catalyst consisting of La-modified ZnZrOx oxide and acidic zeolite

Addition of proper amount of La produces more oxygen vacancies on ZnZrOx(nLa), hence promoting the formation of methanol. Upon coupling with H-SAPO-34, ZnZrOx(0.3La)/H-SAPO-34 catalyst shows a C2=–C4= selectivity in hydrocarbons as high as 83.2%.

Intermediates of Carbon Monoxide Oxidation on Praseodymium Monoxide Molecules: Insights from Matrix-Isolation IR Spectroscopy and Quantum-Chemical Calculations

Identifying reaction intermediates in gas-phase investigations will provide understanding for the related catalysts in fundamental aspects including bonding interactions of the reaction species, oxidation states (OSs) of the anchored atoms, and reaction mechanisms. Herein, carbon monoxide (CO) oxidation by praseodymium monoxide (PrO) molecules has been investigated as a model reaction in solid argon using matrix-isolation IR spectroscopy and quantum-chemical calculations. Two reaction intermediates, OPr(η¹-CO) and OPr(η²-CO), have been trapped and characterized in argon matrixes. The intermediate OPr(η²-CO) shows an extremely low C-O stretching band at 1624.5 cm^-1. Quantum-chemistry studies indicate that the bonding in OPr(η¹-CO) is described as "donor-acceptor" interactions conforming to the Dewar-Chatt-Duncanson motif. However, the bonding in OPr(η²-CO) results evidently from a combination of dominant ionic forces and normal Lewis "acid-base" interactions. The electron density of the singly occupied bonding orbital is strongly polarized to the CO fragment in OPr(η²-CO). Electronic structure analysis suggests that the two captured species exhibit Pr(III) OSs. Besides, the pathways of CO oxidation have been discussed.

Selective oxidation of 5-hydroxymethylfurfural to 2,5-furandicarboxylic acid over Au/CeO2 catalysts: the morphology effect of CeO2

A morphological effect of Au/CeO₂ catalysts in 5-hydroxymethylfurfural (HMF) oxidation.

Capping experiments reveal multiple surface active sites in CeO2 and their cooperative catalysis

Understanding of surface active sites (SAS) of CeO₂ is crucial to its catalytic applications. In the present study, we have employed capping experiments, DFT calculations, and spectroscopic characterization to study pristine CeO₂ catalyst. We find that multiple SAS coexist on the CeO₂ surface: oxygen vacancies as redox sites and the coordinately unsaturated Ce cations near the oxygen vacancies and the neighboring oxygen ions as Lewis acid–base sites. Dimethylsulfoxide (DMSO), pyridine, and benzoic acid are utilized to cap the redox sites, Lewis acid sites, and base sites, respectively. Selective capping on the redox site does not have much effect on the acid–base catalysis, and vice versa, indicating the distinct surface proximity and independent catalysis of these SAS. We draw attention to a relationship between the well-known redox sites and the surface Lewis acid and Lewis base pairs on CeO₂ surface, which are responsible for driving various heterogeneous catalytic reactions.

Capping with pyridine, benzoic acid, and DMSO in catalytic reactions reveals the locations of surface active sites of CeO₂.

Selectively creating oxygen vacancies on PrCe/SiO2 catalysts for the transformation of a furfural–acetone adduct into a functionalized 1,3-diene

Oxygen vacancies were selectively created on PrCe/SiO₂ for efficient transformation of a furfural–acetone adduct into a functionalized 1,3-diene.

Facile synthesis of hierarchically porous carbonaceous materials derived from olefin/aldehyde precursors using silica as templates

Porous carbon is exceptionally useful, but it remains a great challenge to develop a facile route to prepare porous carbon materials with hierarchical structure and enhanced porosity. This work demonstrates a novel synthetic pathway for hierarchical carbonaceous materials (HCM) using isobutene and formaldehyde as carbon precursors via silica templates impregnated with phosphorus. Different from the traditional nanocasting method, the formation of the carbon structure is caused by heavy coke deposits on the solid catalyst in the course of the olefin/aldehyde vapor reaction. The coke-derived carbonaceous materials indicated by transmission electron microscopy (TEM) and nitrogen adsorption–desorption measurement are hierarchically mesoporous structures with a large surface area (971 m² g⁻¹) and pore volume (1.91 cm³ g⁻¹). We have demonstrated for the first time that the olefin/aldehyde reaction may provide a convenient route to develop a porous carbon texture. The newly developed method may lead to porous carbon having scientific and technological importance in adsorption and catalysis applications.

This work presents a novel procedure to synthesize hierarchically porous carbonaceous materials by coke formation.

Formaldehyde–isobutene Prins condensation over MFI-type zeolites

H-ZSM-5 was identified as the most efficient catalyst for the liquid phase Prins condensation of formaldehyde with isobutene to 3-methyl-3-buten-1-ol and subsequently isoprene.