Modification of the oxygen storage capacity of CeO2–ZrO2 mixed oxides after redox cycling aging

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.

Catalytic Steam Reforming of Biomass-Derived Oxygenates for H2 Production: A Review on Ni-Based Catalysts

The steam reforming of ethanol, methanol, and other oxygenates (e.g., bio-oil and olive mill wastewater) using Ni-based catalysts have been studied by the scientific community in the last few years. This process is already well studied over the last years, being the critical point, at this moment, the choice of a suitable catalyst. The utilization of these oxygenates for the production of “green” H2 is an interesting alternative to fuel fossils. For this application, Ni-based catalysts have been extensively studied since they are highly active and cheaper than noble metal-based materials. In this review, a comparison of several Ni-based catalysts reported in the literature for the different above-mentioned reactions is carried out. This study aims to understand if such catalysts demonstrate enough catalytic activity/stability for application in steam reforming of the oxygenated compounds and which preparation methods are most adequate to obtain these materials. In summary, it aims to provide insights into the performances reached and point out the best way to get better and improved catalysts for such applications (which depends on the feedstock used).

Olive Mill Wastewater Valorization through Steam Reforming Using Multifunctional Reactors: Challenges of the Process Intensification

Olive oil mill wastewater (OMW) is a polluting stream derived from the production of olive oil and is a source of environmental pollution; this is relevant in many countries around the world, but particularly in all the Mediterranean region where major producers are located. In this effluent, several pollutants are present—namely, sugars, fatty acids, and polyphenols, among others. Nowadays, to reduce the pollutant load, several treatment techniques are applied, but these technologies have numerous cost and efficiency problems. For this reason, the steam reforming of the OMW (OMWSR) presents as a good alternative, because this process decreases the pollutant load of the OMW and simultaneously valorizes the waste with the production of green H2, which is consistent with the perspective of the circular economy. Currently, the OMWSR is an innovative treatment alternative in the scientific field and with high potential. In the last few years, some groups have studied the OMWSR and used innovative reactor configurations, aiming to improve the process’ effectiveness. In this review, the OMW treatment/valorization processes, the last developments on catalysis for OMWSR (or steam reforming of similar species present in the effluent), as well as the last advances on OMWSR performed in multi-functional reactors are addressed.

Characterization of Surface Species during Benzene Hydroxylation over a NiO-Ceria-Zirconia Catalyst

NiO/ceria-zirconia (CZ) is a promising catalyst for the selective oxidation of benzene, as the Lewis-acidic NiO clusters can activate C-H bonds and the redox-active CZ support can activate O₂ and supply active oxygen species for the reaction. In this study, we used transmission in situ infrared (IR) spectroscopy to examine surface species formed from benzene, water, oxygen, phenol, and catechol on a NiO/CZ catalyst. The formation of surface species from benzene and phenol was compared at different temperatures in the range of 50-200 °C in the presence and absence of water vapor. We also examined the role of the NiO clusters and the CZ support during benzene activation by comparing the surface species formed on NiO-CZ with those formed on a Ni-free CZ support and on a NiO/SiO₂ catalyst. The spectrum of surface species from dosing benzene at 180 °C provides evidence for C-H bond activation. Specifically, the observation of C-O stretching vibrations indicates the formation of phenolate species. Introduction of water enhances these IR signals and introduces several additional peaks, indicating that a variety of different surface species are formed. These results show that NiO/CZ could catalyze direct conversion of benzene to phenol.

Catalytic ketonization of palmitic acid over a series of transition metal oxides supported on zirconia oxide-based catalysts

Modification of a ZrO2 based catalyst with selected transition metals dopants has shown promising improvement in the catalytic activity of palmitic acid ketonization. Small amounts of metal oxide deposition on the surface of the ZrO2 catalyst enhances the yield of palmitone (16-hentriacontanone) as the major product with pentadecane as the largest side product. This investigation explores the effects of addition of carefully chosen metal oxides (Fe2O3, NiO, MnO2, CeO2, CuO, CoO, Cr2O3, La2O3 and ZnO) as dopants on bulk ZrO2. The catalysts are prepared via a deposition-precipitation method followed by calcination at 550 °C and characterized by XRD, BET-surface area, TPD-CO2, TPD-NH3, FESEM, TEM and XPS. The screening of synthesized catalysts was carried out with 5% catalyst loading onto 15 g of pristine palmitic acid and the reaction carried out at 340 °C for 3 h. Preliminary studies show catalytic activity improvement with addition of dopants in the order of La2O3/ZrO2 < CoO/ZrO2 < MnO2/ZrO2 with the highest palmitic acid conversion of 92% and palmitone yield of 27.7% achieved using 5% MnO2/ZrO2 catalyst. Besides, NiO/ZrO2 exhibits high selectivity exclusively for pentadecane compared to other catalysts with maximum yield of 24.9% and conversion of 64.9% is observed. Therefore, the changes in physicochemical properties of the dopant added ZrO2 catalysts and their influence in palmitic acid ketonization reaction is discussed in detail.

Yb3+, Er3+ Codoped Cerium Oxide Upconversion Nanoparticles Enhanced the Enzymelike Catalytic Activity and Antioxidative Activity for Parkinson's Disease Treatment

Oxidative stress plays an important role in Parkinson's disease (PD) and is considered a therapeutic target for PD. However, most therapeutic antioxidants show limitations due to their low reactive oxygen species (ROS) catalytic properties and low crossing of blood-brain barrier. Herein, the antioxidative activity of Yb3+ and Er3+ double-doped CeO2-x (Yb/Er/CeO2-x) upconversion nanoparticles (UCNPs) is obtained for PD treatment. Doping of Yb3+ and Er3+ ions increases oxygen vacancies, which leads to higher enzymelike catalytic activities compared to CeO2-x nanoparticles alone. Tyrosine hydroxylase protein and glial fibrillary acidic protein expression in substantia nigra and striatum as well as the open-field activity test indicates that Yb/Er/CeO2-x is effective for treatment of PD. The activities of glutathione peroxidase and total antioxidant capacity increase and the production of ROS decreases with Yb/Er/CeO2-x UCNP treatment compared with MPTP-induced injury. This indicates that the mechanism of PD treatment is to catalyze ROS products. There have been no reports to date on the usage of Yb/Er/CeO2-x as an antioxidant for PD treatment. Yb/Er/CeO2-x UCNPs cross the blood-brain barrier and exhibit biocompatibility and antioxidant catalytic properties, which decrease the ROS and effectively help in treating PD.

Production of renewable oleo-furan surfactants by cross-ketonization of biomass-derived furoic acid and fatty acids

Production of an oleo-furan surfactant precursor from biomass-derived furoic acid and fatty acid via cross-ketonization.

Potential of Ceria-Zirconia-Based Materials in Carbon Soot Oxidation for Gasoline Particulate Filters

ZrO2 and Ce0.8Zr0.2O2 mixed oxides were prepared and tested in the oxidation of carbon soot at different oxygen partial pressures and degrees of catalyst/soot contact to investigate their activity under typical gasoline direct injection (GDI) operating conditions. Under reductive atmospheres, generation of oxygen vacancies occurs in Ce0.8Zr0.2O2, while no reduction is observed on ZrO2. Both materials can oxidize carbon under high oxygen partial pressures; however, at low oxygen partial pressures, the presence of carbon can contribute to the reduction of the catalyst and formation of oxygen vacancies, which can then be used for soot oxidation, increasing the overall performance. This mechanism is more efficient in Ce0.8Zr0.2O2 than ZrO2, and depends heavily on the interaction and the degree of contact between soot and catalyst. Thus, the ability to form oxygen vacancies at lower temperatures is particularly helpful to oxidize soot at low oxygen partial pressures, and with higher CO2 selectivity under conditions typically found in GDI engine exhaust gases.

One-pot synthesis of cerium and praseodymium co-doped carbon quantum dots as enhanced antioxidant for hydroxyl radical scavenging

The antioxidant activity of ceria nanoparticles is tightly regulated by size distribution and heteroatom doping. Inspired by this rule, cerium and praseodymium codoped carbon quantum dots (Ce/Pr-CQDs) were synthesized through the one-pot hydrothermal carbonization method. Taking intrinsic advantage of CQDs, the resultant Ce/Pr-CQDs exhibited uniform and ultra-small morphology with an average size of 2.8 nm, which led to an increased proportion of Ce³⁺. In addition, the doping of Pr into Ce-CQDs improved the redox properties. As we expected, the Ce/Pr-CQDs possessed enhanced hydroxyl radical scavenging properties compared with the cerium-doped carbon quantum dots (Ce-CQDs). Furthermore, Ce/Pr-CQDs with favorable biocompatibility and negligible cytotoxicity are readily internalized into cytoplasm, decreasing the level of reactive oxygen species (ROS). Taken together, the resultant Ce/Pr-CQDs displayed great potential for applications relating to oxidative-stress-associated disease.

Novel Fe-doped CePO4 catalyst for selective catalytic reduction of NO with NH3: The role of Fe3+ ions

Novel Fe-doped CePO₄ (Fe_xCe_1-x) catalyst was firstly successfully synthesized via a simple co-precipitation method and demonstrated excellent NH₃-SCR performance in comparison with FePO₄ and CePO₄. In order to study the promoting effects of Fe³⁺ ion on the NH₃-SCR activity of CePO₄ catalyst, various characterizations were conducted. It was found that NH₃ capacity of Fe_xCe_1-x catalyst was controlled by P sites and depended on their specific surface area. Interestingly, Fe species in Fe_xCe_1-x were not a Lewis acid site for NH₃ adsorption, but it could promote the activation of NH₃. More importantly, Fe³⁺ doping could induce the redox equilibrium of Fe³⁺ + Ce³⁺ ⇆ Fe²⁺ + Ce⁴⁺, which significantly improved redox properties of CePO₄ catalyst. Accordingly, improved catalytic activity of Fe_xCe_1-x catalysts could be attributed to the collective effects of the higher surface area, better redox properties and easily activated NH₃. Among them, superior redox property of Fe_xCe_1-x catalysts was the main reason boosting their high catalytic activity. Finally, the reaction process analyzed by in situ DRIFT proposed that the NH₃-SCR reaction over CePO₄ and Fe_xCe_1-x occurred mainly via Eley-Rideal mechanism. We anticipated this work could promote the development of novel NH₃-SCR catalyst.

Enhanced properties of Pd/CeO2-nanorods modified with alkaline-earth metals for catalytic oxidation of low-concentration methane

A series of Pd/CeO₂-nanorods catalysts modified with alkaline-earth metals were prepared by the incipient impregnation method.

Improved Oxidase Mimetic Activity by Praseodymium Incorporation into Ceria Nanocubes

Ceria nanocubes (NC) modified with increasing concentrations of praseodymium (5, 10, 15, and 20 mol %) have been successfully synthesized by a hydrothermal method. The as-synthesized Pr-modified ceria nanocubes exhibit an enhanced oxidase-like activity on the organic dye TMB within a wide range of concentrations and durations. The oxidase activity increases with increasing Pr amounts in Pr-modified ceria nanocubes within the investigated concentration range. Meanwhile, these Pr-modified ceria nanocubes also show higher reducibility than pure ceria nanocubes. The kinetics of their oxidase mimetic activity is fitted with the Michaelis-Menten equation. A mechanism has been proposed on how the Pr incorporation could affect the energy level of the bands in ceria and hence facilitate the TMB oxidation reaction. The presence of Pr³⁺ species on the surface also contributes to the increasing activity of the Pr-modified ceria nanocubes present higher oxidase activity than pure ceria nanocubes.

A comparative study of manganese–cerium doped metal–organic frameworks prepared via impregnation and in situ methods in the selective catalytic reduction of NO

Impregnation and in situ doping were applied for the preparation of MnCe loaded MOFs and the behavior of the catalysts in the SCR was investigated.

Ni nanocluster on modified CeO2–ZrO2 nanoporous composite for tri-reforming of methane

Modified Ni-CeO₂–ZrO₂ nanoporous catalysts have been synthesized by using a very facile solvothermal approach and urea deposition precipitation method. The catalyst system is highly stable for more than 100 h with almost a constant syngas ratio of 2.1 and >95% methane conversion at 800 °C in the tri-reforming reaction of methane.

Hydrodeoxygenation of Guaiacol over Ceria-Zirconia Catalysts

The hydrodeoxygenation of guaiacol is investigated over bulk ceria and ceria-zirconia catalysts with different elemental compositions. The reactions are performed in a flow reactor at 1 atm and 275-400 °C. The primary products are phenol and catechol, whereas cresol and benzene are formed as secondary products. No products with hydrogenated rings are formed. The highest conversion of guaiacol is achieved over a catalyst containing 60 mol % CeO2 and 40 mol % ZrO2 . Pseudo-first-order activation energies of 97-114 kJ mol(-1) are observed over the mixed metal oxide catalysts. None of the catalysts show significant deactivation during 72 h on stream. The important physicochemical properties of the catalysts are characterized by X-ray diffraction (XRD), temperature-programmed reduction, titration of oxygen vacancies, and temperature-programmed desorption of ammonia. On the basis of these experimental results, the reasons for the observed reactivity trends are identified.