Synthesis of porous CuO-CeO2 nanospheres with an enhanced low-temperature CO oxidation activity

Hybrid Biochar/Ceria Nanomaterials: Synthesis, Characterization and Activity Assessment for the Persulfate-Induced Degradation of Antibiotic Sulfamethoxazole

Biochar from spent malt rootlets was employed as the template to synthesize hybrid biochar-ceria materials through a wet impregnation method. The materials were tested for the activation of persulfate (SPS) and subsequent degradation of sulfamethoxazole (SMX), a representative antibiotic, in various matrices. Different calcination temperatures in the range 300-500 °C were employed and the resulting materials were characterized by means of N2 adsorption and potentiometric mass titration as well as TGA, XRD, SEM, FTIR, DRS, and Raman spectroscopy. Calcination temperature affects the biochar content and the physicochemical properties of the hybrid materials, which were tested for the degradation of 500 μg L-1 SMX with SPS (in the range 200-500 mg L-1) in various matrices including ultrapure water (UPW), bottled water, wastewater, and UPW spiked with bicarbonate, chloride, or humic acid. Materials calcined at 300-350 °C, with a surface area of ca. 120 m2 g-1, were the most active, yielding ca. 65% SMX degradation after 120 min of reaction in UPW; materials calcined at higher temperatures as well as bare biochar were less active. Degradation decreased with increasing matrix complexity due to the interactions amongst the surface, the contaminant, and the oxidant. Experiments in the presence of scavengers (i.e., methanol, t-butanol, and sodium azide) revealed that sulfate and hydroxyl radicals as well as singlet oxygen were the main oxidative species.

A Review on Metal- and Metal Oxide-Based Nanozymes: Properties, Mechanisms, and Applications

Since the ferromagnetic (Fe3O4) nanoparticles were firstly reported to exert enzyme-like activity in 2007, extensive research progress in nanozymes has been made with deep investigation of diverse nanozymes and rapid development of related nanotechnologies. As promising alternatives for natural enzymes, nanozymes have broadened the way toward clinical medicine, food safety, environmental monitoring, and chemical production. The past decade has witnessed the rapid development of metal- and metal oxide-based nanozymes owing to their remarkable physicochemical properties in parallel with low cost, high stability, and easy storage. It is widely known that the deep study of catalytic activities and mechanism sheds significant influence on the applications of nanozymes. This review digs into the characteristics and intrinsic properties of metal- and metal oxide-based nanozymes, especially emphasizing their catalytic mechanism and recent applications in biological analysis, relieving inflammation, antibacterial, and cancer therapy. We also conclude the present challenges and provide insights into the future research of nanozymes constituted of metal and metal oxide nanomaterials.

Antisolvent Route to Ultrathin Hollow Spheres of Cerium Oxide for Enhanced CO Oxidation

Cerium(IV) oxide (CeO₂), or ceria, is one of the most abundant rare-earth materials that has been extensively investigated for its catalytic properties over the past two decades. However, due to the global scarcity and increasing cost of rare-earth materials, efficient utilization of this class of materials poses a challenging issue for the materials research community. Thus, this work is directed toward an exploration of making ultrathin hollow ceria or other rare-earth metal oxides and mixed rare-earth oxides in general. Such a hollow morphology appears to be attractive, especially when the thickness is trimmed to its limit, so that it can be viewed as a two-dimensional sheet of organized nanoscale crystallites, while remaining three-dimensional spatially. This ensures that both inner and outer shell surfaces can be better utilized in catalytic reactions if the polycrystalline sphere is further endowed with mesoporosity. Herein, we have devised our novel synthetic protocol for making ultrathin mesoporous hollow spheres of ceria or other desired rare-earth oxides with a tunable shell thickness in the region of 10 to 40 nm. Our ceria ultrathin hollow spheres are catalytically active and outperform other reported similar nanostructured ceria for the oxidation reaction of carbon monoxide in terms of fuller utilization of cerium. The versatility of this approach has also been extended to fabricating singular or multicomponent rare-earth metal oxides with the same ultrathin hollow morphology and structural uniformity. Therefore, this approach holds good promise for better utilization of rare-earth metal elements across their various technological applications, not ignoring nano-safety considerations.

MOF Embedded and Cu Doped CeO2 Nanostructures as Efficient Catalyst for Adipic Acid Production: Green Catalysis

Greatly efficient chemical processes are customarily based upon a catalyst activating the process pathway to achieve higher yields of a product with desired specifications. Catalysts capable of achieving good performance without compromising green credentials are a pre-requisite for the development of a sustainable process. In this study, CeO2 nanoparticles were tested for their catalytic activity with two different configurations, one as a hybrid of CeO2 nanoparticles with Zeolitic Immidazole Framework (ZIF-67) and second being doped Cu cations into CeO2 nanoparticles. Physicochemical and catalytic activity was investigated and compared for both systems. Each hybrid was synthesized by embedding the CeO2 nanoparticles into the microporous structure of ZIF-67, and Cu doped CeO2 nanoparticles were prepared by a facile hydrothermal route. As a catalytic test, it was employed for the oxidation of cyclohexene to adipic acid (AA) as an alternative to expensive noble metal-based catalysts. Heterogeneous ZIF-67/CeO2 found catalytical activity towards the oxidation of cyclohexene with nearly complete conversion of cyclohexene into AA under moderate and co-catalyst free reaction conditions, whereas Cu doped CeO2 nanoparticles have shown no catalytic activity towards cyclohexene conversion, depicting the advantages of the porous ZIF-67 structure and its synergistic effect with CeO2 nanoparticles. The large surface area catalyst could be a viable option for the green synthesis of many other chemicals.

Recent Advances on the Rational Design of Non-Precious Metal Oxide Catalysts Exemplified by CuOx/CeO2 Binary System: Implications of Size, Shape and Electronic Effects on Intrinsic Reactivity and Metal-Support Interactions

Catalysis is an indispensable part of our society, massively involved in numerous energy and environmental applications. Although, noble metals (NMs)-based catalysts are routinely employed in catalysis, their limited resources and high cost hinder the widespread practical application. In this regard, the development of NMs-free metal oxides (MOs) with improved catalytic activity, selectivity and durability is currently one of the main research pillars in the area of heterogeneous catalysis. The present review, involving our recent efforts in the field, aims to provide the latest advances—mainly in the last 10 years—on the rational design of MOs, i.e., the general optimization framework followed to fine-tune non-precious metal oxide sites and their surrounding environment by means of appropriate synthetic and promotional/modification routes, exemplified by CuOx/CeO2 binary system. The fine-tuning of size, shape and electronic/chemical state (e.g., through advanced synthetic routes, special pretreatment protocols, alkali promotion, chemical/structural modification by reduced graphene oxide (rGO)) can exert a profound influence not only to the reactivity of metal sites in its own right, but also to metal-support interfacial activity, offering highly active and stable materials for real-life energy and environmental applications. The main implications of size-, shape- and electronic/chemical-adjustment on the catalytic performance of CuOx/CeO2 binary system during some of the most relevant applications in heterogeneous catalysis, such as CO oxidation, N2O decomposition, preferential oxidation of CO (CO-PROX), water gas shift reaction (WGSR), and CO2 hydrogenation to value-added products, are thoroughly discussed. It is clearly revealed that the rational design and tailoring of NMs-free metal oxides can lead to extremely active composites, with comparable or even superior reactivity than that of NMs-based catalysts. The obtained conclusions could provide rationales and design principles towards the development of cost-effective, highly active NMs-free MOs, paving also the way for the decrease of noble metals content in NMs-based catalysts.

Facile preparation of highly active and stable CuO–CeO2 catalysts for low-temperature CO oxidation via a direct solvothermal method

CuO–CeO₂ catalysts prepared by a direct solvothermal method exhibit high activity and stability for low-temperature CO oxidation.

Tuning the Catalytic Properties of Copper-Promoted Nanoceria via a Hydrothermal Method

Copper-cerium mixed oxide catalysts have gained ground over the years in the field of heterogeneous catalysis and especially in CO oxidation reaction due to their remarkable performance. In this study, a series of highly active, atomically dispersed copper-ceria nanocatalysts were synthesized via appropriate tuning of a novel hydrothermal method. Various physicochemical techniques including electron paramagnetic resonance (EPR) spectroscopy, X-ray diffraction (XRD), N2 adsorption, scanning electron microscopy (SEM), Raman spectroscopy, and ultraviolet-visible diffuse reflectance spectroscopy (UV-Vis DRS) were employed in the characterization of the synthesized materials, while all the catalysts were evaluated in the CO oxidation reaction. Moreover, discussion of the employed mechanism during hydrothermal route was provided. The observed catalytic activity in CO oxidation reaction was strongly dependent on the nanostructured morphology, oxygen vacancy concentration, and nature of atomically dispersed Cu2+ clusters.

Facilely fabricating mesoporous nanocrystalline Ce–Zr solid solution supported CuO-based catalysts with advanced low-temperature activity toward CO oxidation

The synergistic effect between CuO and mesoporous Ce–Zr solid solution greatly enhanced the advanced low-temperature catalytic activity toward CO oxidation.

Hollow copper–ceria microspheres with single and multiple shells for preferential CO oxidation

The triple-shelled CuO/CeO₂ exhibits superior catalytic performance for CO-PROX due to its fine-tunable geometric and electronic interactions.

Litchi-peel-like hierarchical hollow copper-ceria microspheres: aerosol-assisted synthesis and high activity and stability for catalytic CO oxidation

Copper-ceria is considered to be a promising system used in exhaust treatment due to its low cost and decent catalytic activity. Herein, we have developed novel litchi-peel-like hollow copper-ceria microspheres with varying Cu contents via an aerosol-assisted route. It is found that the dextrin in the spray solution plays a significant role as a sacrificial template and leads to the formation of this hierarchical hollow structure, in which higher surface area and active CuOx species with higher dispersion result in better catalytic activity compared to the usual hollow samples. The litchi-peel-like sample with 20% Cu exhibits the best reactivity for CO oxidation, namely 50% conversion at 83 °C and 100% conversion at 120 °C. Importantly, this novel copper-ceria sample displays outstanding catalytic stability involving cycle stability, long-term stability and thermal stability, which is attributed to step-stabilized strong interaction between CuOx species and CeO2. The superior catalytic activity and stability beyond commercial 5 wt% Pt/Al2O3 provides it with the potential to be a substitute for Pt-based catalysts in practical applications.

Optimization of N2O decomposition activity of CuO–CeO2 mixed oxides by means of synthesis procedure and alkali (Cs) promotion

The fine-tuning of CuO–CeO₂ mixed oxides by means of synthesis procedure (co-precipitation) and alkali promotion (1.0 at Cs per nm²) towards highly active deN₂O catalysts is demonstrated.

Hierarchical porous NiCo2O4/CeO2 hybrid materials for high performance supercapacitors

Hierarchical porous NiCo₂O₄/CeO₂ hybrid materials are successfully synthesized via a simple solvothermal method and subsequent heat treatment and exhibit remarkable electrochemical performances in supercapacitors.

Design of Porous/Hollow Structured Ceria by Partial Thermal Decomposition of Ce-MOF and Selective Etching

Metal-organic frameworks (MOFs) have been widely used to prepare corresponding porous metal oxides via thermal treatment. However, high temperature treatment always leads to obtained metal oxides with a large crystallite size, thus decreasing their specific surface area. Different from the conventional complete thermal decomposition of MOFs, herein, using Ce-MOF as a demonstration, we choose partial thermal decomposition of MOF, followed by selective etching to prepare porous/hollow structured ceria because of the poor stability of Ce-MOF under acidic conditions. Compared with the ceria derived from complete thermal decomposition of Ce-MOF, the as-prepared ceria is demonstrated to be a good support for copper oxide species during the CO oxidation catalytic reaction. Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and hydrogen temperature-programmed reduction (H₂-TPR) analysis revealed that the as-prepared ceria is favorable for strengthening the interaction between the ceria and loaded copper oxide species. This work is expected to open a new, simple avenue for the synthesis of metal oxides from MOFs via partial thermal decomposition.

Dealloying assisted high-yield growth of surfactant-free <110> highly active Cu-doped CeO2 nanowires for low-temperature CO oxidation

CeO₂ is widely used as a commercial CO oxidation catalyst, but it suffers from high-temperature (>200 °C) complete conversion. Despite enormous efforts made to promote its low-temperature activity by interfacing CuO and CeO₂, it is still a long-standing challenge to balance the desired catalytic activity with high-yield preparation. Creating intimate synergistic interfaces between Cu and Ce species and exploring surfactant-free large-scale methods are both critical and challenging. To address these concerns, we synthesized highly active Cu doped CeO₂ nanowires for low-temperature CO oxidation, relying on intentionally maneuvering precursor alloy compositions and a high-yield dealloying method. The favorable one-dimensional doping structure inherited from the nanowire bundles of the as-dealloyed precursors, clean surfaces and intimate synergistic effects between Cu and Ce contribute to excellent CO oxidation performances, with 5% room-temperature conversion triggered at 35 °C and 100% conversion at 100 °C. 96% of O₂ selectivity at 88 °C in CO preferential oxidation was also obtained. The long-term durability for 24 hours at 100% CO conversion without any decay confirms the robust characteristics of the catalysts. Moreover, this work offers some insights into the reasonable design of alloy precursors to realize property-oriented alloys to nanowires batch transformation for the study of industrial catalysts.

CO oxidation on mesoporous SBA-15 supported CuO–CeO2 catalyst prepared by a surfactant-assisted impregnation method

A series of mesoporous SBA-15 supported CuO–CeO₂ catalysts were prepared by a surfactant-assisted impregnation method with PEG 200 as the surfactant.

Solubility product difference-guided synthesis of Co3O4–CeO2 core–shell catalysts for CO oxidation

Co₃O₄–CeO₂ core–shell catalysts are successfully fabricated by an ion exchange procedure between Co(CO₃)_0.35Cl_0.2(OH)_1.1 nanorods and Ce³⁺ aqueous solution, followed by a calcination step.

CeO2 decorated CuO hierarchical composites as inverse catalyst for enhanced CO oxidation

CeO₂ decorated CuO hierarchical composites were prepared and was used as inverse catalyst for enhanced CO oxidation.

Facile and Mild Strategy to Construct Mesoporous CeO2-CuO Nanorods with Enhanced Catalytic Activity toward CO Oxidation

CeO2-CuO nanorods with mesoporous structure were synthesized by a facile and mild strategy, which involves an interfacial reaction between Ce2(SO4)3 precursor and NaOH ethanol solution at room temperature to obtain mesoporous CeO2 nanorods, followed by a solvothermal treatment of as-prepared CeO2 and Cu(CH3COO)2. Upon solvothermal treatment, CuO species is highly dispersed onto the CeO2 nanorod surface to form CeO2-CuO composites, which still maintain the mesoporous feature. A preliminary CO catalytic oxidation study demonstrated that the CeO2-CuO samples exhibited strikingly high catalytic activity, and a high CO conversion rate was observed without obvious loss in activity even after thermal treatment at a high temperature of 500 °C. Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and hydrogen temperature-programmed reduction (H2-TPR) analysis revealed that there is a strong interaction between CeO2 and CuO. Moreover, it was found that the introduction of CuO species into CeO2 generates oxygen vacancies, which is highly likely to be responsible for high catalytic activity toward CO oxidation of the mesoporous CeO2-CuO nanorods.

Gravity-Driven Multiple Collision-Enhanced Catalytic Soot Combustion over a Space-Open Array Catalyst Consisting of Ultrathin Ceria Nanobelts

More than 122 times higher contact efficiency between soot and catalysts is achieved over the as-prepared CeO(2) nanobelt array catalysts as compared with the powder nanoparticle catalyst. A novel gravity-driven multiple collision-enhanced soot combustion mechanism is proposed for the first time.

Preparation of hollow CuO@SiO2 spheres and its catalytic performances for the NO + CO and CO oxidation

The hollow CuO@SiO₂ spheres with a mean diameter of 240 nm and a thin shell layer of about 30 nm in thickness was synthesized using an inorganic SiO₂ shell coating on the surface of Cu@C composite that was prepared by a two-step hydrothermal method. The obtained hollow CuO@SiO₂ spheres were characterized by ICP-AES, nitrogen adsorption-desorption, SEM, TEM, XRD, H₂-TPR, CO-TPR, CO-TPD and NO-TPD. The results revealed that the hollow CuO@SiO₂ spheres consist of CuO uniformly inserted into SiO₂ layer. The CuO@SiO₂ sample exhibits particular catalytic activities for CO oxidation and NO + CO reactions compared with CuO supported on SiO₂ (CuO/SiO₂). The higher catalytic activity is attributed to the special hollow shell structure that possesses much more highly dispersed CuO nanocluster that can be easy toward the CO and NO adsorption and the oxidation of CO on its surface.

Mesoporous ZnS-NiS Nanocomposites for Nonenzymatic Electrochemical Glucose Sensors

Mesoporous ZnS-NiS composites are prepared via ion- exchange reactions using ZnS as the precursor. The prepared mesoporous ZnS-NiS composite materials have large surface areas (137.9 m(2) g(-1)) compared with the ZnS precursor. More importantly, the application of these mesoporous ZnS-NiS composites as nonenzymatic glucose sensors was successfully explored. Electrochemical sensors based on mesoporous ZnS-NiS composites exhibit a high selectivity and a low detection limit (0.125 μm) toward the oxidation of glucose, which can mainly be attributed to the morphological characteristics of the mesoporous structure with high specific surface area and a rational composition of the two constituents. In addition, the mesoporous ZnS-NiS composites coated on the surface of electrodes can be used to modify the mass transport regime, and this alteration can, in favorable circumstances, facilitate the amperometric discrimination between species. These results suggest that such mesoporous ZnS-NiS composites are promising materials for nonenzymatic glucose sensors.

Glutamine-assisted synthesis of Cu-doped CeO2 nanowires with an improved low-temperature CO oxidation activity

Glutamine (GLN)-assisted Cu-doped CeO₂ nanowires exhibit an outstanding performance for CO oxidation and can completely convert CO at 90 °C.

Facile synthesis of well-dispersed CeO2–CuOx composite hollow spheres with superior catalytic activity for CO oxidation

Well-dispersed CeO₂–CuO_x composite hollow spheres have been successfully synthesized through a facile reflux method using carbon spheres as sacrificial templates.

Low-temperature CO oxidation on CuO/CeO2catalysts: the significant effect of copper precursor and calcination temperature

The performance of CuO/CeO₂catalysts for CO oxidation strongly depends on the type of copper precursor and the calcination temperature.

Flower-Like Mn-Doped CeO2Microstructures: Synthesis, Characterizations, and Catalytic Properties

Mn-doped CeO2flower-like microstructures have been synthesized by a facile method, involving the precipitation of metallic alkoxide precursor in a polyol process from the reaction of CeCl3·7H2O with ethylene glycol in the presence of urea followed by calcination. By introducing manganese ions, the composition can be freely manipulated. To investigate whether there was a hybrid synergic effect in CH4combustion reaction, further detailed characteristics of Mn-doped CeO2with various manganese contents were revealed by XRD, Raman, FT-IR, SEM, EDS, XPS, OSC, H2-TPR, and N2adsorption-desorption measurements. The doping manganese is demonstrated to increase the storage of oxygen vacancy for CH4and enhance the redox capability, which can efficiently convert CH4to CO2and H2O under oxygen-rich condition. The excellent catalytic performance of MCO-3 sample, which was obtained with the starting Mn/Ce ratios of 0.2 in the initial reactant compositions, is associated with the larger surface area and richer surface active oxygen species.

Shape-controlled synthesis and catalytic application of ceria nanomaterials

Because of their excellent properties and extensive applications, ceria nanomaterials have attracted much attention in recent years. This perspective provides a comprehensive review of current research activities that focus on the shape-controlled synthesis methods of ceria nanostructures. We elaborate on the synthesis strategies in the following four sections: (i) oriented growth directed by the crystallographic structure of cerium-based materials; (ii) oriented growth directed by the use of an appropriate capping reagent; (iii) growth confined or dictated by various templates; (iv) other potential methods for generating CeO(2) nanomaterials. In this perspective, we also discuss the catalytic applications of ceria nanostructures. They are often used as active components or supports in many catalytic reactions and their catalytic activities show morphology dependence. We review the morphology dependence of their catalytic performances in carbon monoxide oxidation, water-gas shift, nitric oxide reduction, and reforming reactions. At the end of this review, we give a personal perspective on the probable challenges and developments of the controllable synthesis of CeO(2) nanomaterials and their catalytic applications.