High-Entropy Oxides: A New Frontier in Photocatalytic CO2 Hydrogenation

Herein, we investigate the potential of nanostructured high-entropy oxides (HEOs) for photocatalytic CO2 hydrogenation, a process with significant implications for environmental sustainability and energy production. Several cerium-oxide-based rare-earth HEOs with fluorite structures were prepared for UV-light driven photocatalytic CO2 hydrogenation toward valuable fuels and petrochemical precursors. The cationic composition profoundly influences the selectivity and activity of the HEOs, where the Ce0.2Zr0.2La0.2Nd0.2Sm0.2O2-δ catalyst showed outstanding CO2 activation (14.4 molCO kgcat-1 h-1 and 1.27 mol CH 3 OH kgcat-1 h-1) and high methanol and CO selectivity (7.84% CH3OH and 89.26% CO) under ambient conditions with 4 times better performance in comparison to pristine CeO2. Systematic tests showed the effect of a high-entropy system compared to midentropy oxides. XPS, in situ DRIFTS, as well as DFT calculation elucidate the synergistic impact of Ce, Zr, La, Nd, and Sm, resulting in an optimal Ce3+/Ce4+ ratio. The observed formate-routed mechanism and a surface with high affinity to CO2 reduction offer insights into the photocatalytic enhancement. While our findings lay a solid foundation, further research is needed to optimize these catalysts and expand their applications.

Degradation of carbamazepine in surface water: performance of Pd-modified TiO2 and Ce-modified ZnO as photocatalysts

Carbamazepine is a widely used antiepileptic drug to control and treat a variety of disorders that is frequently detected in surface water, and in municipal and urban wastewater. This recalcitrant pollutant could be removed by alternative advanced oxidation technology such as heterogeneous photocatalysis. Ce-modified ZnO and Pd-modified TiO2 were synthesized by a microwave-assisted sol-gel method. According to the characterizations (Raman spectroscopy, UV-Vis diffuse reflectance spectroscopy, scanning electron microscopy, and X-ray photoelectron spectroscopy), a mixture of oxides was determined in both materials: CeO2/ZnO and PdO/TiO2. Photocatalytic degradation of carbamazepine in pure water under visible light (3 h) was assayed. The degradation percentage obtained with each catalyst was 80%, 53%, 20%, and 9% for ZnO, Ce-modified ZnO, TiO2, and Pd-modified TiO2, respectively. The leaching of Zn as a possible source of water contamination was tested, finding the lowest value for Ce-modified ZnO by adjusting the initial pH up to neutrality. Later, an environmentally relevant concentration of carbamazepine (228 µg L-1) was assayed, using local surface water (pH = 8.3). Despite the presence of other compounds in the real water matrix, after 5 h of photocatalysis, a 56% of degradation of the pharmaceutical and low leaching of Zn were achieved. The use of Ce-modified ZnO activated by visible light is a promising strategy for the abatement of pharmaceutical active compounds.

Cerium Oxide Nanoparticles Confined in Doped Mesoporous Carbons: A Strategy to Produce Catalysts for Imine Synthesis

A group of (doped N or P) carbons were synthesized using soluble starch as a carbon precursor. Further, ceria nanoparticles (NPs) were confined into these (doped) carbon materials. The obtained solids were characterized by various techniques such as N2 physisorption, XRD, TEM, SEM, XPS, and XAS. These materials were used as catalysts for the oxidative coupling between benzyl alcohol and aniline as the model reaction. Ceria immobilized on mesoporous-doped carbon shows higher activity than the other materials, benchmark catalysts, and most of the previously reported catalysts. The control of the ceria NP size, the presence of Ce3+ cations, and an increment in the disorder in the ceria NP structure caused by a support-ceria interaction could increase the number of oxygen vacancies and improve its catalytic performance. CN-meso/CeO2 was also used as the catalyst for a rich scope of substrates, such as substituted aromatic alcohols, linear alcohols, and different types of amines. The influence of various reaction parameters (substrate content, reaction temperature, and catalyst content) on the activity of this catalyst was also checked.

Pd-Ceria/CNMs Composites as Catalysts for CO and CH4 Oxidation

The application of composite materials as catalysts for the oxidation of CO and other toxic compounds is a promising approach for air purification. In this work, the composites comprising palladium and ceria components supported on multiwall carbon nanotubes, carbon nanofibers and Sibunit were studied in the reactions of CO and CH₄ oxidation. The instrumental methods showed that the defective sites of carbon nanomaterials (CNMs) successfully stabilize the deposited components in a highly-dispersed state: PdO and CeO₂ nanoparticles, subnanosized PdO_x and Pd_xCe_1-xO_2-δ clusters with an amorphous structure, as well as single Pd and Ce atoms, are formed. It was shown that the reactant activation process occurs on palladium species with the participation of oxygen from the ceria lattice. The presence of interblock contacts between PdO and CeO₂ nanoparticles has an important effect on oxygen transfer, which consequently affects the catalytic activity. The morphological features of the CNMs, as well as the defect structure, have a strong influence on the particle size and mutual stabilization of the deposited PdO and CeO₂ components. The optimal combination of highly dispersed PdO_x and Pd_xCe_1-xO_2-δ species, as well as PdO nanoparticles in the CNTs-based catalyst, makes it highly effective in both studied oxidation reactions.

Potential of rare-earth compounds as anticorrosion pigment for protection of aerospace AA2198-T851 alloy

In this study, the anticorrosion potential of carboxylic compounds; Lanthanum 4-hydroxycinnamate La(4OHCin)₃, Cerium 4-hydroxycinnamate Ce(4OHCin)₃ and Praseodymium 4-hydroxycinnamate Pr(4OHCin)₃ for the protection of Al-Cu-Li alloy was investigated in 3.5% NaCl solution using electrochemical tests (EIS and PDP), scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). The findings achieved show a very good correlation between electrochemical responses and surface morphologies of the exposed alloy, indicating a modification of the surface by precipitation of the inhibitor species, leading to effective protection against corrosion. At optimum concentration 200 ppm, the trend of inhibition efficiency η (%) increases in the order Ce(4OHCin)₃ 93.35% > Pr(4OHCin)₃ 85.34% > La(4OHCin)₃ 82.25%. XPS complemented the findings by detecting and providing information about the oxidation states of the protective species.

Ag Catalysts Supported on CeO2, MnO2 and CeMnOx Mixed Oxides for Selective Catalytic Reduction of NO by C3H6

In the present study CeO₂, MnO₂ and CeMnO_x mixed oxide (with molar ratio Ce/Mn = 1) were prepared by sol-gel method using citric acid as a chelating agent and calcined at 500 °C. The silver catalysts (1 wt.% Ag) over the obtained supports were synthesized by the incipient wetness impregnation method with [Ag(NH₃)₂]NO₃ aqueous solution. The selective catalytic reduction of NO by C₃H₆ was investigated in a fixed-bed quartz reactor using a reaction mixture composed of 1000 ppm NO, 3600 ppm C₃H₆, 10 vol.% O₂, 2.9 vol.% H₂ and He as a balance gas, at WHSV of 25,000 mL g^-1 h^-1.The physical-chemical properties of the as-prepared catalysts were studied by several characterization techniques, such as X-ray fluorescence analysis, nitrogen adsorption/desorption, X-ray analysis, Raman spectroscopy, transmission electron microscopy with analysis of the surface composition by X-ray energy dispersive spectroscopy and X-ray photo-electron spectroscopy. Silver oxidation state and its distribution on the catalysts surface as well as the support microstructure are the main factors determining the low temperature activity in NO selective catalytic reduction. The most active Ag/CeMnO_x catalyst (NO conversion at 300 °C is 44% and N₂ selectivity is ~90%) is characterized by the presence of the fluorite-type phase with high dispersion and distortion. The characteristic "patchwork" domain microstructure of the mixed oxide along with the presence of dispersed Ag⁺/Ag_n^δ+ species improve the low-temperature catalyst of NO reduction by C₃H₆ performance compared to Ag/CeO₂ and Ag/MnO_x systems.

Core-Sheath Pt-CeO2/Mesoporous SiO2 Electrospun Nanofibers as Catalysts for the Reverse Water Gas Shift Reaction

One-dimensional (1D) core-sheath nanofibers, platinum (Pt)-loaded ceria (CeO₂) sheath on mesoporous silica (SiO₂) core were fabricated, characterized, and used as catalysts for the reverse water gas shift reaction (RWGS). CeO₂ nanofibers (NFs) were first prepared by electrospinning (ES), and then Pt nanoparticles were loaded on the CeO₂ NFs using two different deposition methods: wet impregnation and solvothermal. A mesoporous SiO₂ sheath layer was then deposited by sol-gel process. The phase composition, structural, and morphological properties of synthesized materials were investigated by scanning electron microscope (SEM), scanning transmission electron microscopy (STEM), X-ray diffraction (XRD), nitrogen adsorption/desorption method, X-ray photoelectron spectroscopy (XPS), inductively coupled plasma-optical emission spectrometry (ICP-OES) analysis, and CO₂ temperature programmed desorption (CO₂-TPD). The results of these characterization techniques revealed that the core-sheath NFs with a core diameter between 100 and 300 nm and a sheath thickness of about 40-100 nm with a Pt loading of around 0.5 wt.% were successfully obtained. The impregnated catalyst, Pt-CeO₂ NF@mesoporous SiO₂, showed the best catalytic performance with a CO₂ conversion of 8.9% at 350 °C, as compared to the sample prepared by the Solvothermal method. More than 99% selectivity of CO was achieved for all core-sheath NF-catalysts.

Determination of the Primary Excitation Spectra in XPS and AES

This paper reviews a procedure that allows for extracting primary photoelectron or Auger electron emissions from homogeneous isotropic samples. It is based on a quantitative dielectric description of the energy losses of swift electrons travelling nearby surfaces in presence of stationary positive charges. The theory behind the modeling of the electron energy losses, implemented in a freely available QUEELS-XPS software package, takes into account intrinsic and extrinsic effects affecting the electron transport. The procedure allows for interpretation of shake-up and multiplet structures on a quantitative basis. We outline the basic theory behind it and illustrate its capabilities with several case examples. Thus, we report on the angular dependence of the intrinsic and extrinsic Al 2s photoelectron emission from aluminum, the shake-up structure of the Ag 3d, Cu 2p, and Ce 3d photoelectron emission from silver, CuO and CeO₂, respectively, and the quantification of the two-hole final states contributing to the L₃M₄₅M₄₅ Auger electron emission of copper. These examples illustrate the procedure, that can be applied to any homogeneous isotropic material.

Photoluminescence and Electrical Properties of n-Ce-Doped ZnO Nanoleaf/p-Diamond Heterojunction

The n-type Ce:ZnO (NL) grown using a hydrothermal method was deposited on a p-type boron-doped nanoleaf diamond (BDD) film to fabricate an n-Ce:ZnO NL/p-BDD heterojunction. It shows a significant enhancement in photoluminescence (PL) intensity and a more pronounced blue shift of the UV emission peak (from 385 nm to 365 nm) compared with the undoped heterojunction (n-ZnO/p-BDD). The prepared heterojunction devices demonstrate good thermal stability and excellent rectification characteristics at different temperatures. As the temperature increases, the turn-on voltage and ideal factor (n) of the device gradually decrease. The electronic transport behaviors depending on temperature of the heterojunction at different bias voltages are discussed using an equilibrium band diagram and semiconductor theoretical model.

Unraveling Ce3+ detection at the surface of ceria nanopowders by UPS analysis

A sequential analysis using Ultra-violet Photoelectron Spectroscopy (UPS) and X-ray Photoelectron Spectroscopy (XPS) on ceria nanopowders has been implemented to identify the influence of the X-ray beam on the surface of this oxide. For the first time, UPS analysis evidenced the photoreductive effect of XPS analysis on ceria after an oxidative in situ pretreatment, leading to an overestimation of the Ce³⁺/Ce⁴⁺ ratio obtained by XPS. Based on this spectroscopy methodology, UPS imposes itself as a leading technique for analyzing powders with minimal impact on the authentic chemical state, thus paving the way for identifying the real ratio of Ce⁴⁺ and Ce³⁺ of ceria after oxidative and reductive in situ treatments.

Synthesis Attempt and Structural Studies of Novel A2CeWO6 Double Perovskites (A2+ = Ba, Ca) in and outside of Ambient Conditions

This comprehensive work showcases two novel, rock-salt-type minerals in the form of amphoteric cerium-tungstate double perovskite and ilmenite powders created via a high-temperature solid-state reaction in inert gases. The presented studies have fundamental meaning and will mainly focus on a detailed synthesis description of undoped structures, researching their possible polymorphism in various conditions and hinting at some nontrivial physicochemical properties like charge transfer for upcoming optical studies after eventual doping with selectively chosen rare-earth ions. The formerly mentioned, targeted A₂BB'X₆ group of compounds contains mainly divalent alkali cations in the form of ^XIIA = Ba²⁺, Ca²⁺ sharing, here, oxygen-arranged clusters (^IIX = O^2-) with purposely selected central ions from f-block ^VIB = Ce^4/3+ and d-block ^VIB' = W^4/5/6+ since together they often possess some exotic properties that could be tuned and implemented into futuristic equipment like sensors or energy converters. Techniques like powder XRD, XPS, XAS, EPR, Raman, and FTIR spectroscopies alongside DSC and TG were involved with an intent to thoroughly describe any possible changes within these materials. Mainly, to have a full prospect of any desirable or undesirable phenomena before diving into more complicated subjects like: energy or charge transfer in low temperatures; to reveal whether or not the huge angular tilting generates large enough dislocations within the material's unit cell to change its initial properties; or if temperature and pressure stimuli are responsible for any phase transitions and eventual, irreversible decomposition.

Facet Engineering of Nanoceria for Enzyme-Mimetic Catalysis

Nanomaterials with natural enzyme-mimicking characteristics have aroused extensive attention in various fields owing to their economical price, ease of large-scale production, and environmental resistance. Previous investigations have demonstrated that composition, size, shape, and surface modification play important roles in the enzymelike activity of nanomaterials; however, a fundamental understanding of the crystal facet effect, which determines surface energy or surface reactivity, has rarely been reported. Herein, fluorite cubic CeO₂ nanocrystals with controllably exposed {111}, {100}, or {110} facets are fabricated as proof-of-concept candidates to study the facet effect on the peroxidase-mimetic activity. Both experiments and theoretical results show that {110}-dominated CeO₂ nanorods (CeO₂ NR) possess the highest peroxidase-mimetic activity due to the richest defects on their surfaces, which are beneficial to capture metal atoms to further enrich their artificial enzymatic functionality for cascade catalysis. For instance, the introduction of atomically dispersed Au on CeO₂ NR surfaces not only enhances the peroxidase activity but also endows the obtained catalyst with glucose oxidase (GO_x)-mimicking activity, which realizes enzyme-free cascade reactions for glucose colorimetric detection. This work not only provides an understanding for crystal facet engineering of nanomaterials to enhance the catalytic activity but also opens up a new way for the design of biomimetic nanomaterials with multiple functions.

Solvothermal synthesis of CeO2-ZrO2-M2O3 (M = La, Y, Bi) mixed oxide and their soot oxidation activity

CeO₂–ZrO₂-M₂O₃ (M = La, Y, Bi) mixed oxide has been prepared by a solvothermal synthesis method. The physico–chemical properties of the mixed oxide have been studied by X-ray powder diffraction (XRD), Raman spectroscopy, BET, X-ray photoelectron spectroscopy (XPS), TEM and temperature-programmed reduction (TPR), and the catalytic activity for soot oxidation has been studied by thermogravimetry (TG). La³⁺, Y³⁺ and Bi³⁺ exhibit positive effects on lowering the oxidation temperature of the soot. The XRD and Raman results showed formation of mixed oxides and TEM images suggested the nanosized nature of the particles. The benefit of yttrium or lanthana doping on the catalytic activity of ceria can be related to active oxygen formation provoked by the defective structure of ceria due to the presence of La³⁺ and Y³⁺. The benefit of Bi³⁺ doping on catalytic activity can be related to the reduction at low temperature both with Bi₂O₃ and ceria.

Nano CeO₂-based oxides with meso-pores have been synthesized by a solvothermal method.

Smart, Biomimetic Periosteum Created from the Cerium(III, IV) Oxide-Mineralized Eggshell Membrane

The periosteum orchestrates the microenvironment of bone regeneration, including facilitating local neuro-vascularization and regulating immune responses. To mimic the role of natural periosteum for bone repair enhancement, we adopted the principle of biomimetic mineralization to delicately inlay amorphous cerium oxide within eggshell membranes (ESMs) for the first time. Cerium from cerium oxide possesses unique ability to switch its oxidation state from cerium III to cerium IV and vice versa, which provides itself promising potential for biomedical applications. ESMs are mineralized with cerium(III, IV) oxide and examined for their biocompatibility. Apart from serving as physical barriers, periosteum-like cerium(III, IV) oxide-mineralized ESMs are biocompatible and can actively regulate immune responses and facilitate local neuro-vascularization along with early-stage bone regeneration in a murine cranial defect model. During the healing process, cerium-inlayed biomimetic periosteum can boost early osteoclastic differentiation of macrophage lineage cells, which may be the dominant mediator of the local repair microenvironment. The present work provides novel insights into expanding the definition and function of a biomimetic periosteum to boost early-stage bone repair and optimize long-term repair with robust neuro-vascularization. This new treatment strategy which employs multifunctional bone-and-periosteum-mimicking systems creates a highly concerted microenvironment to expedite bone regeneration.

Remarkable enhancement in the N2 selectivity of NH3-SCR over the CeNb3Fe0.3/TiO2 catalyst in the presence of chlorobenzene

The simultaneous removal of NO_x and dioxins is the frontier of environmental catalysis, which is still in the initial stage and poses several challenges. In this study, a series of CeNb₃Fe_x/TiO₂ (x = 0, 0.3, 0.6, and 1.0) catalysts were prepared by the sol-gel method and examined for the synergistic removal of NO_x and CB. The CeNb₃Fe_0.3/TiO₂ catalyst exhibits an optimum catalytic performance, with an NO_x conversion greater than 95% at 260-380 °C. It also exhibits an optimal CB oxidation activity, in which CB promoted both the NO_x conversion and N₂ selectivity below 250 °C. Moreover, the more favorable ratios of Ce⁴⁺ to Ce³⁺ and plentiful surface-adsorbed oxygen species are the reasons why CeNb₃Fe_0.3/TiO₂ catalyst has better catalytic activity than other catalysts at the lower temperature. Simultaneously, owing to the modulation of Fe to the redox properties of Ce and Nb, the large number of oxygen vacancies and acid sites was generated, and the CeNb₃Fe_0.3/TiO₂ catalyst is beneficial to NO_x reduction and CB oxidation. Furthermore, the results of in situ DRIFTS study reveal the NH₃-SCR reactions over CeNb₃Fe_0.3/TiO₂ catalysts are mainly conformed to by the L-H mechanism (< 350 °C) and E-R mechanism (> 350 °C), respectively, and the multi-pollutant conversion mechanism in the synergistic reaction was systematically studied.

Design of Ordered Mesoporous CeO2-YSZ Nanocomposite Thin Films with Mixed Ionic/Electronic Conductivity via Surface Engineering

Mixed ionic and electronic conductors represent a technologically relevant materials system for electrochemical device applications in the field of energy storage and conversion. Here, we report about the design of mixed-conducting nanocomposites by facile surface modification using atomic layer deposition (ALD). ALD is the method of choice, as it allows coating of even complex surfaces. Thermally stable mesoporous thin films of 8 mol-% yttria-stabilized zirconia (YSZ) with different pore sizes of 17, 24, and 40 nm were prepared through an evaporation-induced self-assembly process. The free surface of the YSZ films was uniformly coated via ALD with a ceria layer of either 3 or 7 nm thickness. Electrochemical impedance spectroscopy was utilized to probe the influence of the coating on the charge-transport properties. Interestingly, the porosity is found to have no effect at all. In contrast, the thickness of the ceria surface layer plays an important role. While the nanocomposites with a 7 nm coating only show ionic conductivity, those with a 3 nm coating exhibit mixed conductivity. The results highlight the possibility of tailoring the electrical transport properties by varying the coating thickness, thereby providing innovative design principles for the next-generation electrochemical devices.

Insight into the promoting effect of support pretreatment with sulfate acid on selective catalytic reduction performance of CeO2/ZrO2 catalysts

In this paper, sulfated ZrO₂ were synthesized via precipitation and impregnation method, and the promoting effects of support sulfation on selective catalytic reduction (SCR) performance of CeO₂/ZrO₂ catalysts were investigated. The results revealed that sulfated ZrO₂ could significantly enhance the SCR activity of CeO₂/ZrO₂ catalysts in a wide temperature range. Especially when S/Zr molar ratio was 0.1, CeO₂/ZrO₂-0.1S catalyst exhibited a large operating temperature window of 251 ∼ 500 °C and its N₂ selectivity was 100 % in the temperature range of 150 ∼ 500 °C. Moreover, CeO₂/ZrO₂-0.1S catalyst possessed a superior low-temperature activity over 0.1S-CeO₂/ZrO₂ catalyst. After exposing to 100 ppm SO₂ for 15 h, a high NO conversion efficiency of CeO₂/ZrO₂-0.1S catalyst (90.7 %) could still be reached. The characterization results indicated that ZrO₂ treated with a proper dosage of sulfate acid was beneficial to enlarge the specific surface area greatly. Sulfated ZrO₂ was also in favor of promoting the transformation of CeO₂ from crystalline state to highly-dispersed amorphous state, and inhibiting the transformation of ZrO₂ from tetragonal to monoclinic phase. It could also enhance the total surface acidity greatly with an increase in both Brønsted acid sites and Lewis acid sites, thus significantly improving NH₃ adsorption on catalyst surface. Besides, the promoting effect of support sulfation on SCR performance of CeO₂/ZrO₂ catalysts was also related with the enhanced redox property, higher Ce³⁺/(Ce³⁺+Ce⁴⁺) ratio and abundant surface chemisorbed labile oxygen. The in-situ DRIFTS results implied that nitrate species coordinated on the surface of CeO₂/ZrO₂-0.1S catalyst could participate in the Selective catalytic reduction with ammonia (NH₃-SCR) reactions at either medium or high temperature, suggesting that both Eley-Rideal (E-R) and Langmuir-Hinshelwood (L-H) mechanisms might be followed in SCR reactions.

Promoting effects of indium doped Cu/CeO2 catalysts on CO2 hydrogenation to methanol

Combining catalyst modification by indium doping and chemometric optimization, the Cu/CeO2 system showed high selectivity to methanol (99.3%) with no CO formation during CO2 hydrogenation.

Specific reactivity of 4d and 5d transition metals supported over CeO2 for ammonia oxidation

Pt/CeO2 catalysts were most active in selective catalytic oxidation of ammonia, where Pt triggered the activation of surface lattice oxygen, and the dehydrogenation of ammonia assisted by surface lattice oxygen was the rate-determining step.

Development of novel inorganic yellowish-tacao color pigments, RbBi1−xCex(MoO4)2 (0 ≤ x ≤ 0.30): revealing crystal structure and color properties

Novel inorganic yellowish-tacao color pigments, RbBi1−xCex(MoO4)2 (0 ≤ x ≤ 0.30), were synthesized by a conventional solid state reaction method. The crystal structure and color properties were investigated in detail.

Atomic / Molecular Layer Deposition of Cerium (III) Hybrid Thin Films using Rigid Organic Precursors

Atomic / molecular layer deposition (ALD/MLD) process for the fabrication of cerium-based metal-organic hybrid films is demonstrated for the first time. The highly reactive cerium (III) guanidinate precursor [Ce(dpdmg)3] was...

A novel electrochemiluminescence immunoassay based on highly efficient resonance energy transfer for florfenicol detection

A novel competitive mechanism electrochemiluminescence (ECL) immunoassay based on resonance energy transfer was used to detect florfenicol for the first time. In this work, CeO₂@TiO₂ nanocomposite, which was used as a donor, was prepared in sol-gel method and the effective band gap of TiO₂ could be reduced by CeO₂, which promoted the ECL emission of TiO₂ and made the ECL performance of the donor more outstanding. The absorption spectrum of Cu₂S and the ECL emission spectrum of the donor could be highly matched, which ensured the occurrence of electrochemiluminescence resonance energy transfer (ECL-RET). In addition, the snowflake-like structure of cuprous sulfide could load more antibodies. It is worth mentioning that as far as we know, there have been no reports of this material as an ECL receptor before. Furthermore, the ECL-RET system based on this has shown excellent performance in the detection of florfenicol. The proposed immunoassay showed satisfactory sensitivity with a wide linear range from 0.001 to 1000 ng mL^-1 and a low detection limit (0.3 pg mL^-1). Due to the remarkable quenching effect and simple assembly process, the immunoassay is of great practical significance and has reference value for the detection of florfenicol or other biological small molecules.

Study on the Mechanism of SO2 Poisoning of MnOx/PG for Lower Temperature SCR by Simple Washing Regeneration

Manganese oxide-supported palygorskite (MnOx/PG) catalysts are considered highly efficient for low-temperature SCR of NOx. However, the MnOx/PG catalyst tends to be poisoned by SO2. The effect of SO2 on activity of the SO2-pretreated poisoning catalysts under ammonia-free conditions was explored. It was determined that the MnOx/PG catalyst tends to be considerably deactivated by SO2 in the absence of ammonia and that water-washed regeneration can completely recover activity of the deactivated catalyst. Based on these results and characterizations of the catalysts, a reasonable mechanism for the deactivation of MnOx/PG catalyst by SO2 was proposed in this study. SO2 easily oxidized to SO3 on the surface of the catalyst, leading to the formation of polysulfuric acid, wrapping of the active component and blocking the micropores. The deactivation of the MnOx/PG catalyst is initially caused by the formation of polysulfuric rather than the deposition of ammonia sulfate, which occurs later.

Effect of Ag doping on Pd/Ag-CeO2 catalysts for CO and C3H6 oxidation

To achieve high fuel efficiency and low emission in automobiles, it is necessary to develop highly active diesel oxidation catalysts (DOCs). Pd/CeO₂ catalysts have been widely used as active catalysts for CO and C₃H₆ oxidation reactions. Additionally, Ag has been reported to enhance the oxygen storage capacity (OSC) of CeO₂, which contributes to the oxidation ability of Pd/CeO₂. In this study, Pd/Ag-CeO₂ catalysts were used for CO and C₃H₆ oxidation reactions. When CeO₂ was doped with appropriate amounts of Ag, reducibility and CO desorption rate were increased, which confirmed the high OSCs of Ag-doped catalysts. However, Ag particles were formed and the Ce³⁺/Ce⁴⁺ ratio decreased when CeO₂ was doped with excess amounts of Ag. In addition, reduced Pd (Pd⁰), which is an active species for C₃H₆ oxidation, was formed and maintained even under oxidative reaction conditions. Since the removal of C₃H₆ is important for the oxidation of CO and C₃H₆, the catalyst with the highest Pd⁰ fraction (Pd/0.1Ag-CeO₂ and Pd/0.3Ag-CeO₂) presented improved catalytic activity. Consequently, the optimal amount of Ag enhanced the OSC of Pd/Ag-CeO₂ catalysts and formed active Pd⁰ species under oxidative conditions, which resulted in the excellent catalytic activity of Pd/Ag-CeO₂ for the CO and C₃H₆ oxidation reaction.

Elucidating the structure, redox properties and active entities of high-temperature thermally aged CuOx-CeO2 catalysts for CO-PROX

CuOx-CeO2 catalysts with different copper contents are synthesized via a coprecipitation method and thermally treated at 700 °C. Various characterization techniques including X-ray diffraction (XRD) Rietveld refinement, N2 adsorption-desorption isotherms, X-ray photoelectron spectra (XPS), UV-Raman, high-resolution transmission electron microscopy (HRTEM), temperature-programmed reduction (TPR) and in situ diffuse reflectance infrared Fourier transform spectra (DRIFTs) were adopted to investigate the structure/texture properties, oxygen vacancies, Cu-Ce interaction and redox properties of the catalysts. After the thermal treatment, the catalysts exhibited outstanding catalytic properties for the preferential oxidation (PROX) of CO (with the T50% of 62 °C and the widest operation temperature window of 85-140 °C), which provided a new strategy for the design of Cu-Ce based catalysts with high catalytic performance. The characterization results indicated that moderately elevating the copper content (below 5%) increases the amount of highly dispersed Cu species in the catalysts, including highly dispersed surface CuOx species and strongly bonded Cu-[Ox]-Ce species, strengthening the Cu-Ce interaction, increasing oxygen vacancies and promoting redox properties, but a further increase in copper content causes the agglomeration of crystalline CuO and decreases the highly dispersed Cu species. This work also provides evidence from the perspective that the catalytic performance of CuOx-CeO2 catalysts for CO-PROX at low and high reaction temperatures is dependent on the redox properties of highly dispersed CuOx species and strongly bonded Cu-[Ox]-Ce species, respectively.

Improved Sulfur Resistance of COMMERCIAl V2O5-WO3/TiO2 SCR Catalyst Modified by Ce and Cu

The accumulation of NH4HSO4 leads to the deactivation of commercial V2O5-WO3/TiO2 catalyst (VWTi) in practical application. The commercial catalyst is modified with 0.3 wt. % Ce and 0.05 wt. % Cu (donated as VWCeCuTi), and its sulfur resistance is noticeably improved. After loading 20 wt. % NH4HSO4, the NOx conversion of VWCeCuTi-S remains 40% at 250 °C, higher than that of VWTi-S (25%). Through a series of characterization analyses, it was found that the damaged surface areas and acid sites are the key factors for the deactivation of S-poisoned samples. However, surface-active oxygen and NO adsorption are increased by NH4HSO4 deposition, and the L–H mechanism is promoted over S-poisoned samples. Due to the interaction between V, Ce and Cu, the surface-active oxygen over VWCeCuTi-S is increased, and then NO adsorption is promoted. In addition, VWCeCuTi-S obtains a higher V5+ ratio and a better redox property than VWTi-S, which in turn accelerates the NH3-SCR reaction. More NO adsorption and encouraged reaction contribute to the better sulfur resistance of VWCeCuTi.

Improvement of low-temperature NH3-SCR catalytic performance over nitrogen-doped MO x -Cr2O3-La2O3/TiO2-N (M = Cu, Fe, Ce) catalysts

A series of MO_x–Cr₂O₃–La₂O₃/TiO₂–N (M = Cu, Fe, Ce) catalysts with nitrogen doping were prepared via the impregnation method. Comparing the low-temperature NH₃-SCR activity of the catalysts, CeCrLa/Ti–N (xCeO₂–yCr₂O₃–zLa₂O₃/TiO₂–N) exhibited the best catalytic performance (NO conversion approaching 100% at 220–460 °C). The physico-chemical properties of the catalysts were characterized by XRD, BET, SEM, XPS, H₂-TPR, NH₃-TPD and in situ DRIFTS. From the XRD and SEM results, N doping affects the crystalline growth of anatase TiO₂ and MO_x (M = Cu, Fe, Ce, Cr, La) which were well dispersed over the support. Moreover, the doping of N promotes the increase of the Cr⁶⁺/Cr ratio and Ce³⁺/Ce ratio, and the surface chemical adsorption oxygen content, which suggested the improvement of the redox properties of the catalyst. And the surface acid content of the catalyst increased with the doping of N, which is related to CeCrLa/TiO₂–N having the best catalytic activity at high temperature. Therefore, the CeCrLa/TiO₂–N catalyst exhibited the best NH₃-SCR performance and the redox performance of the catalysts is the main factor affecting their activity. Furthermore, in situ DRIFTS analysis indicates that Lewis-acid sites are the main adsorption sites for ammonia onto CeCrLa/TiO₂–N and the catalyst mainly follows the L–H mechanism.

A series of MO_x–Cr₂O₃–La₂O₃/TiO₂–N (M = Cu, Fe, Ce) catalysts with nitrogen doping were prepared via the impregnation method.

Insight into the Contributions of Surface Oxygen Vacancies on the Promoted Photocatalytic Property of Nanoceria

Oxygen vacancies (OVs) have critical effects on the photoelectric characterizations and photocatalytic activity of nanoceria, but the contributions of surface OVs on the promoted photocatalytic properties are not clear yet. In this work, we synthesized ceria nanopolyhedron (P-CeO₂), ceria nanocube (C-CeO₂) and ceria nanorod (R-CeO₂), respectively, and annealed them at 600 °C in air, 30%, 60% or pure H₂. After annealing, the surface OVs concentration of ceria elevates with the rising of H₂ concentration. Photocatalytic activity of annealed ceria is promoted with the increasing of surface OVs, the methylene blue photodegradation ratio with pure hydrogen annealed of P-CeO₂, C-CeO₂ or R-CeO₂ is 93.82%, 85.15% and 90.09%, respectively. Band gap of annealed ceria expands first and then tends to narrow slightly with the rising of surface OVs, while the valence band (VB) and conductive band (CB) of annealed ceria changed slightly. Both of photoluminescence spectra and photocurrent results indicate that the separation efficiency of photoinduced electron-hole pairs is significantly enhanced with the increasing of the surface OVs concentration. The notable weakened recombination of photogenerated carrier is suggested to attribute a momentous contribution on the enhanced photocatalytic activity of ceria which contains surface OVs.

Rational Development of Guanidinate and Amidinate Based Cerium and Ytterbium Complexes as Atomic Layer Deposition Precursors: Synthesis, Modeling, and Application

Owing to the limited availability of suitable precursors for vapor phase deposition of rare-earth containing thin-film materials, new or improved precursors are sought after. In this study, we explored new precursors for atomic layer deposition (ALD) of cerium (Ce) and ytterbium (Yb) containing thin films. A series of homoleptic tris-guanidinate and tris-amidinate complexes of cerium (Ce) and ytterbium (Yb) were synthesized and thoroughly characterized. The C-substituents on the N-C-N backbone (Me, NMe2 , NEt2 , where Me=methyl, Et=ethyl) and the N-substituents from symmetrical iso-propyl (iPr) to asymmetrical tertiary-butyl (tBu) and Et were systematically varied to study the influence of the substituents on the physicochemical properties of the resulting compounds. Single crystal structures of [Ce(dpdmg)3 ] 1 and [Yb(dpdmg)3 ] 6 (dpdmg=N,N'-diisopropyl-2-dimethylamido-guanidinate) highlight a monomeric nature in the solid-state with a distorted trigonal prismatic geometry. The thermogravimetric analysis shows that the complexes are volatile and emphasize that increasing asymmetry in the complexes lowers their melting points while reducing their thermal stability. Density functional theory (DFT) was used to study the reactivity of amidinates and guanidinates of Ce and Yb complexes towards oxygen (O2 ) and water (H2 O). Signified by the DFT calculations, the guanidinates show an increased reactivity toward water compared to the amidinate complexes. Furthermore, the Ce complexes are more reactive compared to the Yb complexes, indicating even a reactivity towards oxygen potentially exploitable for ALD purposes. As a representative precursor, the highly reactive [Ce(dpdmg)3 ] 1 was used for proof-of-principle ALD depositions of CeO2 thin films using water as co-reactant. The self-limited ALD growth process could be confirmed at 160 °C with polycrystalline cubic CeO2 films formed on Si(100) substrates. This study confirms that moving towards nitrogen-coordinated rare-earth complexes bearing the guanidinate and amidinate ligands can indeed be very appealing in terms of new precursors for ALD of rare earth based materials.

Thermocatalytic CO2 Conversion over a Nickel-Loaded Ceria Nanostructured Catalyst: A NAP-XPS Study

Despite the increasing economic incentives and environmental advantages associated to their substitution, carbon-rich fossil fuels are expected to remain as the dominant worldwide source of energy through at least the next two decades and perhaps later. Therefore, both the control and reduction of CO₂ emissions have become environmental issues of major concern and big challenges for the international scientific community. Among the proposed strategies to achieve these goals, conversion of CO₂ by its reduction into high added value products, such as methane or syngas, has been widely agreed to be the most attractive from the environmental and economic points of view. In the present work, thermocatalytic reduction of CO₂ with H₂ was studied over a nanostructured ceria-supported nickel catalyst. Ceria nanocubes were employed as support, while the nickel phase was supported by means a surfactant-free controlled chemical precipitation method. The resulting nanocatalyst was characterized in terms of its physicochemical properties, with special attention paid to both surface basicity and reducibility. The nanocatalyst was studied during CO₂ reduction by means of Near Ambient Pressure X-ray Photoelectron Spectroscopy (NAP-XPS). Two different catalytic behaviors were observed depending on the reaction temperature. At low temperature, with both Ce and Ni in an oxidized state, CH₄ formation was observed, whereas at high temperature above 500 °C, the reverse water gas shift reaction became dominant, with CO and H₂O being the main products. NAP-XPS was revealed as a powerful tool to study the behavior of this nanostructured catalyst under reaction conditions.

Growth, sintering, and chemical states of Co supported on reducible CeO2(111) thin films: The effects of the metal coverage and the nature of the support

The growth, sintering, and interaction of cobalt with ceria were studied under ultrahigh vacuum conditions by vapor-deposition of Co onto well-defined CeO_x(111) (1.5 < x < 2) thin films grown on Ru(0001). Charge transfer from Co to ceria occurs upon deposition of Co on CeO_1.96 and partially reduced CeO_1.83 at 300 K. X-ray photoelectron spectroscopy studies show that Co is oxidized to Co²⁺ species at the cost of the reduction of Ce⁴⁺ to Ce³⁺, at a lesser extent on reduced ceria. Co²⁺ is the predominant species on CeO_1.96 at low Co coverages (e.g., ≤0.20 ML). The ratio of metallic Co/Co²⁺ increases with the increase in the Co coverage. However, both metallic Co and Co²⁺ species are present on CeO_1.83 even at low Co coverages with metallic Co as the major species. Scanning tunneling microscopy results demonstrate that Co tends to wet the CeO_1.96 surface at very low Co coverages at room temperature forming one-atomic layer high structures of Co-O-Ce. The increase in the Co coverage can cause the particle growth into three-dimensional structures. The formation of slightly flatter Co particles was observed on reduced CeO_1.83. In comparison with other transition metals including Ni, Rh, Pt, and Au, our studies demonstrate that Co on ceria exhibits a smaller particle size and higher thermal stability, likely arising from strong metal-support interactions. The formed particles upon Co deposition at 300 K are present on the ceria surface after heating to 1000 K. The Co-ceria interface can be tuned by varying the Co metal coverage, the annealing temperature, and the nature of the ceria surface.

Enhancing Bifunctional Electrocatalytic Activities of Oxygen Electrodes via Incorporating Highly Conductive Sm3+ and Nd3+ Double-Doped Ceria for Reversible Solid Oxide Cells

Solid oxide cells (SOCs) are mutually convertible energy devices capable of generating electricity from chemical fuels including hydrogen in the fuel cell mode and producing green hydrogen using electricity from renewable but intermittent solar and wind resources in the electrolysis cell mode. An effective approach to enhance the performance of SOCs at reduced temperatures is by developing highly active oxygen electrodes for both oxygen reduction and oxygen evolution reactions. Herein, highly conductive Sm³⁺ and Nd³⁺ double-doped ceria (Sm_0.075Nd_0.075Ce_0.85O_2-δ, SNDC) is utilized as an active component for reversible SOC applications. We develop a novel La_0.6Sr_0.4Co_0.2Fe_0.8O_3 -δ (LSCF)-SNDC composite oxygen electrode. Compared with the conventional LSCF-Gd-doped ceria oxygen electrode, the LSCF-SNDC exhibits ∼35% lower cathode polarization resistance (0.042 Ω cm² at 750 °C) owing to rapid oxygen incorporation and surface diffusion kinetics. Furthermore, the SOC with the LSCF-SNDC oxygen electrode and the SNDC buffer layer yields a remarkable performance in both the fuel cell (1.54 W cm^-2 at 750 °C) and electrolysis cell (1.37 A cm^-2 at 750 °C) modes because the incorporation of SNDC promotes the surface diffusion kinetics at the oxygen electrode bulk and the activity of the triple phase boundary at the interface. These findings suggest that the highly conductive SNDC material effectively enhances both oxygen reduction and oxygen evolution reactions, thus serving as a promising material in reversible SOC applications at reduced temperatures.