A review on oxygen storage capacity of CeO2-based materials: Influence factors, measurement techniques, and applications in reactions related to catalytic automotive emissions control

Role of H2O Adsorption in CO Oxidation over Cerium-Oxide Cluster Anions (CeO2)nO- (n = 1-4)

Water (H2O) is ubiquitous in the environment and inevitably participates in many surface reactions, including CO oxidation. Acquiring a fundamental understanding of the roles of H2O molecules in CO oxidation poses a challenging but pivotal task in real-life catalysis. Herein, benefiting from state-of-the-art mass-spectrometric experiments and quantum chemical calculations, we identified that the dissociation of a H2O molecule on each of the cerium oxide cluster anions (CeO2)nO- (n = 1-4) at room temperature can create a new atomic oxygen radical (O•-) that then oxidizes a CO molecule. The size-dependent reactivity of H2O-mediated CO oxidation on (CeO2)nO- clusters was rationalized by the orbital compositions (O2p) and energies of the lowest unoccupied molecular orbitals of active O•- radicals modified by H2O dissociation. Our findings not only provide new insights into H2O-mediated CO oxidation but also demonstrate the importance of H2O in modulating the reactivity of the O•- radicals.

Insight into the effect of exposed crystal facets of anatase TiO2 on HCHO catalytic oxidation of Mn-Ce/TiO2

Indoor formaldehyde pollution seriously jeopardizes human health. The development of efficient and stable non-precious metal catalysts for low-temperature catalytic degradation of formaldehyde is a promising approach. In this study, TiO2 {001} and {101} supports were loaded with different ratios of Mn and Ce active components, and the effects of the ratios of the active components on the catalytic activity were investigated. The elemental oxidation states, redox capacities, active oxygen mobilities and acid site distributions of the catalysts were determined using characterization techniques such as XPS, H2-TPR, O2-TPD, and NH3-TPD. In situ infrared spectroscopy was utilized to reveal the differences in the two-step dehydrogenation reactions of dioxymethylene (DOM) in 5Mn1Ce/Ti-NS and 5Mn1Ce/Ti-NP. Density-functional theory was used to investigate the differences in the catalytic steps and maximum energy barriers of Mn-Ce/Ti-NS and Mn-Ce/Ti-NP for HCHO. The differences in catalytic activity due to the influence of the manganese and cerium active components on the {001} and {101} crystal faces of anatase titanium dioxide are comprehensively revealed. Exposure of the supported crystalline surfaces alters the catalytic activity centers and reaction pathways at the molecular level. This study provides experimental and theoretical guidance for the selection of exposed crystalline surfaces for loaded catalysts.

Low-temperature redox activity and alcohol ammoxidation performance on Cu- and Ru-incorporated ceria catalysts

Transition-metal-incorporated cerium oxides with Cu and a small amount of Ru (Cu0.18Ru0.05CeOz) were prepared, and their low-temperature redox performance (<423 K) and catalytic alcohol ammoxidation performance were investigated. Temperature-programmed reduction/oxidation under H2/O2 and in situ X-ray absorption fine structure revealed the reversible redox behavior of the three metals, Cu, Ru, and Ce, in the low-temperature redox processes. The initially reduced Ru species decreased the reduction temperature of Cu oxides and promoted the activation of Ce species. Cu0.18Ru0.05CeOz selectively catalyzed the production of benzonitrile in the ammoxidation of benzyl alcohol. H2-treated Cu0.18Ru0.05CeOz showed a slightly larger initial conversion of benzyl alcohol than O2-treated Cu0.18Ru0.05CeOz, suggesting that the reduced structure of Cu0.18Ru0.05CeOz was active for the ammoxidation. The integration of both Cu and Ru resulted in the efficient promotion of ammoxidation, in which the Ru species were involved in the conversion of benzyl alcohol and Cu species were required for selective production of benzonitrile.

Mn and Co decorated biomorphic ceria fiber catalysts for soot and benzene total oxidation

Mn or Co supported CeO2 fiber catalysts were synthesized following a biotemplating route and evaluated in soot combustion and benzene total oxidation. The catalysts were characterized by SEM, EDX, N2 physisorption, FTIR-ATR, XRD, RAMAN and XPS. SEM results confirmed that the "twisted ribbon" morphology of the biotemplate was mostly maintained. XRD and Raman showed that Mn and Co cations partially insert into ceria lattice and also segregate at the surface of the fibers. XPS allowed to determine that both set of catalysts exhibit Ce3+ and Ce4+ species, in addition to adsorbed and lattice oxygen. Also, the average oxidation state (AOS) of surface Mn could be calculated. Compared to bare Fib Ce, the performances for both reactions were improved for the supported catalysts, except from the catalyst with lowest Mn content for soot combustion. The catalytic activity was discussed in terms of the physicochemical features of the supported catalysts.

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.

Microfluidic Immunosensor Platform for Sensitive Detection of Human Epidermal Growth Factor Receptor-2 Based on Enhanced Cathode Electrochemiluminescence of Bimetallic Nanoclusters

In this work, a microfluidic immunosensor chip was developed by incorporating microfluidic technology with electrochemiluminescence (ECL) for sensitive detection of human epidermal growth factor receptor-2 (HER2). The immunosensor chip can achieve robust reproducibility in mass production by integrating multiple detection units in a series. Notably, nanoscale materials can be better adapted to microfluidic systems, greatly enhancing the accuracy of the immunosensor chip. Ag@Au NCs closed by glutathione (GSH) were introduced in the ECL microfluidic immunosensor system with excellent and stable ECL performance. The synthesized CeO2-Au was applied as a coreaction promoter in the ECL signal amplification system, which made the result of HER2 detection more reliable. In addition, the designed microfluidic immunosensor chip integrated the biosensing system into a microchip, realizing rapid and accurate detection of HER2 by its high throughput and low usage. The developed short peptide ligand NARKFKG (NRK) achieved an effective connection between the antibody and nanocarrier for improving the detection efficiency of the sensor. The immunosensor chip had better storage stability and sensitivity than traditional detection methods, with a wide detection range from 10 fg·mL-1 to 100 ng·mL-1 and a low detection limit (LOD) of 3.29 fg·mL-1. In general, a microfluidic immunosensor platform was successfully constructed, providing a new idea for breast cancer (BC) clinical detection.

Structural Heredity in Catalysis: CO2 Self-Selective CeO2 Nanocrystals for Efficient Photothermal CO2 Hydrogenation to Methane

The chemical inertness of CO2 molecules makes their adsorption and activation on a catalyst surface one of the key challenges in recycling CO2 into chemical fuels. However, the traditional template synthesis and chemical modification strategies used to tackle this problem face severe structural collapse and modifier deactivation issues during the often-needed post-processing procedure. Herein, a CO2 self-selective hydrothermal growth strategy is proposed for the synthesis of CeO2 octahedral nanocrystals that participate in strong physicochemical interactions with CO2 molecules. The intense affinity for CO2 molecules persists during successive high-temperature treatments required for Ni deposition. This demonstrates the excellent structural heredity of the CO2 self-selective CeO2 nanocrystals, which leads to an outstanding photothermal CH4 productivity exceeding 9 mmol h-1 mcat -2 and an impressive selectivity of >99%. The excellent performance is correlated with the abundant oxygen vacancies and hydroxyl species on the CeO2 surface, which create many frustrated Lewis-pair active sites, and the strong interaction between Ni and CeO2 that promotes the dissociation of H2 molecules and the spillover of H atoms, thereby greatly benefitting the photothermal CO2 methanation reaction. This self-selective hydrothermal growth strategy represents a new pathway for the development of effective catalysts for targeted chemical reactions.

Effect of Metal Oxides (CeO2, ZnO, TiO2, and Al2O3) as the Support for Silver-Supported Catalysts on the Catalytic Oxidation of Diesel Particulate Matter

This work presented the influence of metal oxides as the support for silver-supported catalysts on the catalytic oxidation of diesel particulate matter (DPM). The supports selected to be used in this work were CeO2 (reducible), ZnO (semiconductor), TiO2 (reducible and semiconductor), and Al2O3 (acidic). The properties of the synthesized catalysts were investigated using XRD, TEM, H2-TPR, and XPS techniques. The DPM oxidation activity was performed using the TGA method. Different states of silver (e.g., Ag° and Ag+) were formed with different concentrations and affected the performance of the DPM oxidation. Ag2O and lattice oxygen, which were mainly generated by Ag/ZnO and Ag/CeO2, were responsible for combusting the VOCs. The metallic silver (Ag°) formed primarily on Ag/Al2O3 and Ag/TiO2 was the main component promoting soot combustion. Contact between the catalyst and DPM had a minor effect on VOC oxidation but significantly affected the soot oxidation activity.

Tailored Platinum Group Metal/Spinel Oxide Catalysts for Dynamically Enhanced Methane Oxidation

A combined experimental and molecular modeling study identifies a family of spinel oxides that in combination with PGM (platinum group metals) provide enhanced methane oxidation activity. With a reduction in greenhouse gas (GHG) emissions urgently needed, there is renewed interest in the use of natural gas vehicles (NGVs) and engines (NGEs) for transportation, commerce, and industrial applications. NGVs and NGEs emit less CO2 than their petroleum-derived counterparts but may emit uncombusted methane, an even more potent GHG. For stoichiometric engines, methane oxidation catalysts containing PGM and spinel oxide in layered architectures offer increased methane oxidation activity and lower light-off temperatures (T50). The reducible spinel oxide has direct and indirect roles that are effectively described by the bulk oxygen vacancy formation energy (Evac). We apply density functional theory (DFT) to identify several earth-abundant, cobalt-rich spinel oxides with favorable Evac, shown to correlate with dynamic oxygen storage capacity (DOSC) and CO and H2 oxidation activity. We experimentally rank-order the DFT-identified spinel oxides in combination with Pt+Pd for their methane oxidation activity measurements, under both time-invariant and modulated feed conditions. We show good agreement between the activity and the DFT-computed reducibility of the spinel oxide. The findings suggest spinel reducibility is a key factor in achieving enhanced low-temperature methane conversion, enabled through a balance of methane activation on the PGM sites and subsequent oxidation of the intermediates and byproducts on spinel oxides. In agreement with its computationally predicted Evac, NiCo2O4 was confirmed to have the highest DOSC and lowest T50 among the tested spinel samples.

Ru-Ce0.7Zr0.3O2-δ as an Anode Catalyst for the Internal Reforming of Dimethyl Ether in Solid Oxide Fuel Cells

The development of direct dimethyl ether (DME) solid oxide fuel cells (SOFCs) has several drawbacks, due to the low catalytic activity and carbon deposition of conventional Ni-zirconia-based anodes. In the present study, the insertion of 2.0 wt.% Ru-Ce0.7Zr0.3O2-δ (ruthenium-zirconium-doped ceria, Ru-CZO) as an anode catalyst layer (ACL) is proposed to be a promising solution. For this purpose, the CZO powder was prepared by the sol-gel synthesis method, and subsequently, nanoparticles of Ru (1.0-2.0 wt.%) were synthesized by the impregnation method and calcination. The catalyst powder was characterized by BET-specific surface area, X-ray diffraction (XRD), field emission scanning electron microscopy with an energy-dispersive spectroscopy detector (FESEM-EDS), and transmission electron microscopy (TEM) techniques. Afterward, the catalytic activity of Ru-CZO catalyst was studied using DME partial oxidation. Finally, button anode-supported SOFCs with Ru-CZO ACL were prepared, depositing Ru-CZO onto the anode support and using an annealing process. The effect of ACL on the electrochemical performance of cells was investigated under a DME and air mixture at 750 °C. The results showed a high dispersion of Ru in the CZO solid solution, which provided a complete DME conversion and high yields of H2 and CO at 750 °C. As a result, 2.0 wt.% Ru-CZO ACL enhanced the cell performance by more than 20% at 750 °C. The post-test analysis of cells with ACL proved a remarkable resistance of Ru-CZO ACL to carbon deposition compared to the reference cell, evidencing the potential application of Ru-CZO as a catalyst as well as an ACL for direct DME SOFCs.

Hydrocarbon adsorption mechanism of modern automobile engines and methods of reducing hydrocarbon emissions during cold start process: A review

With the global emphasis on environmental protection and increasingly stringent emission regulations for internal combustion engines, there is an urgent need to overcome the problem of large hydrocarbon (HC) emissions caused by unstable engine cold starts. Synergistic engine pre-treatment (reducing hydrocarbon production) as well as after-treatment devices (adsorbing and oxidizing hydrocarbons) is the fundamental solution to emissions. In this paper, the improvement of hydrocarbon emissions is summarized from two aspects: pre-treatment and after-treatment. The pre-treatment for engine cold start mainly focuses on summarizing the intake control, fuel, and engine timing parameters. The after-treatment mainly focuses on summarizing different types of adsorbents and modifications (mainly including different molecular sieve structures and sizes, preparation conditions, silicon aluminum ratio, ion exchange modification, and heterogeneity, etc.), adsorptive catalysts (mainly including optimization of catalytic performance and structure), and catalytic devices (mainly including coupling with thermal management equipment and HC trap devices). In this paper, a SWOT (strength, weakness, opportunity, and threat) analysis of pre-treatment and after-treatment measures is conducted. Researchers can obtain relevant research results and seek new research directions and approaches for controlling cold start HC emissions.

La2O3-CeO2-Supported Bimetallic Cu-Ni DRM Catalysts

The present work is focused on nickel catalysts supported on La2O3-CeO2 binary oxides without and with the addition of Cu to the active component for the dry reforming of methane (DRM). The catalysts are characterized using XRD, XRF, TPD-CO2, TPR-H2, and low-temperature N2 adsorption-desorption methods. This work shows the effect of different La:Ce ratios (1:1 and 9:1) and the Cu addition on the structural, acid base, and catalytic properties of Ni-containing systems. The binary LaCeOx oxide at a ratio of La:Ce = 1:1 is characterized by the formation of a solid solution with a fluorite structure, which is preserved upon the introduction of mono- or bimetallic particles. At La:Ce = 9:1, La2O3 segregation from the solid solution structure is observed, and the La excess determines the nature of the precursor of the active component, i.e., lanthanum nickelate. The catalysts based on LaCeOx (1:1) are prone to carbonization during 6 h spent on-stream with the formation of carbon nanotubes. The Cu addition facilitates the reduction of the Cu-Ni catalyst carbonization and increases the number of structural defects in the carbon deposition products. The lanthanum-enriched LaCeOx (9:1) support prevents the accumulation of carbon deposition products on the surface of CuNi/La2O3-CeO2 9:1, providing high DRM activity and an H2/CO ratio of 0.9.

Local environmental engineering for highly stable single-atom Pt1/CeO2catalysts: first-principles insights

Single-atom Pt1/CeO2catalysts may cope with the high cost and durability issues of fuel cell electrocatalysts. In the present study, the stability and underlying interaction mechanisms of the Pt1/CeO2system are systematically investigated using first-principles calculations. The Pt adsorption energy on CeO2surfaces can be divided into chemical interaction and surface deformation parts. The interaction energy, mainly associated with the local chemical environment, i.e. the number of Pt-O bonds, plays a major role in Pt1/CeO2stability. When forming a Pt-4O configuration, the catalytic system has the highest stability and Pt is oxidized to Pt2+. An electronic metal-support interaction mechanism is proposed for understanding Pt1/CeO2stability. In addition, our calculations show that the Pt1/CeO2(100) system is dynamically stable, and the external O environment can promote the further oxidation of Pt to Ptn+(2 ≤n< 4). The present study provides useful guidance for the experimental development of highly stable and efficient electrocatalysts for fuel cell applications.

Direct Oxidation of Hibiscus cannabinus Stalks to Vanillin Using CeO2 Nanostructure Catalysts

Biomass lignin can be used to produce vanillin through an oxidation process. Although its purity is high, the processing time and separation efficiency are not ideal. This research aims to produce vanillin directly from Kenaf stalks without separating the lignin first from the lignocellulosic biomass. This method is greener because it does not require the separation of cellulose and hemicellulose from the biomass, thus minimizing the use of acid and alkaline solutions and saving time. A high oxygen storage capacity and release capacity of ceria as an oxidation catalyst contribute to the reversable redox properties between Ce4+ and Ce3+ in ceria lattice. Cerium oxide nanostructures were synthesized using a hydrothermal method treated under alkaline NaOH, followed by drying at 120 °C for 16 h and calcining at different temperatures between 400 and 600 °C for the direct oxidation of Kenaf stalks to vanillin under microwave irradiation. The catalysts were characterized for their physicochemical properties using XRD, N2 adsorption-desorption isotherms and TEM. All synthesized CeO2 nanostructures showed the presence of diffraction peaks assigned to the presence of cubic fluorite. The N2 adsorption-desorption isotherms showed that all catalysts possess a Type IV isotherm, indicating a mesoporous structure. The TEM image shows the uniform shape of the CeO2 nanostructures, while HRTEM images show that the CeO2 nanostructures are single-crystalline in nature. All catalysts were tested for the direct oxidation of Kenaf stalks using H2O2 as the oxidizing agent in temperatures ranging from 160 to 180 °C for 10-30 min with 0.1-0.3 g catalyst loading under 100-500 W of microwave irradiation. The CeO2-Nps-400 catalyst produced the highest vanillin yields of 3.84% and 4.32% for the direct oxidation of Kenaf stalks and extraction of lignin from Kenaf stalks, respectively. Compared to our earlier study, the highest vanillin yields of 2.90% and 3.70% for direct biomass and extracted lignin were achieved using a Ce/MgO catalyst.

Synthesis of Co,Ce Oxide Nanoparticles Using an Aerosol Method and Their Deposition on Different Structured Substrates for Catalytic Removal of Diesel Particulate Matter

The synthesis of Co and Ce oxide nanoparticles using precipitation of precursor salt solutions in the form of microdroplets generated with a nebulizer proved to be an efficient, fast and inexpensive method. Different morphologies of single oxides particles were obtained. Ceria nanoparticles were almost cube-shaped of 8 nm average size, forming 1.3–1.5 μm aggregates, whereas cobalt oxide appeared as rounded-edged particles of 37 nm average size, mainly forming nanorods 50–500 nm. Co3O4 and CeO2 nanoparticles were used to generate structured catalysts from both metallic (stainless steel wire mesh monoliths) and ceramic (cordierite honeycombs) substrates. Ceria Nyacol was used as a binder to favor the anchoring of catalytic particles thus enhancing the adhesion of the coating. The resulting structured catalysts were tested for the combustion of diesel soot with the aim of being used in the regeneration of particulate filters (DPFs). The performance of these structured catalysts was similar to or even better than that exhibited by the catalysts prepared using commercial nanoparticles. Among the catalysts tested, the structured systems using ceramic substrates were more efficient, showing lower values of the maximum combustion rate temperatures (TM = 410 °C).

Effective and Efficient Porous CeO2 Adsorbent for Acid Orange 7 Adsorption

A porous CeO₂ was synthesized following the addition of guanidine carbonate to a Ce³⁺ aqueous solution, the subsequent addition of hydrogen peroxide and a final hydrothermal treatment. The optimal experimental parameters for the synthesis of porous CeO₂, including the amounts of guanidine carbonate and hydrogen peroxide and the hydrothermal conditions, were determined by taking the adsorption efficiency of acid orange 7 (AO7) dye as the evaluation. A template-free hydrothermal strategy could avoid the use of soft or hard templates and the subsequent tedious procedures of eliminating templates, which aligned with the goals of energy conservation and emission reduction. Moreover, both the guanidine carbonate and hydrogen peroxide used in this work were accessible and eco-friendly raw materials. The porous CeO₂ possessed rapid adsorption capacities for AO7 dye. When the initial concentration of AO7 was less than 130 mg/L, removal efficiencies greater than 90.0% were obtained, achieving a maximum value of 97.5% at [AO7] = 100 mg/L and [CeO₂] = 2.0 g/L in the first 10 min of contact. Moreover, the adsorption-desorption equilibrium between the porous CeO₂ adsorbent and the AO7 molecule was basically established within the first 30 min. The saturated adsorption amount of AO7 dye was 90.3 mg/g based on a Langmuir linear fitting of the experimental data. Moreover, the porous CeO₂ could be recycled using a NaOH aqueous solution, and the adsorption efficiency of AO7 dye still remained above 92.5% after five cycles. This study provided an alternative porous adsorbent for the purification of dye wastewater, and a template-free hydrothermal strategy was developed to enable the design of CeO₂-based catalysts or catalyst carriers.

Progress on metal-support interactions in Pd-based catalysts for automobile emission control

The interactions between metals and oxide supports, so-called metal-support interactions (MSI), are of great importance in heterogeneous catalysis. Pd-based automotive exhaust control catalysts, especially Pd-based three-way catalysts (TWCs), have received considerable research attention owing to its prominent oxidation activity of HCs/CO, as well as excellent thermal stability. For Pd-based TWCs, the dispersion, chemical state and thermal stability of Pd species, which are crucial to the catalytic performance, are closely associated with interactions between metal nanoparticles and their supporting matrix. Progress on the research about MSI and utilization of MSI in advanced Pd-based three-way catalysts are reviewed here. Along with the development of advanced synthesis approaches and engine control technology, the study on MSI would play a notable role in further development of catalysts for automobile exhaust control.

Ni-Free SOFC Anode Material with Thermal and Redox Stabilities for the Direct Utilization of Ethanol

The direct utilization of anhydrous ethanol in solid oxide fuel cells (SOFC), with oxygen-storage anode materials of the type Cu-(ZrxCe1−xY0.2O2−δ-Al2O3), is presented. The ceramic processing of CeO2-Al2O3 and 8YSZ (8% mol yttria stabilized zirconia) favors the reaction between Ceria and 8YSZ. Therefore, anode materials composed of active solid solutions, such as (Zr0.25Ce0.75)0.8Y0.2O1.9 (cubic) and (Zr0.50Ce0.50)0.8Y0.2O1.9 (tetragonal), in addition to the Al2O3 phase, are produced and prevent the formation of CeAlO3. The anodes exhibited an excellent oxygen storage capacity, OSC, between 415 to 446 µmolg−1. This occurred due to the replacement of Ce4+ by Zr4+, generating structural defects that increase the oxygen ion mobility and the activity of the Ce4+/Ce3+ redox pair. The anode material presenting the cubic phase showed a better electrochemical performance. The Al2O3 phase provided thermal stability and prevented the coarsening of the solid solution and loss of Ceria’s redox activity. It allowed for SOFC operation at high temperatures, since the yield increased as the operating temperature rose from 750 to 950 °C. An analysis of the results before and after the SOFC operation at 950 °C for 200 h revealed that there was no significant copper grains coarsening since the performance increased with the temperature. The redox behavior during the SOFC operation is also explained through a theoretical physical–chemical mechanism.

High Catalytic Efficiency of a Nanosized Copper-Based Catalyst for Automotives: A Physicochemical Characterization

The global trend in restrictions on pollutant emissions requires the use of catalytic converters in the automotive industry. Noble metals belonging to the platinum group metals (PGMs, platinum, palladium, and rhodium) are currently used for autocatalysts. However, recent efforts focus on the development of new catalytic converters that combine high activity and reduced cost, attracting the interest of the automotive industry. Among them, the partial substitution of PGMs by abundant non-PGMs (transition metals such as copper) seems to be a promising alternative. The PROMETHEUS catalyst (PROM100) is a polymetallic nanosized copper-based catalyst for automotives prepared by a wet impregnation method, using as a carrier an inorganic mixed oxide (CeO2-ZrO2) exhibiting elevated oxygen storage capacity. On the other hand, catalyst deactivation or ageing is defined as the process in which the structure and state of the catalyst change, leading to the loss of the catalyst's active sites with a subsequent decrease in the catalyst's performance, significantly affecting the emissions of the catalyst. The main scope of this research is to investigate in detail the effect of ageing on this low-cost, effective catalyst. To that end, a detailed characterization has been performed with a train of methods, such as SEM, Raman, XRD, XRF, BET and XPS, to both ceria-zirconia mixed inorganic oxide support (CZ-fresh and -aged) and to the copper-based catalyst (PROM100-fresh and -aged), revealing the impact of ageing on catalytic efficiency. It was found that ageing affects the Ce-Zr mixed oxide structure by initiating the formation of distinct ZrO2 and CeO2 structures monitored by Raman and XRD. In addition, it crucially affects the morphology of the sample by reducing the surface area by a factor of nearly two orders of magnitude and increasing particle size as indicated by BET and SEM due to sintering. Finally, the Pd concentration was found to be considerably reduced from the material's surface as suggested by XPS data. The above-mentioned alterations observed after ageing increased the light-off temperatures by more than 175 °C, compared to the fresh sample, without affecting the overall efficiency of the catalyst for CO and CH4 oxidation reactions. Metal particle and CeZr carrier sintering, washcoat loss as well as partial metal encapsulation by Cu and/or CeZrO4 are identified as the main causes for the deactivation after hydrothermal ageing.

Enhanced Stability and Catalytic Performance of Active Rh Sites on Al2O3 Via Atomic Layer Deposited ZrO2

Modulating the Rh active sites on surfaces of Al₂O₃ is crucial to developing effective three-way catalysts. Herein, an ultralow amount of ZrO₂ (0.0179%) was deposited onto Al₂O₃ nanorods via atomic layer deposition (ALD) to form a catalyst with both thermal stability and low-temperature activity. The results demonstrate that the ALD-ZrO₂ is conducive to improve the catalytic activity of the Rh site and inhibit the formation of irreducible Rh species at high temperature. The obtained catalysts show satisfactory performance for a model NO-CO reaction even after thermal aging at 1050 °C. This strategy shows that a molecularly precise synthesis can lead to the robust promotion of Rh activity under low temperature and provide a promising path toward reducing the deactivation of catalysts at high temperature.

TiO2 nanosheet supported MnCeOx: a remarkable catalyst with enhanced low-temperature catalytic activity in o-DCB oxidation

Morphology engineering was an effective strategy for 1,2-dichlorobenzene (o-DCB) oxidation. Herein, TiO₂ nanosheet supported MnCeO_x (TiMn15Ce30-NS) showed excellent catalytic activity with T_50% = 156 °C and T_90% = 238 °C, which was better than the T_50% = 213 °C and T_90% = 247 °C for TiO₂ nano truncated octahedron supported MnCeO_x (TiMn15Ce30-NTO). TiMn15Ce30-NS also exhibited enhanced water resistance (T_50% = 179 °C, T_90% = 240 °C), and good stability with the o-DCB conversion retained at 98.9% for 12 h at 350 °C. The excellent catalytic activity of TiMn15Ce30-NS could be mainly ascribed to the preferentially exposed {001} crystal plane and Ce addition which favored the higher concentration of Mn⁴⁺ and surface active oxygen, along with stronger interaction between MnO_x and CeO_x. The present results deepen the understanding of the morphology-dependent effect on o-DCB oxidation.

Shape-Controlled Pathways in the Hydrogen Production from Ethanol Steam Reforming over Ceria Nanoparticles

The ethanol surface reaction over CeO₂ nanooctahedra (NO) and nanocubes (NC), which mainly expose (111) and (100) surfaces, respectively, was studied by means of infrared spectroscopy (TPSR-IR), mass spectrometry (TPSR-MS), and density functional theory (DFT) calculations. TPSR-MS results show that the production of H₂ is 2.4 times higher on CeO₂-NC than on CeO₂-NO, which is rationalized starting from the different types of adsorbed ethoxy species controlled by the shape of the ceria particles. Over the CeO₂(111) surface, monodentate type I and II ethoxy species with the alkyl chain perpendicular or parallel to the surface, respectively, were identified. Meanwhile, on the CeO₂(100) surface, bidentate and monodentate type III ethoxy species on the checkerboard O-terminated surface and on a pyramid of the reconstructed (100) surface, respectively, are found. The more labile surface ethoxy species on each ceria nanoshape, which are the monodentate type I or III ethoxy on CeO₂-NO and CeO₂-NC, respectively, react on the surface to give acetate species that decompose to CO₂ and CH₄, while H₂ is formed via the recombination of hydroxyl species. In addition, the more stable monodentate type II and bidentate ethoxy species on CeO₂-NO and CeO₂-NC, respectively, give an ethylenedioxy intermediate, the binding of which is facet-dependent. On the (111) facet, the less strongly bound ethylenedioxy desorbs as ethylene, whereas on the (100) facet, the more strongly bound intermediate also produces CO₂ and H₂ via formate species. Thus, on the (100) facet, an additional pathway toward H₂ formation is found. ESR activity measurements show an enhanced H₂ production on the nanocubes.

Interaction between Nickel Oxide and Support Promotes Selective Catalytic Reduction of NOx with C3H6

Selective catalytic reduction of NO x by C 3 H 6 (C 3 H 6 -SCR) was investigated over NiO catalysts supported on different metaloxides. A NiAlO x mixed oxide phase was formed over NiO/γ-Al 2 O 3 catalyst, inducing an immediate interaction between NiO x and AlO x species. Such interaction resulted in a charge transfer from Ni to Al site and the formation of Ni species in high oxidation state. In comparison to other NiO-loaded catalysts, NiO/γ-Al 2 O 3 catalyst exhibited the highest NO x conversion at temperature higher than 450 °C, but a poor C 3 H 6 oxidation activity due to the decreased nucleophilicity for surface oxygen species. By temperatureprogramed NO oxidation, it is indicated that nitrate species were rapidly formed and stably maintained at high temperature over NiO/γ-Al 2 O 3 catalyst. In situ transient reactions further verified the LangmuirHinshelwood mechanism for C 3 H 6 -SCR, where both gaseous NO and C 3 H 6 were adsorbed and activated on catalyst surface and reacted to generate N 2 . Due to the strong metal-support interaction over NiO/γ-Al 2 O 3 catalyst, both nitrate and C x H y O z intermediates were well preserved to attain high C 3 H 6 -SCR activity.

Mechanisms of temperature-dependent oxygen absorption/release and appearance of intermediate phase in κ-Ce2Zr2O8: study based on oxygen vacancy formation energy computations

This study clarified the mechanisms of the temperature-dependent oxygen absorption/release properties and appearance of the intermediate phase for κ-Ce2Zr2O8, which is known to have a high oxygen storage/release capacity (OSC). First-principle computations revealed that the vacancy formation energies depend on the number of vacancies and can be categorized into two groups: low-energy and high-energy. The intermediate phase observed experimentally was assigned to the state after all the oxygen vacancies in the low-energy group were formed. We also found that the mechanism of the improved OSC performance by Ti substitution could be explained in terms of the vacancy formation energies.

Exploring the Influence of Synthesis Parameters on the Optical Properties for Various CeO2 NPs

Cerium oxide (CeO₂) nanoparticles were synthesized with a chemical precipitation method in different experimental conditions using cerium nitrate hexahydrate (Ce(NO₃)₃·6H₂O) as a precursor, modifying the solution pH, the reaction time, and Co atoms as dopants, in order to tune the band gap energy values of the prepared samples. The physical characteristics of the synthesized ceria nanoparticles were evaluated by Fourier transform infrared (FT-IR) spectroscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), UV–Vis analyses and photoluminescence measurements. XRD data revealed a pure cubic fluorite structure of CeO₂ NPs, the estimation of crystallite sizes by Scherrer’s formula indicates the formation of crystals with dimensions between 11.24 and 21.65 nm. All samples contain nearly spherical CeO₂ nanoparticles, as well as cubic, rhomboidal, triangular, or polyhedral nanoparticles that can be identified by TEM images. The optical investigation of CeO₂ samples revealed that the band gap energy values are between 3.18 eV and 2.85 eV, and, after doping with Co atoms, the E_g of samples decreased to about 2.0 eV. In this study, we managed to obtain CeO₂ NPs with E_g under 3.0 eV by only modifying the synthesis parameters. In addition, by doping with Co ions, the band gap energy value was lowered to 2.0 eV. This aspect leads to promising results that provide an encouraging approach for future photocatalytic investigations.

Soot oxidation in low-O2 and O2-free environment by lanthanum-based perovskites: structural changes and the effect of Ag doping

The use of La-based, Cu (LCO), Mn (LMO) and Fe (LFO) perovskites doped with Ag were studied for potential application as cGPF soot oxidation catalysts. Special emphasis was placed on...

Effect of oxygen storage materials on the performance of Pt-based three-way catalysts

Pt supported on oxygen storage materials (CeO2 and CeO2–ZrO2) as effective three-way catalysts.

Improvement of the Oxygen Storage/Release Speed of YBaCo4O7+δ Synthesized by a Glycine-Complex Decomposition Method

The present study explores the oxygen storage capacity of YBaCo₄O_7+δ prepared by a glycine-complex decomposition method. We reported for the first time that the YBaCo₄O_7+δ sample was successfully synthesized at such a low temperature of 800 °C by this method. The YBCO-800 N sample exhibited a faster oxygen absorption/desorption speed than that of high calcination temperature samples, and the time required for complete oxygen storage/release was 5 and 6 min at 360 °C, respectively. Moreover, the superior performance observed for this product in the temperature swing adsorption process makes it a promising candidate in oxygen production technologies. This research demonstrated that the glycine-complex decomposition method is an effective method for improving the oxygen storage property of YBaCo₄O_7+δ and provides a new insight into designing other novel oxygen storage materials.

Atomic level fluxional behavior and activity of CeO2-supported Pt catalysts for CO oxidation

Reducible oxides are widely used catalyst supports that can increase oxidation reaction rates by transferring lattice oxygen at the metal-support interface. There are many outstanding questions regarding the atomic-scale dynamic meta-stability (i.e., fluxional behavior) of the interface during catalysis. Here, we employ aberration-corrected operando electron microscopy to visualize the structural dynamics occurring at and near Pt/CeO₂ interfaces during CO oxidation. We show that the catalytic turnover frequency correlates with fluxional behavior that (a) destabilizes the supported Pt particle, (b) marks an enhanced rate of oxygen vacancy creation and annihilation, and (c) leads to increased strain and reduction in the CeO₂ support surface. Overall, the results implicate the interfacial Pt-O-Ce bonds anchoring the Pt to the support as being involved also in the catalytically-driven oxygen transfer process, and they suggest that oxygen reduction takes place on the highly reduced CeO₂ surface before migrating to the interfacial perimeter for reaction with CO.

Revealing the Effect of Synthesis Conditions on the Structural, Optical, and Antibacterial Properties of Cerium Oxide Nanoparticles

Cerium oxide nanoparticles were prepared by a precipitation method using Ce(IV) sulphate as precursor dispersed in glycerol with varying synthesis parameters such as temperature or precipitating agent. The structural and morphological characteristics of the obtained nanoparticles were investigated by X-ray diffraction, transmission electron microscopy, and diffuse reflectance spectroscopy. The crystallite size of the nanoparticles varied between 13 and 17 nm. The presence of Ce3+ and Ce4+ was proved by XPS data in the CeO2 samples and the conservation of the fluorite structure was evinced by X-ray diffractograms with a contraction of the lattice parameter, regardless of the size of the nanoparticle. From diffuse reflectance spectra, two band gap energy values for the direct transition were observed. Depending on the synthesis condition, the red shift of gap energy and the blue shift of Urbach energy with increasing content of Ce3+ were ascertained. The antibacterial tests revealed that the cerium oxide nanoparticles show good antimicrobial activity towards the common pathogens Escherichia coli and Staphylococcus aureus.

Oxygen-Storage Materials to Stabilize the Oxygen Redox Activity of Three-Layered Sodium Transition Metal Oxides

To double the energy density of lithium- and sodium-ion batteries there is a need to activate simultaneously cationic and anionic redox reactions at the intercalation-type electrodes. In contrast to the cationic redox activity, the oxygen redox activity enforces an enhancement in the surface reactivity of the oxides leading to their poor reversibility and cycling stability. Herein, we propose a new concept to stabilize oxygen redox activity by using oxygen-storage materials as an efficient buffer supplying and receiving oxygen during alkali ion intercalation. As a proof-of-concept, the study is focused on CeO₂ as a modifier of sodium nickel-manganese oxide with a three-layer sequence, P3-Na_2/3Ni_1/2Mn_1/2O₂. The CeO₂-modified P3-Na_2/3Ni_1/2Mn_1/2O₂ displays a drastic increase in the reversible capacity following the order Na⁺ intercalation < Li⁺ intercalation < Li⁺,Na⁺ cointercalation.

First of Its Kind Automotive Catalyst Prepared by Recycled PGMs-Catalytic Performance

The production of new automotive catalytic converters requires the increase of the quantity of Platinum Group Metals in order to deal with the strict emission standards that are imposed for vehicles. The use of PGMs coming from the recycling of spent autocatalysts could greatly reduce the cost of catalyst production for the automotive industry. This paper presents the synthesis of novel automotive Three-Way Catalysts (PLTWC, Pd/Rh = 55/5, 60 gPGMs/ft3) and diesel oxidation catalysts (PLDOC, Pt/Pd = 3/1, 110 gPGMs/ft3) from recovered PGMs, without further refinement steps. The catalysts were characterized and evaluated in terms of activity in comparison with benchmark catalysts produced using commercial metal precursors. The small-scale catalytic monoliths were successfully synthesized as evidenced by the characterization of the samples with XRF analysis, optical microscopy, and N2 physisorption. Hydrothermal ageing of the catalysts was performed and led to a significant decrease of the specific surface area of all catalysts (recycled and benchmarks) due to sintering of the support material and metal particles. The TWCs were studied for their activity in CO and unburned hydrocarbon oxidation reactions under a slightly lean environment of the gas mixture (λ > 1) as well as for their ability to reduce NOx under a slightly rich gas mixture (λ < 1). Recycled TWC fresh catalyst presented the best performance amongst the catalysts studied for the abatement of all pollutant gases, and they also showed the highest Oxygen Storage Capacity value. Moreover, comparing the aged samples, the catalyst produced from recycled PGMs presented higher activity than the one synthesized with the use of commercial PGM metal precursors. The results obtained for the DOC catalysts showed that the aged PLDOC catalyst outperformed both the fresh catalyst and the aged DOC catalyst prepared with the use of commercial metal precursors for the oxidation of CO, hydrocarbons, and NO. The latter reveals the effect of the presence of several impurities in the recovered PGMs solutions.