Oxygen Storage Capacity Research Articles

Catalytic activity of Zr/CeO2-Al2O3 catalyst for diesel soot oxidation: synthesis, characterization, and performance evaluation.

Diesel soot is a significant contributor to air pollution. Soot particles present in diesel engine exhaust have a negative impact on the environment and human health. Diesel oxidation catalysts (DOCs) and diesel particulate filters (DPFs) currently use noble metal-based catalysts for soot oxidation. Due to the use of noble metals in the catalyst, the cost of diesel after-treatment systems is steadily rising. As a result, diesel vehicles have become commercially less viable than gasoline vehicles and electronic vehicles. The study focuses on an alternative diesel oxidation catalyst with efficiency similar to that of a noble metal catalyst but with a much lower cost. CeO2-Al2O3 catalysts are known for their oxygen storage capacity and high redox activity, making them suitable for soot oxidation. Adding Zr to these catalysts has been shown to influence their structural and chemical properties, significantly affecting their catalytic behavior. Therefore, the current study is focused on using Zr/CeO2-Al2O3 as a substitute for noble metal-based catalysts to enhance its performance for diesel soot oxidation in automotive exhaust. Evaporation-induced self-assembly (EISA) was used to prepare 1, 3, and 5 weight (wt) % Zr supported mesoporous CeO2-Al2O3 catalysts. Morphological, structural, and physicochemical properties of the synthesized catalysts were examined using Brunauer-Emmett-Teller (BET) absolute isotherm, Scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Temperature programmed reduction (TPR), and Temperature-programmed desorption of ammonia (NH3-TPD). XRD, BET, and SEM data confirmed that the catalysts were mesoporous and low-crystalline with a high surface area. The soot oxidation activity of the catalysts was evaluated using a thermogravimetric analysis (TGA) technique. The loose contacts soot oxidation activity test suggested that 50% oxidation of soot occurred at 390°C in the absence of a catalyst. T50 of CeO2-Al2O3 catalyzed soot oxidation was 296°C. Adding Zr to the catalyst significantly improved catalytic activity for diesel soot oxidation. We observed a further drastic change in T50 of soot over 1, 3, and 5% Zr/CeO2-Al2O3, which were 220°C, 210°C, and 193°C, respectively. According to these results, incorporating Zr into the CeO2-Al2O3 catalyst significantly improved the oxidation process of soot.

Impact of Mid-to-Low-Ash, Low-Viscosity Lubricants on Aftertreatment Systems after 210,000-Kilometer Real-World Road Endurance Trials

Engine lubricants globally face the challenge of meeting the demands of new engine technologies while enhancing energy efficiency and reducing emissions. Lubricants must enhance their performance and sustainability, improve reliability in complex and harsh environments, and minimize environmental impact and health risks. This study explores the influence of two different formulations of low viscosity lubricants, tested through actual road endurance trials, on a hybrid vehicle’s aftertreatment system performance and overall emission levels. The study includes 120,000 km of endurance testing in four different challenging environments in China, as well as 90,000 km of endurance testing in a typical urban and highway driving cycle in a large city. Results indicate that emissions from the test vehicles during the 120,000 km and 210,000 km durable Worldwide harmonized Light vehicle Test Cycles (WLTCs) meet China’s Stage 6 light-duty vehicle emission standards, with the 210,000 km Real Driving Emission test (RDE) results also conforming to these standards. Relative to fresh TWC, the light-off temperature increased by a mere 60 °C, and the oxygen storage capacity declined by around 19% following endurance testing. Additionally, the GPF exhibited satisfactory performance after 210,000 km of endurance testing, showing lower backpressure values compared to the fresh-coated samples, with no notable ash buildup observed in the substrate. Drawing on the outcomes of actual road endurance testing, this study illustrates that employing low-to-mid-ash-content, low-viscosity lubricants is both compatible and reliable for aftertreatment systems in present or advanced hybrid technologies. Premium lubricants facilitate vehicles in sustaining compliant and stable emission performance, even amid harsh environments and complex operating conditions. Furthermore, the tested lubricants effectively inhibit excessive aging of the aftertreatment system over prolonged mileage. Moreover, this study discusses the feasibility of rapid aging evaluation methods for aftertreatment systems based on engine test benches, juxtaposed with actual road endurance testing. These findings and conclusions offer crucial references and guidance for enhancing lubricant performance and sustainability. Subsequent studies can delve deeper into the correlation between lubricant performance and environmental impact, alongside optimization strategies for lubricants across various vehicle models and usage scenarios.

Zr doping on CeO2 nanocube catalysts to enhance oxygen storage capacity for Water-Gas shift reaction

Zr was doped on Co/CeO2 cubic catalysts to enhance oxygen storage capacity (OSC) in the water–gas shift (WGS) reaction using waste-derived synthesis gas. Zr concentrations (0, 0.22, 1.86, and 7.01 wt%) were changed systemically to see the effect of Zr on OSC. The analysis of the characteristics reveals that the newly synthesized catalysts demonstrate superior OSC compared to the CeO2 supported Co catalyst previously developed by our lab. The catalyst with the highest Zr content (7.01 wt%) demonstrated substantial carbon monoxide conversion after 50 h, highlighting the critical role of OSC in catalytic WGS stability. Conversely, a minimal Zr addition (0.22 wt%) resulted in the highest initial catalytic activity, which was attributed to an above-average Brunauer–Emmett–Teller surface area, Co dispersion, and relatively sufficient OSC. The findings emphasize that Zr doping considerably enhances the OSC of Co/CeO2 cubic catalysts, which is essentially linked to catalytic performance such as stability and activity. These insights confirm that precise Zr doping is a crucial strategy for modulating OSC, thereby enhancing the physicochemical properties of catalysts for improved efficiency in environmental and industrial applications, particularly in WGS reactions.

Study on the Catalytic Activity Modification of Pr and Nd Doped Ce0.7Zr0.3O2 Catalysts for Simultaneous Removal of PM and NOX

Cerium-zirconium composite oxides (Ce0.7Zr0.3O2) have a remarkable effect on catalytic removal of carbon particles (PM) and nitrogen oxides (NOX) emitted from diesel engine, in order to further improve the thermal stability, oxygen storage capacity and low temperature catalytic REDOX performance of cerium zirconium composite oxides (Ce0.7Zr0.3O2), a small amount of Pr and Nd rare earth elements are doped to improve the catalytic activity of cerium zirconium composite oxides. In this paper, the composite oxide of Pr6O11–Nd2O3–CeO2–ZrO2 is prepared by unsteady co-precipitation method, and the physicochemical properties of the composite oxide catalyst are analyzed by BET, SEM, XRD and ICP. The gas adsorption capacity and catalytic activity of composite oxide catalysts are measured by temperature programmed reaction technology (TPR). The results show that the composite oxide of Pr0.05Nd0.05Ce0.6Zr0.3O2 prepared by using rare earth elements Pr and Nd inhibits the growth process of grain, refining the grain, and improving the sintering phenomenon at high temperature. The addition of Pr and Nd causes lattice defects, increases the number of oxygen vacancies, and improves the mobility of lattice oxygen, namely promotes oxide oxygen storage property, gas adsorption and catalytic oxidation reduction ability. After modification, Pr0.05Nd0.05Ce0.6Zr0.3O2 has good resistance to high temperature aging performance, prolongs the service life, reduces the PM lowest ignition temperature and minimum catalytic activity temperature of nitrogen oxide, and promotes the NOX reduction rate. For Pr0.05Nd0.05Ce0.6Zr0.3O2, the lowest ignition temperature of PM is about 150 °C, and the lowest catalytic activity temperature of NO is about 130 °C. The maximum CO2 production rate is 68.3%, and the maximum NO reduction rate is 45%.

Construction of porous Cu/CeO2 catalyst with abundant interfacial sites for effective methanol steam reforming

Methanol is a promising hydrogen carrier for fuel cell vehicles (FCVs) via methanol steam reforming (MSR) reaction. Ceria supported copper catalyst has attracted extensive attentions due to the extraordinary oxygen storage capacity and abundant oxygen vacancies. Herein, we developed a colloidal solution combustion (CSC) method to synthesize a porous Cu/CeO2(CSC) catalyst. Compared with Cu/CeO2 catalysts prepared by other methods, the Cu/CeO2(CSC) catalyst possesses highly dispersed copper species and abundant Cu+-Ov-Ce3+ sites at the copper-ceria interface, contributing to methanol conversion of 66.3 %, CO2 selectivity of 99.2 %, and outstanding hydrogen production rate of 490 mmol gcat−1 h−1 under 250 °C. The linear correlation between TOF values and Cu+-Ov-Ce3+ sites amount indicates the vital role of Cu+-Ov-Ce3+ sites in MSR reaction, presenting efficient ability in activation of water. Subsequently, a deep understanding of CSC method is further presented. In addition to serving as a hard template, the colloidal silica also acts as disperser between nanoparticles, enhancing the copper-ceria interactions and facilitating the generation of Cu+-Ov-Ce3+ sites. This study offers an alternative approach to synthesize highly dispersed supported copper catalysts.

Investigation of bionano additives in red algae Cyanidioschyzon merolae ultrasonified MgO/MWCNT catalyzed biodiesel in optimized engine performance

Renewable energy research is burgeoning with the anticipation of finding neat liquid fuel. Ultra sonification assisted biodiesel was derived from red algae Cyanidioschyzon merolae, with biodiesel yield of 98.9%. The results of GC MS of the prepared biodiesel showed higher concentration of methyl palmitate, methyl oleate, and stearate. This composition is appreciable, as this plays significance in desirable pour & cloud point properties. NMR spectrum revealed the ester linkages, presence of olefins, and α methyl position in olefins. Mixture of 30 wt% of biodiesel in diesel exhibited work efficiency, and also exhibited low pour point and, lower viscosity values. CeO2 and Fe2O3 nano particles were bio reduced, and were added as nano additive in biodiesel. 1:1 ratio of CeO2 and Fe2O3 added to biodiesel maximised the combustion ability of fuel owing to the oxygen storage capacity of CeO2. Further, this combination produced a satisfactory calorific value. Imbalanced ratios disrupted the catalytic and oxygen storage effects, reduced the overall energy release and calorific value of the biodiesel blend. Pour point and cetane number value of biodiesel blend ultrasonifacted with 1:1 mass ratio of Fe2O3 and CeO2 was observed to be around −7 °C and 53 °C respectively, and was better than other compositions. 1:1 mass ratio of NPS blended with 30 wt% BD in diesel showed tremendous increase in brake thermal efficiency, torque, and power. HC, NOX, and SOX emissions were reduced by 42.8%, 19.3%, and 57% respectively with 1:1 Fe2O3 and CeO2 mixed biodiesel blend. CeO2 favourably improved the oxygen storage capacity of the fuel, whereas Fe2O3 showed decrease in formation of gums and sediments in biodiesel.

Environment-Driven Variability in Absolute Band Edge Positions and Work Functions of Reduced Ceria.

The absolute band edge positions and work function (Φ) are the key electronic properties of metal oxides that determine their performance in electronic devices and photocatalysis. However, experimental measurements of these properties often show notable variations, and the mechanisms underlying these discrepancies remain inadequately understood. In this work, we focus on ceria (CeO2), a material renowned for its outstanding oxygen storage capacity, and combine theoretical and experimental techniques to demonstrate environmental modifications of its ionization potential (IP) and Φ. Under O-deficient conditions, reduced ceria exhibits a decreased IP and Φ with significant sensitivity to defect distributions. In contrast, the IP and Φ are elevated in O-rich conditions due to the formation of surface peroxide species. Surface adsorbates and impurities can further augment these variabilities under realistic conditions. We rationalize the shifts in energy levels by separating the individual contributions from bulk and surface factors, using hybrid quantum mechanical/molecular mechanical (QM/MM) embedded-cluster and periodic density functional theory (DFT) calculations supported by interatomic-potential-based electrostatic analyses. Our results highlight the critical role of on-site electrostatic potentials in determining the absolute energy levels in metal oxides, implying a dynamic evolution of band edges under catalytic conditions.

Mitigating deactivation in dry methane reforming by lanthanum catalysts for enhanced hydrogen production: A review

Catalyst deactivation in dry methane reforming, resulting from coke accumulation and sintering, has long captivated academic interest due to its negative impact on catalytic performance and hindrance to industrial scalability. Thus, developing efficient catalysts capable of sustaining high reforming activity and stability is crucial. Lately, lanthanum (La) has gained popularity in catalysis for its ability to enhance performance and resist coking, owing to its great basicity, redox capabilities, and high oxygen storage capacity. As a result, diverse strategies for incorporating La into catalysts, including support, promoter, bimetallic combinations, and perovskite formation, have been extensively explored. Herein, this review delves into various advancements in lanthanum-based catalysts and their effectiveness in dry methane reforming while addressing catalyst deactivation and regeneration. Finally, the prospect of La-based catalysts in dry methane reforming is also emphasized in this review.

Transition metal oxides in CO2 driven oxidative dehydrogenation: Uncovering their redox properties

Extensive research efforts have been devoted to using greenhouse gas CO2 in upgrading bio-derived feedstock to value-added chemicals using the oxidative dehydrogenation route (CO2-ODH) with low-energy input. To realize the effective deployment of CO2-ODH at an industrial scale, it is imperative to advance the development of robust catalysts that can selectively catalyze C-H over C-C bonds, while simultaneously demonstrating thermodynamic stability to coke formation or sintering. Transition metal-based catalysts exhibit significant potential for being highly selective and reactive in the simultaneous conversion of CO2 and hydrocarbons, owing to their surface reducibility, well-balanced acid/base properties, and dynamic oxygen storage capacity. To stimulate further optimization, it's crucial to discover key design principles, potential trends and descriptors, and effective strategies to fine-tune the catalyst materials. This review comprehensively examines experimental and theoretical research aimed at pinpointing the key catalytic characteristics that affect selectivity in transition metal-based mono, bi, and multimetal oxides. It covers aspects like combinations of active metals and supports, effects of composition and alloying, interfacial structures, adsorption strengths, dynamics of in-situ restructuring, defect creation, surface morphology, and electronic properties, among others. We wrap up by suggesting approaches to overcome present obstacles in catalyst design and reactor technology, potentially bridging the lab-to-industry gap in this domain.

Surface oxygen vacancy vs oxygen storage capacity in cubic ceria based nanocatalysts for low temperature catalytic combustion of fuels

A series of praseodymium (Pr) doped cubic ceria nanoparticles (CeO2 NPs) with different ratio of cerium (Ce) and ‘Pr’ was synthesized by hydrothermal method. Manganese (‘Mn’) doped cubic CeO2 NPs with 10:90 ratio of Mn:Ce and undoped cubic CeO2 NPs have also been synthesized. The crystalline structure of the synthesized nanomaterials has been studied by powder X-Ray diffraction (XRD) and Rietveld analysis. In the Raman spectrum, the intensity of F2g signal at 450–460 cm−1 decreased while the intensity of extrinsic vacancy at 570–580 cm−1 increased by doping with ‘Pr’ or ‘Mn’ in cubic CeO2 nanocrystals. X-ray photoelectron spectroscopy (XPS) results showed that surface oxygen vacancy of cubic CeO2 NPs increased by doping with 25 % of ‘Pr’. The ‘Pr’ doped CeO2 NPs (Pr:Ce = 25:75) exhibited higher surface adsorption dynamic oxygen storage capacity (OSCDyn), while the ‘Mn’ doped cubic CeO2 NPs (Mn:Ce = 10:90) showed increased bulk lattice OSCDyn. The ‘Pr’ doped cubic CeO2 NPs (Pr:Ce = 25:75) exhibited better low temperature catalytic combustion activity, and their nanodispersion in mineral turpentine oil (MTO) added liquefied petroleum gas (LPG) exhibited better fuel efficiency with a flame temperature of 912 °C.

Simultaneous catalytic oxidation of Hg0 and NO over CoxCuy metal oxides catalyst

In this work, Co3O4, CoxCuy and CuO metal oxides catalysts were synthesized by coprecipitation method and tested in catalytic oxidation of Hg0 and NO. The Co3Cu1 catalyst exhibited nearly 100% Hg0 oxidation efficiency at 100–400 ℃ and 84% NO oxidation efficiency at 250 ℃. Respectively, 1155.2 μg g−1 Hg0 adsorption capacity and 92.9 μmol g−1 NOx adsorption capacity over Co3Cu1 catalyst were measured by Hg0-TPD and NOx-TPD. The largest BET specific surface area of Co3Cu1 catalyst was obtained, reaching 26.2 m2 g−1. And H2-TPR demonstrated that the first reduction peak temperature (192 ℃) of Co3Cu1 catalyst was much lower than that of other catalysts. O2-TPD illustrated that the oxygen storage capacity and oxygen mobility ability of Co3Cu1 catalyst were higher than that of other catalysts. These results were consistent with the results of Hg0 and NO oxidation activity tests. In addition, in-situ DRIFTS spectra of NO adsorption indicated that the band at 1390 cm−1 over Co3Cu1 catalyst disappeared after the pretreatment of Hg0. And the transient experiments of Hg0 adsorption suggested that Hg0 could also be extruded from the surface of Co3Cu1 catalyst after the introduction of NO. It was speculated that there might be competitive adsorption between Hg0 and NO over Co3Cu1 catalyst. Finally, the XPS characterization demonstrated that the Oα and the redox cycle of Co3+ + Cu+ ↔ Co2+ + Cu2+ were involved in Hg0-NO simultaneous oxidation. The Co3Cu1 catalyst was an excellent candidate for Hg0-NO oxidation reaction.

New method for the preparation of hierarchical nanotube K0.3xMnxCe1-xOδ catalysts and their excellent catalytic performance for soot combustion

A series of nanofibrous K-Mn-Ce composite oxide catalysts were prepared via a centrifugal spinning method for the first time, and their physicochemical properties were studied. The prepared K0.3xMnxCe1-xOδ metal oxide catalyst, which is a composite of CeO2 and cryptopotassium manganese-type K2-xMn8O16, exhibits a hierarchical nanotube structure with uniform nanoneedles on its surface. During the process of soot oxidation, CeO2 utilizes its unique oxygen storage and release capacity to supply oxygen species. Simultaneously, the excellent redox properties of K2-xMn8O16 effectively promote valence cycling of the active components and produce more active oxygen species. This synergistic effect effectively enhances the intrinsic activity of the catalysts. Among the prepared catalysts, K0.15Mn0.5Ce0.5Oδ exhibits the highest catalytic performance, with 10% (T10), 50% (T50), and 90% (T90) soot conversion temperatures of 267 °C, 309 °C, and 338 °C, respectively, and shows good stability and water and sulfur resistance. Based on their simple preparation, low cost, and good catalytic performance, K0.3xMnxCe1-xOδ composite metal oxide catalysts have good potential in catalytic soot combustion applications.

The effect of the oxygen storage material on a three-way catalyst spatio-temporally resolved with Spaci-MS

A methodology that allows the estimation of the stored oxygen (oxygen storage capacity (OSC)) along the TWC catalyst length by spatio-temporally resolving the O2 profiles during rich to lean cycle conditions with the use of the Spaci-MS technique has been developed. As a case study, the effect of the presence of mixed cerium-zirconium oxide as oxygen storage material has been investigated. The oxygen storage capacity for the TWC containing Ce material was much higher than without. The study also explores the reaction pathways typical of TWC along the catalyst coordinates by spatio-temporally resolving O2, H2, CO, and NO, as well as the related products and intermediates providing important understanding on, for example, the water-gas shift reaction leading to H2 production and how they develop differently depending on the OSM (oxygen storage material) in the catalyst. H2 production occurs closer to the front of the TWC length in the case of the catalyst without Ce, and results in an earlier production of undesired NH3 from NO reaction with H2. However, more N2O has been observed for the catalyst with Ce, which suggests the catalyst composition could be optimised to minimize overall secondary emissions.

MOX-TiO2 (M=Pt, Pd, Ru) for alcoholysis reaction from furfuryl alcohol to ethyl levulinate

Simple noble metal oxides (PtOx, PdOx, RuOx) based titanium dioxide (Pt–TiO2, Pd–TiO2, Ru–TiO2) were prepared using a facile sol-gel method. The conversion of furfuryl alcohol (FAL) to ethyl levulinate (EL) was studied. Full characterizations were performed using XRD, XPS, Raman and in situ FT-IR. An in-depth study of acidic strength and sites distribution (Brønsted or Lewis) was conducted by NH3-TPD, pyridine-IR. The profiles of H2-TPR and O2-TPD suggested enhanced reducibility and optimum oxygen storage capacity in Pt–TiO2. Remarkable FAL conversion (94.4%), EL yield (89.6%) with productivity (21.3 × 103 molEL/mmolPt h) and TOF (22.5 × 103 molFAL/mmolPt h) were obtained. Metal productivity follows the order: Pt (21.3 × 103 molEL/mmolPt h) > Ru (11.5 × 103 molEL/mmolRu h) > Pd (3.6 × 103 molEL/mmolPd h). Two different reaction pathways were proposed. From computational calculations of charge density differences and Ead value, a robust electron transfer capacity was found in Pt–TiO2, as well as an advantageous FAL adsorption as compared to other catalytic systems.

Investigating the effect of oxygen vacancy on electronic, optical, thermoelectric and thermodynamic properties of CeO2 (ceria) for energy and ReRAM applications: A first-principles quantum analysis

CeO2 thin film-based devices have become hot favorite candidates for researchers due to the outstanding characteristics of ceria such as memory storage materials, high oxygen storage capacity, excellent chemical and thermal stability, high transparency in visible region and highly tunable energy band structures. Developing suitable materials for industrial uses like optoelectronic and thermoelectric devices is the primary goal of researchers in the field of renewable energy. Herein, we have investigated the optical, thermoelectric and thermodynamic properties of CeO2 and [Formula: see text] as promising candidates for energy applications using first-principles calculations. We can observe significant absorption of incident photons by CeO2 and [Formula: see text] near UV region. The highest peaks of the [Formula: see text] are present around 3.7[Formula: see text]eV in spin [Formula: see text] channel, however, in spin [Formula: see text] channel, the highest peaks of the [Formula: see text] are present around 3.5[Formula: see text]eV. The most intense peaks that emerge are due to the transitions of O[[Formula: see text]] to Ce [[Formula: see text]]. The investigated values of [Formula: see text] reveal that CeO2 and [Formula: see text] are active optical materials. CeO2 and [Formula: see text] reflect a negligible number of incident photons ([Formula: see text]%) in the entire energy range. The positive value of the S shows that the CeO2 under study is p-type semiconductor, while [Formula: see text] is n-type semiconductor as its S value is negative. The S values for CeO2 are close to the established standard. As a result, CeO2 is a viable thermoelectric material for use in devices. The figure of merit (ZT) spectra reveals that CeO2 ([Formula: see text]) is a more capable candidate for thermoelectric materials compared to [Formula: see text] ([Formula: see text]). The investigated thermodynamic parameters reveal that CeO2 and [Formula: see text] are dynamically stable compounds.

Mechanistic insights into methane total oxidation over Cu/Hydroxyapatite catalyst synthesized with β-Cyclodextrin assistance

The total oxidation of methane (CH4), a highly stable alkane volatile organic compound (VOC), using low-cost Cu-based catalysts, has garnered considerable attention. Nonetheless, challenges such as Cu particle agglomeration and the lack of consensus on mechanism of CH4 total oxidation over Cu-based catalysts remain. In this work, β-cyclodextrin (βCD) was introduced during Cu/hydroxyapatite catalyst (βCD-Cu/HAP) preparation, and its catalytic performance in CH4 total oxidation was compared with the Cu/HAP catalyst. Both materials were prepared using the wet impregnation method and thoroughly characterized. It was found that utilization of βCD, which decomposed during calcination, led to smaller Cu particle size (from 61 to 34 nm) and better Cu dispersion (from 1.9 to 3.5 %), resulting in an enhancement of the catalyst reduction properties. Additionally, the βCD-Cu/HAP catalyst possessed a higher oxygen storage capacity, demonstrating its superior ability to replenish the oxygen vacancies. The βCD-Cu/HAP catalyst activity was double that of the original Cu/HAP catalyst with a 20kJmol-1 lower activation energy, as determined by fitting the initial reaction rate to a power-law model. Further, Langmuir–Hinshelwood (LH), Eley–Rideal (ER), and Mars–van Krevelen (MVK) type rate expressions were regressed to the experimental data. After statistical and physico-chemical assessments, the MVK mechanism involving two oxidized sites and one reduced site with H2O adsorption on oxidized sites was identified as the most appropriate model for describing the experimental data. These findings offer an enhanced understanding of CH4 total oxidation, guiding the development of efficient, low-cost catalysts for this reaction. Environmental ImplicationVolatile organic compounds (VOCs) pose significant environmental and health issues due to their toxicity and widespread sources. Among VOCs, alkane contribute to a large proportion of the VOCs emitted, with light alkanes being particularly challenging to mitigate due to their high stability. Methane, the most stable light alkanes, is the focus of this study. Catalytic oxidation technology offers a promising solution for VOC mitigation. In our work, we conducted a mechanistic investigation of methane total oxidation, aiming at deepening our understanding of catalytic oxidation of light alkanes, thereby contributing to substantial environmental benefits.

Abundance of Low-Energy Oxygen Vacancy Pairs Dictates the Catalytic Performance of Cerium-Stabilized Zirconia.

Cerium-stabilized zirconia (Ce1-xZrxOy, CZO) is renowned for its superior oxygen storage capacity (OSC), a key property long believed to be beneficial to catalytic oxidation reactions. However, 50% Ce-containing CZO recorded with the highest OSC has disappointingly poor performance in catalytic oxidation reactions compared to those with higher Ce contents but lower OSC ability. Here, we employ global neural network (G-NN)-based potential energy surface exploration methods to establish the first ternary phase diagram for bulk structures of CZO, which identifies three critical compositions of CZO, namely, 50, 60, and 80% Ce-containing CZO that are thermodynamically stable under typical synthetic conditions. 50% Ce-containing CZO, although having the highest OSC, exhibits the lowest O vacancy (Ov) diffusion rate. By contrast, 60% Ce-containing CZO, despite lower OSC (33.3% OSC compared to that of 50% Ce-containing CZO), reaches the highest Ov diffusion ability and thus offers the highest CO oxidation catalytic performance. The physical origin of the high performance of 60% Ce-containing CZO is the abundance of energetically favorable Ov pairs along the ⟨110⟩ direction, which reduces the energy barrier of Ov diffusion in the bulk and promotes O2 activation on the surface. Our results clarify the long-standing puzzles on CZO and point out that 60% Ce-containing CZO is the most desirable composition for typical CZO applications.

Adsorption and gas sensitive behavior of Co2+ doped TiO2(101) crystal planes

Density functional theory (DFT) and Electrochemical Impedance Spectroscopy (EIS) were used to study the molecular adsorption behavior of the Co2+ doped TiO2(101) crystal plane, and the ethanol molecular gas sensitivity test was performed. Theoretical models indicate that doping leads to oxygen defects on the crystal plane and further chemisorption of two oxygen molecules, resulting in reduced electrical conductivity and improved oxygen storage capacity on the crystal plane. Ethanol molecules do not compete with N2, O2, and H2O molecules on doped crystal planes because of their different adsorption active sites, which means that the response time of gas-sensitive detection of ethanol molecules is short and is not interfered with the air molecules in the test environment. These results were confirmed by EIS and gas sensitivity experiments. The change of electrical conductivity after the adsorption of molecules on the crystal plane was confirmed by EIS. The enhanced oxygen storage capacity of the doped crystal plane was confirmed by the expansion of the linear response range of gas-sensitive detection from 20-100 ppm before doping to 20–1200 ppm. This provides a scientific basis for effectively shortening the gas-sensitive response time, increasing the concentration range, improving the oxygen-carrying capacity, and enhancing the catalytic and gas-sensitive properties of the material.

Tailored SrFeO3-δ for chemical looping dry reforming of methane

Chemical looping dry reforming of methane (CL-DRM) is a highly efficient process that converts two major greenhouse gases (CH4 and CO2) into syngas ready for the feedstock of liquid fuel production. One of the major obstacles facing this technology now is creating oxygen carriers that are stable and reactive. We fabricated high-performance Sr0.98Fe0.7Co0.3O3-δ perovskite-structured oxygen carrier by combining A-site defects and B-site doping of SrFeO3-δ. During isothermal CL-DRM tests at 850 °C, Sr0.98Fe0.7Co0.3O3-δ achieved 87% CH4 conversion and 94% CO selectivity in the CH4 partial oxidation reaction, followed by a syngas yield of 8.5 mmol/g, and CO yield of 4.2 mmol/g in CO2 decomposition. A-site defect engineering of the perovskite creates abundant oxygen vacancies and enhances oxygen storage capacity (OSC). Co-doping of the B-site of Sr0.98FeO3-δ increases oxygen mobility and CH4/CO2 activation, resulting in high activity in the CL-DRM process. This methodology resulted in high ionic mobility and facilitated the rapid diffusion of oxygen in the bulk phase, thereby increasing the redox properties of SrFeO3-δ. The oxygen carrier exhibits excellent structural stability and regeneration ability in successive redox cycles. This strategy offers a simple but very effective pathway to tailor OSC, oxygen mobility, and oxygen vacancies of perovskite-structured materials for chemical looping or redox-involved processes.

Recent Advances of CeO2-Based Composite Materials for Photocatalytic Applications.

Photocatalysis has the advantages of practical, sustainable and environmental protection, so it plays a significant role in energy transformation and environmental utilization. CeO2 has attracted widespread attention for its unique 4 f electrons, rich defect structures, high oxygen storage capacity and great chemical stability. In this paper, we review the structure of CeO2 and the common methods for the preparation of CeO2-based composites in the first part. In particular, we highlight the co-precipitation method, template method, and sol-gel method methods. Then, in the second part, we introduce the application of CeO2-based composites in photocatalysis, including photocatalytic CO2 reduction, hydrogen production, degradation, selective organic reaction, and photocatalytic nitrogen fixation. In addition, we discuss several modification techniques to improve the photocatalytic performance of CeO2-based composites, such as elemental doping, defect engineering, constructing heterojunction and morphology regulation. Finally, the challenges faced by CeO2-based composites are analyzed and their development prospects are prospected. This review provides a systematic summary of the recent advance of CeO2-based composites in the field of photocatalysis, which can provide useful references for the rational design of efficient CeO2-based composite photocatalysts for sustainable development.