Catalytic Oxidation Performance Research Articles

A High Nucleus Cu-Incorporated Giant Phosphotungstate with Photocatalytic Oxidation C-H of Toluene.

Exploring a novel photocatalyst for catalytic oxidation of toluene is a sustainable strategy for energy conversion in times of an energy crisis. However, designing an effective photocatalyst for the conversion of toluene remains challenging. Herein, a novel organic monophosphonate-modified high nucleus Cu-incorporated polyoxotungstate, K8H33[{Cu0.5(H2O)4}{Cu2(O3PCH2COO)(1,4,9-α-P2W15O56)}]4·Cl·60H2O (1), has been intentionally synthesized by a self-assembly process utilizing conventional aqueous method. It reveals that 1 contains a polyanion of [{Cu0.5(H2O)}4{Cu2(O3PCH2COO)(1,4,9-α-P2W15O56)}]440- composed of four Dawson-type {1,4,9-α-P2W15} subunits, forming an oval-shaped structure and further connecting into a three-dimensional (3D) framework by lateral {Cu(H2O)4}2+. Interestingly, the trivacant {1,4,9-α-P2W15} subunits were observed in the organophosphonate acid-functionalized polyoxometalates for the first time. Notably, 1 exhibits a wonderful performance in catalytic oxidation of the recalcitrant C(sp3)-H bond of toluene to benzoic acid with a conversion as high as 97% under visible light utilizing O2 as an oxidant.

Musa acuminata free tepal (MAFT) crop- mediated synthesis of copper oxide nanocatalyst (MAFT-CuO nanocatalyst): Investigation of aerobic oxidation and dye decolourization via eco-friendly approach

Crop development is used to address environmental problems in the industry. Environmental pollutants, particularly humble or toxic chemicals and dyes, are contaminants in industrial wastewater. Recently, green technology has become important for controlling the chemical risks associated with environmental issues. This study focused on valuable crop materials to form green catalysts that can be used to control chemical toxicity in industrial wastewater. In this study, Musa acuminata-free tepal (MAFT) crops and musa were used to mediate the formation of copper nanocatalyst for environmental pollution. The synthesised nanocatalyst was analysed by XPS, XRD, TEM, SEM, FT-IR, GC-EI-MS, and TGA-DSC. The production of Cu–O in the 512 cm−1 peak range was verified by FT-IR analysis. The XRD peaks associated with the cubic crystalline structures of copper (110) and (200) were used to confirm the Musa acuminata-free tepal CuO nanocatalyst. The SEM images of the Cu and CuO nanocatalyst in the Musa acuminata free tepal showed that the particles were almost spherical. The size of the synthesised Musa acuminata free tepal CuO nanocatalyst core-shell nanostructures was identified using HR-TEM. GC-MS investigations also verified the aerobic oxidation of the main alcohol to aldehyde, with a retention time of 30.34. The MAFT was 80 % of CBB G250 dye decolourised at 24 h, and the MAFT-CuO nanocatalyst was decolourised the CBB G250 dye at 80 % in 20 min and aerobic oxidation at the same time (dual application). Furthermore, our nanocatalyst could be effectively recycled without significant loss of catalytic activity, and the use of safe, environmentally benign MAFT-Cu and CuO nanocatalyst is considered a green chemistry approach that helps avoid wastewater treatment. MAFT-Cu and CuO nanocatalyst were successfully synthesised using Musa acuminata free tepal extract assisted by reflux sample preparation system instruments as a new, green, eco-friendly, and fast process for nanocatalyst synthesis. In the past, there have been no reported applications of MAFT-Cu and CuO nanocatalyst for decolourisation and aerobic oxidation. Nevertheless, we were able to accomplish these procedures with the help of CuO and MAFT-Cu nanocatalyst. Therefore, the most effective naturally occurring environmental catalysts for aerobic oxidation processes are MAFT-CuO nanocatalyst. They are non-toxic and environmentally benign, exhibit strong aerobic oxidation catalytic performance, and have long-lasting benefits for water quality. Additionally, they are more recoverable and biodegradable.

Covalent graft of Polypyridineruthenium(II) Complex-ZnTPP dyad with fullerol and immobilization onto TiO2 for enhanced photoassisted water oxidation activity

The covalent linkage of the light-harvester with the water oxidation catalyst is an effective way to construct heterogeneous catalysts with both light harvesting ability and catalytic oxygen evolution activity, and remains a challenge for simulated photosynthesis systems. Herein, two heterogeneous composite catalysts of ZnTPPtpyRubpyPHFTiO2 and ZnTPPtpyRubpyTiO2, with both the light harvesting capability and the catalytic water oxidation (CWE) performance, were successfully designed and prepared, and were fully characterized. Research indicated that the transfer mode of the photo-generated carrier for the two photo-assisted heterogeneous catalysts follows the type II mechanism, and the photo-generated holes promote the CWE activity. Compared to the dark condition (with TOF values of 42.3 and 41.8, respectively), ZnTPPtpyRubpyPHFTiO2 and ZnTPPtpyRubpyTiO2 exhibit superior CWE activity and efficiency in the illumination condition (with TOF values of 120 and 48.31, respectively). Fullerol, playing the role of an electron acceptor and an electron-pool, promotes charge separation and electron storage, which leads to a better suppression in charge recombination and enhancement in charge injection for ZnTPPtpyRubpyPHFTiO2. Therefore, ZnTPPtpyRubpyPHFTiO2 demonstrates a significantly improved catalytic activity in the illumination condition with a much higher TOF value compared to that of ZnTPPtpyRubpyTiO2.

Catalytic combustion of toluene over highly dispersed Pt NPs embedded in porous TiO2 via in situ pyrolysis of MOFs

In this work, a series of x wt% Pt@TiO2 (x = 0.18, 0.42, and 0.84) catalysts with highly dispersed Pt nanoparticles (NPs) are synthesized via pyrolysis method using Ti-based metal-organic frameworks (MOFs) as precursors. Physicochemical properties of the catalysts are characterized by a number of analytical techniques. It is shown that all samples possess mesoporous structure with surface area of 59–75.6 m2/g, thus can suppress the aggregation of Pt NPs, and enhance toluene adsorption and diffusion. The 0.84 wt% Pt@TiO2 catalyst exhibits the best catalytic performance for toluene oxidation (T90% =150 °C at space velocity = 20,000 mL/ (g h)), which is attributed to the higher surface area, abundant adsorbed oxygen and Pt0 species, and strong interaction between Pt NPs and TiO2. In addition, the possible reaction mechanism of toluene oxidation is proposed based on in situ DRIFTS technique.

Completely Inorganic Deep Eutectic Solvents for Efficient and Recyclable Liquid-Liquid Interface Catalysis.

Organic acid-based deep eutectic solvents (DESs) as catalysts always suffer from weak stability and low recyclability due to the accumulation of organic oxidative products in the DES phase. Herein, a completely inorganic deep eutectic solvent (IDES) ZnCl2/PA with zinc chloride (ZnCl2) and phosphoric acid (PA) as precursors is constructed to realize liquid-liquid interface catalysis for desulfurization of fuel and product self-separation for the first time. Owing to the inorganic nature, the organic oxidative products are accumulated at the interface between the IDES and fuel rather than the IDES phase. With this unique feature, the IDES can be reused for at least 15 times without any further treatment in oxidative desulfurization process, showing a state-of-the-art cycle-regeneration stability. Moreover, compared with the reported organic DESs, the IDES also reveals more attractive catalytic oxidative desulfurization performance. Experimental and theoretical studies indicate that the strong coordination Zn···O═P and the strong adsorption energy between IDES and sulfides enhance the activation of H2O2 to reactive oxygen species, leading to the superior catalytic performance in oxidative desulfurization of fuel.

Unlocking the superior flexibility and enhanced catalytic oxidation performance of CoTiO3 nanofibrous membranes through zirconium doping

The development of continuous CoTiO3 (CTO) fibers with prominent catalytic oxidation activity, tunable fibrous structures, and improved recyclability is appealing for application in efficient organic wastewater treatment; however, inescapable flaws remain, such as their inherent brittleness and adverse operability. Herein, a facile and effective strategy is proposed for the fabrication of flexible and mechanically robust CTO nanofibrous membranes through a combination of element doping and sol–gel-assisted electrospinning. Compared with pristine CTO fibers, the resulting zirconium-doped CoTiO3 (ZCTO) nanofibrous membranes displayed remarkably enhanced flexibility and tensile mechanics, which were attributed to their lower crystallinity, smaller grain size, and fewer fiber surface defects. The developed ZCTO fibrous membrane demonstrated exceptional resistance to bending fatigue, retaining a polymer-like bending rigidity of approximately 25 mN even after undergoing 200 reciprocating bending cycles. Furthermore, the incorporation of zirconium into CTO clearly had an advantageous effect on the formation of oxygen vacancies, thereby enhancing the surface adsorption of peroxymonosulfate (PMS), accelerating the electron transfer process, and weakening the peroxy bonds. The tetracycline degradation efficiency of the ZCTO fibers remained at 81.4% within 10 min after 5 continuous cycles. Benefiting from their robust mechanical properties and excellent catalytic activity, the fabricated membranes demonstrated outstanding dynamic catalytic performance under gravity-driven conditions. More importantly, the reported strategy might be adopted and extended to develop a wide range of ceramic fibers with enhanced flexibility and mechanics for catalytic oxidation.

Derivatives of Br-doped metal-organic framework for improved acetaldehyde adsorption-photocatalytic oxidation

Different Br-doped metal-organic frameworks (MOFs) derived (Brx@UiO-66) have been prepared by heat treatment using UiO-66 as the precursor. The experimental results showed that Br0.2@UiO-66 exhibited the best photocatalytic oxidation and adsorption performances toward acetaldehyde. In the dynamic system, the acetaldehyde removal rate and adsorption capacity of Br0.2@UiO-66 were 93.2 % and 230.59 mg/g, respectively. The improvement of the photocatalytic performance can be attributed to the presence of Br ions and CBr bonds, which facilitated the rapid separation of electrons and holes and the production of •O2−. In addition, Br0.2@UiO-66 had a better adsorption performance than 300UiO-66, mainly because of the increased Lewis acidity of the metal active sites due to Br doping. Radical capture experiments indicated that •O2− and e- were the primary active substances in acetaldehyde oxidation, and allowed establishing the possible mechanism of acetaldehyde oxidation. This work shows that MOFs can have high catalytic oxidation performances toward volatile organic compounds (VOCs) while retaining their adsorption capacity, and can be used for practical applications in the adsorption-catalytic integrated degradation of VOCs.

Remarkable enhancement of CO oxidation over Pt1/CeO2 catalysts by atomically dispersed tungsten

Ceria-supported atomically dispersed Pt is of great interest in CO oxidation due to their unique catalytic performance and high metal utilization. However, the intrinsic activity of the Pt1/CeO2 single atom catalysts may not be desirable due to the overstabilization of Pt2+ species in the CeO2 matrix. Herein, the local environment of Pt2+ species was tailored by introducing a tungsten oxide additive into the Pt1/CeO2 catalyst, achieving a dramatic improvement in catalytic performance for CO oxidation at low temperatures. The optimized catalyst with 2.5 wt% W loading achieved 100 % CO conversion at 150 °C, which was 120 °C lower than that of the unmodified Pt/CeO2 catalyst. Through in situ infrared spectroscopy and temperature-programmed reduction characterizations, as well as theoretical calculations, we concluded that the tungsten additive modulate the interactions between Pt2+ species and CeO2. Thus, the reducibility of Pt was enhanced, which facilitated the formation of catalytically active metallic Pt0 species during the reaction.

Deep understanding the formation of MnCoOx in-situ grown on foam nickel towards efficient lean methane catalytic oxidation

Methane is the second largest greenhouse gas in the world, with a stronger greenhouse effect than carbon dioxide. The efficient elimination of methane in the atmosphere has important engineering significance in slowing down global temperature rise, energy resource utilization, collaborative control of pollutants, and promoting technological innovation. In this work, a general hydrothermal synthesis method was introduced to in-situ construct four different morphologies of MnCoOx (including rod-, spherical-, filamentous- and bulk-shape) on foam nickel (NF). The synthesis of MnCoOx/NF with different morphologies was due to changes in NF pretreatment conditions and precipitants, which affected the nucleation and growth rates of MnCoOx, ultimately resulting in different morphologies. When the four different morphologies of MnCoOx/NF were used as catalysts for lean methane catalytic oxidation, MnCoOx/NF-r exhibited the best excellent catalytic activity, and the T90 occurred at 428 °C in space velocity of 48,000 mL g−1 h−1. Such an outstanding performance was attributed to the unique properties of the MnCoOx/NF-r including the larger surface area and more oxygen vacancies for providing more active sites and a higher oxygen migration rate, which was very beneficial for improving the catalytic oxidation performance of methane.

The acceleration of the active phase transition of NiCoFe hydroxide by Ta doping to achieve Long-Time seawater electrolysis at Ampere-Level current density

Considering the regional distribution of freshwater resources, acquiring hydrogen by seawater electrolysis has lower cost and feasibility. NiCoFe-based materials have been widely studied due to their excellent catalytic oxidation performance in freshwater. However, the large amount of chloride ions in seawater will severely erode the catalytic site and greatly reduce the catalyst's lifetime. In this paper, a two-dimensional nanosheet quaternary metal hydroxide electrode composed of Ni, Co, Fe, and Ta elements was synthesized via a facile one-step hydrothermal method for efficient oxygen evolution reaction (OER) in seawater electrolysis. Structural characterization and in-situ test revealed that the incorporation of Ta not only optimized the electronic structure of the catalyst but also accelerated the formation of the γ-NiOOH phase, making the active phase is protected from being attacked by Cl- ions during the formation process, enhancing its OER activity while achieving extended durability. The catalyst was operated at an ampere-level of 1 A cm-2 for over one month (800 h), and no significant degradation was observed. This work provides a promising strategy for developing cost-effective, efficient, and stable catalysts for challenging applications in seawater electrolysis.

Design strategies for MOFs-derived Ce10-xZrxOy catalysts with polyhedral coordination to enhance soot combustion

Various cerium-based metal–organic frameworks (Ce-MOFs and Ce10-xZrx-MOFs) and their derivatives (Ce10-xZrxOy complex oxide catalysts) with different structures and properties by modulating the organic ligands (i.e., trimesic acid (BTC), 1,2,4,5-benzenetetracarboxylic acid (PMA), and terephthalic acid (BDC)) and transition metal elements via the solvothermal method. The performance of these catalysts was tested in the diesel soot oxidation reaction. In contrast, morphology engineering and the introduction of heteroatom zirconium to modify CeO2 can significantly improve the catalytic activity and stability of the catalyst. Among them, the best Ce5Zr5Oy-BDC shows remarkable catalytic performance for soot oxidation, converting 90% of soot particles into CO2 at about 410 °C. A series of characterization results demonstrate that the engineering of morphology provides a highly active polycrystalline surface for the adhesion of reactants, and the electron transfer system caused by Zr doping weakens the Ce-O bond. With the help of their combined action, the exposed polycrystal surfaces greatly enhance the oxygen vacancy content and the ability to generate reactive oxygen species. The DFT investigations shows that the presence of Zr can weaken the Ce-O link, result in favorable defect structures, and the reactive oxygen species of formation were promoted. This study provides an idea for the design of non-precious metal catalysts with high activity and stability.

Investigation of catalytic methane oxidation over Ag/Co2MOx (M = Co, Ni, Cu) catalysts with varying interfacial electron transfer

Atom-doped Co3O4 catalysts loaded with Ag were examined as cost-effective catalysts for methane oxidation. The synthesized Ag/Co2NiOx catalysts exhibited distinctive surface characteristics in contrast with Ag/Co3O4 and Ag/Co2CuOx catalysts prepared using a similar method. Characterization results unveiled that Ag/Co2NiOx featured a higher presence of active surface oxygen species, lattice defects, a larger surface area, and enhanced reducibility. A methane oxidation catalytic performance followed the sequence: Ag/Co2NiOx > Ag/Co3O4 > Ag/Co2CuOx. The investigation delved into methane degradation pathways on the surfaces of three catalysts, examining their behavior under both aerobic and anaerobic atmospheres through in-situ DRIFTS analysis. Furthermore, introducing Ag showed a marked positive effect on Co-Ni mixed oxide, inducing electron transfer and a more active electron system, whereas it exhibited an inverse impact within the surface of Co-Cu mixed oxide. This work provides innovative perspectives on the development of forthcoming environmental catalysts.

Cyclable CuⅠ-Ov-Mn sites accelerate O2 activation to enhance photo-driven catalytic oxidation performance

Molecular oxygen activation (MOA) plays a crucial function in various oxidation reactions. Nonetheless, facile, continuous and efficient MOA remains challenging. Herein, we have successfully constructed recyclable CuⅠ-Ov-Mn sites (Ov: oxygen vacancy) for MOA by incorporating Cu single atoms in MnO2 matrix. The localized photogenerated electron at CuⅡ site drives the generation of electron-rich CuⅠ species and an adjacent photoinduced Ov, which possesses stronger O2 affinity and affords a durable O2 activation site. The CuⅡ/CuⅠ cycle accelerates the separation of charge carriers to supply adequate photogenerated electrons and assures the renewability of photoinduced Ov, thus realizing rapid and sustained O2 activation and generating abundant monatomic oxygen ions (O-). Consequently, Cu-MnO2 catalyst performed extraordinarily high activity in O2-involved reactions. For instance, in toluene oxidation, toluene conversion reached as high as 96 %, comparable to that on the state-of-the-art supported Pt catalysts. This work will bring more possibilities for modulating the O2-involved oxidative reactions.

Tuning the crystallinity of the MnOx catalysts to promote toluene catalytic oxidation

ABSTRACT In this paper, the MnOx catalysts with excellent toluene oxidation performance were prepared by a simple precipitation method. The physicochemical properties of the prepared MnOx catalysts were investigated by XRD, BET, H2-TPR, O2-TPD and XPS. The obtained results revealed that the crystallinity of the prepared MnOx catalysts could be effectively regulated by changing the (NH4)2CO3/Mn(NO3)2 molar ratio, and thus affecting the oxygen vacancy concentration of the prepared MnOx catalysts. The prepared MnOx-4 catalyst with the (NH4)2CO3/Mn(NO3)2 molar ratio of 4.0 had the poor crystallinity and small grain size, which effectively promoted the oxygen defects in the MnOx catalyst to be formed. At the same time, the MnOx-4 catalyst had a large specific surface area, the highest low temperature reducibility and the largest number of oxygen vacancies and surface adsorbed oxygen species, which allowed more surface oxygen species to participate in the redox reaction, and promoted the toluene deep oxidation. Therefore, when the (NH4)2CO3/Mn(NO3)2 molar ratio was 4.0, the prepared MnOx-4 catalyst exhibited an excellent toluene catalytic oxidation performance and robust catalytic stability. What’s more, the toluene oxidation conversion on the MnOx-4 catalyst reached 99% at 230°C, and the MnOx-4 catalyst showed excellent resistance to water vapour.

Catalytic activity of ceria-based solid solutions with low-content dopants

Ceria-based solid solutions (M0.01Ce0.99O2) with low-content dopants were synthesized by the co-precipitation method, followed by calcination at the temperature of 500 °C. The effect of doping on catalytic performance in CO oxidation was investigated, and the catalyst physicochemical properties were studied. The introduction of even a small amount of metal dopants significantly increased the activity of catalysts. Thus, the most active catalysts were systems when doping ceria with metals Cu, Mn, and Co, i.e., with a small ionic radius and having multivalent oxidation states. It is shown that the high activity was a result of the increased interaction of Mδ+ with ceria due to facile electron exchange between Mδ+ and Ce4+/Ce3+, the redox cycle was one of the key factors in the CO oxidation, as well as well-integrated metal species in ceria lattice, especially in subsurface layer.

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.

Efficient targeted acquisition 2,5-furandicarboxylic acid derived from 5-hydroxymethylfurfural over novel copper and vanadium oxide-functionalized catalysts

2,5-Furandicarboxylic acid (FDCA), which is recognized as a valuable alternative to petroleum-derived terephthalic acid and produce more bio-based polymers, has attracted considerable attention in recent years. Herein, a series of nitrogen-containing polymer nanosheets bearing Cu2+ and VO2+ (Cu2+-VO2+/PDVTA) were designed and displayed superior catalytic performance in the selective oxidation of 5-hydroxymethylfurfural (HMF) to FDCA. The catalyst was characterized by FT-IR, SEM, XPS, TG, UV–Vis DRS, PL, and ICP-AES analysis techniques. The effects of various reaction parameters, including the tert-butyl hydroperoxide dosage, temperature, and solvents on the HMF oxidation were systematically investigated, and the results were discussed in details. The Cu2+-VO2+/PDVTA catalyst achieved 100% conversion of HMF with 98.6% selectivity toward FDCA without the requirement for any basic additives under mild conditions (90 °C, 10 h), as well as has a good reusability. Coupling of the active sites of Cu2+ and VO2+ provide a synergistic effect for FDCA production. This study may provide a novel method for the development of efficient non-precious metal catalyst without addition of alkali additives, benefiting the valorization of furan-based compounds into high-valued chemicals in industrial processes.

Improving Oxidative Catalytic Efficiency for Fuels Desulfurization Using Hybrid Materials Based in MOF‐808@SBA‐15

This work unveils a route for a new generation of heterogeneous polyoxometalate (POMs) based catalysts associated to the preparation of hybrid materials as a triad of POMs, mesoporous silica (SBA‐15) and microporous MOF structures (MOF‐808). The prepared catalyst, PMo12@MOF‐808@SBA‐15, with the main active center the phosphomolybdic acid (PMo12), was successfully applied for the desulfurization of a multicomponent fuel. Its oxidative catalytic performance showed to be considerable superior to the isolated POM@MOF and able to be recycled for more catalytic cycles without active loss. The higher catalytic performance seems to be directly related with the preparation of a more amorphous MOF structure within the channels of SBA‐15, in the presence of active POM guests.

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 of O2 on the Preferred -O-Au Sites of Small Gold Oxide Clusters: Charge-dependent Interaction and Activation.

Decades of research have illuminated the significant roles of gold/gold oxide clusters in small molecule catalytic oxidation. However, many fundamental questions, such as the actual sites to adsorb and activate O2 and the impact of charge, remain unanswered. Here, we have utilized an improved genetic algorithm program coupled with the DFT method to systematically search for the structures of Au1-5Ox-/+/0 (x = 1-4) and calculated binding interactions between Au1-5Ox-/+/0 (x = 1-2) and O2, aiming to determine the active sites and to elucidate the impact of different charge states in gold oxide systems. The results revealed that the reactivity of all three kinds of small gold oxide clusters toward O2 is strongly site-dependent, with clusters featuring an -O-Au site exhibiting a preference for adsorption. The charges on small gold oxide clusters significantly impact the interaction strength and the activation degree of adsorbed O2: in the case of anionic cluster, the interaction between O2 and the -O-Au sites leads to a chemical reaction involving electron transfer, thereby significantly activating O2; in neutral and cationic clusters, the adsorption of O2 on their -O-Au sites can be viewed as an electrostatic interaction. Pointedly, for cationic clusters, the highly concentrated positive charge on the Au atom of the -O-Au sites can strongly adsorb but hardly activate the adsorbed O2. These results have certain reference points for understanding the gold oxide interfaces and the improved catalytic oxidation performance of gold-based systems in the presence of atomic oxygen species.