Active Lattice Oxygen Research Articles

Study on the structural evolution and heat transfer performance of Cu supported on regular morphology CeO2 in CO catalytic combustion and chemical looping combustion

Chemical looping combustion (CLC) and catalytic combustion (CC), which are potential technologies to promote CO→CO2 efficient conversion and energy conservation for the steelmaking off-gas, are investigated in reaction activity, structure evolution catalysts/oxygen carriers (OCs) and energy recovery using Cu/CeO2 materials. Activity results suggest that the rod-shaped samples with well-defined (100) crystal faces exhibit higher activity than the sphere-shaped samples with (111) crystal faces, obtaining the optimized copper content of 3 wt%. IR spectra confirmed the proposed reaction pathway that the CO adsorbed on copper sites (Cu+–CO) at the Cu–Ce interface reacts with adjacent surface lattice oxygen. The gaseous oxygen continuously migrates to the external surface of materials, thus resulting in strongly exothermic CO self-sustained combustion during CC. Such a violent reaction does not cause obvious evolution of chemical composition, crystalline phase and structure. Since the active lattice oxygen is gradually consumed but not replenished by external gaseous O2 in time, CO combustion is not self-sustained during CLC. Therefore, the reduction cycle is no longer confined to the surface of the material but penetrates deep into its body, which accelerates Cu+ enrichment at the surface and leads to irreversible sintering and agglomeration of the material.

Electrochemical Etching Switches Electrocatalytic Oxygen Evolution Pathway of IrOx /Y2 O3 from Adsorbate Evolution Mechanism to Lattice-Oxygen-Mediated Mechanism.

Oxygen evolution reaction (OER) plays key roles in electrochemical energy conversion devices. Recent advances have demonstrated that OER catalysts through lattice oxygen-mediated mechanism (LOM) can bypass the scaling relation-induced limitations on those catalysts through adsorbate evolution mechanism (AEM). Among various catalysts, IrOx , the most promising OER catalyst, suffers from low activities for its AEM pathway. Here, it is demonstrated that a pre-electrochemical acidic etching treatments on the hybrids of IrOx and Y2 O3 (IrOx /Y2 O3 ) switch the AEM-dominated OER pathway to LOM-dominated one in alkali electrolyte, delivering a high performance with a low overpotential of 223mV at 10mA cm-2 and a long-term stability. Mechanism investigations suggest that the pre-electrochemical etching treatments create more oxygen vacancies in catalysts due to the dissolution of yttrium and then provide highly active surface lattice oxygen for participating OER, thereby enabling the LOM-dominated pathway and resulting in a significantly increased OER activity in basic electrolyte.

Highly Disordered Fe-Doped CeO2 with Oxygen Vacancies Facilitates Electrocatalytic Water Oxidation

The practical application of electrocatalytic water splitting is hindered by the sluggish anodic oxygen evolution reaction (OER), where the exploration of efficient and stable electrocatalysts toward water oxidation remains a great challenge. Herein, we report an active iron-doped ceria (FeOx/CeO2) catalyst with a highly disordered feature decorated on three-dimensional (3D) nickel foam, which can directly serve as the superior OER electrode in alkaline media. The highly disordered Fe-doped CeO2 catalyst displays remarkable OER performance with a low overpotential of 252 mV to achieve 10 mA cm–2, a small Tafel slope of 45 mV dec–1, and long-term durability for at least 48 h with a stable structure. The superior OER activity of FeOx/CeO2 is attributed to the lattice oxygen activation mechanism facilitated by its disordered structure as well as the high electrochemical surface area. This study provides valuable insights into the rational design of efficient OER catalysts through tailoring the catalyst structure and reaction pathway.

Frontispiz: Activating Lattice Oxygen in Spinel ZnCo2O4 through Filling Oxygen Vacancies with Fluorine for Electrocatalytic Oxygen Evolution

Electrocatalysis. In their Research Article (e202301408), Zhao-Qing Liu et al. report the activation of lattice oxygen in spinel ZnCo2O4 through filling oxygen vacancies with fluorine, thus resulting in a highly active catalyst for electrocatalytic oxygen evolution.

Frontispiece: Activating Lattice Oxygen in Spinel ZnCo2O4 through Filling Oxygen Vacancies with Fluorine for Electrocatalytic Oxygen Evolution

Electrocatalysis. In their Research Article (e202301408), Zhao-Qing Liu et al. report the activation of lattice oxygen in spinel ZnCo2O4 through filling oxygen vacancies with fluorine, thus resulting in a highly active catalyst for electrocatalytic oxygen evolution.

Oxygen activity regulation over LaNiO3 perovskites by Ti substitution for chemical looping partial oxidation of methane

The oxygen species in oxygen carriers directly influence the reaction performance in chemical looping processes. This paper describes the relationship between oxygen species and performance in chemical looping partial oxidation of methane (CLPOM) over LaNixTi1-xO3-δ (x = 0, 0.25, 0.5, 0.75 and 1) perovskites. Due to the increase of Ti substitution, the predominate reaction during CLPOM gradually changes from complete oxidation to partial oxidation. Quasi in situ XPS characterization suggests that the relative concentration of nucleophilic lattice oxygen species for partial oxidation increases with Ti substitution, while the relative concentration of electrophilic adsorbed oxygen species for complete oxidation decreases. The moderate Ti substitution for LaNi0.5Ti0.5O3-δ provides the suitable lattice oxygen activity for the methane partial oxidation. Moreover, LaNi0.5Ti0.5O3-δ exhibits high cyclic stability in redox cycles. This work demonstrates that the regulation of oxygen species distribution and activity is feasible to tailor the reaction performance of oxygen carriers in chemical looping processes.

Novel insight into the effect of relative humidity on the acetone photocatalytic decomposition using Ag−CeO2 under vacuum ultraviolet illumination: Catalytic synergies, performance, and mechanistic interpretation

The present work reports on the impact of relative humidity (RH) on the process of acetone oxidation in the absence and presence of Ag − CeO2 photocatalysts, including 185 nm vacuum UV (VUV) photolysis, ozonation, ozonation + 254 nm UV photolysis, and 254 nm UV photolysis treatment processes. The photocatalysts were evaluated by Raman, SEM, XRD, HRTEM, EPR, EDS, and XPS techniques. The information from characterization tests revealed that modification of ceria structure by the introduction of Ag nanoparticles increases the photocatalyst oxygen storage ability, which promotes the oxygen vacancies formation, resulting in the lattice oxygen activation. The attained data demonstrated the dual role of RH in the process of acetone oxidation under VUV irradiation. Compared to the dry condition, the introduction of RH = 25, 45, and 65% to the VUV photolysis system enhances the conversion of acetone remarkably from 40% to 60, 68, and 72%, respectively. However, the acetone oxidation did not change significantly in the presence of RH = 25–65% over the Ag − CeO2/VUV system. This observation confirms the dual role of RH; while RH boosted the gas phase photooxidation reactions, it poisoned the gas–solid interface, leading to an inhibitory effect on the catalytic oxidation reactions. Moreover, the results showed that the lower level of relative humidity (e.g., RH = 5%) over the Ag − CeO2 under VUV light not only enhances the acetone oxidation to 88% but also, through the participation of the catalytic ozonation, decomposed the formed O3 and increased the selectivity of the reaction towards complete oxidation up to 97%. The acetone oxidation mechanism was studied where the EPR results show that both.OH and.O2– contribute to acetone oxidation. Finally, the Ag − CeO2/VUV reusability was assessed in a way that the in-situ procedure for photocatalyst regeneration was utilized to inhibit the catalyst deactivation.

Highly efficient catalytic CO oxidation by balancing the crystal and mesoporous structure of Ta2O5 carrier combined with cobalt

Because the combination of Co and common support (Al, Ti, et al.) usually shows poor catalytic activity, tantalum has been introduced for CO conversion as a novel carrier due to the excellent performance. In this work, Co3O4 was loaded on four forms of tantalum support (amorphous, mesoporous, crystalline and crystalline mesoporous, abbreviated as Co/Ta-am, Co/Ta-me, Co/Ta-cry and Co/Ta-cm, respectively). And among these four states, Co/Ta-cm presents the highest CO conversion rate. The temperature of 90% CO conversion rate of Co/Ta-cm is approximately 130 ℃ at the high space velocity of 780,000 h−1, which is 70%, 82% and 88% higher than that of Co/Ta-cry, Co/Ta-me and Co/Ta-am, respectively. Moreover, the characteristics of the catalyst have been studied by XRD, SEM, BET, TGA, and H2-TPR, and the results reveal that Co/Ta-cm has the excellent crystallinity and stability, and the morphology is regular. X-ray photon spectroscopy and in-situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTs) have been performed to investigate the reaction mechanism, which indicates that Co3+ is the active component and lattice oxygen plays a critical role in CO oxidation.

Synergistic catalysis on atomic Ru-doped manganese oxide for aerobic oxidation of biomass-derived 5-hydroxymethylfurfural

Catalytic oxidation of biomass derived 5-Hydroxymethylfurfural (HMF) feedstock is a promising route to produce value-added chemicals 2, 5-diformylfuran (DFF). Here, we find that incorporating monatomic Ru into the crystalline lattice of α-MnO2 can trigger synergetic catalysis for aerobic oxidation of HMF. Ru species can not only act as active sites for HMF conversion, but also activate surface oxygen species by creating rich oxygen vacancies on the α-MnO2. As result, such catalyst delivers much higher DFF productivity than that of Ru located in the tunnel of support (110 °C, 1.5 MPa, 1 h) and state-of-the-art Ru-based catalysts. Furthermore, the direct conversion of fructose into DFF was realized by combination of Amberlyst-15 and Ru-MnO2 HT catalyst in one-pot via two-step. Characterization and kinetic results indicated that atomically dispersed Ru hosted in the crystalline lattice of support created abundant oxygen vacancies and thus weakened the Mn-O bond, resulting in facile lattice oxygen activation.

Coupling acid catalysis and selective oxidation over MoO3-Fe2O3 for chemical looping oxidative dehydrogenation of propane

Redox catalysts play a vital role in chemical looping oxidative dehydrogenation processes, which have recently been considered to be a promising prospect for propylene production. This work describes the coupling of surface acid catalysis and selective oxidation from lattice oxygen over MoO3-Fe2O3 redox catalysts for promoted propylene production. Atomically dispersed Mo species over γ-Fe2O3 introduce effective acid sites for the promotion of propane conversion. In addition, Mo could also regulate the lattice oxygen activity, which makes the oxygen species from the reduction of γ-Fe2O3 to Fe3O4 contribute to selectively oxidative dehydrogenation instead of over-oxidation in pristine γ-Fe2O3. The enhanced surface acidity, coupled with proper lattice oxygen activity, leads to a higher surface reaction rate and moderate oxygen diffusion rate. Consequently, this coupling strategy achieves a robust performance with 49% of propane conversion and 90% of propylene selectivity for at least 300 redox cycles and ultimately demonstrates a potential design strategy for more advanced redox catalysts.

Revealing the Excellent Low-Temperature Activity of the Fe1–xCexOδ-S Catalyst for NH3-SCR: Improvement of the Lattice Oxygen Mobility

The development of selective catalytic reduction catalysts by NH3(NH3-SCR) with excellent low-temperature activity and a wide temperature window is highly demanded but is still very challenging for the elimination of NOx emission from vehicle exhaust. Herein, a series of sulfated modified iron-cerium composite oxide Fe1-xCexOδ-S catalysts were synthesized. Among them, the Fe0.79Ce0.21Oδ-S catalyst achieved the highest NOx conversion of more than 80% at temperatures of 175-375 °C under a gas hourly space velocity of 100000 h-1. Sulfation formed a large amount of sulfate on the surface of the catalyst and provided rich Brønsted acid sites, thus enhancing its NH3 adsorption capacity and improving the overall NOx conversion efficiency. The introduction of Ce is the main determining factor in regulating the low-temperature activity of the catalyst by modulating its redox ability. Further investigation found that there is a strong interaction between Fe and Ce, which changed the electron density around the Fe ions in the Fe0.79Ce0.21Oδ-S catalyst. This weakened the strength of the Fe-O bond and improved the lattice oxygen mobility of the catalyst. During the reaction, the iron-cerium composite oxide catalyst showed higher surface lattice oxygen activity and a faster replenishment rate of bulk lattice oxygen. This significantly improved the adsorption and activation of NOx species and the activation of NH3 species on the catalyst surface, thus leading to the superior low-temperature activity of the catalyst.

Inhibition of Structural Transformation and Surface Lattice Oxygen Activity for Excellent Stability Li-Rich Mn-Based Layered Oxides

Li-rich Mn-based layered oxides (LLOs) are one of the most promising cathode materials, which have exceptional anionic redox activity and a capacity that surpasses 250 mA h/g. However, the change from a layered structure to a spinel structure and unstable anionic redox are accompanied by voltage attenuation, poor rate performance, and problematic capacity. The technique of stabilizing the crystal structure and reducing the surface oxygen activity is proposed in this paper. A coating layer and highly concentrated oxygen vacancies are developed on the material's surface, according to scanning electron microscopy, transmission electron microscopy, and X-ray photoelectron spectroscopy. In situ EIS shows that structural transformation and oxygen release are inhibited during the first charge and discharge. Optimized 3@LRMA has an average attenuation voltage of 0.55 mV per cycle (vs 1.7 mV) and a capacity retention rate of 93.4% after 200 cycles (vs 52.8%). Postmortem analysis indicates that the successful doping of Al ions into the crystal structure effectively inhibits the structural alteration of the cycling process. The addition of oxygen vacancies reduces the surface lattice's redox activity. Additionally, surface structure deterioration is successfully halted by N- and Cl-doped carbon coating. This finding highlights the significance of lowering the surface lattice oxygen activity and preventing structural alteration, and it offers a workable solution to increase the LLO stability.

Halogen chlorine triggered oxygen vacancy-rich Ni(OH)2 with enhanced reaction kinetics for pseudocapacitive energy storage

Two-dimensional (2D) Ni(OH)2 nanosheets can theoretically expose their active sites of 100%. Whereas, their intrinsic easy accumulation and low conductivity lead to weak and unsustainable reaction kinetics. Herein, we propose a novel halogen chlorine-triggered electrochemical etching strategy to controllably manage the reaction kinetics of 2D Ni(OH)2 nanosheets (EE/Cl-Ni(OH)2). It is found that halogen chlorine doping can adjust the interlamellar spacing flexibly and promote the lattice oxygen activation to achieve controlled construction of superficial oxygen defects at the adjustable voltage. The optimal EE/Cl-Ni(OH)2 electrode exhibits a high rate capability and excellent specific capacity of 206.9 mA h g−1 at 1 A g−1 in a three-electrode system, which is more than twice as high as the pristine Ni(OH)2. Furthermore, EE/Cl-Ni(OH)2 cathode and FeOOH@rGO anode are employed for developing an aqueous Ni-Fe battery with an excellent energy density of 83 W h kg−1, a high power density of 17051 W kg−1, and robust durability over 20,000 cycles. This strategy exploits a fresh channel for the ingenious fabrication of high-efficiency and stable nickel-based deficiency materials for energy storage.

Highly Oxidized Oxide Surface toward Optimum Oxygen Evolution Reaction by Termination Engineering.

The oxygen evolution reaction (OER) is a critical step for sustainable fuel production through electrochemistry process. Maximizing active sites of nanocatalyst with enhanced intrinsic activity, especially the activation of lattice oxygen, is gradually recognized as the primary incentive. Since the surface reconfiguration to oxyhydroxide is unavoidable for oxygen-activated transition metal oxides, developing a surface termination like oxyhydroxide in oxides is highly desirable. In this work, we demonstrate an unusual surface termination of (111)-facet Co3O4 nanosheet that is exclusively containing edge-sharing octahedral Co3+ similar to CoOOH that can perform at approximately 40 times higher current density at 1.63 V (vs RHE) than commercial RuO2. It is found that this surface termination has an oxidized oxygen state in contrast to standard Co-O systems, which can serve as active site independently, breaking the scaling relationship limit. This work forwards the applications of oxide electrocatalysts in the energy conversion field by surface termination engineering.

Insights into the interface of NiCo2O4 spinel /LaCoO3 perovskite nano-composite for CO and soot oxidation

In the quest for the development of thermally stable, highly active and low-cost catalysts for use in catalyzed diesel particulate filter, nano-composites are new areas of research. Therefore, we reported the easy synthesis of spinel NiCo2O4/perovskite LaCoO3 nano-composite, and its individual oxides NiCo2O4 and LaCoO3 for comparison. The detailed insights into the physio-chemical characteristics of formed NiCo2O4/ LaCoO3 nano-composite were done based on various characterization analysis such as X-ray diffraction (XRD), Fourier transform infrared (FT-IR), N2 physiosorption, scanning electron microscopy-energy dispersive spectroscopy (SEM-EDX), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS). The characterization analysis of NiCo2O4/LaCoO3 revealed the successful formation of a chemical interface possessing strong interfacial interaction, resulting in desirable physicochemical characteristics such as small crystallite size, abundant mesoporosity, high specific surface area and activation of surface lattice oxygen. Owing to the desirable characteristics, the activity results over NiCo2O4/LaCoO3 nano-composite showed the excellent CO oxidation performance and high soot oxidation activity, recyclability and thermal stability. This work mainly attempts to emphasize the effectiveness of the facile, inexpensive and conventionally used precipitation method for the successful formation of highly efficient nano-composites.

Promotion Effects of Ce-Doping on Catalytic Oxidation of Ethane over Pt/CexTi1−xO2

The catalytic oxidation of VOCs is widely acknowledged as the most available technology to reduce air pollution. Among the catalysts for VOCs, 1 wt%-Pt/TiO2 catalysts using metal as a doping element have shown amazing potential in many fields. However, achieving high catalytic performance at relatively low temperatures based on the activation of molecules is still a formidable challenge owing to the catalytic activity being highly dependent on temperature. Here, the role of the rare earth metal Ce in the catalytic oxidation of ethane was studied by preparing Pt/CexTi1−xO2 (x = 0, 0.002, 0.005, 0.01, 0.02, and 0.05) catalysts. When the Ce/(Ce+Ti) molar ratio was 0.01, Pt/Ce0.01Ti0.99O2 achieved 90% ethane conversion at 436 °C. This reaction temperature is 15% lower than that for Pt/TiO2. The characterization results show that the doping of Ce caused lattice expansion of TiO2 and its distortion brought about by oxygen vacancies. Additionally, the appropriate amount of Ce-doping can alter the interaction between the active component Pt and the carrier TiO2, thereby improving the activity and concentration of the active surface lattice oxygen species of the catalyst. These results provide a foundation for the design of the catalytic oxidation of VOCs under mild operating conditions.

Interfacial engineering enables surface lattice oxygen activation of SmMn2O5 for catalytic propane combustion

Surface lattice oxygen (Olatt) over transition metal oxides plays a pivotal role in catalytic combustion of automobile exhaust. The insufficient Olatt activity at low temperatures, however, remains the key problem restricting its practical application. To overcome this deficiency, we activated the Olatt of mullite SmMn2O5 through the interface fabrication with spinel Co3O4. The optimized Co3O4/SmMn2O5 catalyst exhibited 90% conversion at 247 °C for the typical automobile exhaust propane combustion, 77 °C lower than the original SmMn2O5. Additionally, Co3O4/SmMn2O5 showed extremely high stability even under harsh operating temperature (e.g., 800 °C). Experimental and theoretical calculation results revealed that the regulated interface of Co3O4/SmMn2O5 facilitated the electrons transfer from SmMn2O5 to Co3O4, contributing to the enhanced propane adsorption and catalytic oxidation activity due to the formation of electrophilic oxygen in SmMn2O5 around the interface. This work can provide a basic understanding of the Olatt activation for developing efficient automobile exhaust combustion catalysts.

Robust TiO2/CuS@TiO2 composites loaded on Ti mesh with outstanding stability and photothermal effects for the enhanced photo-degradation of organic pollutions in a flowing device

A scalable strategy with commercial feasibility was developed to in situ generate TiO2 nanowires/amorphous CuS@TiO2 nanolayer (TiO2/CuS@TiO2) composites on the surface of titanium mesh through a sequent hydrothermal method, successive ionic layer adsorption and reaction (SILAR), and atomic layer deposition (ALD) techniques. The TiO2/CuS@TiO2 composites could respectively harness the incident light with different spectra at the photothermal center (CuS, visible and near-infrared light) and photocatalytic center (TiO2, UV and visible light), which leads to the effective utilization of the solar energy. Benefiting from the CuS photothermal-induced local heating effect of CuS, the adjacent micro-zone temperature could be elevated and the activation energy barrier could be reduced by 10.5 kJ mol−1, which promotes the activation of surface lattice oxygen and dissolved oxygen in the photocatalytic process. Meanwhile, the ALD generated TiO2 nanolayer could both serve as reactive centers but also protecting armor for the CuS, which prohibited the peeling and oxidation of the thermal centers, leading to a high stability of the photocatalyst, which exhibits no obvious fading after 20-cycle reuse. A flow reactor was conceived and made by 3D print and the Ti-mesh based photocatalyst was integrated, which demonstrates high photocatlytic performances, manifesting its great potential for large-scale water treatment.

Promotion effect of CO oxidation via activation of surface lattice oxygen by single atom Cu/MnO2 catalyst

The catalytic oxidation of CO by single-atom transition metal catalysts has always been the focus of researchers. Herein, we report a strategy for the preparation of Cu single-atom anchored on MnO2 by oxalate chelation-assisted hydrothermal method, and the obtained Cu/MnO2–0.25 catalyst with the optimal molar ratio achieved about 90% CO conversion at 80 °C. The strong electronic interaction between Cu and MnO2 not only effectively inhibits the aggregation of Cu single atoms, but also the formed Cu-O-Mn hybrid structure activates the adjacent surface lattice oxygen, further improving the catalytic oxidation performance of CO at low and medium temperatures. The elevated activity is achieved at the single-atom active site by the Mars-van Krevelen (MvK) mechanism. This work provides a simple and reliable method for the rational design of stable transition metal single-atom catalysts and deepens the understanding of metal-support strong interactions (SMSI).

Acid-etched spinel CoMn2O4 with highly active surface lattice oxygen species for significant improvement of catalytic performance of VOCs oxidation

The strategy of acid-etching was applied to improve the catalytic activity of spinel CoMn2O4, and 0.06 M (acid etching concentration) catalyst exhibited a nearly 16-fold increase in toluene reaction rate at 210 °C compared with pristine catalyst. The crystal, nanosphere and mesoporous structures of 0.06 M catalyst were not damaged significantly. And importantly, the presence of rich oxygen vacancies weakened the metal-oxygen bond strength and improved the mobility of surface lattice oxygen species to enhance the catalytic performance. The active surface lattice oxygen reacted directly with toluene over 0.06 M catalyst, which was significantly different with that the bulk lattice oxygen had to migrate to the surface for toluene oxidation over the pristine catalyst. Meanwhile, the formation and consumption rates of intermediates were significantly accelerated over 0.06 M catalyst with abundant oxygen vacancies. This work provides vital experimental proof for understanding the relationship between the oxygen vacancies and lattice oxygen species participating in toluene oxidation.