Active Lattice Oxygen Research Articles

Characterization and mechanism of red-mud-catalyzed steam gasification of corn stover

Catalytic biomass gasification has received extensive attention from scholars worldwide. This study proposes steam gasification of corn stover using red mud (RM), an industrial solid waste, as a catalyst to produce high-quality reducing gas. Experiments were conducted at different reaction temperatures and gasification times. Characterization of RM and its three main components, Fe2O3, CaCO3, and Al2O3, in the catalytic steam gasification process of corn stover, was performed and its catalytic mechanism was explored by characterizing magnetic separation products. Results show that an increase in reaction temperature significantly promotes the production of CO, CO2, and H2. The promotion of steam to H2 production is caused by the gas-phase reaction and gasification of fixed carbon (FC). Fe2O3 promotes gas-phase reactions, such as the water–gas shift reaction, and effectively catalyzes the steam gasification of FC as an intermediate reactant. The addition of Al2O3 is beneficial for the production of CH4 and H2. The CO2 produced by the decomposition of CaCO3 inhibits the water–gas shift and methane-steam reforming reactions, thus reducing H2 output. The addition of RM is beneficial for the production of H2 and CO2 and inhibits the production of CO. Compared with pure Fe2O3, the superior pore structure and unique solid solution structure of RM provide Fe2O3 with more active surface lattice oxygen, higher redox performance, larger gas–solid contact area, superior ability to prevent carbon deposition, and better catalytic ability.

An effective strategy to improve the photothermocatalytic activity of Co3O4 for VOCs degradation: Specifically enhancing the surface lattice oxygen activity

Co3O4 catalysts with active surface lattice oxygen were constructed via a simple solvothermal method by adopting isopropyl alcohol (IPA) or tert-butyl alcohol (TBA) as solvent. The obtained Co3O4-IPA and Co3O4-TBA exhibit flower-like structures with (112) planes exposed on the surface. Due to abundant unsaturated Co3+ sites existing on the (112) plane, the content and activity of surface lattice oxygen on Co3O4-IPA and Co3O4-TBA are much higher than that on Co3O4-MA and Co3O4-EA, which prepared with methyl alcohol or ethyl alcohol as a solvent. The robust surface lattice oxygen on Co3O4-IPA and Co3O4-TBA facilitates the ring-opening process during photothermocatalytic oxidation of toluene, significantly promoting the catalytic performance. In the static atmosphere, about 98% of toluene conversion and 80% of CO2 yield can be achieved on Co3O4-IPA and Co3O4-TBA under full-spectrum light irradiation of 325 mW/cm2, much higher than 89% and 73% of conversion, 50% and 26% of CO2 yield on Co3O4-EA and Co3O4-MA, respectively.

Improving benzene catalytic oxidation on Ag/Co3O4 by regulating the chemical states of Co and Ag

Silver (9 wt.%) was loaded on Co3O4-nanofiber using reduction and impregnation methods, respectively. Due to the stronger electronegativity of silver, the ratios of surface Co3+/Co2+ on Ag/Co3O4 were higher than on Co3O4, which further led to more adsorbed oxygen species as a result of the charge compensation. Moreover, the introducing of silver also obviously improved the reducibility of Co3O4. Hence the Ag/Co3O4 showed better catalytic performance than Co3O4 in benzene oxidation. Compared with the Ag/Co3O4 synthesized via impregnation method, the one prepared using reduction method (named as AgCo-R) exhibited higher contents of surface Co3+ and adsorbed oxygen species, stronger reducibility, as well as more active surface lattice oxygen species. Consequently, AgCo-R showed lowest T90 value of 183°C, admirable catalytic stability, largest normalized reaction rate of 1.36 × 10−4 mol/(h·m2) (150°C), and lowest apparent activation energy (Ea) of 63.2 kJ/mol. The analyzing of in-situ DRIFTS indicated benzene molecules were successively oxidized to phenol, o-benzoquinone, small molecular intermediates, and finally to CO2 and water on the surface of AgCo-R. At last, potential reaction pathways including five detailed steps were proposed.

Highly active and stable plate-like ZSM‑5 supported MnOx catalysts for toluene Oxidation: Effect of preparation methods

Catalysts consisting of MnOx supported on plate-like ZSM-5 with the Si/Al ratio of 70 (MnOx/PZ5) were synthesized using four different methods: in-situ growth (MnOx/PZ5-IG), ammonia precipitation (MnOx/PZ5-AP), citric acid complexation (MnOx/PZ5-CA), and traditional impregnation (MnOx/PZ5-TI). The catalytic activity of these catalysts for toluene oxidation was evaluated, and their physicochemical properties were characterized by several technologies. The results showed the catalytic activity for toluene oxidation was significantly influenced by the preparation methods. Notably, MnOx/PZ5-IG demonstrated the highest catalytic activity for oxidation of toluene with the specific activity per unit mass of Mn with 2.12 × 10-6 at 250 °C, 3.8 times higher than that of MnOx/PZ5-CA, offering new ideas for the design of low-cost materials for VOCs elimination in the future. The excellent performance of MnOx/PZ5-IG could be attributed to the higher Mn4+ ratio with more reducible, active surface adsorbed oxygen and dispersion of MnOx, which also showed high stability. Finally, the reaction mechanism analyzed by in-situ DRIFTS found that MnOx/PZ5-IG promoted the activity of surface lattice oxygen, conducive to increasing the reaction rate and facilitating the ring opening of benzene, thus, deepening the oxidation of toluene to CO2 and H2O.

Clarify the effect of different metals doping on α-MnO2 for toluene adsorption and deep oxidation

α-MnO2 doped with four metals (Cu, Ce, Co, Fe) were prepared via a redox co-precipitation method. MnCu exhibited the highest activity and the temperature required for achieving 90% toluene conversion was 224℃ at a weight hourly space velocity of 30000 mL·g−1·h−1. Moreover, MnCu possessed outstanding thermal stability and resistance to H2O. The optimal crystal structure, appropriate Mn3+/Mn4+ proportion, and superior redox properties of MnCu contributed to the generation of oxygen vacancies and the highest lattice oxygen (Olat) mobility. Both surface and bulk lattice oxygen consumed in MnCu can be supplemented promptly by gaseous oxygen. Therefore, a balance between toluene adsorption and deep oxidation was built in MnCu to ensure the continuous oxidation of toluene. Although the abundant surface defects and a relatively active surface lattice oxygen accelerated the adsorption and activation of toluene over MnFe, it exhibited the poorest activity. This was because the deep oxidation of toluene was inhibited owing to poor lattice oxygen migration. The adsorbed toluene and part intermediates might cover the catalyst surface preventing the continuous oxidation of toluene. This further illustrated that the deep oxidation of toluene was much more important than the adsorption for the design of MnO2-based mixed oxide catalysts.

Revealing oxygen transfer between Mn3O4 and CuMn2O4 and its effect on enhanced catalytic oxidization of VOCs

Hybrid catalysts are widely utilized in various environmental catalysis, such as catalytic oxidization and reduction. However, most works usually treat a hybrid catalyst as a whole, and seldom report explores interface behavior of active species between components in the hybrid. In this work, we investigated mechanism for enhanced catalytic oxidization of toluene by a mixture of Mn3O4 and CuMn2O4. The mixture removed 99% of toluene at 240 °C, far bigger than CuMn2O4 (53%) and Mn3O4 (23%). In brief, Mn3O4 had plenty of bulk lattice oxygens, which were inactive for toluene catalytic oxidization. After forming an interface between Mn3O4 and CuMn2O4, oxygen vacancy formed on the interface during the catalysis, and transferred the bulk lattice oxygen to the interface, forming active lattice oxygen. Therefore, the number of active sites was increased, resulting in an enhanced catalytic performance. This conclusion was verified in other hybrids, including Mn3O4/CuFeOx, Mn3O4/CuCeOx, and Mn3O4/CuCoOx. The main result of this work helps to understand the catalytic mechanism of volatile organic compounds by hybrid oxides. These results are also in favor of designing and optimizing catalysts.

Disordered Rocksalts with Lattice Oxygen Activation as Efficient Oxygen Evolution Electrocatalysts

Disordered Rocksalts with Lattice Oxygen Activation as Efficient Oxygen Evolution Electrocatalysts

Hg0 removal performance of magnetic raffinate slag-based sorbents: Mechanism study on oxidation modification

The sulfur-containing carbon-based sorbent was regarded as potential sorbent for the removal of toxic elemental mercury (Hg0). However, due to its lower reaction temperature and the stronger Hg0 oxidation capacity of oxides at higher temperature, oxidation modification on sulfur-containing raffinate slag-based sorbents was proposed in the study. The effects of O2, H2O2 and KMnO4 oxidation modification on Hg0 removal performance and physicochemical properties of sorbents were investigated. The oxidation modification had little effect on pore structure of sorbents, but mainly affected the content and valence state of sulfur and oxygen elements. Compared with H2O2 oxidation, KMnO4 oxidation was more conducive to forming active lattice oxygen (Oα). The valence state of manganese bound with Oα influenced Hg0 capture a lot, and Oα in MnO2 showed strong oxidation capacity to Hg0. Active S22−and Oα in A850-0.1KMnO4-12h sorbent could both promote the Hg0 removal with HgS and HgO formed in used sorbent. The saturated magnetization of A850-0.1KMnO4-12h sorbent was 5.39 emu·g−1, making it possible to separate mercury-containing sorbents from fly ash. It showed good resistance to low concentration of SO2, and NO could promote its Hg0 removal ability. Meanwhile, KMnO4 oxidation successfully improved the Hg0 removal performance at higher reaction temperature and gas hourly space velocity.

CaO-Promoted Lattice Oxygen Activation and Antichlorine Poisoning over Mullite for Catalytic Chlorobenzene Combustion

CaO-Promoted Lattice Oxygen Activation and Antichlorine Poisoning over Mullite for Catalytic Chlorobenzene Combustion

Differences between atomically-dispersed and particulate Pt supported catalysts on synergistic photothermocatalytic oxidation of VOCs from cooking oil fumes

The control of volatile organic compounds (VOCs) from cooking oil fumes via synergic photothermocatalytic oxidation not only saves energy, but also helps to reduce carbon emissions. Differences between the copper oxide−ceria (CC) supported atomically-dispersed (Pt1/CC) and particulate Pt (PtNPs/CC) on photothermocatalytic heptane oxidation were investigated. The conversion efficiency at 170 oC of heptane oxidation over the Pt1/CC catalyst was 55% higher than that over the PtNPs/CC catalyst. PtNPs/CC showed a larger capacity of heptane adsorption, but limited amounts of the adsorbed oxygen and active surface lattice oxygen species were difficult to completely oxidize the over-adsorbed heptane. Heptane and its intermediates gradually accumulated at the active sites, resulting in poor catalytic activity and stability. However, Pt1/CC possessed a strong electron donating ability due to its unique coordination unsaturated sites and electron structure, which was conducive to oxygen activation. This allowed rapid conversion of heptane and intermediates, accelerating oxidation of the adsorbed heptane to CO2 and H2O. The complete oxidation of 500 ppm heptane was basically achieved at 190 oC and an optical power density of 300 mW/cm2.

Rapid supplement of active oxygen by constructing Pt-Fe alloy structure to improve catalytic stability for furniture paints industry VOCs removal

To improve the air quality, volatile organic compounds (VOCs) elimination via a stable catalytic oxidation is important. The enhancement in the catalytic stability of toluene and iso-hexane removal is investigated by constructing the Pt-Fe alloy structure. The Pt-Fe alloy structure not only weakens the toluene adsorption, but also improves the lattice oxygen mobility. The Mars-van Krevelen mechanism is presented over the Pt1Fe1.5/M during toluene oxidation, instead of the initial Langmuir-Hinshelwood mechanism. For Pt1Fe1.5/M, the strong ability of O2 activation and the fast migration of lattice oxygen will provide sufficient surface lattice oxygen to ensure a continuous toluene oxidation. An excellent catalytic stability is detected over the catalysts with the high activity of lattice oxygen, which are accelerated by the weaker adsorption and higher temperature during iso-hexane oxidation. Generally, the crucial role of the replenishment speed of active oxygen species is clarified in a stable process of VOCs oxidation. It is valuable for the up-to-standard emission of VOCs from the furniture paints industry.

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.