Mobility Of Lattice Oxygen Research Articles

Facile construction and enhanced catalytic activity of Co-Mn oxide with rich amorphous/crystalline interfaces for propane oxidation

Cobalt-manganese (Co-Mn) composite oxides show high potential for the catalytic oxidation of volatile organic compounds (VOCs). However, the low defect content and poor oxygen mobility of perfect spinel structure crystalline always make it difficult to effectively activate C–H bonds of propane. Here, the catalyst with rich amorphous MnOx/crystalline Co3O4 interfaces was prepared, and the catalytic combustion activity for propane was determined. The rich amorphous/crystalline interfaces CMO-400 (i.e. Co-Mn oxide calcined at 400 °C) catalyst exhibited the best catalytic activity for propane with T90 of 200 °C among all bimetallic Co-Mn oxides. Various characterizations and corresponding results have demonstrated that the abundant amorphous/crystalline interfaces could improve the catalytic performances, attributed to high oxygen vacancy concentration, low temperature reducibility, weak Mn−O bond strength, and good surface lattice oxygen mobility. It is noteworthy that the interface engineering of amorphous/crystalline is an effective strategy in VOCs catalytic oxidation.

Ce-based three-dimensional mesoporous microspheres with Mn homogeneous incorporation for toluene oxidation

Ce-based three-dimensional (3D) mesoporous microspheres with Mn homogeneous incorporation were synthesized. The CeMn-0.4, characterized by a Ce/Mn molar ratio of 6:4, demonstrated exceptional catalytic activity and stability. The formation of CeMn solid solution strengthened the Ce-Mn interaction, yielding higher concentrations of Ce3+ and Mn4+. Mn4+ initiated toluene preliminary activation owing to its robust oxidative properties, while Ce3+ contributed to oxygen vacancy generation, enhancing the activation of gaseous oxygen and lattice oxygen mobility. Integrating experiments and Density Functional Theory (DFT) calculations elucidated the oxygen reaction mechanisms. A portion of oxygen was converted into surface reactive oxygen species (Oads) that directly oxidized toluene. Additionally, the presence of oxygen vacancies promoted the participation of oxygen in toluene oxidation by converting it into lattice oxygen, which was crucial for the deep oxidation of toluene. Diffuse Reflectance Fourier Transform Infrared Spectroscopy (DRIFTS) indicated the accumulation of benzene-ring intermediates on the catalyst surface hindered continuous toluene oxidation. Thus, the abundant oxygen vacancies in CeMn-0.4 played a pivotal role in sustaining the oxidation process by bolstering the activation of gaseous oxygen and the mobility of lattice oxygen.

Comparative study of Mn oxide catalysts on toluene oxidation: The effect of Mn valence electronic structures

Understanding the structure-activity relationship of Mn-based oxide catalysts is of great importance for the rational development of highly performance catalysts for VOCs catalytic oxidation. However, the knowledge of the electronic structure-catalytic oxidation activity relationship over Mn-based oxide catalysts is still limited. Herein, we investigated the typical MnxOy (Mn3O4, MnO2, and Mn2O3) with different valence electronic structures by using various characterizations and DFT calculations. The MnO2 exhibits superior intrinsic activities (RS, 1.14×10−9 mol·m−2·s−1) when compared with Mn3O4 (0.54×10−9 mol·m−2·s−1) and Mn2O3 (0.45×10−9 mol·m−2·s−1) for toluene catalytic oxidation. The solid experimental and DFT calculation results show that the d-band center of Mn determines the intrinsic activity. The superior catalytic oxidation activity of MnO2 can be attributed to its higher d-band center (-1.03 eV) in comparison with that of Mn3O4 (-1.25 eV) and Mn2O3 (-1.59 eV). The higher d-band center can weaken the surface Mn-O bonds strength (k = 290.9 N/m) and strengthen the gaseous O2 adsorption simultaneously, then enhancing the mobility of surface lattice oxygen and the amount of adsorbed oxygen species. This work firstly reveals the intrinsic relationship between catalytic oxidation activity and d electronic structure over Mn-based oxide catalysts and provides knowledge that will advance the design of high-performance catalysts for catalytic oxidation.

Advances and Challenges in Oxygen Carriers for Chemical Looping Partial Oxidation of Methane

To cope with global warming and increasing carbon emissions, the chemical looping process has attracted attention due to its excellent ability to convert fossil fuel and capture CO2. In this case, chemical looping partial oxidation technology has become the focus of attention due to its advantages in the production of syngas and hydrogen, especially with respect to the design and selection of oxygen carriers, which directly affect the efficiency of the production of syngas and hydrogen. In particular, the conversion of methane can reach 95% in the chemical looping partial oxidation of methane, and the selectivity of syngas, in the range of 700 °C to 900 °C at atmospheric pressure, can reach 99% for twenty or more cycles. In this review, from the perspective of metal oxide selection and structure regarding the chemical looping partial oxidation process, we discuss the role of oxygen carriers in the chemical looping partial oxidation cycle, in which the specific surface area, the lattice oxygen mobility, and the thermal stability are understood as the important factors affecting reactivity. We hope to summarize the design and development of efficient oxygen carriers with high oxygen-carrying capacity and syngas selectivity, as well as contribute to the selection, design, optimization, and redox reaction mechanism of redox catalysts.

The fabrication of Mn single atoms/clusters on Al2O3 for enhanced catalytic NO oxidation

The exploitation of transitional metal catalysts for high-efficient conversion of NO to NO2 still persists as an imperative issue due to the high cost of currently used Pt–based catalysts. Herein, we report a TEA-modification strategy to anchor Mn single atoms/clusters on Al2O3 (Mn/Al2O3-T) for NO oxidation. Activity tests show that Mn/Al2O3-T (T83 = 275 °C) displays a superior NO-to-NO2 capacity compared with the unmodified Mn nanoparticle on Al2O3 (Mn/Al2O3-B, T66 = 300 °C) and Pt/Al2O3 (T43 = 350 °C) counterparts. Comprehensive characterization and DFT calculations discover that the effective adjustment of TEA can promote the generation of coordination unsaturated Mn sites with elongated Mn-O bonds, which can improve the mobility of surface lattice oxygen and facilitate the activation of molecular oxygen. Additionally, reducing Mn size from nanoparticles to single atoms/clusters favors the formation of labile nitrate species and facile desorption of NO2, thereby regenerating active sites and accelerating overall NO oxidation reaction.

Modulating Lattice Oxygen Activity of Iron-Based Triple-Conducting Nanoheterostructure Air Electrode via Sc-Substitution Strategy for Protonic Ceramic Cells.

Iron-based perovskite air electrodes for protonic ceramic cells (PCCs) offer broad application prospects owing to their reasonable thermomechanical compatibility and steam tolerance. However, their insufficient electrocatalytic activity has considerably limited further development. Herein, oxygen-vacancy-rich BaFe0.6Ce0.2Sc0.2O3-δ (BFCS) perovskite is rationally designed by a facile Sc-substitution strategy for BaFe0.6Ce0.4O3-δ (BFC) as efficient and stable air electrode for PCCs. The BFCS electrode with an optimized Fe 3d-eg orbital occupancy and more oxygen vacancies exhibits a polarization resistance of ≈ 0.175Ωcm2 at 600°C, ≈ 1/3 of the BFC electrode (≈0.64Ωcm2). Simultaneously, BFCS shows favorable proton uptake with a low proton defect formation enthalpy (- 81kJmol-1). By combining soft X-ray absorption spectroscopy and electrical conductivity relaxation studies, it is revealed that the enhancement of Fe4+-O2- interactions in BFCS promotes the activation and mobility of lattice oxygen, triggering the activity of BFCS in both oxygen reduction and evolution reactions (ORR/OER). The single cell achieves encouraging output performance in both fuel cell (1.55 Wcm-2) and electrolysis cell (-2.96Acm-2 at 1.3V) modes at 700°C. These results highlight the importance of activating lattice oxygen in air electrodes of PCCs.

Mn-MIL-100 non-thermally derived MnOx catalysts for toluene oxidation

Herein, a novel preparation method via non-thermal derivation by using Mn-MIL-100 as the precursor to synthesize MnOx catalysts was proposed. The synthesized catalysts were applied to toluene oxidation. Characterizations and experiments results showed that the more surface Mn3+, Oads species, large surface area, better low-temperature reducibility and higher lattice oxygen mobility of Mn-Na2CO3 prepared via Na2CO3 treatment induced its great catalytic activity for toluene oxidation.

Biomass based oxygenates modified Fe-Mn oxide with improved surface lattice oxygen mobility for the chemical looping-oxidative dehydrogenation of ethane to ethylene

Chemical looping-oxidative dehydrogenation (CL-ODH) is a promising technology for ethylene production from ethane. Exploring low cost and high activity redox catalysts to improve ethylene yield in the field of CL-ODH of ethane is necessary. In this study, a mesoporous Fe0.4Mn0.6Ox redox catalyst with tunable lattice oxygen mobility was synthesized by a green solid-state grinding method, which used biomass based oxygenates as pore-forming and carbothermal reducing agent. The Fe0.4Mn0.6Ox-0.3 xylitol redox catalyst prepared by this method possessed excellent catalytic performance, the ethane conversion rate and the ethylene selectivity reached 54.23% and 92.42%, respectively. It has been demonstrated that the highly active lattice oxygen in Fe0.4Mn0.6Ox catalyst plays a key role in the ethane catalytic conversion. The high concentration of oxygen vacancies weakens metal–oxygen bonds, thereby promoting the migration of bulk-phase lattice oxygen to the redox catalyst surface to replenish the surface lattice oxygen. This work provides insights into the effects of biomass-based oxygenate species and doping levels on the lattice oxygen mobility of Fe0.4Mn0.6Ox redox catalysts during the CL-ODH of ethane.

Influence of organic sulfur gas-phase sulfation on the NH3-SCR activity of CeO2 catalyst: The competitive adsorption and conversion of CS2 and COS at a low hydrolysis temperature

In this study, a simplified approach is proposed to realize the gas-phase sulfation of CS2 or/and COS at the hydrolysis temperature for further facilitating the NH3-SCR activity of CeO2 in diverse conditions. A low-temperature oxidation conversion process for the adsorbed CS2 or COS on cubic fluorite CeO2 surface is developed. It is found that the gas-phase sulfation of organic CS2 or/and COS at 50 °C enhances the mobility of lattice oxygen of cubic fluorite CeO2 and the concentration of oxygen defects for the sulfated CeO2 catalyst, but the kinds of organic COS/CS2 can regulate the formed types and quality of sulfur-containing species on the catalyst surfaces during the gas-phase sulfation. and the formed sulfates under the gas-phase sulfation of CS2 are more active than those of COS, and CeO2-CS2-50 °C-3 h presents the best mobility of lattice oxygen, the largest concentration of adsorbed oxygen and the best NH3-SCR activity. Furthermore, the competitive adsorption and conversion of CS2 and COS is disadvantageous for the formation of oxygen vacancies on the catalyst surfaces compared to single CS2 or COS. However, the long-time durability testing coupling re-cycle experiments can optimize the oxygen vacancy defects and increase the concentration of chemisorbed oxygen of the sulfated CeO2-CS2 + COS-50 °C-24 h catalyst via optimizing the oxidization of sulfur element to sulfur oxides or/and sulfates, thereby improves its NH3-SCR activity. And the sulfated CeO2 catalyst by the gas-phase sulfation of organic COS + CS2 presents a good stability for NH3-SCR reaction. This study specifies a novel approach to simplify the gas-phase sulfation process of CeO2 catalyst, which is valuable in promotion of the NH3-SCR activity of CeO2 and reduction of cost in experimental procedures.

Engineering lattice oxygen mobility and optimizing reaction pathway via tuning Cu-Co interactions for efficient elimination of volatile organic compounds: A metal–organic framework template approach

Incorporating a secondary metal into individual cobalt oxides has been viewed as an efficacious approach in creating intermetallic interactions. Nonetheless, the processes involved in the construction of intermetallic interactions, as well as the underlying mechanisms that contribute to catalytic activity, remain largely elusive in current scientific understanding. In this work, a range of Cu-Co bimetallic oxides were synthesized through various preparation methods, employing MOFs as templates. Notably, the hydrothermally-synthesized Cu/Co-HT catalyst exhibited impressive catalytic qualities for toluene combustion, with T50 = 229 °C and T90 = 239 °C, alongside exceptional stability and moisture resistance (under 10 vol. % of water) for at least 100 h. The optimal catalyst Cu/Co-HT is attributed to the stronger Cu-Co interaction, which leading to larger specific surface area and weaker Co-O bond strength. And it also affects the chemical properties, such as get more Co3+ and lattice oxygen species by a redox (Co2++Cu2+→Co3++Cu+), better electron transfer performance and low-temperature reducibility. In addition, the reaction mechanism of toluene over the surface of Cu/Co-HT was also revealed by in-situ DRIFTS. It was observed that the bimetallic catalyst, characterized by robust Cu-Co interactions, optimized the reaction pathway for toluene oxidation compared to pure Co3O4. This facilitation led to the direct conversion of benzyl alcohol into benzoate and carboxylate, thereby bypassing the intermediate step involving benzaldehyde, which enhancing the reaction speed, yielding a long-term stable and efficient operational performance. This study reveals that optimize the physicochemical properties of catalytic by enhancing bimetallic interactions is an effective strategy for improving catalytic behavior.

Oxygen carrier prepared by solvent-free grinding and biomass based oxygenates for chemical looping oxidative dehydrogenation of isobutane

The chemical looping oxidative dehydrogenation of isobutane is an effective and novel strategy for producing isobutene. It is extremely necessary but challenging to design excellent oxygen carriers for this strategy. Here, a solvent-free grinding approach is presented to prepare ZnMo0.45V0.55Ox oxygen carrier with tailorable oxygen vacancy content via biomass based oxygenate as carbothermal reductive agent. As a result, ZnMo0.45V0.55Ox-0.3 vitamin C oxygen carrier demonstrates a much higher isobutane conversion of 17.61 % and isobutene selectivity of 82.55 %, whereas it is 7.99 % of isobutane conversion and 22.66 % of isobutene selectivity for ZnMo0.45V0.55Ox without vitamin C addition. The performance for the ZnMo0.45V0.55Ox-0.3 vitamin C is closely related to the surface area and the metal-oxygen bond strength. Large surface area can provide more accessible active sites, which can facilitate the isobutane's diffusion, adsorption and activation. High oxygen vacancy content results in weak metal-oxygen bond strength, which leads to high mobility of lattice oxygen.

Formaldehyde Ambient-Temperature Decomposition over Pd/Mn3O4-MnO Driven by Active Sites' Self-Tandem Catalysis.

The widespread presence of formaldehyde (HCHO) pollutant has aroused significant environmental and health concerns. The catalytic oxidation of HCHO into CO2 and H2O at ambient temperature is regarded as one of the most efficacious and environmentally friendly approaches; to achieve this, however, accelerating the intermediate formate species formation and decomposition remains an ongoing obstacle. Herein, a unique tandem catalytic system with outstanding performance in low-temperature HCHO oxidation is proposed on well-structured Pd/Mn3O4-MnO catalysts possessing bifunctional catalytic centers. Notably, the optimized tandem catalyst achieves complete oxidation of 100 ppm of HCHO at just 18 °C, much better than the Pd/Mn3O4 (30%) and Pd/MnO (27%) counterparts as well as other physical tandem catalysts. The operando analyses and physical tandem investigations reveal that HCHO is primarily activated to gaseous HCOOH on the surface of Pd/Mn3O4 and subsequently converted to H2CO3 on the Pd/MnO component for deep decomposition. Theoretical studies disclose that Pd/Mn3O4 exhibits a favorable reaction energy barrier for the HCHO → HCOOH step compared to Pd/MnO; while conversely, the HCOOH → H2CO3 step is more facilely accomplished over Pd/MnO. Furthermore, the nanoscale intimacy between two components enhances the mobility of lattice oxygen, thereby facilitating interfacial reconstruction and promoting interaction between active sites of Pd/Mn3O4 and Pd/MnO in local vicinity, which further benefits sustained HCHO tandem catalytic oxidation. The tandem catalysis demonstrated in this work provides a generalizable platform for the future design of well-defined functional catalysts for oxidation reactions.

Determination of characteristic properties of Co3O4 loaded LaFe x Al12−x O19 hexaaluminates

Abstract Hexaaluminates are drawing attention due to their exceptional mechanical and thermal stability. They can be proposed for applications as catalysts or catalyst support materials in high-temperature reactions. In this study, various LaFe x Al12−x O19 samples (x = 0.25, 0.5, 1, and 2) have been synthesized using the sol–gel method. Subsequently, these hexaaluminate samples were impregnated with cobalt oxide to form more active centers on the hexaaluminate support. The influence of the iron (Fe) content on the crystal structure, redox properties, and oxygen immobility has been investigated through X-ray diffraction, hydrogen temperature-programmed reduction, and oxygen temperature-programmed desorption techniques. Among the Co3O4@LaFe x Al12−x O19 samples, those with x ≥ 1 exhibited a hexaaluminate crystalline structure, demonstrating a higher lattice oxygen mobility.

Engineering multi-component 3DOM FeVCrOx catalysts with high oxygen mobility for the oxidative dehydrogenation of 1-butene with CO2.

Oxidative dehydrogenation (ODH) of 1-butene with CO2 to 1,3-butadiene (BD) via Fe-based catalysts is a promising strategy, and the mobility of lattice oxygen plays a key role in the catalytic reaction. However, the catalytic activity of Fe-based catalysts is limited by the poor lattice oxygen mobility. To improve the mobility of lattice oxygen and optimize the ODH reaction, a series of 3DOM Fe-based catalysts (FeVAlOx, FeCrAlOx, and FeVCrAlOx) were prepared by PMMA template method. Among these samples, the multi-component FeVCrAlOx samples showed the best catalytic activity, and the 1-butene conversion of the multi-component catalyst could reach 88.3%, the BD yield could reach 27.5%. Further study found that the introduction of multi-component elements (V and Cr) not only promoted the formation of the γ-Fe2O3 phase but also formed more active components (V5+ and Cr6+). More importantly, the lattice oxygen mobility was also significantly improved. In addition, the reaction in the presence of water conditions was studied by activity tests and in situ DRIFTS tests. The results show that CO2 was present in the form of HCO3-. The utilization of CO2 was improved and the reaction path was changed.

Effect of acid sites modification on the catalytic combustion of 1,2-dichloroethane: Revealing the synergy between NbOx and CeO2

1,2-Dichloroethane are primarily sourced from the emissions of the chlor-alkali industry, resulting in severe pollution of soil, air, and water. In this work, Nb/CeO2 catalysts were prepared by impregnation method, and their performance for EDC oxidation was evaluated. The addition of Nb improved the activity, selectivity, and stability of CeO2. Nb was highly dispersed on CeO2 surface in the form of NbOx, and partially entered the lattice of CeO2. This caused lattice distortion and more surface defects, thereby increasing the number of oxygen vacancies. NbOCe bonds formed in between Nb and CeO2 weakened the CeO bonds and enhanced lattice oxygen mobility. The presence of NbOx increased the number of Lewis acid (NbO) and Brønsted acid (Nb-OH) sites, which facilitated the cleavage of CCl and CC bonds. Increased acidity promoted the removal of Cl species in the form of HCl and effectively mitigated the chlorine poisoning of CeO2. In-situ DRIFTS results indicated that EDC oxidation on Nb/CeO2 catalysts followed a Mars-van Krevelen mechanism and progressed via the pathway of alcoholate → formate/methoxy → COx.

Regulating asymmetric oxygen vacancies in copper-ceria catalysts for achievement of excellent toluene catalytic oxidation

Regulation of oxygen vacancy upon metal oxide catalysts is an effective strategy for improving the catalytic activity in the oxidation of volatile organic compounds. Herein, copper (Cu) ions were introduced into ceria (CeO2) catalysts via the modulation of preparation methods (ball-milling, co-precipitation and sol-gel method) to generate asymmetric oxygen vacancies (AOVs) with varying concentrations at the Cu-CeO2 interface, thereby enhancing the catalytic performance towards toluene. The presence of abundant AOVs promotes the rapid conversion of the redox couples of Ce4+/Ce3+ and Cu+/Cu2+ according to Cu+-OV-Ce3+ ↔ Cu2+-O(ad)2--Ce4+, enhancing the redox property and lattice oxygen mobility of the catalyst synthesized by ball-milling strategy (BM-CuCe). Moreover, the AOVs expedite the backfilling and activation of gaseous oxygen, leading to a transformation of rate-determining steps into the cracking of aromatic rings, significantly improving the catalytic activity towards toluene. The BM-CuCe catalyst, with the highest AOVs concentration, exhibits the excellent catalytic activity, water-resistance capability as well as stability. This work sheds light on the promoting effect of AOVs in the catalytic oxidation of toluene and contributes an attractive strategy for designing highly efficient metal oxide catalysts.

Exploring the influence of chemical state of Cu species on CO-SCR performance in spinel-type CuM2O4 (M = Co, Mn, Fe, Ni, and Cr): The synergy between Cu2+ and surface oxygen vacancy

The influence of the chemical state of Cu species in spinel-type catalysts on the selective catalytic reduction (SCR) of NO with CO has not been well understood. A series of CuM2O4 (M = Co, Mn, Fe, Ni, and Cr) were synthesized and studied in this work. Notably, CuCo2O4 demonstrated the best CO-SCR performance, exhibiting the de-NOx activity exceeding 90 % in a broad temperature window of 143–381 °C. Furthermore, CO conversion surpassed 90 % above 225 °C. Characterizations revealed that the synergy between Cu2+ and surface oxygen vacancy in the Cu2+–Ov–Mδ+ sites (δ represents the M cations in the lower valence states) played a vital role in enhancing the CO-SCR performance of the CuM2O4 catalysts. The superior CO-SCR performance of CuCo2O4 was also attributed to the optimal interplay between Cu and Co cations, resulting in superior Cu2+/Cu+ redox cycle and improved lattice oxygen mobility. In situ DRIFTS verified that Cu2+ was the primary site during the CO-SCR reaction, and two possible mechanisms (oxygen vacancy-assisted and lattice oxygen-assisted routes) over CuM2O4 were carefully proposed. This study unravels the nature of the CO-SCR activity of the CuM2O4 catalysts and provides novel perspectives on the development of Cu-based catalysts for CO-SCR applications.

Promotional effect of stannum on Pd/CeO2 catalysts for CO and C3H6 co-oxidation

The successful control of hydrocarbon and CO emissions from low-temperature diesel exhausts requires the use of highly active co-oxidation catalysts. In this study, Sn was used to enhance the catalytic performance of Pd/CeO2 in CO and C3H6 co-oxidation conditions. CeO2 with added stannum (Sn) was prepared as a support using the co-precipitation method, and Pd was loaded onto the support using the impregnation method. After Sn addition (the optimal Ce/Sn ratio is 0.75:0.25), the T50 values of CO and C3H6 are reduced by 20 and 32 °C, respectively. A series of characterization methods indicates that the addition of Sn to the support greatly enhances its lattice oxygen mobility and increases the proportion of PdO. During the co-oxidation process, stronger lattice oxygen mobility allows CO to react faster through the Mars–van Krevelen mechanism, weakening the competition with C3H6 for O2. A higher PdO content enhances the C3H6 oxidation capability. Moreover, CO can more readily reduce PdO than Pd2+ in solid solution with the support, which consequently further enhances co-oxidation activity. Therefore, the addition of Sn is a simple and effective strategy for enhancing the performance of Pd/CeO2 catalysts in CO and C3H6 co-oxidation reactions. Furthermore, the promotional effect of CO achieved in this study contributes to a deeper understanding of the interactions that occur during the co-oxidation of C3H6 and CO.

New Insights into the Effect of Ce Doping on the Catalytic Performance and Hydrothermal Stability of Cu-USY Zeolite Catalysts for the Selective Catalytic Reduction of NO with NH3

5Cu-USY and Ce-doped 5Cu8Ce-USY zeolite catalysts were prepared by the conventional impregnation method. The obtained catalysts were subjected to the hydrothermal ageing process. The catalytic performance of the selective catalytic reduction of NOx with NH3 (NH3-SCR) was evaluated on both fresh and aged catalysts. Physical/chemical characterizations such as X-ray diffraction (XRD), H2 temperature-programmed reduction (H2-TPR), and X-ray photoelectron spectroscopy (XPS) were performed, along with detailed in situ diffuse reflectance infrared Fourier-transform spectroscopy (DRIFTS) experiments including CO adsorption, NH3 adsorption, and NO + O2 reactions. Results showed that, for the 5Cu-USY catalyst, hydrothermal ageing treatment could somehow improve the low-temperature SCR activity, but it also led to significant formation of unfavorable byproducts NO2 and N2O. Such an activity change can be attributed to hydrothermal ageing inducing the migration of isolated Cu+ species in the sodalite cavities towards the super cages of the USY zeolites. The increased content of Cu+ species in the super cages was beneficial for the low-temperature activity improvement, but, at the same time, it also facilitated ammonia oxidation at high temperatures. Ce doping after hydrothermal ageing has a “double-edged sword” effect on the catalytic performance. First of all, Ce doping can inhibit Cu species migration by self-occupying the internal cage sites; thus, the catalytic performance of 5Cu8Ce-USY-700H remains stable after ageing. Secondly, Ce doping introduces a CuOx–CeO2 strong interaction, which facilitates lattice oxygen mobility by forming more oxygen vacancies so as to increase the concentration of surface active oxygen. These changes, on the one hand, could help to promote further oxidative decomposition of nitrate/nitrite intermediates and improve the catalytic performance. But, on the other hand, it also causes the byproduct generation to become more severe.

Exploring the effects of potassium-doping on the reactive oxygen species of CeO2 (110) for formaldehyde catalytic oxidation: A DFT study

The influence of K-doping on the reactive oxygen species and elementary reactions of HCHO catalytic oxidation has not been well understood. Herein, a density functional theory (DFT) study was conducted and found that the introduction of K-doping advantageously changed the electronic structures of both Ce and O atoms on the (110) crystal plane of CeO2. This change, in turn, facilitated the adsorption and activation of HCHO and O2 molecules, enhanced the mobility of lattice oxygen, and reduced the energy barrier associated with HCHO oxidation. The adsorbed oxygen species were generated through the direct dissociation of O2 on the CeO2 (110) surface. However, in the case of K-CeO2 (110), it was more probable for the adsorbed oxygen species to be produced by gaseous O2 filling the oxygen vacancy, followed by dissociation. Additionally, the incorporation of K-doping proved to be advantageous in facilitating the formation of hydroxyl groups by promoting the dissociation of water molecules. The inclusion of hydroxyl groups facilitated the HCHO adsorption and reduced the energy barrier for its subsequent oxidation. The findings provide new insights into the development of novel catalysts for HCHO removal with high performance through alkali metal modification.