Enhanced Oxygen Mobility Research Articles

Revealing the promotional effect of Zr and phosphate Co-decorated on δ-MnO2 catalysts for highly efficient catalytic elimination of chlorinated VOCs: An experimental and theoretical study

The development of advanced catalysts for catalytic oxidation of CVOCs still presents challenges in terms of low activity, chlorination poisoning and the formation of toxic byproducts. In this study, a series of nP-MnxZry catalysts with exceptional catalytic oxidation activity were developed for the removal of CVOCs in industry. Among them, 15P‐MZ exhibited the optimal catalytic activity and stability for CB degradation, achieving a T90 of 180 ℃. Notably, the CB oxidation rate of 15P‐MZ was found to be 5.76 times higher than that of MnO2 at 155 °C. Structure and properties analysis combining with DFT calculations revealed that the dual modification strategy involved Zr doping and phosphate loading induced the formation of high concentration of oxygen vacancy over 15P‐MZ, which enhanced oxygen mobility, facilitating the breakage of the aromatic ring. Meanwhile, this strategy introduced more Brønsted acid sites, promoting the dissociation of Cl in the form of HCl, thereby inhibiting the formation of polychlorinated byproducts. Moreover, the activation effect of phosphate on the dissociation of H2O further promoted the Cl dissociation, thereby regenerating more active sites and improving catalytic activity and stability in humid environment, making it more promising for industrial applications.

Modulate synthesis of CeMn solid solution using various alcohols for toluene catalytic oxidation: synergistic effect of Ce-Mn and reaction mechanism

A redox co-precipitation method was employed to synthesize CeMn homogeneous solid solutions, utilizing various alcohols as activating agents. Ethanol effectively orchestrated the precipitation of CeO2 and MnOx, promoting their co-growth. As a result, the CeMn-EA achieved 90 % toluene conversion at 218 ℃ (T90 =218 ℃) with a weight hourly space velocity (WHSV) of 48000 ml/(g·h). It also demonstrated high adaptability to increased WHSV, suggesting its potential for industrial-scale applications. The uniform dispersion of Ce and Mn accelerated the coupling between Ce3+/Ce4+ and Mn4+/Mn3+, engineering numerous oxygen vacancies, which enhanced the activation of gas-phase oxygen and the mobility of lattice oxygen. In situ DRIFTS confirmed that toluene oxidation accommodated both Langmuir-Hinshelwood (L-H) and Mars-van Krevelen (MvK) mechanisms, with benzoate identified as a pivotal intermediate. Enhanced oxygen mobility facilitated the cleavage of the benzene ring, which was the rate-determining step. Additionally, the introduction of H2O significantly enhanced the dissociation and adsorption of toluene and facilitated the activation of gas-phase oxygen. At higher temperatures, H2O could further activate lattice oxygen engaging in toluene oxidation. Environmental ImplicationVolatile organic compounds (VOCs) have emerged as major air pollutants due to the changes in air pollution patterns. They can act as precursors to near-surface ozone and haze. Toluene, a typical VOC, is primarily released from anthropogenic sources and poses significant risks to human health and the environment. Ce-based catalysts have been demonstrated efficiency in toluene oxidation due to their excellent oxygen storage and release properties. This study synthesized CeMn homogeneous solid solutions utilizing various alcohols as activating agents, which possessed abundant oxygen vacancies and optimum oxygen activation capacity to oxidize toluene in time.

In-situ reconstruction of LaCoO3-Co3O4 hetero-interface over lanthanum modified Co3O4 nanocatalyst for improved catalytic activity and sintering resistance in methane combustion

Nanoparticles-based catalysts still suffer from deactivation due to sintering and structural collapse through long-time running at high reaction temperature. Developing simple strategy for improving the sintering resistance of nanoparticles is of great importance for fabrication of durable heterogeneous catalysts. In this work, lanthanum was used to prevent Co3O4 nanoparticles from sintering with restricting growth of nanocrystals by in-situ generation of LaCoO3 perovskite phase during thermal ageing process, further building LaCoO3-Co3O4 hetero-interface with strong interfacial effect. Specifically, the Co3O4 nanocatalyst was loaded with different amount of La by traditional impregnation method and a series of characterizations were carried out to explore the physical and chemical properties of the as-prepared catalysts, including XRD, Raman, BET, SEM, HRTEM, XPS, H2-TPR and O2-TPD. It was found that 5 wt% La-Co3O4 has the highest catalytic activity in CH4 combustion and the value of T90 (temperature of 90% methane conversion) between fresh and aged was only 9 ºC, while this value was 108 ºC over pure Co3O4 sample. The Raman, XPS, H2-TPR and O2-TPD results exhibited that the synergistic effect between Co3O4 and LaCoO3 could not only induce lattice distortion in Co3O4 with more defects and adsorbed oxygen species, enhanced oxygen mobility and reducibility, but also significantly suppress the growth of Co3O4 nanocrystals during thermal ageing treatment.

Enhanced oxygen mobility of Mn-Ce solid solution catalysts for polysaccharide-assisted catalytic oxidation of toluene

This paper discusses the modification of (MnCe)Ox by incorporating various metallic and non-metallic auxiliaries. The findings reveal that the introduction of dextran as a modifier has a positive impact on the catalyst's performance for oxidation of toluene. Complexation reactions between dextran molecules and metal ions lead to a weakening of the M(Mn/Ce)-O bond energy, resulting in increased lattice distortions and oxygen vacancies. Moreover, the mobility of lattice oxygen species was enhanced. The hydroxyl species within the dextran molecule not only promoted the generation of reactive oxygen species but also created acidic sites that reduced the accumulation of intermediates and enhanced selectivity. Optimization of the dextran ratio was conducted, and the results indicated that the MC-2 %-D catalyst exhibited T50 and T90 values of 190 °C and 219 °C. Dextran demonstrated valence regulation function as it contributes to constructing a porous structure and enriching active substances such as Mn3+/Ce3+. The excellent redox properties were maintained based on the formation of some lattice defects. O2-TPD and O 1 s spectroscopic analyses demonstrated that highly migratory and reproducible reactive oxygen species on the catalyst's surface synergistically interact with lattice oxygen, ensuring a continuous and efficient toluene-catalysed oxidation reaction.

Engineering Ag-O-Mn bridges with enhanced oxygen mobility over Ag substituted LaMnO3 perovskite catalyst for robustly boosting toluene combustion

Perovskite oxide, as a promising candidate for volatile organic compounds combustion, is incapable in practical application at present due to its low intrinsic activity resulting from inadequate active oxygen species. However, balancing the concentration of active oxygen species and robust structure for perovskite oxide is still challenging. Herein, an efficient perovskite-based catalyst (denoted as TA-La0.9Ag0.1MnO3) was constructed through Ag substitution and subsequently tartaric acid etching of LaMnO3, which exhibits robustly boosted catalytic performance for toluene combustion compared with pristine LaMnO3, causing a ∼100 °C lower T90. In this study, Ag substitution could weaken the La-O hybridization, which effectively facilitates La cations removal by subsequent acid etching, thus sufficiently exposing active Ag and Mn species and generating more surface lattice oxygen, but also constructs Ag-Mn-O bridges within the matrix of Ag substituted LaMnO3. Acid etching enables the activation of Ag-O-Mn bridges with strong electron transfer ability from O to Ag atom, promoting the mobility of lattice oxygen, and consequently the low-temperature oxidation ability. Additionally, the exposed Ag and Mn as Lewis acid sites can effectively improve the adsorption capacity toward toluene molecules, which synergistically facilitates the toluene abatement. Notably, TA-La0.9Ag0.1MnO3 also exhibits superb long-term stability, water-resistance, and high thermal stability up to 650 °C.

Efficient Oxidative Dehydrogenation of Ethylbenzene over K/CeO2 with Exceptional Styrene Yield

Oxidative dehydrogenation (ODH) is an alternative for styrene (ST) production compared to the direct dehydrogenation process. However, ODH with O2 or CO2 suffers from either over-oxidation or endothermic property/low ethylbenzene conversion. Herein, we proposed an ODH process with a CO2-O2 mixture atmosphere for the efficient conversion of ethylbenzene (EB) into styrene. A thermoneutral ODH is possible by the rationalizing of CO2/O2 molar ratios from 0.65 to 0.66 in the temperature range of 300 to 650 °C. K modification is favorable for ethylbenzene dehydrogenation, and 10%K/CeO2 achieved the highest ethylbenzene dehydrogenation activity due to the enhanced oxygen mobility and CO2 adsorbability. The catalyst achieved 90.8% ethylbenzene conversion and 97.5% styrene selectivity under optimized conditions of CO2-4O2 oxidation atmosphere, a temperature of 500 °C, and a space velocity of 5.0 h−1. It exhibited excellent catalytic and structural stability during a 50 h long-term test. CO2 induces oxygen vacancies in ceria and promotes oxygen exchange between gaseous oxygen and ceria. The ethylbenzene dehydrogenation in CO2-O2 follows a Mars-van Krevelen (MvK) reaction mechanism via Ce3+/Ce4+ redox pairs. The proposed ODH strategy by using oxygen vacancies enriched catalysts offers an important insight into the efficient dehydrogenation of ethylbenzene at mild conditions.

Perovskite modified catalysts with improved coke resistance for steam reforming of glycerol to renewable hydrogen fuel

AbstractCatalytic steam reforming of renewable feedstock to renewable energy or chemicals always goes with intense coking activities that produce carbonaceous products leading to low performance and eventual catalyst deactivation. Supported metal catalyst such as Ni/Al2O3 is known to catalysed gasification and decomposition of biomass feedstock largely for renewable fuel production with promising results. Catalyst deactivation from high carbon deposition, agglomeration and phase transformations resulting to rapid deactivation are some of the issues identified with the use of the catalyst. In this work, improvement on the coke resistance and catalytic properties of Ni/Al2O3 catalyst is sought via the use of a thermally stable and coke‐resistant perovskite La0.75Sr0.25Cr0.5Mn0.5O3‐δ (LSCM) as catalyst promoter/modifier and involving Zirconia‐doped Ceria (Ce‐Zr) as alternative support in steam reforming of pure and by‐product glycerol. The stabilizing influence of the LSCM on the Ni catalyst has improved stability against agents of deactivation with a consequent significant improvement of catalytic activity of Ni/Al2O3 in H2 production and robust suppression of carbon deposition. Particularly, the synergy between the LSCM promoter and alternative Ce0.75Zr0.25O2 support enhanced the basic and redox properties known for Ce0.75Zr0.25O2 support in contrast to the week acid centres in γ‐Al2O3 support which further improved nickel stability, catalyst–support interaction with a resultant high catalytic activity and robust coke suppression as a result of enhanced oxygen mobility. There is correlation between the product distribution, nature of coke deposited and reforming temperature as well as type of support and structural modification. Hence, integration of a robust perovskite material as a catalyst promoter and choice of support could be tailored in design and development of robust catalyst systems to improve the performance of supported metal catalysts, particularly the suppression of carbon deposition for hydrocarbon and biomass conversion to renewable fuel or chemicals.

Engineering of oxygen vacancy defect in CeO2 through Mn doping for toluene catalytic oxidation at low temperature

Catalytic oxidation is considered a highly effective method for the elimination of volatile organic compounds. Oxygen vacancy defect engineering in a catalyst is considered an effective approach for high-performance catalysts. Herein, a series of doped MnxCe1-xO2 catalysts (x = 0.05–0.2) with oxygen vacancy defects were synthesized by doping low-valent Mn in a CeO2 lattice. Different characterization techniques were utilized to inspect the effect of doping on oxygen vacancy defect generation. The characterization results revealed that the Mn0.15Ce0.85O2 catalyst has the maximum oxygen vacancy concentration, leading to increased active oxygen species and enhanced oxygen mobility. Thus, Mn0.15Ce0.85O2 catalyst showed an excellent toluene oxidation activity with 90% toluene conversion temperature (T90) of 197 °C at a weight hourly space velocity of 40,000 mL g−1 h−1 as compared to undoped CeO2 (T90 = 225 °C) and Ce based oxides in previous reports. In addition, the Mn0.15Ce0.85O2 catalyst displayed strong recyclability, water resistant ability and long-time stability. The in situ DRIFT results showed that the Mn0.15Ce0.85O2 catalyst has a robust oxidation capability as toluene is quickly adsorbed and actuated as compared to CeO2. Thus, the present work lays the foundation for designing a highly active catalyst for toluene elimination from the environment.

Microalgae gasification over Ni loaded perovskites for enhanced biohydrogen generation

Steam gasification of microalgae upon perovskite oxide-supported nickel (Ni) catalysts was carried out for H2-rich gas production. Ni-perovskite oxide catalysts with partial substitution of B in perovskite structures (Ni/CaZrO3, Ni/Ca(Zr0.8Ti0.2)O3, and Ni/Ca(Zr0.6Ti0.4)O3) were synthesized and compared with those of the Ni/Al2O3 catalyst. The perovskite oxide supports improved Ni dispersion by reducing the particle size and strengthening the Ni-support interaction. Higher gas yields and H2 selectivity were obtained using Ni-perovskite oxide catalysts rather than Ni/Al2O3. In particular, Ni/Ca(Zr0.8Ti0.2)O3 showed the highest activity and selectivity for H2 production because of the synergetic effect of metallic Ni and elements present in the perovskite structures caused by high catalytic activity coupled with enhanced oxygen mobility. Moreover, increasing the temperature promoted the yield of gas and H2 content. Overall, considering the outstanding advantages of perovskite oxides as supports for Ni catalysts is a promising prospect for H2 production via gasification technology.

Promotional mechanism of activity of CeEuMnOx ternary oxide for low temperature SCR of NOx

Due to strong synergistic effect of the elements, a series of XEuMnOx ternary oxides (X = Ce, Ni, Co, Sb, Sn, Mo) were synthesized by one-pot co-precipitation method, and composite components were identified and optimized to maintain high activity and superior SO2 and H2O endurance in selective catalytic reduction of NOx with NH3 (NH3-SCR). NOx conversion of CeEuMnOx ternary oxide catalysts attains more than 90% at 100–250 °C, and finally achieves 74% under existence of 50 × 10−6 SO2 and 10 vol% H2O at 230 °C. The facile electron transfer through redox cycle of Mn3+ + Ce4+ ↔ Mn4+ + Ce3+ and enhanced oxygen mobility can promote formation of more Mn species in high oxidation state and chemisorbed oxygen, accelerating oxidation of NO and the adsorbed NO2 formed can facilitate “fast SCR” reaction to improve low-temperature activity. In situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) study reveals that addition of Ce to EuMnOx catalyst boosts adsorption of NH3 and NOx species. NH3 species are activated as crucial intermediate (NH2) to promote NH3-SCR reaction. This research provides a novel material for practical deNOx application of stationary source combustion flue gas in the future.

The remarkable oxidation of trichloroethylene in a post-plasma-catalytic system over Ag-Mn-Ce/HZSM-5 catalysts

The degradation of trichloroethylene (TCE) is of paramount importance due to its harmful effect on human health and the environment. In this study, a remarkable oxidation of the toxic TCE was achieved by using a hybrid system integrating a corona discharge reactor and a series of Ag-Mn-Ce/HZSM-5 catalysts. The combination of plasma and catalysis significantly promoted TCE oxidation compared with the plasma alone system. A maximum TCE removal efficiency (100 %) and an energy yield of 204 g·kWh−1 were obtained in the plasma-catalytic system by using the Ag4MnCeOx/HZSM-5 (4 wt% Ag loading) catalyst in dry air with a weight hourly space velocity of 200000 mL·g−1·h−1. In contrast, the plasma alone system showed only a removal efficiency of 34.8 % and an energy yield of 83 g·kWh−1 under the same conditions. By adding Ag, the surface adsorbed oxygen was activated and the reducibility of catalyst was promoted, which enhanced oxygen mobility and improved the oxidation of TCE. Furthermore, relative humidity (RH) had an important effect on TCE oxidation. The highest CO2 selectivity (71.86 %) and CO selectivity (22.21 %) were obtained at an RH of 20 %. The decomposition pathway of TCE in the post-plasma-catalytic system was proposed. This study is expected to provide a feasible method for the control of chlorine-containing waste gas.

Boosting propane purification on Pt/ZrOSO4 nanoflowers: Insight into the roles of different sulfate species in synergy with Pt

Herein, ZrOSO4 nanoflowers with high sulfates content and the coexistence of (SO3)ad and SO42- species has been developed as the support of Pt-based catalysts for propane combustion. Compared with the Pt catalysts supported on conventional sulfated-ZrO2 and ZrO2, the Pt/ZrOSO4 gives the highest specific reaction rate of 355 μmol gPt−1 s−1 at 190 °C, the TOF value on Pt/ZrOSO4 is 2 times of that on Pt/sulfated-ZrO2 and 7 times of that on Pt/ZrO2. Differentfrom that only SO42- on the Pt/sulfated-ZrO2, there are two sulfate species on the Pt/ZrOSO4, conventional SO42- and (SO3)ad. The presence of sulfates not only leads to the formation of Brønsted acid sites and promotes the propane adsorption, but also significantly affects the chemical states of Pt species. The interaction between Pt and SO42- results in the formation of reactive Pt0 species, which facilitates the CC bond activation, and the Pt-(SO3)ad electronic interaction is beneficial for the generation of the metastable Pt+, which further promotes propanecombustion via heterolytic CH bond activation. Moreover, the Pt/ZrOSO4 also can provide active oxygen species with enhanced oxygen mobility and reactivity due to the presence of Pt-O-SO3 species, which can accelerate the oxidation of reaction intermediates. This workcontributes to in-depth insight into the role of different sulfate species for propane combustion over Pt-based catalysts.

Performance characteristics of novel magnetic-field applied polymer electrolyte membrane fuel cells under various operating conditions

In this study, the oxygen reduction reaction (ORR) performance improvement of polymer electrolyte membrane fuel cells (PEMFCs) is investigated using a low magnetic field density. The transient performance of a PEMFC using a magnetic field (MF-PEMFC) was measured and analyzed by varying the cell temperature, voltage, relative humidity, and pre-humidification time. Based on the results, the mechanism of the performance improvement of MF-PEMFC was revealed, and a strategy to maximize its performance was proposed. Enhanced oxygen mobility by a magnetic field led to a higher ORR performance and membrane humidification was accelerated by the vigorous ORR. The performance improvement of MF-PEMFC was more substantial under unfavorable membrane humidification conditions such as high temperature and low operating voltage. The maximum performance improvement of MF-PEMFC compared to that of normal PEMFC was 8.6% at 40% relative humidity, 0.30 V voltage, and 80 ℃ cell temperature due to an enhanced self-humidification effect. In addition, the maximum performance improvement and stability of MF-PEMFC were obtained with the proper pre-humidification time. In conclusion, using a magnetic field can improve the performance and stability of PEMFCs under unfavorable operating conditions.

Preparation of Co-Ce-O catalysts and its application in auto-thermal reforming of acetic acid

The well-dispersed Co species which partly incorporated into the lattice of CeO 2 (nanorod) was successfully synthesized, and a higher proportion of Ce 3+ /(Ce 3+ + Ce 4+ ) and enhanced oxygen mobility were thus obtained, which accounts for the high reactivity in auto-thermal reforming of acetic acid. • Well-dispersed Co species partly doped into the lattice of CeO 2 (nanorod). • Enhanced oxygen mobility and higher Ce 3+ was observed over Co-Ce-O (nanorod). • Co-Ce-O (nanorod) presents high hydrogen yield of 2.69 mol-H 2 /mol-HAc at 600 °C. As the preparation method was vital to modify the structure of catalysts, Co-Ce-O oxides were fabricated via different hydrothermal methods and evaluated in auto-thermal reforming (ATR) of acetic acid (HAc) for hydrogen production. Results of characterizations, including XRD, BET, H 2 -TPR, SEM and XPS, indicated the structure and electronic characteristics of each catalyst varied with different synthesis methods. In the case of CC-R with the morphology of nanorod, well-dispersed Co species were partly incorporated into the lattice of CeO 2 support, resulting in a higher proportion of Ce 3+ /(Ce 3+ + Ce 4+ ) and enhanced oxygen mobility. Consequently, it exhibited a promising catalytic performance in a 10-h testing in ATR of HAc: HAc conversion maintained at 96.8% with hydrogen yield recorded at 2.69 mol-H 2 /mol-HAc at 600 °C, while almost no by-product was detected, demonstrating its potential for hydrogen production.

Multi-defects engineering of NiCo2O4 for catalytic propane oxidation

High-performance non-noble metal catalyst development is always the pursuit for the VOCs oxidation. Herein, a multi-defective spinel catalyst was intelligently built with a mechano-chemical strategy by Na assisted milling of NiCo2O4, wherein, the incorporation of Ni into the spinel oxide could introduce cationic defects, the etching by Na brought anionic defects, while the milling process fractured the bulk and facilitated the exposure of surface defects. Thereout, the obtained D-NiCo2O4 was endowed with a significantly elevated oxygen vacancies, raised active oxygen species, enhanced oxygen mobility and an increased specific surface area. The beneficial features promise D-NiCo2O4 a superb activity for propane catalytic oxidation, exhibiting a T50 (temperature at 50% propane conversion) of 187 °C and T90 (temperature at 90% propane conversion) of 194 °C at propane space velocity of 60,000 mL·g−1·h−1, which outperformed that of pristine NiCo2O4 and Co3O4 catalyst, making itself one of the most outstanding non-noble metal catalysts for propane oxidation. This work set the paradigm to enhance the VOCs oxidation performance of metal oxide catalyst by multi-defects engineering.

O-vacancy-rich porous MnO2 nanosheets as highly efficient catalysts for propane catalytic oxidation

Constructing non-noble robust catalysts for deep catalytic oxidation of obstinate light alkanes at low temperature is of great value and significance. Herein, we designed a facile solvent-thermal-reduction strategy to fabricate an O-vacancy-rich porous MnO2 nanosheet (MnO2−PS) catalyst for propane catalytic oxidation. The abundant vacancies in MnO2−PS catalysts can significantly promote its redox ability and oxygen activation capacity, and then provide more active oxygen species with enhanced oxygen mobility and reactivity, thus accelerate the cleavage of C-H bond and the decomposition of intermediates. Meanwhile, benefiting from the porous nanosheet structure, MnO2−PS catalyst possesses highly accessible surface and high density of exposed active sites, thus facilitating the adsorption and the activation of reactant molecule. At the same time, the catalyst also exhibits good thermal stability and water resistant ability. This robust and efficient catalytic system may provide some enlightenments for designing feasible catalyst with high-performance for deep catalytic destruction of VOCs.

N-doped CoAl oxides from hydrotalcites with enhanced oxygen vacancies for excellent low-temperature propane oxidation

A series of nitrogen-doped CoAlO (N-CoAlO) were constructed by a hydrothermal route combined with a controllable NH3 treatment strategy. The effects of NH3 treatment on the physico-chemical properties and oxidation activities of N-CoAlO catalysts were investigated. In comparison to CoAlO, a smallest content decrease in surface Co3+ (serving as active sites) while a largest increased amount of surface Co2+ (contributing to oxygen species) are obtained over N-CoAlO/4h among the N-CoAlO catalysts. Meanwhile, a maximum N doping is found over N-CoAlO/4h. As a result, N-CoAlO/4h (under NH3 treatment at 400°C for 4 hr) with rich oxygen vacancies shows optimal catalytic activity, with a T90 (the temperature required to reach a 90% conversion of propane) at 266°C. The more oxygen vacancies are caused by the co-operative effects of N doping and suitable reduction of Co3+ for N-CoAlO/4h, leading to an enhanced oxygen mobility, which in turn promotes C3H8 total oxidation activity dominated by Langmuir-Hinshelwood mechanism. Moreover, in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTs) analysis shows that N doping facilities the decomposition of intermediate species (propylene and formate) into CO2 over the catalyst surface of N-CoAlO/4h more easily. Our reported design in this work will provide a promising way to develop abundant oxygen vacancies of Co-based catalysts derived from hydrotalcites by a simple NH3 treatment.

Anionic defects engineering of Co3O4 catalyst for toluene oxidation

Development of advanced metal oxide catalysts for volatile organic compounds (VOCs) abatement is of great environmental and economic importance. Herein, a defective Co3O4 catalyst is delineated via N doping. The anionic defects engineering significantly facilitated the oxygen vacancies formation, leading to a distorted lattice structure, increased active surface oxygen and enhanced oxygen mobility of Co3O4 catalyst. These features promise an excellent toluene oxidation performance with 50% toluene conversion temperature (T50) of 208 °C and 90 % toluene conversion temperature (T90) of 218 °C at a space velocity of 60,000 mL g−1h−1, about 33 °C and 53 °C lower than that of the pristine Co3O4, respectively. Meanwhile, the N doped Co3O4 catalyst maintains a high hydrothermal stability at 210 °C. This work exemplifies the significance of anionic defects for the intrinsic catalytic oxidation ability improvement, providing a guidance for the upgradation of the metal oxide for the application of VOCs catalytic degradation and beyond.

Enhancing the Catalytic Activity of Lanthanum-Ceria Fluorite for Methane Conversion in SOFC

A2B2O7 compounds have unique properties, such as good thermal stability, oxygen mobility, ionic conductivity, etc. Such compounds with tailored compositions exhibit good catalytic properties in a variety of high-temperature reactions, such as reform and oxidative coupling of methane (OCM). An effective catalyst for OCM must have electrophilic oxygen mobility and alkalinity on its surface. A typical A2B2O7 compound that contains a trivalent rare earth metal at site A, such as La, can provide the necessary surface alkalinity for a good OCM catalyst. Previous studies show that La2Ce2O7 (LCO) catalysts perform well in OCM due to the selective mobile oxygen sites, suitable alkaline sites, and high thermal stability. Doping LCO with Ca increases the alkalinity, which can considerably increase selectivity for ethylene in the OCM reaction. We have studied calcium-doped lanthanum ceria materials as a catalytic layer in solid oxide fuel cells reactors for methane conversion to ethylene. We have explored the combustion synthesis to obtain homogeneous La2-xCaxCe2O7 powders with x = 0, 0.25, and 0.50 (LCO, LCa25, and LCa50, respectively). X-ray diffraction (XRD) showed that the calcium addition in LCO formed a single-phase solid solution. The crystalline structure of the synthesized materials is the disordered fluorite-type, as indicated by both XRD and Raman analysis. Raman spectroscopy data evidenced the presence of surface oxygen vacancies on all materials, which may benefit the OCM reaction. SEM images of as-prepared powders obtained evidenced a similar microstructure composed of porous sponge-like agglomerated particles with irregular shape, expected from the combustion synthesis (Fig. 1). Ca-doping changed the sintering behavior by reducing the onset of shrinkage during the sintering process. Impedance spectroscopy data showed increased ionic conductivity with increasing Ca-doping. Such an increase is more evident at high measuring temperature (800 oC) and indicates enhanced oxygen mobility that are expected to contribute to OCM reaction.Figure 1: Scanning electron microscope micrographs of La2-xCaxCe2O7 (x = 0, 0.25, and 0.50) as-prepared powders obtained by combustion method. Figure 1

Enhanced oxygen mobility of nonreducible MgO-supported Cu catalyst by defect engineering for improving the water-gas shift reaction

Understanding how to tune the properties of metal oxides is essential for developing metal oxide-supported catalysts with enhanced activity. Here, nonreducible MgO-supported Cu (MgCu) catalysts were prepared by varying the content of MgO. The rate of the water–gas shift reaction over the MgCu50 catalyst was 70 μmol CO g−1s−1 at 300 °C, which is twice that achieved with reported metal oxide-supported catalysts. The limited reducibility of MgO was overcome by introducing abundant defects by effectively replacing Mg2+ with Cu2+, which resulted in significant changes in the electron density of MgO. CO-pulse titration experiments proved that the defect-rich MgO-supported catalyst exhibited highly enhanced activity toward CO due to abundant active oxygen species on the surface. The reconstruction of active surface oxygen in MgO was markedly promoted in the catalysts with higher MgO content, as well as at higher temperatures. This study demonstrates the feasibility of utilizing nonreducible MgO as an active support for reactions where redox properties are important.