O2 Temperature-programmed Desorption Research Articles

Low temperature oxidation of diesel soot particles over one-dimensional 2 × 3 tunnel-structured Na2Mn5O10 catalysts

Tunnel-structured manganese oxides have drawn widespread research attention due to their excellent oxidation properties for the soot oxidation reaction. In this study, a series of romanechite Na2Mn5O10 catalysts with a 2 × 3 tunnel structure were synthesized via a facile hydrothermal method. The as-synthesized catalysts were investigated using X-ray diffraction, scanning and transmission electron microscopy, H2 and soot temperature-programmed reduction, O2 temperature-programmed desorption, NO temperature-programmed oxidation, X-ray photoelectron spectroscopy, and other measurements. Among all the catalysts, the Na1MnyOδ-120 catalyst exhibited the best catalytic performance for soot combustion, with T10, T50, and T90 values of 281 ℃, 317 ℃, and 343 ℃, respectively, which were considerably reduced to 271 ℃, 310 ℃, and 335 ℃ in the existence of 10% H2O. The results of multiple characterization methods indicated that the Na2Mn5O10 catalysts exhibit good reducibility, strong oxygen adsorption and activation capacity, and NO to NO2 oxidation ability. Moreover, the active sites (Mn and oxygen vacancies) and reaction mechanism (Langmuir–Hinshelwood) were also revealed by in-situ DRIFT and density functional theory calculations results. This study details a new strategy for the design and synthesis of efficient soot oxidation catalysts with practical application prospects.

Oxygen adsorption capability and electrochemical properties induced by oxygen vacancies in cerium-doped LaFeO3 perovskite oxide

The effect of Ce doping on the electrochemical properties of LaFeO3 perovskite oxides was investigated in terms of the oxygen adsorption capability and polarization resistance. The Ce-doped LaFeO3 perovskite oxide had a single perovskite phase with an orthorhombic structure. The presence of oxygen vacancies was confirmed by EPR spectra and O 1 s core-level spectra. An O2 temperature-programmed desorption profile demonstrated an increase in the quantity of surface-active oxygen species, with LCFO5 exhibiting the highest oxygen adsorption capability. The area-specific resistance gradually decreased with the cerium doping from 11.36 Ωcm2 (LFO) to 4.65 Ω cm2 (LCFO5). A notable decrease of 68 % was confirmed in the polarization resistance related to the mass transfer, from 7.66 Ωcm2 (LFO) to 2.44 Ωcm2 (LCFO5). This significant decrease indicates an enhanced oxygen reduction reaction activity, which is attributed to the accelerated oxygen adsorption reaction.

Tailoring the electrochemical reduction kinetics of dual-phase BaCe0.5Fe0.5O cathode via incorporating Mo for IT-SOFCs

The BaCe0.5Fe0.5O3-δ (BCF) cathode consists of the ion-electron mixed conducting phase BaCe0.15Fe0.85O3-δ (BCF1585) and the proton-conducting phase BaCe0.85Fe0.15O3-δ (BCF8515). In this paper, the electrochemical performance is improved by incorporating the high valence element Mo into the BCF and applied to intermediate-temperature solid oxide fuel cells (IT-SOFCs). High-temperature X-ray diffraction (HT-XRD) and O2-temperature programmed desorption (O2-TPD) results show that Mo doping enhances the structural stability of BCF. The X-ray photoelectron spectroscopy (XPS) results suggest that the introduction of Mo increases the amount of adsorbed oxygen and thus the oxygen reduction reaction (ORR) catalytic activity. Compared to BCF, the polarization impedance of BaCe0.5Fe0.45Mo0.05O3-δ (BCFM) at 800°C is 0.154 Ω·cm2, a reduction of 22%. Meanwhile, the BCFM output power at 800°C is 778.01 mW·cm-2, an improvement of 32.17%, and maintains a stable current density after 250 h at 0.7 V. The results demonstrate that Mo doping is an effective strategy to enhance the electrochemical performance of BCF.

Tuning the oxygen vacancy and acidity of V-Ag-Ce/TiO2 catalyst for selective gas-phase oxidation of toluene to benzaldehyde

Toluene gas-phase oxidation is a green, chlorine-free production process for benzaldehyde but its conversion efficiency is still unsatisfying due to the lack of highly efficient catalyst. Here the selective oxidation of toluene to benzaldehyde over V-Ag-Ce/TiO2 under an air atmosphere was investigated. The catalyst was prepared by impregnation and characterized by scanning electron microscope (SEM), N2 adsorption-desorption, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Electron paramagnetic resonance (EPR), H2 temperature programmed reduction (H2-TPR), O2 temperature programmed desorption (O2-TPD), and NH3 temperature programmed desorption (NH3-TPD). The amount of oxygen vacancy and acid of the catalyst can be tuned through adjusting the V:Ag:Ce ratio. Over the optimum catalyst (V:Ag:Ce = 4:2:1, molar ratio), 92% benzaldehyde selectivity with a 27% toluene conversion can be obtained at 550 °C. Medium amounts of oxygen vacancy (0.43) and acidity (0.10 mmol/g) are found to be conducive to the conversion of toluene to benzaldehyde. This study has important theoretical guiding significance for improving conversion efficiency from toluene to benzaldehyde by gas-phase aerobic oxidation.

Defect engineered efficient catalytic transfer hydrogenation of furfural to furfuryl alcohol in ethanol by Co-doped LaMnO3

As energy and CO2 concerns have become important aspects of scientific research, researchers are focusing on the development of alternative and green energies. Biomass is a significant energy source due to its cyclic utilization process and ability to renew CO2. The catalytic transfer hydrogenation (CTH) of sugar-derived furfural (FF) into furfuryl alcohol (FA) has attracted increasing attention; however, designing and synthesizing efficient nonnoble catalysts remains challenging. In this work, an oxygen defect-abundant LaMnO3 perovskite (R-LM4C-3h) was synthesized by combining the advantages of both Co heteroatom doping and H2 reduction. Raman, O2 temperature programmed desorption (O2-TPD), X-ray photoelectron spectroscopy (XPS), electron paramagnetic resonance (EPR), and electrochemical impedance spectroscopy (EIS) characterizations revealed that R-LM4C-3h exhibited abundant oxygen defects that improved its electronic properties. As a result, adsorption ability for FF was enhanced, the reaction energy barrier was decreased, and CTH catalytic activity was promoted. A 93.6 mol% FA yield with 100 % FF conversion was achieved using ethanol as the hydrogen source. The oxygen defect-mediated catalyst also exhibited excellent stability with almost no activity reduction after 5 cycles. This surface reconstruction strategy for obtaining perovskites by fabricating abundant oxygen defects provides a superior opportunity to better explore the structure–function relationship of catalysts and develop efficient nonnoble metal-based catalysts.

Fe-Doped Ba0.9K0.1FexCo1–xO3−δ Perovskite Cathode Material for Low-Temperature Solid Oxide Fuel Cells

This study systematically investigated the effects of a single B-site dopant (Fe, x = 0–1.0) on the structure and oxygen reduction reaction of the Ba0.9K0.1CoO3−δ (BKC) material used as a cathode for low-temperature solid oxide fuel cells (LT-SOFCs). The structural, electronic, and electrocatalytic properties of the cathode materials prepared by a sol–gel method were comparatively characterized. The results indicated that cubic perovskite structure BKFxC (Fe, x = 0.5, 0.6) materials had been formed by calcination at 900 °C for 5 h. Moreover, in order to examine the electrochemical properties of BKFxC, the BKFxC cathode was constructed on the Sm0.075Nd0.075Ce0.85O2−δ (SNDC) electrolyte (BKFC/SNDC/BKFC: denoted as symmetric cells); the lowest polarization resistance (RP) was obtained for the BKF0.5C symmetric cell (1.6 Ω·cm2 at 550 °C), which demonstrated much higher electrocatalytic activity than that of a similar cell with the BKF0.6C cathode (2.87 Ω·cm2 at 550 °C). A single cell with the BKF0.5C cathode achieved a top power density of 752 mW·cm–2 at 550 °C, which is 0.35 times higher than that of the single cell with the BKF0.6C cathode (power density: 556 mW·cm–2). The corresponding total interface RP of the fuel cell was 0.303 Ω·cm2, lower than that of the doping amount of 0.6 (550 °C, 0.402 Ω·cm2). Meanwhile, O2 temperature-programmed desorption (O2-TPD) and thermogravimetric (TG) analysis were used to characterize the valence of Fe and Co changing from +4 to +3 as well as the stable structure of the material from room temperature to 600/1000 °C. As a result, a highly efficient method for the innovative BKFC cathode was developed in this work.

Improved photocatalytic H2O2 production of boron doped g-C3N4 by controllably co-modifying nanosized PDI and Ag

Herein, boron-doped g-C3N4 (BCN) is first modified with perylene diimide (PDI) nanosheets driven by the π−π interactions, and subsequently decorated with nanosized Ag through the photodeposition method. The optimal PDI/BCN-Ag photocatalyst achieves a H2O2 production rate of 143 μmol g−1 h−1 without any sacrificial agents under visible light irradiation, which is about13-fold improvement compared with pristine g-C3N4. The boosted photoactivity is mainly ascribe to the enhanced charge separation due to the cascade S-scheme charge transfer between the coupled PDI and BCN, and the promoted oxygen activation from the introduced nanosized Ag by means of the time-resolved surface photovoltage responses and fluorescence spectra, kelvin probe measurement analyses, O2 temperature-programmed desorption and electron paramagnetic resonance spectroscopy. Notably, there is a dual channel for H2O2 production on PDI/BCN-Ag. The two-electron oxygen reduction dominated by the produced •O2− radicals occurs on the Ag nanoparticles, whereas the two-electron water oxidation occurs on the PDI.

Pt/doped mullite catalysts with abundant oxygen vacancies and enhanced oxygen migration capacity for NO oxidation

Deep catalytic removal of nitrogen oxides is one of the widespread research topics, mainly limited by the low temperature activity and hydrothermal stability of the first step for NO oxidation. Oxygen vacancies (Ov) and oxygen migration capacity play a crucial role in this challenge. Particularly, tuning the Mn-O coordination environment according to the radius and valence differences of dopant ions can increase Ov, while accelerate oxygen migration by constructing Pt/mullite interfaces. Here, based on the hydrothermal stability of Pt/mullite to NO oxidation, we designed Mg2+- and Ba2+-doped catalysts. And the NO oxidation performance of the Mg2+-doped catalyst was significantly enhanced compared to the undoped catalysts (After hydrothermal aging, turnover frequency = 1.9 s−1 at 150 °C and activation energy = 21 kJ/mol). Meanwhile, all catalysts tested with simulated diesel exhaust and the NO oxidation performance showed essentially no decrease after 16 h of hydrothermal aging at 800 °C. Furthermore, X-ray photoelectron spectroscopy (XPS) and electron paramagnetic resonance (EPR) demonstrated the Ov content of doped catalysts increased significantly. In addition, O2 temperature programmed desorption (O2-TPD) and Thermogravimetry (TG) proved that the oxygen migration capacity of doped catalysts was enhanced by several times. Notably, the simple doping method is general for the modification of other mullites and worthy of industrial application.

High-efficiency palladium/halloysite nanotubes catalyst for toluene catalytic oxidation: Characterization, performance and reaction mechanism

In this study, the halloysite treated with nitric acid was designed as a functionalized support material for favoring surface availability and dispersion of nanometric palladium (Pd) nanoparticles. The prepared supported catalysts were characterized by X-ray photoelectron spectroscopy (XPS), Fourier-transform infrared (FT-IR) spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), H2 temperature-programmed reduction (H2-TPR), and O2 temperature-programmed desorption (O2-TPD). The catalytic performance and reaction mechanism of toluene oxidation were evaluated and proposed. Scanning and transmission electron microscopy images showed that 4–5 nm diameter Pd nanoparticles were uniformly dispersed on the external and edge surfaces of the A-Hal nanotubes and no obvious aggregations observed. The Pd nanoparticles were mainly present in the zero-valent state. The ratio of metallic Pd to Pd oxide species and adsorbed (Oads) to lattice (Olatt) presented a maximum value of 2.54 and 23.0, respectively, when the Pd loading was 0.5%. The prepared support catalysts exhibited a satisfactory catalytic performance and cycling stability for toluene conversion. Among the analyzed samples, the 0.5% Pd/A-Hal catalyst exhibited the highest catalytic activity for toluene oxidation, stability, and water resistance. Toluene conversions of 50% and 90% were obtained at 167 and 185 °C, respectively. In situ diffuse reflection Fourier transform spectroscopy measurements confirmed the intermediates generated during toluene oxidation and revealed that toluene oxidation occurred via the benzyl alcohol → benzaldehyde → benzoic acid → maleic anhydride reaction pathway over the obtained catalysts. These results were attributed to the high content of metal Pd species, abundant Oads species, and low-temperature reducibility. These results indicate that Hal support catalysts are promising materials for application in environmental protection.

CO oxidation over CuOx/TiO2 catalyst: The importance of oxygen vacancies and Cu+ species

It is well documented that the existence of oxygen vacancies and active Cu species can improve CO oxidation activity over TiO2 substrate. Herein, TiO2-supported copper catalysts (CuOx/TiO2) with different ratio of oxygen vacancies (Ov) and Cu+ has been synthesized. The existence and amount of Ov and Cu+ species were characterized by transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and electron paramagnetic resonance spectrum (EPR). The synergetic effect between Cu+ and oxygen vacancies was investigated in terms of O2 temperature-programmed desorption (O2–TPD), H2 temperature-programmed reduction (H2–TPR) and in situ DRIFTS spectra. Cu+ is the adsorption site for CO molecules, the abundant Ov can significantly activate molecular oxygen, which effectively oxidize the adsorbed CO molecules. The most suitable ratio between Cu+ and Ov has been confirmed. The CuOx/TiO2(Cu+ rich) catalyst (51% Cu+, 26.3% Ov) shows superior CO oxidation activity (T90 = 136 °C) compared to CuOx/TiO2(Ov rich) catalyst (39% Cu+, 28.5% Ov, T90 > 350 °C). This work provides comprehensive investigation of the role for abundant oxygen vacancies and Cu+ in CO oxidation reactions.

Achieving efficient toluene mineralization over ordered porous LaMnO3 catalyst: The synergistic effect of high valence manganese and surface lattice oxygen

To elucidate the role of high valence manganese and surface lattice oxygen in catalyst for catalytic combustion of toluene, herein, a porous LaMnO3 catalyst was firstly fabricated using ordered mesoporous carbon (OMC) as a hard-template. Compared with pristine LaMnO3-bulk, the optimal porous LaMnO3 exhibited boosted catalytic performance for toluene combustion, leading to a ∼50 ℃ lower T90% (required temperatures for 90% toluene conversions). The results of N2 adsorption–desorption measurement, X-ray photoelectron spectroscope, O2 temperature-programmed desorption and H2 temperature-programmed reduction indicated that the optimal porous LaMnO3 displayed high molar ratios of surface Mn4+/Mn3+ and Olatt/Oads, which exposed abundant active sites and promoted the preferential low-temperature catalytic oxidation of toluene. Simultaneously, the increased content of high valence manganese (Mn4+) and surface lattice oxygen (Olatt) in porous LaMnO3 catalyst accelerated the cycle of toluene deep oxidation. Combined with the analysis of toluene intermediates by in situ diffuse reflectance infrared Fourier transform spectroscopy, the toluene degradation mechanism over porous LaMnO3 was also explored. This work provides a feasible strategy for design of porous Mn-based perovskite catalyst with a high efficiency and stability for catalytic combustion of VOCs.

Co-Precipitated Mn0.15Ce0.85O2−δ Catalysts for NO Oxidation: Manganese Precursors and Mn-Ce Interactions

Two Mn0.15Ce0.85O2−δ mixed oxides were synthesized by a co-precipitation method using Mn(NO3)2 and KMnO4 as the manganese precursors, respectively. Structural analyses by X-ray powder diffraction and Raman spectroscopy reveal the formation of MnOx-CeO2 solid solutions. The Mn0.15Ce0.85O2−δ catalyst prepared from the high-valent manganese precursor exhibits higher activity for the catalytic oxidation of NO. The advantage of KMnO4 is related to the improved redox property of the catalyst as supported by H2 temperature-programmed reduction (TPR) and O2 temperature-programmed desorption (TPD). The Mn-Ce interactions create more Mn4+, Ce3+ and oxygen vacancies on the KMnO4-synthesized mixed oxides based on the Raman and X-ray photoelectron spectra (XPS).

Catalytic behavior of Mo–Bi–Fe–Co–K–M–O (M=Ce, Gd, CeGd) catalysts for selective oxidation of isobutene

The further improvement of methacrolein (MAL) selectivity from isobutene (IB) oxidation is crucial and challenging. In this study, based on the typical Mo–Bi–Fe–Co–K–O mixed metal oxide, the rare earth element Gd-doped, Ce-doped and CeGd co-doped catalysts were prepared by co-precipitation strategy to increase the selectivity of MAL from 47.9% to 49.8%, 64.2% and 68.6%, respectively. In order to elucidate in-depth the promoting effect of Ce and/or Gd, various characterizations were utilized including X-ray diffraction patterns (XRD), Raman, X-ray fluorescence spectrometry (XRF), X-ray photoelectron spectroscopy (XPS), O2-temperature programmed desorption (O2-TPD), H2-temperature programmed reduction (H2-TPR), CO2-temperature programmed desorption (CO2-TPD), IB-temperature programmed desorption (i-C4-TPD) and in-situ IB-Fourier transform infrared spectroscopy (IB-FTIR). Both Ce and Gd finely regulate the bulk and surface structure of the catalyst, thus altering the redox ability, oxygen mobility and storage ability and basicity. Compared with Ce, Gd addition slightly regulates the variation of Co2+/Co3+ redox couples, greatly enhances the interaction among the components on the catalyst, thus only increases the content of surface oxygen species and has little effect on their mobility. While Ce-containing catalyst performs stronger oxygen storage and migration ability, thus leading to the overproduction of surface Odefect species, which are proposed to be the active sites for the production of MAL and COx. The CeGd co-doped catalyst possesses the proper content of surface Odefect species, thus exhibits much higher MAL selectivity. Moreover, the promoting mechanism of Ce and/or Gd over IB oxidation is proposed. Therefore, this work is helpful for understanding the influence of rare earth elements on the structure of mixed metal oxides and the olefin selective oxidation reaction.

Highly efficient removal of ozone by amorphous manganese oxides synthesized with a simple hydrothermal method

Amorphous manganese oxides (MnOx) were synthesized by facile hydrothermal reactions between potassium permanganate and manganese acetate. Synthesis parameters, including hydrothermal time and temperature and molar ratio of precursors, significantly affected the ozone removal performance and structure property of MnOx. Amorphous MnOx-1.5, which was prepared at the Mn2+/Mn7+ molar ratio of 1.5 under hydrothermal conditions of 120°C and 2 hr, showed the highest ozone removal rate of 93% after 480 min at the room temperature, RH (relative humidity) = 80% and WHSV (weight hourly space velocity) = 600 L/(g·hr). The morphology, composition and structure of catalysts were investigated with X-ray diffractometer (XRD), Raman spectra, N2 physisorption, field emission scanning electron microscope (FESEM), X-ray photoelectron spectroscopy (XPS), H2 temperature-programmed reduction (H2-TPR), O2 temperature-programmed desorption (O2-TPD) and in situ diffuse reflectance infrared Fourier transform spectroscopy (in situ DRIFTS). It was confirmed that high catalytic activity of amorphous MnOx for ozone removal was mainly ascribed to its abundant oxygen vacancies, high oxygen mobility and large specific surface area.

A-site disubstituted of La1−xSrxNi0.8Fe0.2O3 perovskite on coal pyrolysis volatiles catalytic cracking: Activity and reaction mechanism

This work focuses on the result of strontium doping on La1−xSrxNi0.8Fe0.2O3 catalytic cracking of coal tar in the COREX process. The results show that Sr doping significantly affected the catalytic performance of perovskite. O2-Temperature programmed desorption (O2-TPD) and X-ray photoelectron spectroscopy (XPS) results show that La0.8Sr0.2Ni0.8Fe0.2O3 (Sr 0.2) has more active oxygen species and higher oxygen mobility. The performance of Sr-doped catalysts is higher than that of LaNi0.8Fe0.2O3, producing less tar and carbon deposition. Moreover, Sr 0.2 exhibited the highest gas yield of 34.6 mmol/gcoal, H2 yield of 27.5 mmol/gcoal, 100% tar conversion rate, and the lowest carbon deposition of 19.4 mg/(g·h). Tar cracking mechanism was proposed by characterization results. The perovskite could serve as a bridge for oxygen migration and simultaneous oxygen supplementation, thus sustaining catalyst activity and durability. The appropriate amount of Sr doping perovskite is favorable to high catalytic activity and anti-carbon deposition at high temperatures. This work could provide some referential value for the highly-efficient cracking of tar.

Boosting hydrogen production by reducible oxygen species over Ni/MTixOy catalysts for the steam reforming of liquefied oil from Saccharina japonica

Hydrogen is a sustainable energy resource. However, H2 is mainly produced by steam reforming of fossil fuels, emitting greenhouse gases. H2 production from macroalgae is a promising alternative to fossil fuels because of the carbon neutrality of the marine biomass. In this study, we investigated the steam reforming of liquefied oil derived from Saccharina japonica over metal titanate-based Ni catalysts (Ni/K2TixOy, Ni/CaTiO3, Ni/SrTiO3, and Ni/BaTiO3). CO temperature-programmed reduction (CO-TPR), and O2 temperature-programmed desorption (O2-TPD) characterizations showed that the reducibility of lattice oxygen on metal titanates depended on metal cation species and was much higher than on the inert Al2O3. SrTiO3 exhibited the highest reducible oxygen content among the metal titanates.Catalytic evaluations showed that Ni/MTixOy catalysts exhibited higher H2 selectivity and catalytic stability than Ni/Al2O3. Ni/Al2O3 exhibited an H2/CO ratio of 1.1, while other Ni/MTixOy catalysts exhibited higher values (2.3–4.4); especially, Ni/SrTiO3 showed the highest H2 selectivity (55.8%) and H2/CO ratio (4.4). The H2 selectivity could be correlated with the amount of reactive lattice oxygen, as quantified by CO-TPR and O2-TPD. Furthermore, reactive oxygen species inhibited coke deposition on Ni/MTixOy catalysts. Overall, the Ni/MTixOy catalysts exhibited a high potential for H2 production by the steam reforming of bio-oil from macroalgae.

Oxygen permeation properties of Bi-doped La0.8Sr0.2FeO3−δ planar ceramic membranes at intermediate temperature

Ceramic oxygen permeable membranes (COPMs) have attracted attention as a “next generation” technology for oxygen separation. However, developing new oxygen permeable membrane materials with high oxygen permeability at an intermediate operating temperature is still challengeable. In this work, a series of perovskite La0.8-xBixSr0.2FeO3-δ (LBSF, x = 0.0, 0.2, 0.3 and 0.4) oxides were synthesized and used as the oxygen permeation membrane materials. The phase structure, electrical conductivity, chemical compatibility with 3 mol% yttria-stabilized zirconia (3YSZ), O2 temperature programmed desorption (O2-TPD) have been evaluated. An asymmetric three-layer structure with “porous-transition-dense” was developed by tape casting, hot-pressing and co-sintering technology. The membrane consists of a porous 3YSZ support layer, a 3YSZ-LBSF transition layer and a dense LBSF functional layer. The oxygen permeability was tested by a new designed electrochemical device based on the limit current method. The best oxygen permeability was found in the composition of La0.4Bi0.4Sr0.2FeO3-δ measured at an intermediate temperature of 800 °C with 20% oxygen partial pressure, which could reach 1.13 mL min−1 cm−2. No obvious degradation was observed on the three-layers La0.4Bi0.4Sr0.2FeO3-δ membrane after a stability test at 800 °C for 150 h under 1.6 V and subsequent 11 times thermal cycling between 700 °C and 800 °C. The membrane exhibited excellent long-term stability and thermal cycling stability.

A highly operating stability, oxygen reduction reaction active and CO2/Cr tolerance perovskite cathode for solid oxide fuel cells

Layered perovskite-related GdBaFe2O5+δ (GBF) and GdBaFeCoO5+δ (GBFC) oxides are systematically studied as advanced air electrodes for intermediate-temperature solid oxide fuel cells (IT-SOFCs). The characterizations of the samples are gauged with the assistance of a variety of techniques, involving X-ray diffractometer (XRD), O2-temperature programmed desorption (O2-TPD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and Fourier transform infrared spectrometry (FT-IR). Results of XRD demonstrate that GBFC has the exact same crystal structure as that of GBF, which displays slight lattice shrinkage. Substitution of Co for Fe increases the TEC from 9.87 × 10−6 K−1 and 16.6 × 10−6 K−1 at 150–700 °C. GBFC shows the highest conductivity of 500 S cm−1 at 520 °C, which complies with the requirement for the cathode of the fuel cell. The polarization resistance (Rp) values of GBF and GBFC are 0.33 Ω cm2 and 0.07 Ω cm2 at 650 °C, respectively. Moreover, a single cell based on Sm0.8Ce0.2O1.9 (SDC) electrolyte-supported is indicative of a peak power density of 0.28 W cm−2 for GBFC cathode at 700 °C. This single cell also exhibits a superior operational stability utilizing dry hydrogen fuel at 600 °C during the tested 220 h. Electrochemical impedance spectroscopy (EIS) and relaxation time distribution (DRT) results are suggestive of the slowly decreasing oxygen reduction kinetics of GBFC cathode with the introduction of CO2 or gaseous Cr species, which may be connected with the formation of carbonate or Cr depositions. Compared to classic materials, GBFC cathode shows very good electrochemical stability and CO2/Cr tolerance.

Soot Oxidation over γ-Al2O3-Supported Manganese-Based Binary Catalyst in a Dielectric Barrier Discharge Reactor

In this work, soot oxidation was conducted over a series of Mn-X/γ-Al2O3 (M = Ce, Co and Cu) binary catalysts in a dielectric barrier discharge reactor. The soot conversion in the plasma–catalytic system was in the order of Mn/γ-Al2O3 (57.7%) > Mn-Co/γ-Al2O3 (53.9%) > Mn-Ce/γ-Al2O3 (51.6%) > Mn-Cu/γ-Al2O3 (47.7%) during the 30 min soot oxidation process at 14 W and 150 °C. Meanwhile, the doping of Ce, Co and Cu slightly improved the CO2 selectivity of the process by 4.7% to 10.3% compared to soot oxidation over Mn/γ-Al2O3.It is worth to note that the order of CO2 selectivity was in the opposite order with soot oxidation rate. The effects of discharge power, oxygen content in the carrier gas and reaction temperature on plasma–catalytic soot oxidation was systematically analyzed. The catalyst characterizations, including N2 adsorption–desorption, X-ray diffraction, X-ray photoelectron spectroscopy, temperature-programmed reduction by H2 and temperature-programmed desorption of O2, were conducted to illustrate the reaction mechanisms of plasma–catalytic soot oxidation and reaction pathways.

Insight into phase structure-dependent soot oxidation activity of K/MnO2 catalyst

In the present study, two nanosized MnO2 with β and δ phase structures and potassium loaded MnO2 catalysts with varied K loading amounts (denoted as K/MnO2) were prepared. Temperature programmed oxidation and isothermal reactions in loose contact modes were employed to examine the soot oxidation activity of the as-prepared catalysts. Characterization results show that as compared with β-MnO2, δ-MnO2 has larger surface area and higher content of hydroxyl groups. Upon K loading, abundant hydroxyl groups in δ-MnO2 effectively sequestrate K cation to form bound K species and free K species are available only at K loading above 3.0 wt.%. In contrast, the majority of K species present as free state in β-MnO2 even at a K loading of 1.0 wt.% due to its very low hydroxyl group content. The O2 temperature-programmed desorption (O2-TPD) demonstrates that the catalysts with free K species exhibit strong ability in activating gaseous O2, whereas the catalysts only having bound K display minor O2 activation capability. As a result, despite of slightly lower activity of β-MnO2 than δ-MnO2, the K/β-MnO2 catalysts exhibit substantially higher activities than K/δ-MnO2 catalysts with identical K loadings. The finding in this study clearly demonstrates that for MnO2 based catalysts, the enhancement of catalytic activity for soot oxidation is highly K loading amount dependent and the dependency is strongly associated with the phase structure of MnO2.