Ceria Oxygen Research Articles

Reaction and deactivation mechanisms of a CeIn/HBEA catalyst with dual active sites for selective catalytic reduction of NOx by CH4

Methane selective catalytic reduction (CH4-SCR) technology has shown promise for controlling NOx emissions from natural gas generator sets. This study presents a highly efficient Ce30In15/HBEA catalyst featuring dual active sites, Al-O–(InO+)-Si site for CH4 activation and ceria oxygen vacancy (Ce3+-□) site for NOx activation. However, the CH4-SCR activity of this catalyst decreased in the presence of H2O, SO2, C3H6, and CO2. The inhibitory effects on CH4-SCR activity followed by the sequence: H2O > SO2 > C3H6 > CO2. In particular, H2O combined with Al-O–(InO+)-Si to form inactive In(OH)3-zz+ species and occupied Ce3+-□, preventing Ce4+-NO3–/NO2– formation. In/Ce sulfate formation via the reaction between SO2 and In/Ce active sites hindered CH4 and NOx adsorption and activation. The formed carbon deposits covered the active sites on the catalyst surface due to incomplete C3H6 oxidation. In comparison, the dual active sites were almost unaffected by CO2. Overall, this study provides a basis for the rational design of novel catalysts for CH4-SCR.

Silicate-induced high-temperature-resistant small-crystallite ceria support enhancing palladium-catalyzed low-concentration methane combustion

High-performance Pd/CeO2 catalysts for the purification of low-concentration methane in waste gases by catalytic combustion have long been pursued, given that methane is a potent greenhouse gas. The reduction in ceria oxygen supply and palladium dispersion, caused by ceria crystallite sintering, deactivates the catalyst. Here, we report an enhanced palladium catalyst supported on a silicate-induced small-crystallite ceria (7.2 nm) calcined at 800 °C, compared to the pristine ceria (50.7 nm). The catalyst was coated on a cordierite monolith for 0.1 vol% methane combustion, achieving 90 % methane conversion at 336 °C, which is 84 °C lower than the temperature required for Pd/CeO2 reference. The small-crystallite ceria exhibited a high oxygen supply capacity due to abundant oxygen vacancies, facilitating the conversion of carbon-containing intermediates from methane dissociation on palladium species, thereby enhancing the catalyst’s intrinsic activity. The catalyst, with increased palladium dispersion, demonstrated a methane reaction rate 6.7 times higher than that of the Pd/CeO2 at 280 °C. This study provides new insights into designing highly efficient Pd/CeO2-based catalysts for low-concentration methane combustion.

Unexpected strong toluene chemisorption over Ag/CeO2 catalysts for total toluene oxidation

The effect of Ag content on the sorption properties and toluene removal activity over Ag/CeO2 catalysts is studied. In this paper, the series of Ag/CeO2 catalysts with Ag content from 1 to 10 wt% are prepared by impregnation method and characterized using a complex of methods: low-temperature N2 adsorption, XRD analysis, TPR-H2, and TEM-HR. For the first time, the strong toluene chemisorption over Ag-containing species accompanied by total oxidation into CO2 is observed. The correlation between the amount of chemisorbed toluene and Ag loading in the catalysts confirms the toluene chemisorption over Ag species and/or Ag-CeO2 interface. The active surface oxygen of ceria oxidizes chemisorbed toluene. The cooperation of active sites on silver and ceria provides both enhanced chemisorption of toluene and its total oxidation. The total removal of toluene (2000 ppm) was achieved at ∼140 °C over 5Ag/CeO2 and 10Ag/CeO2 catalysts due to both chemisorption and total oxidation of toluene.

Lattice-Stabilized Chromium Atoms on Ceria for N2O Synthesis.

The development of selective catalysts for direct conversion of ammonia into nitrous oxide, N2O, will circumvent the conventional five-step manufacturing process and enable its wider utilization in oxidation catalysis. Deviating from commonly accepted catalyst design principles for this reaction, reliant on manganese oxide, we herein report an efficient system comprised of isolated chromium atoms (1 wt %) stabilized in the ceria lattice by coprecipitation. The latter, in contrast to a simple impregnation approach, ensures firm metal anchoring and results in stable and selective N2O production over 100 h on stream up to 79% N2O selectivity at full NH3 conversion. Raman, electron paramagnetic resonance, and in situ UV-vis spectroscopies reveal that chromium incorporation enhances the density of oxygen vacancies and the rate of their generation and healing. Accordingly, temporal analysis of products, kinetic studies, and atomistic simulations show lattice oxygen of ceria to directly participate in the reaction, establishing the cocatalytic role of the carrier. Coupled with the dynamic restructuring of chromium sites to stabilize intermediates of N2O formation, these factors enable catalytic performance on par with or exceeding benchmark systems. These findings demonstrate how nanoscale engineering can elevate a previously overlooked metal into a highly competitive catalyst for selective ammonia oxidation to N2O, paving the way toward industrial implementation.

Pt Current Collectors Artificially Boosting Ceria Oxygen Surface Exchange Coefficients

The SOFC/SOEC community has an oxygen surface exchange measurement reproducibility crisis. This is exemplified by a >1,000 times variation in the literature-reported chemical oxygen surface exchange coefficient (k chem) values of Pr0.1Ce0.9O2−x (PCO) at 700 °C in air, a >10,000 times variation in the literature-reported k chem values of La0.6Sr0.4FeO3-x (LSF) at 650 °C in air, and a >100,000 times variation in the literature-reported k chem values of Ba0.6Sr0.4Co0.8Fe0.2O3-x (BSCF) at 500 °C in air. Many of these k chem values have been determined electrically (often via Electrochemical Impedance Spectroscopy or Electrical Conductivity Relaxation) using precious metal current collectors. Unfortunately, the Time-of-Flight Secondary Ion Mass Spectroscopy and Curvature Relaxation k chem measurements performed here on Pulsed Laser Deposited Pr0.1Ce0.9O2−x (PCO) thin films show that unpolarized Pt current collectors can dramatically improve PCO k chem values (by up to 2 orders of magnitude) through i) a reduction in the PCO surface Si concentration, and/or ii) Pt diffusion into the underlying PCO lattice. Further, this phenomenon can occur in PCO thin films only exposed to mild temperatures of 500 °C. Hence, it seems likely that precious metal current collectors may be responsible for at least some of the large k chem variation reported in the literature for “identical” materials tested under “identical” conditions.Reference: Ma Y, Burye TE, Nicholas JD. Pt Current Collectors Artificially Boosting Praseodymium Doped Ceria Oxygen Surface Exchange Coefficients. Journal of Materials Chemistry A. 2021; 9: 24406.

Modelling of NO Reduction on CeO2-Supported Pt and Pd Nanoclusters

ABSTRACT The reduction mechanism of NO to N2 on CeO2-supported Pt and Pd nanoclusters (Pt/CeO2 and Pd/CeO2) is analyzed using density functional theory. Different NO decomposition and N2 formation pathways are evaluated, and the thermodynamically preferable paths are identified. The energy barrier of NO decomposition on Pt/CeO2 indicates that the rate of reaction via metallic cluster sites and the ceria oxygen vacancies are comparable. In contrast, the cluster metallic sites of the Pd/CeO2 induce a lower energy barrier of NO decomposition relative to the oxygen CeO2 vacancy sites. The N2 formation on the Pt/CeO2 preferentially occurs via the N–N association, whereas the N2O deoxidation is energetically preferred on the Pd/CeO2.

Concerted oxygen diffusion across heterogeneous oxide interfaces for intensified propane dehydrogenation

Propane dehydrogenation (PDH) is an industrial technology for direct propylene production which has received extensive attention in recent years. Nevertheless, existing non-oxidative dehydrogenation technologies still suffer from the thermodynamic equilibrium limitations and severe coking. Here, we develop the intensified propane dehydrogenation to propylene by the chemical looping engineering on nanoscale core-shell redox catalysts. The core-shell redox catalyst combines dehydrogenation catalyst and solid oxygen carrier at one particle, preferably compose of two to three atomic layer-type vanadia coating ceria nanodomains. The highest 93.5% propylene selectivity is obtained, sustaining 43.6% propylene yield under 300 long-term dehydrogenation-oxidation cycles, which outperforms an analog of industrially relevant K-CrOx/Al2O3 catalysts and exhibits 45% energy savings in the scale-up of chemical looping scheme. Combining in situ spectroscopies, kinetics, and theoretical calculation, an intrinsically dynamic lattice oxygen “donator-acceptor” process is proposed that O2- generated from the ceria oxygen carrier is boosted to diffuse and transfer to vanadia dehydrogenation sites via a concerted hopping pathway at the interface, stabilizing surface vanadia with moderate oxygen coverage at pseudo steady state for selective dehydrogenation without significant overoxidation or cracking.

Diesel soot combustion over ceria catalyst: Evolution of functional groups on soot surfaces

The use of ceria catalyst is a common way to promote the soot combustion during DPF regeneration, due to the superior capability to store and release oxygen. In this work, the oxidation behavior and evolutions of surface functional groups have been critically discussed to reveal the mechanism of soot catalytical oxidation, based on the results derived from temperature-programmed-oxidation (TPO) experiments, X-ray photoelectron spectroscopy, Fourier Transfer Inferred spectrometer, and Raman scattering spectrometer. Before the TPO test, the soot samples with and without ceria were annealed at up to 500℃ in pure N2 gas. During the thermal annealing, the reaction between soot and desorbed lattice oxygen in ceria leads to damage of the graphitic network and proliferation of the strongly oxidized OCO groups, defects, and disorder structure on soot surface. In consequence, the onset temperature for the mixture of diesel soot and ceria in loose-contact condition slightly elevates than the pure diesel soot. At initial soot catalytical oxidation, ceria enhances the consumption of amorphous carbon and generation of sp3 hybridized carbon. As the oxidation process evolves, ceria gives a boost to the complete saturation of C vacancy and the generation of larger O groups on soot surfaces. Meanwhile, the damage of the PAHs matrix occurs with the assistant of ceria catalyst, probably by facilitating the O desorption on the basal-plane C atoms. All these differences induced by ceria facilitate the oxidation reactions in the subsequent phases.

(Invited) Chemical Stability and Performance of Rare Earth Nickelate Oxygen Electrodes for Reversible Solid Oxide Cells

Composite rare-earth nickelate-rare-earth doped ceria oxygen electrodes have inherent chemical instabilities. Over the last year, we have made progress on achieving chemical stability and high performance using a strategy of heavily doping the ceria phase with rare-earth cations. A higher dopant concentration of a rare-earth cation in the ceria phase ensures thermodynamic stability of the nickelate phase in contact with the ceria phase. In particular, composite oxygen electrodes comprising lanthanum nickelate La2NiO4+δ (LNO) - lanthanum doped ceria (LDC) and neodymium nickelate Nd2NiO4+δ (NNO) - neodymium doped ceria (NDC) have been electrochemically tested in both solid oxide fuel cell (SOFC) and solid oxide electrolysis cell (SOEC) modes. The performance of these cells have been compared to a composite strontium doped lanthanum manganite (LSM)-8 mol% yttria stabilized zirconia (YSZ) electrode. Both nickelate based electrodes achieve far superior performance compared to the LSM electrodes. We also report impedance measurements from symmetrical cells featuring LNO and NNO electrodes, analyzed using a distribution of relaxation times (DRT) approach. The DRT analysis reveals significant differences in the rate controlling steps in oxygen reduction and incorporation steps between the two materials. Lastly, oxygen surface exchange results for LNO and NNO are also reported which show different oxygen exchange kinetics when measured on dense versus porous materials which have implications for deploying these materials in reversible solid oxide cells.

Pt Current Collectors Artificially Boosting Si-Contaminated Praseodymium Doped Ceria Oxygen Surface Exchange Coefficients

The chemical oxygen surface exchange coefficient (kchem ) values used to quantify and rank oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) catalyst performance for high-temperature, oxygen-exchange-enabled devices (such as Solid Oxide Fuel Cells, Solid Oxide Electrolysis Cells, oxygen sensors, etc.) are often determined electrically, with the aid of precious metal current collectors. In addition, due to ease of introducing siliceous contaminants during the manufacturing and operation of these devices, the performance of their oxygen exchange catalysts are often impacted by Si surface contaminants.Here, Curvature Relaxation (KR), Time-of-Flight Secondary Ion Mass Spectroscopy (ToF-SIMS), X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), and X-Ray Photoelectron Spectroscopy (XPS) analyses performed on Pulsed Laser Deposited thin films of the oxygen exchange catalyst Pr0.1Ce0.9O2-x (PCO) show that siliceous surface phases only a few nanometers thick are capable of 1) reducing the PCO chemical oxygen surface exchange coefficient by approximately 3 orders of magnitude and 2) approximately doubling the activation energy for oxygen incorporation and removal. Further, the results show that unpolarized platinum current collectors dramatically improve the kchem of Si-contaminated PCO by reducing the Si concentration at the PCO surface and/or diffusing into the PCO; even for PCO thin films only exposed to mild temperatures of 500 oC. This suggests that precious metal current collectors are likely responsible for some of the large kchem variation reported in the literature for “identical” materials tested under “identical” conditions. Figure 1

Highly active Ni/CeO2 for the steam reforming of acetic acid using CTAB as surfactant template

A series of CTAB-templated Ni/Ce catalysts were synthesized by adding CTAB during the hydrothermal synthesis of ceria to improve the pore structure of catalysts. Their catalytic performance was evaluated in the steam reforming of acetic acid and the effects of CTAB concentration on the porous structures, reducibilities, morphology, and activity of catalysts were studied. The catalysts were characterized by BET, XRD, H2-TPR, XPS, HRTEM, in-situ DRIFTS, DTG, FTIR, and temperature-programmed reaction to elucidate the structure-activity relationship of the catalyst. The results showed that owing to the CTAB assistance, a high surface area of ceria could be achieved, which induced a better Ni dispersion with a smaller Ni size, strengthened the interaction between Ni and CeO2, and promoted the reducibility of Ni, obtaining higher activity and lower methane yield than Ni/Ce. Among these prepared samples, Ni/Ce–C6 showed the highest surface area and the best catalytic performance with a hydrogen yield of up to 82.5% even at a low temperature (550 °C). Owing to the stronger Ni-ceria interaction of Ni/Ce–C6, the lattice oxygen in ceria migrates easily to the Ni surface, interacts with the reaction intermediates, and thus improves the CO2/CO ratio in the products. Much more CO and CO2 and less CH4 were observed over Ni/Ce–C6 during the temperature-programmed reaction, indicating its high activity. In-situ DRFITS characterization demonstrated that the two types of catalysts had similar reaction intermediates but various adsorption and conversion abilities toward the acetic acid. More reaction intermediates were adsorbed at low temperatures and a higher conversion was obtained over Ni/Ce–C6 owing to its better Ni dispersion. The CTAB assistance inhibited the formation of amorphous carbon but facilitated the formation of graphitic carbon at ∼637 °C which did not induce catalyst deactivation.

Understanding the conduction mechanism of acceptor-doped ceria oxygen ion conductors by photoluminescence analysis

Doping or co-doping is a universal and extremely effective strategy for enhancing ion conductivity by modulating the coordination surroundings of oxygen vacancies in oxygen ion conductors. Herein, the structural origin and conduction mechanism of bulk conduction upon cation doping, exemplified in Ce0.85Sm0.15-xLaxO2-δ (x = 0, 0.03, 0.06, 0.09, 0.12, and 0.15) polycrystalline oxygen ion conductors, were investigated by employing the structure-sensitive photoluminescence properties of Sm3+ ions. Photoluminescence results show that the oxygen vacancies, introduced by La3+ substitutions, moved from near the coordination positions of La3+ ions to those of Sm3+ and Ce4+ ions. This occurred when the Sm3+ ions were substituted by La3+ ions. Compared with Samarium doped Ceria (SDC), the oxygen vacancies in Lanthanum-doped ceria (LDC) are more likely to be located around the Ce4+ ions rather than around the trivalent doping cations. For acceptor-doped CeO2-based oxygen ion conductors, the key factor in the activation energy of bulk conduction, Eαbulk, is the cation electronegativity on the oxygen vacancy migration path rather than the defect association and local lattice distortion on the oxygen vacancy migration path in the lattice. The significance of cation electronegativity to ion conduction proposed in this study would be beneficial for understanding the conduction mechanism and for optimising the electrical properties of various ion conductors. In addition, the strategy developed in this study to shed light on the relationship between cation doping and local structures by photoluminescence could be extended to other ion conductors in solid oxide fuel cells, oxygen sensors, oxygen concentration cells, and memristors.

Integrated carbon capture and utilization: Synergistic catalysis between highly dispersed Ni clusters and ceria oxygen vacancies

Integrated carbon capture and utilization (ICCU) presents an ideal solution to address anthropogenic carbon dioxide (CO2) emissions from industry and energy sectors, facilitating CO2 capture and subsequent utilization through conversion into high-value chemicals, as opposed to current release into the atmosphere. Herein, we report the synergistic coupling of porous CaO, as a sorbent for CO2 capture, and Ni doped CeO2 nanorods, as catalytic sites for CO2 reduction. It is found that ceria is shown to possess the capacity for CO2 utilization, however, critically it only results in the generation of CO due to the weak CO-ceria bonding. The addition of Ni active sites gives rise to CH4 being the predominant product, via the strong interaction between Ni species and CO, which facilitates further reduction. Through tuning Ni loadings, we have evaluated the role of catalytic active site size, with a Ni loading of only 0.5 wt% providing optimal performance through the formation of sub-nanometer sized clusters. This near-atomic active site dispersion gives rise to CH4 productivity and selectivity of 1540 mmol g−1 Ni and 85.8%, respectively, with this optimal combination of catalyst and sorbent demonstrating high stability over 10 cycles of ICCU process. These observations in parallel with the synergistic coupling of earth-abundant, low-cost materials (CaO and Ni) will have broad implications on the design and implementation of high efficiency, cost-effective ICCU materials and processes.

Effect of the dispersion behavior of cerium oxygen species on CO2 adsorption performance

The dispersion behaviors of metal oxygen species on the carrier surface have an important effect on the performances of them. The dispersion behaviors of cerium oxygen (CeOx) species on the surface of Canna indica L. based biochar are investigated via anchoring the different amounts of Ce(NO3)3 onto the surface of biochar by a hydrothermal reaction method. The dispersion behaviors are characterized by XRD, SEM, EDS. The effect of dispersive behavior on its own properties can be characterized by Raman, XPS and BET. The CO2 adsorption performances of the different dispersive behaviors are detected by gas chromatography. Results showed that the dispersion behaviors of CeOx species on the biochar is affected by the molar ratio of CeOx species and biochar. In addition, the specific surface area, pore volume and average pore diameter of the composites, the interaction between with CeOx species and carrier biochar and the concentration of oxygen vacancy in CeOx species are all affected by the dispersion behaviors of the loaded CeOx species. Most importantly, the CO2 adsorption performance of the composites are different duo to the different dispersion behaviors. CeOx-5/bio-C (the composite with the molar ratio of CeOx species and biochar is 5%) has the highest CO2 adsorption performance and the adsorption capacity is 112.88 μmol/gCeO2. Therefore, the dispersion behavior of the CeOx species on the surface of the carrier has a great influence on its own properties and adsorption performance.

Rare earth Nickelate electrodes containing heavily doped ceria for reversible solid oxide fuel cells

The electrochemical performance of composite rare-earth nickelate-rare-earth doped ceria oxygen electrodes, with a high level of rare-earth doping in ceria are reported. Additionally, the chemical stability of these compositions is reported at both the sintering (1240 °C) and operating temperature (800 °C). Specifically, a lanthanum nickelate La 2 NiO 4+δ (LNO) −50 mol% lanthanum doped ceria (LDC50) oxygen electrode and a neodymium nickelate Nd 2 NiO 4+δ (NNO) −50 mol% neodymium doped ceria (NDC50) oxygen electrode are tested in solid oxide fuel cell (SOFC) and solid oxide electrolysis cell (SOEC) modes and compared to a composite (La 0.75 Sr 0.25 ) 0.95 MnO 3±δ (LSM)-8 mol% yttria stabilized zirconia (YSZ) electrode. The LNO–LDC50 oxygen electrode reaches a current density which is approximately three times that of the LSM-YSZ electrode in SOFC mode at 0.7 V and approximately two times the LSM-YSZ electrode at 1.2 V in SOEC mode. Similarly the NNO-NDC50 oxygen electrode reaches a current density which is approximately two times and approximately one and a half times that of LSM-YSZ at 0.7 V and 1.2 V respectively. Oxygen surface exchange results for LNO and NNO are also reported which show different oxygen exchange kinetics during oxidation versus reduction steps. • Rare-earth nickelate oxygen electrodes have been stabilized and are reversible. • Nickelates show equally good performance in SOFCs and SOECs. • Symmetrical cells provide corroboration of results from full cells.

Stable High Performance Rare-Earth Nickelate Based Oxygen Electrodes for Reversible Solid Oxide Fuel Cells and Electrolyzers

The performance of composite rare-earth nickelate-rare-earth doped ceria composite oxygen electrodes, with a high concentration of rare-earth doping in ceria to stabilize the nickelate phases are reported. Additionally, the stability of these compositions is reported at both the sintering (1240°C) and operating temperatures (800°C). Specifically, a lanthanum nickelate La2NiO4+δ (LNO) -45 mol% lanthanum doped ceria (LDC45) oxygen electrode has been tested in both solid oxide fuel cell (SOFC) and solid oxide electrolysis cell (SOEC) modes. The performance of this cell has been compared with a composite oxygen electrode comprising 20 mol% strontium doped lanthanum manganite (LSM)-10 mol% scandia 1 mol% ceria stabilized zirconia (SSZ) electrode. The LNO–LDC45 composite oxygen electrode shows a 65% increase in current density at 0.8 V, and a 260% increase in current density at 1.2 V compared to LSM-SSZ oxygen electrodes in SOFC and SOEC mode respectively. Additionally, long term performance data shows that this superior performance can be maintained for long operating times at 1.2 V in SOEC mode at 800°C. Supplemental cell tests also show comparable performance for a composite neodymium nickelate Nd2NiO4+δ (NNO)- 50 mol% neodymium doped ceria (NDC50) and a composite LNO- 50 mol% lanthanum doped ceria (LDC50) electrode.

Promoting the Methane Oxidation on Pd/CeO2 Catalyst by Increasing the Surface Oxygen Mobility via Defect Engineering

AbstractMethane is a useful chemical resource, but removing it, a powerful greenhouse gas, is important to prevent global warming. In this study, the methane oxidation activity of conventional Pd/CeO2 catalyst was improved by enhancing the oxygen mobility of ceria surface via the simple defect engineering. Raman spectroscopy demonstrates that the defect concentration of ceria surface is reduced after high temperature treatments. Cryogenic hydrogen‐temperature‐programmed‐reduction curves indicate that the surface oxygen of ceria in Pd/CeO2 catalysts with the reduced defect concentration became mobile, resulting in the facile reduction at the lower temperature. X‐ray diffraction, X‐ray photoelectron and X‐ray adsorption spectroscopies show that the improvement in the surface oxygen mobility does not originate from the change in PdOx particle size nor its oxidation state. As a result, the temperature of 50 % conversion of methane shifted by 25 °C to the lower temperature on Pd/CeO2 catalyst with the reduced defect concentration. This work highlights that the catalytic activity can be enhanced by promoting the active participation of the surface oxygen of support.

Enhancing Bifunctional Electrocatalytic Activities of Oxygen Electrodes via Incorporating Highly Conductive Sm3+ and Nd3+ Double-Doped Ceria for Reversible Solid Oxide Cells

Solid oxide cells (SOCs) are mutually convertible energy devices capable of generating electricity from chemical fuels including hydrogen in the fuel cell mode and producing green hydrogen using electricity from renewable but intermittent solar and wind resources in the electrolysis cell mode. An effective approach to enhance the performance of SOCs at reduced temperatures is by developing highly active oxygen electrodes for both oxygen reduction and oxygen evolution reactions. Herein, highly conductive Sm3+ and Nd3+ double-doped ceria (Sm0.075Nd0.075Ce0.85O2-δ, SNDC) is utilized as an active component for reversible SOC applications. We develop a novel La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF)-SNDC composite oxygen electrode. Compared with the conventional LSCF-Gd-doped ceria oxygen electrode, the LSCF-SNDC exhibits ∼35% lower cathode polarization resistance (0.042 Ω cm2 at 750 °C) owing to rapid oxygen incorporation and surface diffusion kinetics. Furthermore, the SOC with the LSCF-SNDC oxygen electrode and the SNDC buffer layer yields a remarkable performance in both the fuel cell (1.54 W cm-2 at 750 °C) and electrolysis cell (1.37 A cm-2 at 750 °C) modes because the incorporation of SNDC promotes the surface diffusion kinetics at the oxygen electrode bulk and the activity of the triple phase boundary at the interface. These findings suggest that the highly conductive SNDC material effectively enhances both oxygen reduction and oxygen evolution reactions, thus serving as a promising material in reversible SOC applications at reduced temperatures.

Pt current collectors artificially boosting praseodymium doped ceria oxygen surface exchange coefficients

Here, Pt current collectors were shown to dramatically increase the oxygen surface exchange coefficient (kchem) of Pr0.1Ce0.9O2−x, suggesting they are likely responsible for a significant portion of the kchem variation in the literature.

Mechanism and Nature of Active Sites for Methanol Synthesis from CO/CO2 on Cu/CeO2

CO2 hydrogenation to methanol can play an important role in meeting sustainability goals of the chemical industry. Herein, we investigated in detail the role of the Cu-CeO2 interactions for methanol synthesis, emphasizing the role of the copper surface and interface sites between copper and ceria for the hydrogenation of CO2 and CO. A combined CO2-N2O titration approach was developed to quantify the exposed metallic copper sites and ceria oxygen vacancies in reduced Cu/CeO2 catalysts. Extensive characterization shows that copper dispersion is strongly enhanced by strong Cu-CeO2 interactions in comparison to Cu/SiO2. CO2 hydrogenation activity data show that the Cu/CeO2 catalysts displayed higher methanol selectivity compared to a reference Cu/SiO2 catalyst. The improved methanol selectivity stems from inhibition of the reverse water-gas-shift activity. The role of CO in CO2-to-methanol conversion was studied by steady-state and transient co-feeding activity measurements together with (quasi) in situ characterization (TPH, XPS, SSITKA and IR spectroscopy). The Cu-CeO2 interface provides active sites for the direct hydrogenation of CO to methanol via a formyl intermediate. Co-feeding of small amounts of CO2 to a CO/H2 mixture poisons these interfacial sites due to the formation of carbonate-like species. Methanol synthesis proceeds mainly via CO2 hydrogenation in which the metallic Cu surface provides the active sites.