Perovskite Matrix Research Articles

Energy storage property of (Pb0.97La0.02)(Zr0.5Sn0.4Ti0.1)O3-(Na0.5Bi0.5)0.94Ba0.06TiO3 ceramics: Effects of antiferroelectric-relaxor transition and improved breakdown strength

(1-x)(Pb0.97La0.02)(Zr0.5Sn0.4Ti0.1)O3-x(Na0.5Bi0.5)0.94Ba0.06TiO3 (x = 0 ∼ 0.4) ceramics have been prepared and investigated. The ceramics consist of perovskite solid solution matrix and precipitated, isolated SnO2 particle, resulting in 0–3 type composite structure. With increasing x value, the room temperature crystal structure of perovskite solid solution transforms from tetragonal to pseudocubic, therefore, the electrical property evaluates form robust antiferroelectric at x = 0, metastable antiferroelectric at x = 0.1, and then relaxor ferroelectric at x > 0.1. Moreover, the breakdown strength is enhanced due to the composite structure and reaches maximum value of 190 kV/cm at x = 0.2. Both the phase transition and enhanced breakdown strength are helpful to improve energy storage property, the x = 0.2 ceramic shows largest recoverable energy density wrec of 1.84 J/cm3, discharge efficiency η of 86.6 %. Especially, both wrec and η illustrates significantly improved thermal stability within 25−125 °C.

Silver-Modified Ba1-xCo0.7Fe0.2Nb0.1O3-δ Perovskite Performing as a Cathodic Catalyst of Intermediate-Temperature Solid Oxide Fuel Cells.

A series of silver (Ag)-modified barium cobalt ferrous niobate (Ba1-xCo0.7Fe0.2Nb0.1O3-δ, BCFN) materials were fabricated using a solid-state method by doping silver cations into the A-site of this perovskite matrix (Ag-BCFN). The electrochemical analyses indicated that the Ag-BCFN cathodic catalysts performed superior to the nonmodified catalysts when applied in intermediate-temperature solid oxide fuel cells (IT-SOFCs). These Ag-BCFN cathodic catalysts displayed a cubic perovskite structure (PDF 75-0227, Pm3̅m, α = 90°) with a high degree of crystallinity, as demonstrated by X-ray powder diffraction analyses. It was also found that the in situ exsolution of the silver ion (Ag+) occurred, where 57.9% of doped Ag+ was reduced into metallic Ag particles with size ranging from 5 to 10 nm, as shown by electron microscopic analyses. The cerium gadolinium oxide (Ce0.9Gd0.1O2-δ) electrolyte-supported symmetrical half cell using different Ag-BCFN formulations of Ba1-xAgxCo0.7Fe0.2Nb0.1O3-δ as electrodes showed a polarization resistance as low as 0.233 Ω·cm2 and an exchange current density of 85.336 mA·cm-2 at 650 °C under ambient pressure. The improved electrochemical kinetics is anticipated to be attributed to two reasons: doping of ions (Ag+) in the A-site of perovskite and in situ exsolved silver nanoparticles (Ag NPs) along the edge and on the surface of BCFNs improving the mobile charge and electrical properties of the material. The remaining Ag+ in the A-site induced the electron redistribution, whereas the Ag NPs were found to increase the electrochemically active sites and enable the formation of a triple-phase boundary. These explanations were confirmed by the density functional theory study, indicating that Ag-doping processes lead to a decrease in the formation energy of oxygen vacancies from 1.72 to 1.42 eV upon the partial substitution of Ba2+ by Ag+ cations.

Three dimensional resistance mapping of self-organized Sr3V2O8 nanorods on metallic perovskite SrVO3 matrix

Self-organized epitaxial nanorods, obtained by an adapted annealing process after deposition of metallic strontium vanadate perovskite (SrVO3) thin films, are analyzed to determine their structural, chemical and electrical properties. After the identification of the Sr3V2O8 phase of the nanorods by electron diffraction; Electron Energy Loss Spectroscopy investigations show the vanadium oxidation state (V5+) for the nanorods. Two scanning probe techniques are deployed to determine the specific local electrical properties of these Sr3V2O8 nanorods. In ambient conditions, local electrical properties are studied by Scanning Spreading Resistance Microscopy based on an Atomic Force Microscope and multiple probe scanning tunneling microscopy is used for the study in ultrahigh vacuum. Both techniques reveal that local electrical resistances of the nanorods are five order of magnitude higher than the resistance of the perovskite SrVO3 matrix. Futhermore, the nanorods are found to be etched by repeating scanning of the conductive Atomic Force Microcopy probe, enabling a three-dimensional depth profile of the nanorods resistance with 3D-Spreading Resistance Microscopy mode. A partial embedding of the nanorods in the underlying SrVO3 film is proved and the impact of the water meniscus at the origin of the selective etching observed during Scanning Spreading Resistance Microscopy, in ambient conditions, is discussed.

Efficient near-infrared light-emitting diodes based on quantum dots in layered perovskite

Light-emitting diodes (LEDs) based on excitonic material systems, in which tightly bound photoexcited electron–hole pairs migrate together rather than as individual charge carriers, offer an attractive route to developing solution-processed, high-performance light emitters. Here, we demonstrate bright, efficient, excitonic infrared LEDs through the incorporation of quantum dots (QDs)1 into a low-dimensional perovskite matrix. We program the surface of the QDs to trigger fast perovskite nucleation to achieve homogeneous incorporation of QDs into the matrix without detrimental QD aggregation, as verified by in situ grazing incidence wide-angle X-ray spectroscopy. We tailor the distribution of the perovskites to drive balanced ultrafast excitonic energy transfer to the QDs. The resulting LEDs operate in the short-wavelength infrared region, an important regime for imaging and sensing applications, and exhibit a high external quantum efficiency of 8.1% at 980 nm at a radiance of up to 7.4 W Sr−1 m−2. Embedding perovskite quantum dots in perovskite leads to bright, efficient 980 nm LEDs with applications in imaging and sensing.

Efficient colloidal quantum dot light-emitting diodes operating in the second near-infrared biological window

Semiconductor colloidal quantum dots (CQDs) offer size- and composition-tunable luminescence of high colour purity. Importantly, their emission can be tuned deep into the second biological near-infrared (NIR-II) window (1,000–1,700 nm). However, applications are hindered by the low efficiencies achieved to date. Here, we report NIR-II CQD light-emitting diodes with an external quantum efficiency of 16.98% and a power conversion efficiency of 11.28% at wavelength 1,397 nm. This performance arises from device engineering that delivers a high photoluminescence quantum yield and charge balance close to unity. More specifically, we employed a binary emissive layer consisting of silica-encapsulated silver sulfide (Ag2S@SiO2) CQDs dispersed in a caesium-containing triple cation perovskite matrix that serves as an additional passivation medium and a carrier supplier to the emitting CQDs. The hole-injection contact also features a thin porphyrin interlayer to balance the device current and enhance carrier radiative recombination. Semiconductor nanocrystals with efficient tunable emission in the 1,000–1,700 nm window could prove useful for applications in deep biological imaging and sensing.

Blue luminescence of Bi3+ in the double perovskite CaLaMgTaO6 matrix for n-UV pumped white light-emitting diodes

A novel Bi3+ activated double perovskite CaLaMgTaO6 phosphor was synthesized and its photoluminescence properties were investigated. CaLaMgTaO6: Bi3+ could be efficiently excited in the wavelength range of 270–400 nm, and exhibit a blue emission band ascribing to the 3P1–1S0 transition of Bi3+. The maximum intensity of the excitation moves from 332 to 351 nm, and the emission band moves from 443 to 434 nm as the concentration of Bi3+ increases from 0.5 to 20 mol %, corresponding to the overlapped luminescence of Bi3+ substituting for La3+ and Ca2+ with substitution preference. Due to the energy transfer between Bi3+ ions, the concentration quenching of Bi3+ in the CaLaMgTaO6 host occurred when the concentration of Bi3+ exceeded 7.5 mol %. The energy transfer mechanism of CaLaMgTaO6: Bi3+ was estimated to be dipole-dipole interaction. Furthermore, the thermal stability of the phosphor was investigated and the corresponding activation energy ΔE was determined to be 0.26 eV. Due to the efficient excitation in near ultraviolet (n-UV) region and the strong blue emission, CaLaMgTaO6: Bi3+ would be a potential blue phosphor for n-UV pumped light-emitting diodes.

Physico-chemical properties and catalytic activity of the sol-gel prepared Ce-ion doped LaMnO3 perovskites

Ce-doped LaMnO3 perovskite ceramics (La1−xCexMnO3) were synthesized by sol-gel based co-precipitation method and tested for the oxidation of benzyl alcohol using molecular oxygen. Benzyl alcohol conversion of ca. 25–42% was achieved with benzaldehyde as the main product. X-ray diffraction (XRD), thermogravimetric analysis (TGA), BET surface area, transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), temperature-programmed reduction (H2-TPR), temperature-programmed oxidation (O2-TPO), FT-IR and UV-vis spectroscopic techniques were used to examine the physiochemical properties. XRD analysis demonstrates the single phase crystalline high purity of the perovskite. The Ce-doped LaMnO3 perovskite demonstrated reducibility at low-temperature and higher mobility of surface O2-ion than their respective un-doped perovskite. The substitution of Ce3+ ion into the perovskite matrix improve the surface redox properties, which strongly influenced the catalytic activity of the material. The LaMnO3 perovskite exhibited considerable activity to benzyl alcohol oxidation but suffered a slow deactivation with time-on-stream. Nevertheless, the insertion of the A site metal cation with a trivalent Ce3+ metal cation led to an enhanced in catalytic performance because of atomic-scale interactions between the A and B active site. La0.95Ce0.05MnO3 catalyst demonstrated the excellent catalytic activity with a selectivity of 99% at 120 °C.

An Amorphous Nickel-Iron-Based Electrocatalyst with Unusual Local Structures for Ultrafast Oxygen Evolution Reaction.

Rationally designing active and durable catalysts for the oxygen evolution reaction (OER) is of primary importance in water splitting. Perovskite oxides (ABO3 ) with versatile structures and multiple physicochemical properties have triggered considerable interest in the OER. The leaching of A site cations can create nanostructures and amorphous motifs on the perovskite matrix, thus facilitating the OER process. However, selectively dissolving A site cations and simultaneously obtaining more active amorphous motifs derived from the B site cations remains a great challenge. Herein, a top-down strategy is proposed to transform bulk crystalline perovskite (LaNiO3 ) into a nanostructured amorphous hydroxide by FeCl3 post-treatment, resulting in an extremely low overpotential of 189 mV at 10 mA cm-2 . The top-down-constructed amorphous catalyst with a large surface area has dual NiFe active sites, where high-valence Ni3+ -based edge-sharing octahedral frameworks are surrounded by interstitial distorted Fe octahedra and contribute to the superior OER performance. This top-down strategy provides a valid way to design novel perovskite-derived catalysts.

Benefiting from Spontaneously Generated 2D/3D Bulk-Heterojunctions in Ruddlesden-Popper Perovskite by Incorporation of S-Bearing Spacer Cation.

2D Ruddlesden–Popper (RP) perovskite solar cells have manifested superior operation durability yet inferior charge transport compared to their 3D counterparts. Integrating 3D phases with 2D RP perovskites presents a compromise to maintain respective advantages of both components. Here, the spontaneous generation of 3D phases embedded in 2D perovskite matrix is demonstrated at room temperature via introducing S‐bearing thiophene−2−ethylamine (TEA) as both spacer and stabilizer of inorganic lattices. The resulting 2D/3D bulk heterojunction structures are believed to arise from the compression‐induced epitaxial growth of the 3D phase at the grain boundaries of the 2D phase through the Pb−S interaction. The as‐prepared 2D TEA perovskites exhibit longer exciton diffusion length and extended charge carrier lifetime than the paradigm 2D phenylethylamine (PEA)‐based analogues and hence demonstrate an outstanding power conversion efficiency of 7.20% with significantly increased photocurrent. Dual treatments by NH4Cl and dimethyl sulfoxide are further applied to ameliorate the crystallinity and crystal orientation of 2D perovskites. Consequently, TEA‐based devices exhibit a stabilized efficiency over 11% with negligible hysteresis and display excellent ambient stability without encapsulation by preserving 80% efficiency after 270 h storage in air with 60 ± 5% relative humidity at 25 °C.

Perovskite-WS2 Nanosheet Composite Optical Absorbers on Graphene as High-Performance Phototransistors.

High-responsivity phototransistors with a structure of perovskite-WS2 nanosheet composite optical absorber and a reduced graphene oxide (rGO) channel layer is demonstrated via a facile and low-cost solution-processing method. The WS2 nanosheets are dispersed within the perovskite matrix, forming the perovskite-WS2 bulk heterojunction (BHJ). The hybrid phototransistor exhibits excellent figures of merit including high photoresponsivity of 678.8 A/W, high specific detectivity of 4.99 × 1011 Jones, high EQE value of 2.04 × 105% and rapid response to photoswitching. The high photoresponsivity could be attributed to the WS2 nanosheets induced photo-generated electron-hole separation promotion effects due to the selective electron trapping effects in the WS2 nanosheets, together with the high carrier mobility of the rGO channel. This work provides a promising platform for constructing high-responsivity photodetectors.

Enhanced magnetoelectric response in bismuth-deficient BiFeO3-BaTiO3 ceramics

The magnetoelectric response of the bismuth-deficient BiFeO3-BaTiO3 ceramics fabricated using a conventional solid-state reaction method was investigated. We found that a ferromagnetic BaFe12O19 phase is produced as a consequence of bismuth-deficiency (Bi-deficiency) and that the ceramics are 0–3 composites of BaFe12O19 and BiFeO3-based perovskite. An enhanced magnetoelectric response can be achieved in Bi-deficient composites as a consequence of the coupling between magnetostriction in the BaFe12O19 phase and the piezoelectric effect in the BiFeO3-based perovskite phase. In comparison with the composite ceramics prepared using a direct mixing method for the two components, Bi-deficient ceramics have a more uniform distribution of the BaFe12O19 phase in the perovskite matrix and a reduction in dielectric loss and conduction. Thus, the magnetoelectric response of Bi-deficient ceramics is greater than that of ceramics fabricated using a direct mixing method. Our work presents a simple approach for the fabrication of BiFeO3-based composite ceramics with uniformly distributed ferromagnetic particles and enhanced ferromagnetic and magnetoelectric responses.

Cooperative Co0 /CoII Sites Stabilized by a Perovskite Matrix Enable Selective C-O and C-C bond Hydrogenolysis of Oxygenated Arenes.

Strontium-substituted lanthanum cobaltite (La0.8 Sr0.2 CoO3 ) matrix-stabilized Co0 /CoII catalytic sites were prepared, which present tunable C-O and C-C hydrogenolysis activity for the vapor-phase upgrading of oxygenated arenes. CoII sites associated with oxygen vacancies were favored at low temperatures and performed selective C-O hydrogenolysis, in which Sr-substitution facilitated oxygen vacancy formation, leading to approximately 10 times higher reactivity compared to undoped LaCoO3 . Co0 sites were favored at high temperatures and performed extensive C-C bond hydrogenolysis, generating a wide range of alkanes. The lower reaction order with P (1.1±0.1) for C-C hydrogenolysis than for C-O hydrogenolysis (2.0±0.1) led to a high selectivity towards C-C hydrogenolysis at low P . The Co3 O4 surfaces featured a narrower temperature window for obtaining the respective optimal CoII and Co0 pairs compared to analogous perovskite surfaces; whereas, the perovskite matrix stabilizes these pairs for selective C-O and C-C hydrogenolysis. This stabilization effect offers an additional handle to control reactivity in oxide catalysts.

Oxygen selective perovskite hollow fiber membrane bundles

Perovskite ceramic hollow fiber membranes (HFMs) have attracted great interest due to their potential application as the novel cost-effective method for oxygen production and favorable features for compact module preparation. However, the practical application of these perovskite HFMs is limited by the inherent brittleness of ceramic material and in cases of thick fiber wall, the insufficient oxygen flux values. In this work, highly asymmetric BaCo0.85Bi0.05Zr0.1O3-δ (BCBZ) perovskite HFMs with a thin dense separation layer supported on the porous BCBZ substrate were fabricated by a modified phase inversion-sintering technique. The perovskite HFMs were integrated in a porous BCBZ perovskite matrix to form a bundle structure to simultaneously achieve high mechanical strength for membrane assembly and high O2 permeation rate. Pure O2 was achieved from air separation by vacuuming the permeate side of the hollow fiber bundles (HFBs). Oxygen recovery rate is a function of multi-factors including operation temperature, air feeding flow rate and the membrane area provided by the HFBs. The thermal cycle and post characterization results of the spent HFBs highlight the good stability of the fabricated HFBs. Oxygen permeation rate increased with the HFM number in the HFBs. Under static air atmosphere and the operation mode of vacuum application, the permeation rate of HFBs containing 3 HFMs (HFB_3) or 7 HFMs (HFB_7) at 1000 °C was 79.01 or 98.12 mL min−1, respectively. Normalized by the overall membrane area, the achieved oxygen flux for HFB_3 or HFB_7 was 13.27 or 7.06 mL cm−2 min−1, respectively, the difference of which is attributed to the limited air convection resulting in the insufficient oxygen supply in the feed once it is extracted.

Laser Emission from Self-Assembled Colloidal Crystals of Conjugated Polymer Particles in a Metal-Halide Perovskite Matrix

Here, we present a hybrid organic/inorganic photonic composite, which generates laser emission from the organic material after pumping the inorganic component. The composite consists of a methylammonium lead-halide perovskite matrix CH3NH3Pb(BrxCl(1–x))3 and monodisperse poly(fluorene-co-divinylbenzene) particles, which have excellent optical feedback and gain. Micrometer-sized conjugated polymer particles (CPPs) are deposited together with the perovskite precursor from solution using a single-step vertical deposition method. The particles self-assemble into a photonic crystal and the perovskite forms an inorganic matrix in the interstitial space. Energy transfer to the polymer particles after optically pumping the metal-halide perovskite is studied in two systems with different halide ratios in the perovskite (Br to Cl: 1/9 and 4/6) to control the overlap of the perovskite emission energy with the absorption of the particles. From time-resolved photoluminescence experiments, we observe nonradiative energ...

Enhancement of energy storage density in antiferroelectric PbZrO3 films via the incorporation of gold nanoparticles

AbstractIn this work, antiferroelectric Au–PbZrO3 (Au–PZO) nanocomposite thin films were prepared by chemical solution deposition (CSD), and the effects of Au concentration on the antiferroelectric properties and the recoverable energy density were investigated. The results showed that the optimal Au concentration in the Au–PZO nanocomposite thin films was about 1 mol% for structural and electric properties. In the Au–PZO nanocomposite thin films with 1 mol% Au, Au nanoparticles (NPs) were distributed uniformly in the perovskite PZO matrix. Moreover, the recoverable energy density was 10.8 J/cm3 at 600 kV/cm, which is 42% higher than that of the pure PZO films. The results demonstrate that adding an appropriate amount of noble metal NPs in antiferroelectric thin films is an effective method to improve the energy storage properties.

Integration of sputter-deposited multiferroic CoFe2O4–BiFeO3 nanocomposites on conductive La0.7Sr0.3MnO3 electrodes

The structure, magnetic and ferroelectric properties of sputtered epitaxial CoFe2O4-BiFeO3 (CFO-BFO) nanocomposite thin films grown on La0.7Sr0.3MnO3 (LSMO) layers on (001) oriented SrTiO3 (STO) substrates and on STO-buffered Si are described. The as-grown LSMO thin films were smooth and poorly conductive but the resistivity was reduced and the surfaces roughened after annealing. Cosputtered CFO and BFO on STO formed vertically aligned nanostructures consisting of epitaxial spinel CFO pillars within a perovskite BFO matrix, but the rough surface of the annealed LSMO film promoted additional CFO pillar orientations. A reorientation of the CFO magnetic easy axis to an in-plane direction occurred as the LSMO became thicker due to changes in the strain state of the CFO pillars. The LSMO underlayer enabled the ferroelectric response of the BFO to be measured. Nanocomposites were grown onto LSMO/SrTiO3/Si which provides a path towards large scale integration of electrically contacted nanocomposites on Si.

Temperature-dependent photoluminescence in hybrid iodine-based perovskites film

Lead halide perovskite has attracted much attention due to its high absorption coefficient, long carrier diffusion length, low binding energy, and low cost. The stability of intrinsic crystal structure in I-based perovskite can be theoretically estimated by calculating cubic structures factor and octahedral factor. Experimental methods to solve the stability of structure in I-based perovskite could be mainly to either incorporate anions (e.g. Cl<sup>–</sup>, Br<sup>–</sup>) or mix cations (e.g. Cs<sup>+</sup>) into I-based perovskite matrix. Moreover, incorporating Br<sup>–</sup> into I-based perovskite leads its band gap to widen, which might be used as a top-cell material to tandem solar cell. However, in order to understand photo-physics process of anion-mixed and/or cation-mixed perovskites, it is essential to further investigate the optical properties such as absorption spectrum, photoluminescence (PL), temperature-dependent PL (TPL) behavior, etc. In this work, anion-mixed and/or cation-mixed perovskite thin films with high quality crystallization and (110) prereferral orientation are synthesized by one-step solution method. All mixed perovskite films are characterized by using X-ray diffraction (Rigaku D MAX-3C, Cu-Kα, <i>λ</i> = 1.54050 Å) and X-ray photoelectron spectroscopy (XPS) (Thermo Scientific Escalab 250Xi). A set of strong peaks of the mixed perovskite films at 14.12° and 28.48°, is assigned to (110) and (220) lattice plane of orthorhombic crystal structure of I-based perovskite, due to preferred orientation. The Pb 4f and I 3d doublet peaks, corresponding to Pb<sup>+2</sup> and I<sup>–</sup> states, are observed in XPS spectra. It should be noted that in the absence of other valence states of Pb and I component at lower/upper binding energy, the chemical element composition ratio of Pb<sup>+2</sup> and I<sup>–</sup> are close to stoichiometric proportion. For optical absorptionspectra, the optical bandgaps of the perovskite films increase with doping concentration of Br<sup>–</sup> increasing. For TPL, the perovskite films with <i>x</i> = 0 and <i>x</i> = 0.05 show abnormal red-shifts in a temperature range from 10 to 100 K. The following blue shifts in a temperature range from 125 to 350 K emerge, which is mainly attributed to band gap widening. However, incorporating more Br<sup>–</sup> into I-based perovskite leads the TPL spectra to monotonically blue-shift. A linear relationship between the TPL peak position and the doping concentration of Br<sup>–</sup> ions is observed at the same temperatures. This indicates that the Br<sup>–</sup> anion in I-based perovskite plays a crucial role in determining the optical properties. The low-temperature and high-temperature (HT) excitonic binding energy at <i>x</i> = 0 are 186 meV and 37.5 meV, respectively. The HT excitonic binding energy first increases and then decreases with the Br<sup>–</sup> concentration in I-based perovskite film increasing. The minimal variation of TPL peak position and FWHM (full width at half maximum) at <i>x</i> = 0.0333 are 13 nm and (25.8 ± 0.5) meV, respectively, suggesting higher temperature stability in optical property. This should contribute to understanding the relationship between temperature-dependent electrical and optoelectronic performance for hybrid mixed perovskite materials and devices.

Thermal conductivity in self-assembled CoFe2O4/BiFeO3 vertical nanocomposite films

The thermal conductivity of self-assembled nanocomposite oxide films consisting of cobalt ferrite (CFO) spinel pillars grown within a single-crystal bismuth ferrite (BFO) perovskite matrix is described as a function of the volume fraction of the spinel. Single phase BFO and CFO had cross-plane thermal conductivities of 1.32 W m−1 K−1 and 3.94 W m−1 K−1, respectively, and the thermal conductivity of the nanocomposites increased with the CFO volume fraction within this range. A small increase (∼5%) in thermal conductivity for the pure CFO phase in the AC-demagnetized state was observed, suggesting possible magnon contributions. Steady state gray-medium based variance-reduced Monte Carlo simulations show consistent trends with experimental data on the dependence of thermal conductivity with the CFO volume fraction.

In situ encapsulation of iron(0) for solar thermochemical syngas production over iron-based perovskite material

Methane-to-syngas conversion plays an important role in industrial gas-to-liquid technologies, which is commercially fulfilled by energy-intensive reforming methods. Here we present a highly selective and durable iron-based La0.6Sr0.4Fe0.8Al0.2O3-δ oxygen carrier for syngas production via a solar-driven thermochemical process. It is found that a dynamic structural transformation between the perovskite phase and a Fe0@oxides core–shell composite occurs during redox cycling. The oxide shell, acting like a micro-membrane, avoids direct contact between methane and fresh iron(0), and prevents coke deposition. This core–shell intermediate is regenerated to the original perovskite structure either in oxygen or more importantly in H2O–CO2 oxidant with simultaneous generation of another source of syngas. Doping with aluminium cations reduces the surface oxygen species, avoiding overoxidation of methane by decreasing oxygen vacancies in perovskite matrix. As a result, this material exhibits high stability with carbon monoxide selectivity above 95% and yielding an ideal syngas of H2/CO ratio of 2/1.

Reversible Segregation of Ni in LaFe0.8Ni0.2O3±δ During Coke Removal

AbstractThe deactivation of supported nickel catalysts by coking is an important technological subject for many chemical processes, especially when high concentrations of unsaturated hydrocarbons are present in the feed gas. Here, the reversible segregation of Ni from a LaFeO3±δ perovskite‐type host lattice was exploited to completely recover a LaFe0.8Ni0.2O3±δ catalyst after it had been deliberately subjected to severe carbon deposition during CO2 methanation in ethylene rich feed gas for several hours. Temperature programmed reduction, X‐ray diffraction, electron microscopy, X‐ray absorption spectroscopy and catalytic activity tests were used to follow the catalyst structure along the various steps of reduction, reaction, coking and subsequent regeneration, while Raman spectroscopy and electron microscopy were used to characterize the nature of the carbon deposits. It is shown that upon reduction Ni atoms segregate to the surface of the perovskite to form catalytic active Ni particles. Oxidation stimulates Ni atoms to readopt the coordination environment of Fe in the perovskite matrix. This property persisted after severe catalyst deactivation by filamentous, partially graphitic carbon. It is demonstrated that simple catalyst reoxidation can be applied to oxidize all carbon deposits while additionally reverting segregated Ni back into the host lattice, thus protecting Ni from particle growth and resultant long‐term loss of catalyst activity over multiple regeneration cycles.