Perovskite-type Catalysts Research Articles

Biomass to hydrogen-rich syngas via catalytic steam reforming of bio-oil

Hydrogen-rich syngas production from the catalytic steam reforming of bio-oil from fast pyrolysis of pinewood sawdust was investigated by using La1−xKxMnO3 perovskite-type catalysts. The effects of the K substitution, temperature, water to carbon molar ratio (WCMR) and bio-oil weight hourly space velocity (WbHSV) on H2 yield, carbon conversion and the product distribution were studied in a fixed-bed reactor. The results showed that La1−xKxMnO3 perovskite-type catalysts with a K substitution of 0.2 gave the best performance and had a higher catalytic activity than the commercial Ni/ZrO2. Both high temperature and low WbHSV led to higher H2 yield. However, excessive steam reduced hydrogen yield. For the La0.8K0.2MnO3 catalyst, a hydrogen yield of 72.5% was obtained under the optimum operating condition (T = 800 °C, WCMR = 3 and WbHSV = 12 h−1). The deactivation of the catalysts mainly was caused by coke deposition.

Synthesis of high surface area CaxLa(1−x)Al(1−x)MnxO(3−δ) perovskite oxides for oxygen reduction electrocatalysis in alkaline media

Performance tradeoffs related to surface area, compositional homogeneity at the oxide surface, and oxygen reduction reaction activity are discussed for perovskite oxide type catalysts synthesized using solid state reaction, hybrid sol–gel, and aerogel synthesis techniques.

Elemental mercury oxidation over manganese-based perovskite-type catalyst at low temperature

La1−xSrxMnO3 (LSx, x=0/0.2/0.4/0.6) perovskite-type oxides catalysts were synthesized for elemental mercury (Hg0) oxidation in simulated coal-fired flue gas at low temperature. LS0.4 exhibited superior catalytic behavior for Hg0 oxidation at 100–200°C. The superior performance was mainly due to the surface adsorbed oxygen species in the catalysts. Effects of different components in the flue gas including HCl, O2, SO2, H2O, NO and NH3 on Hg0 oxidation efficiencies were studied. The results suggested that HCl significantly enhanced Hg0 oxidation efficiency in the presence of O2 and 10ppmv HCl was sufficient for enhancing the oxidation process. As the catalyst had strong oxygen storage capacity, the Hg0 oxidation activity was less dependent on O2 concentration. As a result, the catalyst could be applied in the power plants burning low-chlorine coals. SO2, H2O and NH3 had inhibitory effect on Hg0 oxidation, while NO enhanced it. SO2 could deactivate the catalyst and the deactivation was irreversible. In terms of mechanism, Hg0 oxidation with LSx could be explained by the suprafacial process (Langmuir–Hinshelwood mechanism) whereby reactive species from adsorbed flue gas components reacted with adsorbed Hg0. The catalyst also had potential for selective catalytic reduction (SCR) of NO with NH3 at low temperature, and the simultaneous removal of NO and Hg0 over LS0.4 was investigated. The NO and Hg0 conversion were higher than 50% and 85% when the space velocity was 40,000h−1, respectively. The results indicated that the catalyst might be used to remove NO and Hg0 simultaneously after the cold-side electrostatic precipitators in flue gas with low concentration of ash.

Catalytic activities of supported perovskite promoter catalysts La2NiMnO6–CuCl2/γ-Al2O3 and La1.7K0.3NiMnO6–CuCl2/γ-Al2O3 for ethane oxychlorination

Supported perovskite promoted catalysts La2NiMnO6–CuCl2/γ-Al2O3 and La1.7K0.3NiMnO6–CuCl2/γ-Al2O3 were prepared by mechanical mixing method, and characterized by XRD, H2-TPR, XRF, XPS and magnetization techniques. The catalyst doped with potassium La1.7K0.3NiMnO6–CuCl2/γ-Al2O3 possesses a large amount of Mn4+ and surface-adsorbed oxygen species, which accelerate the oxidation of Cu+ by a circular reaction and increase the release of Cl2, and therefore promote the conversion of C2H6 and the selectivity to C2H3Cl. The catalyst La1.7K0.3NiMnO6–CuCl2/γ-Al2O3 shows better catalytic activity for ethane oxychlorination with the C2H6 conversion of 100% and the C2H3Cl selectivity to 59.4%. The total selectivity to C2H4 and C2H3Cl maintains over 81% in 95h. This study points out a potential way to develop more active perovskite-type oxide catalysts for ethane oxychlorination.

Hierarchical Mesoporous/Macroporous Perovskite La0.5Sr0.5CoO3-x Nanotubes: A Bifunctional Catalyst with Enhanced Activity and Cycle Stability for Rechargeable Lithium Oxygen Batteries.

Perovskites show excellent specific catalytic activity toward both oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) in alkaline solutions; however, small surface areas of the perovskites synthesized by traditional sol-gel methods lead to low utilization of catalytic sites, which gives rise to poor Li-O2 batteries performance and restricts their application. Herein, a hierarchical mesporous/macroporous perovskite La0.5Sr0.5CoO3-x (HPN-LSC) nanotube is developed to promote its application in Li-O2 batteries. The HPN-LSC nanotubes were synthesized via electrospinning technique followed by postannealing. The as-prepared HPN-LSC catalyst exhibits outstanding intrinsic ORR and OER catalytic activity. The HPN-LSC/KB electrode displays excellent performance toward both discharge and charge processes for Li-O2 batteries, which enhances the reversibility, the round-trip efficiency, and the capacity of resultant batteries. The synergy of high catalytic activity and hierarchical mesoporous/macroporous nanotubular structure results in the Li-O2 batteries with good rate capability and excellent cycle stability of sustaining 50 cycles at a current density of 0.1 mA cm(-2) with an upper-limit capacity of 500 mAh g(-1). The results will benefit for the future development of high-performance Li-O2 batteries using hierarchical mesoporous/macroporous nanostructured perovskite-type catalysts.

Biomass to hydrogen-rich syngas via catalytic steam gasification of bio-oil/biochar slurry

The catalytic steam gasification of bio-oil/biochar slurry (bioslurry) for hydrogen-rich syngas production was investigated in a fixed-bed reactor using LaXFeO3 (X=Ce, Mg, K) perovskite-type catalysts. The effects of elemental substitution in LaFeO3, temperature, water to carbon molar ratio (WCMR) and bioslurry weight hourly space velocity (WbHSV) were examined. The results showed that La0.8Ce0.2FeO3 gave the best performance among the prepared catalysts and had better catalytic activity and stability than the commercial 14wt.% Ni/Al2O3. The deactivation caused by carbon deposition and sintering was significantly depressed in the case of La0.8Ce0.2FeO3 catalyst. Both higher temperature and lower WbHSV contributed to more H2 yield. The optimal WCMR was found to be 2, and excessive introducing of steam reduced hydrogen yield. The La0.8Ce0.2FeO3 catalyst gave a maximum H2 yield of 82.01% with carbon conversion of 65.57% under the optimum operating conditions (temperature=800°C, WCMR=2 and WbHSV=15.36h−1).

Enhancement of ethylbenzene dehydrogenation of perovskite-type BaZrO3 catalyst by a small amount of Fe substitution in the B-site

The purpose of this study was to clarify the effect of a transition metal (Mn, Fe, Co) substitution in the BaZrO3 catalyst on the performance of ethylbenzene dehydrogenation (EBDH) with steam. The BaZrO3 catalyst showed a high performance for the EBDH without steam, however the co-feeding of steam produced a significant decrease in the EBDH activity. By partially substituting the Zr site in the BaZrO3 catalyst with Mn or Fe, the dehydrogenation activity was dramatically improved, while the Co-substituted catalyst showed a significantly low activity. In particular, the Fe substitution of a small percentage from 2 to 4% was effective for the drastic enhancement of the EBDH performance with steam. Comparing the styrene yield over the BaFe0.02Zr0.98O3 catalyst with that over the industrial potassium-promoted iron oxide (Fe–K) catalyst, the BaFe0.02Zr0.98O3 catalyst produced a higher styrene yield than the Fe–K catalyst. From the ESR measurement, we found that the Fe-substituted BZO catalyst had the defect–dipole (Fe3+–Vox) in its structure after EBDH with steam. Highly-active BaFe0.02Zr0.98O3 catalyst had a large amount of the defect–dipole and therefore an increase of the oxygen mobility. On the other hand, although low-active catalyst had a large amount of the defect–dipole, but the non-uniformity in the environment of the defect–dipole was increased. Such differences might cause a redox property and a performance for EBDH with steam. The drastic change in activity and environment around the oxygen defect by a small amount of Fe substitution is reported for the first time in the field of perovskite catalysts.

The effect of promoters in La0.9M0.1Ni0.5Fe0.5O3 (M = Sr, Ca) perovskite catalysts on dry reforming of methane

Nickel-based catalysts are typically used for syngas production via reforming reactions. The reforming of methane using carbon dioxide, called dry reforming of methane (DRM), is an effective way to produce syngas from these two notable greenhouse gases. However, Ni-based catalysts used for DRM undergo severe coke deposition. In the current study, perovskite-type oxide catalysts were prepared using the modified EDTA-cellulose method and characterized by the N2 physisorption, TPR, CO2-TPD, XRD, TGA, SEM and TEM-EDX techniques. The influence of partial substitution of La by Sr/Ca was investigated in the dry reforming reaction for the production of synthesis gas, and the basicity of the catalysts was varied by substituting the A site with either Sr or Ca, which modified the catalytic activity under the tested conditions. It was found that the perovskite catalysts demonstrated superior carbon resistance during the reaction, with La0.9Ca0.1Ni0.5Fe0.5O3 catalyst exhibiting the best catalytic performance among the prepared perovskite catalysts.

Cyanosilylation of benzaldehyde with TMSCN over perovskite-type oxide catalyst prepared by thermal decomposition of heteronuclear cyano complex precursors

The perovskite-type oxide catalyst, SmFeO3, prepared by decomposition method of heteronuclear cyano complex precursor (CN method) was applied to liquid-phase organic reaction, cyanosilylation of benzaldehyde with TMSCN. The maximum catalytic activity per catalyst weight was achieved at 800 °C of calcination temperature in CN method and it was found that the catalytic activity was strongly related to the crystallinity of SmFeO3 catalyst. The catalytic reaction performed in the presence of pyridine and 2,6-di-tert-butylpyridine suggests that the catalytically active sites are the Bronsted acid sites formed on the SmFeO3 catalyst. The catalytic activity of SmFeO3 catalyst prepared by CN method was much higher than those of acid catalysts: SiO2–Al2O3 and Amberlyst.

Characterization of supported Ni catalysts for aqueous-phase reforming of glycerol

The aqueous phase reforming (APR) over supported nickel-based catalysts was investigated as a feasibility study for hydrogen production from glycerol, byproduct of biodiesel produced by trans-esterification of triglycerides. Four different Ni-supported catalysts (Ni/LaAlO3, Ni/CeO2, Ni/MgO, and Ni/MgAl) were examined for the glycerol reforming in terms of the catalytic activities and the level of resistance. The APR of glycerol over Ni-supported catalysts showed that the conversion of glycerol to gas and H2 selectivity were strongly dependent on the support and amount of Ni loading. A perovskite type catalyst, Ni/LaAlO3, showed the highest reforming performance and good stability. A perovskite-type catalyst showed the glycerol conversion to 36% and the maximum value of H2 and CO2 selectivity to 96% and 81%. And the reforming gas composition in gas phase was measured to H2 61%, CO2 32%, CH4 6%, and CO 1% in the APR over Ni/LaAlO3. Comparison results of the reported results showed that Ni supported catalysts in the present study showed good performance for the APR to produce hydrogen from renewable resources.

Effects of polyvinyl-pyrrolidone in a polyol method on preparation of a perovskite-type catalyst for steam-CO2 reforming of methane

A La0.8Sr0.2NiO3 perovskite-type catalyst was investigated to develop a stable catalyst for methane steam-CO2 reforming (SCR) in a gas to liquid-floating production storage and offloading process. The perovskite-type catalyst, supported on α-Al2O3, was prepared by a polyol method. The effect of the concentration of polyvinyl-pyrrolidone (PVP) on its reducibility, structural properties, and prevention of carbon deposition was characterized by X-ray diffraction (XRD), H2-temperature programmed reduction (H2-TPR), Fourier transform infrared spectrometry (FT-IR), scanning electron microscope (SEM), and thermogravimetric analysis (TGA). We also conducted methane SCR using the catalysts. At 1 M PVP, the perovskite structure was established completely without impurities; thus, it demonstrated the highest catalytic activity, 73.3% and 46.9% for CH4 and CO2 conversions, respectively. After the reaction, the weight fraction of carbon deposition on the perovskite catalyst was 0.3–0.4% and 1.9% on the Ni catalyst, which indicates that the perovskite-type catalyst superiorly suppresses carbon deposition during methane SCR.

Effect of A-site substitution in perovskites: Catalytic properties of PrMnO3 and Ba/K/Ce substituted PrMnO3 for CO and PM oxidation

ABO3 type perovskite based catalysts with PrMnO3 composition and its A site substituted variants Pr0.8A0.2MnO3+δ/−δ (A=Ba or K or Ce) have been synthesized by sol–gel method. A systematic study has been carried out to understand the change in physicochemical properties, catalytic properties and related mechanistic aspects of the A site substituted ABO3 type perovskite materials with the help of XRD, BET-SA, SEM, XPS and H2-TPR techniques. These studies have inferred the altered oxidation states of B site cation Mn, as well as change in overall redox properties of PrMnO3, as a function of A site substitution. On the other hand, to study the impact on catalytic properties, these catalysts have been evaluated for two different reactions namely, CO and PM oxidation. The substitution/promotion of alkali metal (K) at A site of the PrMnO3 decreases its catalytic activity towards CO oxidation. However, Ba and Ce substitution in PrMnO3 enhanced the CO oxidation activity. The catalytic activity for PM oxidation was prominently enhanced with the substitution of K at the A site of PrMnO3 as well as with that of Ba and Ce substitutions. XRD, BET-SA, XPS and TPR data enabled to correlate the material properties with the catalytic activity, pointing out the role of substitution element with different valence state. The structure–property correlation for these two different reactions therefore, brings out certain findings about the role of substituted cation in PrMnO3 perovskite type catalysts.

Methane partial oxidation over a LaCr0.85Ru0.15O3 catalyst: Characterization, activity tests and kinetic modeling

A new LaCr0.85Ru0.15O3 perovskite-type catalyst for CH4 partial oxidation with a high activity and selectivity for syngas with good thermal stability and resistance against coking has been developed. In this paper, the catalyst preparation method, catalyst characterization, results of catalytic tests in a micro-reactor and kinetic modeling are discussed. A partial incorporation of Ru in the perovskite support has been demonstrated which can be responsible for the reported high activity and stability for this catalyst. Reactivity tests have been carried out at both low and high GHSV regimes (≈1–2×107h−1); for the latter case the CH4–O2 partial oxidation reaction system has been studied at incomplete methane (7–18%) and O2 (20–65%) conversion, as rarely reported in the literature. The variation of temperature (650–850°C) and feed gas composition (in terms of CH4, CO, CO2, H2 and H2O inlet partial pressure) allowed to study the reaction system over a wide range of experimental conditions gaining insight in the reaction mechanism. A kinetic model is proposed where CH4 partial oxidation, H2 and CO oxidation and water–gas shift are used to describe the involved lumped reaction network. External diffusion resistances have been found to be negligible whereas internal diffusion resistances have been accounted for by means of a single particle model able to describe the concentration profiles inside the catalyst pellet. Pre-exponential factors and activation energy values for all reactions have been estimated by means of a least square fitting of the experimental data. It is found that CH4 partial oxidation dominates the first region of the catalyst bed while H2 and CO oxidation become important in the remaining part of the bed.

Dopant Effect of Barium Zirconate-Based Perovskite-Type Catalysts for the Intermediate-Temperature Reverse Water Gas Shift Reaction

The reverse water gas shift (RWGS) reaction catalyzed by barium zirconate-based perovskite-type catalysts doped with Y, Zn, and Ce was investigated in terms of activities and chemical stabilities of various catalysts. All of the catalysts showed stable performances for the RWGS reaction at 600 °C for 5 h, and in particular, the BaZr0.8Y0.16Zn0.04O3 (BZYZ) catalyst showed an outstanding activity with an average CO2 conversion of 37.5% and a CO selectivity of 97%. Insertion of additional Ce into the BZYZ structure did not have any positive effect on catalytic activity for the RWGS reaction, even though the ionic conductivity of BZYZ was improved by Ce insertion.

Perovskite Catalysts—A Special Issue on Versatile Oxide Catalysts

Perovskite-type catalysts have been prominent oxide catalysts for many years due to attributes such as flexibility in choosing cations, significant thermal stability, and the unique nature of lattice oxygen. Nearly 90% metallic elements of the Periodic Table can be stabilized in perovskite’s crystalline framework [1]. Moreover, by following the Goldschmidt rule [2], the A- and/or B-site elements can be partially substituted, making perovskites extremely flexible in catalyst design. One successful example is the commercialization of noble metal-incorporated perovskites (e.g., LaFe0.57Co0.38Pd0.05O3) for automotive emission control used by Daihatsu Motor Co. Ltd. [3]. Thus, growing interest in, and application of perovskites in the fields of material sciences, heterogeneous catalysis, and energy storage have prompted this Special Issue on perovskite catalysts. [...]

Self-cleaning perovskite type catalysts for the dry reforming of methane

Gas-to-liquid processes are generally used to convert natural gas or other gaseous hydrocarbons into liquid fuels via an intermediate syngas stream. This includes the production of liquid fuels from biomass-derived sources such as biogas. For example, the dry reforming of methane is done by reacting CH4 and CO2, the two main components of natural biogas, into more valuable products, i.e., CO and H2. Nickel containing perovskite type catalysts can promote this reaction, yielding good conversions and selectivities; however, they are prone to coke laydown under certain operating conditions. We investigated the addition of high oxygen mobility dopants such as CeO2, ZrO2, or YSZ to reduce carbon laydown, particularly using reaction conditions that normally result in rapid coking. While doping with YSZ, YDC, GDC, and SDC did not result in any improvement, we show that a Ni perovskite catalyst (Na0.5La0.5Ni0.3Al0.7O2.5) doped with 80.9 ZrO2 15.2 CeO2 gave the lowest amount of carbon formation at 800 °C and activity was maintained over the operating time.

Direct NO decomposition over C-type cubic Y2O3–Pr6O11–Eu2O3 solid solutions

C-type cubic Y2O3–Pr6O11–Eu2O3 solid solutions were synthesized by a co-precipitation method and their catalytic activities for direct NO decomposition were investigated. Among the catalysts synthesized, the (Y0.78Pr0.15Eu0.07)2O3±δ catalyst exhibited high NO decomposition activity; NO conversion to N2 was as high as 84% at 900°C in the absence of O2 (NO/He atmosphere). This catalyst also sustained a high level of NO conversion even in the presence of O2 or CO2, compared with those of the conventional perovskite-type catalyst for direct NO decomposition.

Pd-supporting LaCoO3 catalyst with structured configuration for water gas shift reaction

The purpose of this study was to develop a structured perovskite-type oxide catalyst for the water gas shift (WGS) reaction, which could make lattice oxygen mobile at a low external heat energy by preparing it as a thin catalyst layer on a metal plate. The thickness of the formed LaCoO3 layer was about 20μm, which was confirmed by FE-SEM and EDX analysis. For enhancing its WGS reaction performance, a palladium (Pd) component was supported on the structured catalyst using various Pd precursors. When using a PdCl2 aqueous solution which was prepared by filtration of the PdCl2 slurry (the filtration liquid), the Pd-supporting LaCoO3 structured catalyst showed a high and stable activity. The reason for such an enhanced activity was that the supported Pd was in a highly dispersed state, which was derived from the electrostatic interaction between [PdCl3(H2O)]− as the anionic charged precursor in the filtration liquid and the oppositely charged LaCoO3 support surface confirmed by a UV–vis measurement. In order to remove the remaining chloride ligand from the Pd-supporting LaCoO3 catalyst surface, a washing treatment was performed by immersing the as-made catalyst in water, NH3 (aq) or NaOH (aq) at pH 11.5 for 30min. Consequently, these washing processes were effective for eliminating the remaining chloride ion from the catalyst surface and improving the shift activity of the catalyst. The catalyst washed using NH3 (aq) showed the highest activity among these catalysts.

Modifying perovskite-type oxide catalyst LaNiO3 with Ce for carbon dioxide reforming of methane

Perovskite-type oxide catalysts LaNiO3 and La1−xCexNiO3 (x ≤ 0.5) were prepared by the Pechini method and used as catalysts for carbon dioxide reforming of methane to form synthesis gas (H2 + CO). The gaseous reactants consisted of CO2 and CH4 in a molar ratio of 1:1. At a GHSV of 10,000 hr−1, CH4 conversion over LaNiO3 catalyst increased from 66% at 600 °C to 94% at 800 °C, while CO2 conversion increased from 51% to 92%. The achieved selectivities of CO and H2 were 33% and 57%, respectively, at 600 °C. To prevent the deposition of carbon and the sintering nickel species, some of the Ni in perovskite-type oxide catalyst was substituted by Ce. Ce provided lattice oxygen vacancies, which activated C–H bonds, and increased the selectivity of H2 to 61% at 600 °C. XRD analysis indicates that the catalyst exhibited a typical perovskite spinel structure and formed La2O2CO3 phases after CO2 reforming. The FE-SEM results reveal carbon whisker of the LaNiO3 catalyst and the BET analysis indicates that the specific surface area increases after the reforming reaction. The H2-TPR results confirm that Ce metals can store and provide oxygen.

Synthesis of LaxK1–xCoO3 nanorod and their catalytic performances for CO oxidation

A series of LaxK1–xCoO3 nanorod oxides with perovskite structure were synthesized by sol-gel method using polyvinyl alcohol (PVA) as additive. These perovskite-type complex oxide catalysts were characterized by the techniques of X-ray diffraction (XRD), infrared (IR), Brumauer-Emmett-Teller (BET) and scanning electron microscopy (SEM). And the results showed that nanorods of La1–xKxCoO3 perovskite-type complex oxides were fabricated by sol-gel method when the mass concentration of PVA was 4% and the calcined temperature kept at 700 °C for 4 h. The catalytic results of CO oxidation showed that the LaxK1–xCoO3 catalysts had high activity. LaCoO3 nanorods exposed more {110} plane than LaCoO3 nanoparticles, which was beneficial to the catalytic oxidation of CO. LaCoO3 nanorods had the best catalytic performance for the oxidation of CO. At 200 °C, the CO conversion could reach 100%.