Perovskite Oxide Catalysts Research Articles

Effects of Nitrogen Doping on Photocatalytic Water-splitting Activity of Pt/KTa0.92Zr0.08O3 Perovskite Oxide Catalyst

Abstract Effects of N doping in KTa(Zr)O3 on the photocatalytic activity under visible light irradiation were investigated and it was found that Pt-loaded K0.93Ta0.92Zr0.08O2.79N0.21 photocatalyst achieved a complete splitting of water under 420 nm cut-off conditions.

Less Costly Catalysts for Controlling Engine Emissions

Perovskite oxide catalysts may be able to control emissions from more fuel-efficient internal combustion engines and replace expensive noble metals.

Neutron Diffraction Studies of Nickel-Containing Perovskite Oxide Catalysts Exposed to Autothermal Reforming Environments

Six nickel-containing perovskite oxides (La1−xSrx)M0.9Ni0.1O3±δ, where x = 0 or 0.2 and M = Cr, Fe, or Mn) were used to catalyze the autothermal reforming of isooctane (C8H18) into a hydrogen-rich gas during short-term tests at 700 °C. To determine the phase stability of the samples in the reducing environment of the reforming reactor, characterization studies of the as-prepared and tested perovskite samples were conducted using powder X-ray diffraction, powder neutron diffraction, transmission electron microscopy, and scanning electron microscopy. We determined that the reducing conditions of the microreactor caused metallic nickel to form in all six compositions. However, the extent of the nickel loss from the perovskite lattices varied: the chromium-containing compositions lost the least nickel, compared to the manganese- and iron-containing compositions, and the strontium-free compositions lost more nickel than their strontium-containing analogs. Five of the six perovskite compositions tested showed no breakdown of the perovskite lattice despite the loss of nickel from the B-sites, producing only the third example of a B-cation-deficient, 3d transition-metal-containing perovskite.

Simultaneous catalytic removal of NOx and diesel soot particulates over La1−Ce NiO3 perovskite oxide catalysts

A series of the La1−xCexNiO3 (0 ⩽ x ⩽ 0.05) perovskite catalysts for simultaneous removal of nitrogen oxides and diesel soot were prepared by the citric acid complexation. The catalysts were characterized by X-ray diffraction, H2 temperature programmed reduction and X-ray photoelectron spectroscopy. The catalytic performances of these catalysts were investigated by the temperature programmed reaction. The results indicated that Ni2+ was the active centers. The partial substitution of Ce for La increased the concentration of Ni2+, enhancing the catalytic activities. The La0.97Ce0.03NiO3 catalyst showed the highest activity. The maximum productivity of N2 and the ignition temperature were 11.8% and 300 °C, respectively.

Preparation of La-Mo-V mixed-oxide systems and their application in the direct synthesis of acetic acid

In this study, mixed metal oxides developed with a perovskite-type structure that show great potential for use in catalysis. Perovskite oxide catalysts with the composition LaMo x V 1 − x O n ( x = 0.1, 0.3, 0.5, 0.7, and 0.9) have been synthesized by the sol-gel method and then used in the ethane dry reforming reaction for the direct synthesis of acetic acid. The influence of the nature of the metallic source (metal, nitrate, acetylacetonate, and ammonium) on gel formation has been studied by Fourier-transform infrared spectroscopy (FT-IR) and thermogravimetric analysis (TGA-DTA). After calcination, the obtained perovskites were characterized by X-ray diffraction (XRD) and energy-dispersive X-ray spectrometry (EDS) coupled with scanning electron microscopy (SEM). The catalysts were then subjected to thermo-programmed reduction (TPR). The surface area (BET) was found to increase from 2.6 m 2/g ( x = 0.1) to 5.1 m 2/g ( x = 1.0) with increasing molybdenum content following calcinations at 750°C, and pure LaMo x V 1 − x O n perovskite was obtained with good homogeneity. The catalysts have been characterized by XRD, SEM, EDS, and carbon analysis (CA). The results indicate that through this synthesis it is possible to obtain highly crystalline, homogeneous and pure solids, with well-defined structures. The direct synthesis of acetic acid from ethane over the perovskite catalysts was studied at temperatures between 450 and 850 °C and elevated pressures between 1 and 8 bar. It was found that the yield of acetic acid and the selectivity of its formation could be increased by incorporating more molybdenum into the perovskite structure. The experimental studies have shown that the calcination temperature and the molybdenum content have a significant influence on the catalytic activity. Amongst the catalysts tested, LaMo 0.7V 0.3O 4.2 exhibited the best activity and stability.

Removal of NOx and diesel soot particulates catalyzed by perovskite-type oxide La0.9K0.1CoO3

The catalytic performance of perovskite composite oxide catalyst La0.9 K0.1 CoO3 coated on catalyst supports by traditional solid state reaction method and sol-gel method were investigated by a series of experiments. The result shows that the catalytic performance of the La0.9 K0.1 CoO3 perovskite composite oxide catalyst synthesized by sol-gel method is superior to that synthesized by solid state reaction method, having lower ignition temperature of the diesel soot particulates, lower start temperature of NOx treatment, and lower concentration of by-product CO.

Properties of DPF System Using Perovskite Catalysts Supported on ZrO2/SiC Fibers

Diesel engine, which is widely used as a power plant for trucks and buses, is most efficient internal combustion engine. However, it generates a large amount of particulate matter (PM) and NOx. Diesel particulate filter (DPF) system is expected to be an effective tool to reduce PM and NOx emissions, but it is far from practical use because of clogging and low heat-resistance. In this work, ZrO2/SiC felt which supported perovskite oxide catalyst is employed as a filter material, and the performances of the new DPF system to reduce PM and NOx emissions were evaluated. As a result, La0.9K0.1CoO3 supported by alkoxide method exhibited promising performance to reduce PM and NOx emissions, and Pt on the perovskite oxide enhanced the PM oxidation performance at about 500°C.

Decomposition of nitric oxide over perovskite oxide catalysts: effect of CO2, H2O and CH4

Direct nitric oxide decomposition over perovskites is fairly slow and complex, its mechanism changing dramatically with temperature. Previous kinetic study for three representative compositions (La0.87Sr0.13Mn0.2Ni0.8O3−δ, La0.66Sr0.34Ni0.3Co0.7O3−δ and La0.8Sr0.2Cu0.15Fe0.85O3−δ) has shown that depending on the temperature range, the inhibition effect of oxygen either increases or decreases with temperature. This paper deals with the effect of CO2, H2O and CH4 on the nitric oxide decomposition over the same perovskites studied at a steady-state in a plug-flow reactor with 1g catalyst and total flowrates of 50 or 100ml/min of 2 or 5% NO. The effect of carbon dioxide (0.5–10%) was evaluated between 873 and 923K, whereas that of H2O vapor (1.6 or 2.5%) from 723 to 923K. Both CO2 and H2O inhibit the NO decomposition, but inhibition by CO2 is considerably stronger. For all three catalysts, these effects increase with temperature. Kinetic parameters for the inhibiting effects of CO2 and H2O over the three perovskites were determined. Addition of methane to the feed (NO/CH4=4) increases conversion of NO to N2 about two to four times, depending on the initial NO concentration and on temperature. This, however, is still much too low for practical applications. Furthermore, the rates of methane oxidation by nitric oxide over perovskites are substantially slower than those of methane oxidation by oxygen. Thus, perovskites do not seem to be suitable for catalytic selective NO reduction with methane.

Synthesis and Characterization of LaCr1−xNixO3Perovskite Oxide Catalysts

A series of perovskite oxide catalysts with the composition LaCr1−xNixO3(0≤x≤1) has been synthesized by a modification of the Pechini method. The oxides have been characterized by powder X-ray diffraction, elemental analysis and surface area measurements. The LaCr1−xNixO3phases have the orthorhombic GdFeO3(x<∼0.6) and the rhombohedral LaAlO3structure (x>0.6), in agreement with previous results. The surface and bulk compositions were shown to be equivalent by XPS measurements. Systematic changes in the binding energies of the Cr 2pand Ni 3pfeatures are indicative of a progressive evolution of the electronic properties with nickel atom content (x). The LaCr1−xNixO3oxides withx≤0.5 were shown by thermogravimetric analysis to be stable at 900°C in H2/H2O with respect to reduction to nickel metal.

Comparative study of Nickel-based perovskite-like mixed oxide catalysts for direct decomposition of NO

The mixed oxides LaNiO 3, La 0.1Sr 0.9NiO 3, La 2NiO 4 and LaSrNiO 4 were prepared and used as catalysts for the direct decomposition of NO. The catalysts were characterized by means of XRD, XPS, O 2-TPD, NO-TPD and chemical analysis. By comparing the physico-chemical properties and catalytic activity for NO decomposition, a conclusion could be drawn as follows. The direct decomposition of NO over perovskite and related mixed oxide catalysts follows a redox mechanism. The lower valent metal ions Ni 2+ and disordered oxygen vacancies seem to be the active sites in the redox process. The oxygen vacancy plays an important role favorable for the adsorption and activation of NO molecules on one hand and on the other hand for increasing the mobility of lattice oxygen which is beneficial to the reproduction of active sites. The presence of oxygen vacancies is one of the indispensable factors to give the mixed oxides a steady activity for NO decomposition.

Oxidative coupling of methane by water as the oxidant on perovskite oxide catalysts

We found that methane was selectively oxidized by water to give C2 hydrocarbons and hydrogen on ATi1−xBxO3−δ (A=Sr, Ba, B=Mg, Ca). The coupling activity and selectivity on SrTi0.4Mg0.6O3−δ in the presence of steam was ∼95%, which was much higher than that on pure SrTiO3. This suggests that the selective oxidative coupling of methane by water was catalyzed by the oxide ion defects on ATi1−xBxO3−δ (A=Sr, Ba, B=Mg, Ca).

Carbonylation of Methanol Using Nickel Complex Catalyst: A Kinetic-Study

In this study, mixed metal oxides developed with a perovskite-type structure that show great potential for use in catalysis. Perovskite oxide catalysts with the composition LaMoxV1 − xOn (x = 0.1, 0.3, 0.5, 0.7, and 0.9) have been synthesized by the sol-gel method and then used in the ethane dry reforming reaction for the direct synthesis of acetic acid. The influence of the nature of the metallic source (metal, nitrate, acetylacetonate, and ammonium) on gel formation has been studied by Fourier-transform infrared spectroscopy (FT-IR) and thermogravimetric analysis (TGA-DTA). After calcination, the obtained perovskites were characterized by X-ray diffraction (XRD) and energy-dispersive X-ray spectrometry (EDS) coupled with scanning electron microscopy (SEM). The catalysts were then subjected to thermo-programmed reduction (TPR). The surface area (BET) was found to increase from 2.6 m2/g (x = 0.1) to 5.1 m2/g (x = 1.0) with increasing molybdenum content following calcinations at 750°C, and pure LaMoxV1 − xOn perovskite was obtained with good homogeneity. The catalysts have been characterized by XRD, SEM, EDS, and carbon analysis (CA). The results indicate that through this synthesis it is possible to obtain highly crystalline, homogeneous and pure solids, with well-defined structures. The direct synthesis of acetic acid from ethane over the perovskite catalysts was studied at temperatures between 450 and 850 °C and elevated pressures between 1 and 8 bar. It was found that the yield of acetic acid and the selectivity of its formation could be increased by incorporating more molybdenum into the perovskite structure. The experimental studies have shown that the calcination temperature and the molybdenum content have a significant influence on the catalytic activity. Amongst the catalysts tested, LaMo0.7V0.3O4.2 exhibited the best activity and stability.

ChemInform Abstract: Oxidative Coupling of Methane over Alkali Halide‐Promoted Perovskite Oxide Catalysts

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Oxidative coupling of methane over alkali halide- promoted perovskite oxide catalysts

Abstract The catalytic performance of some alkali halide-promoted perovskite oxides as well as that of the perovskite oxides alone for the oxidative coupling of methane were investigated. Although the perovskite oxides alone showed relatively low catalytic activity, a noticeable increase in activity and C2 selectivity was observed when the oxides were promoted by alkali halides. Sodium chloride ( NaCl ) was the most effective promoter among the alkali halides. Of the perovskite oxides examined in the present study, the catalytic activity of PbTiO3 was most remarkably promoted by addition of NaCl, because it showed almost no activity for the reaction in the absence of NaCl. The maximum C2 yield of 28.2% was obtained for an NaCl (0.2 mol against 1 mol of PbTiO3) added PbTiO3 catalyst, where methane conversion and C2 selectivity were 50.7% and 55.7%, respectively, under the conditions;Pch4=10.1 kPa,PO2 = 5.1 kPa,PHe = 86.1 kPa, total gas flow-rate =100 ml STP/min, temperature = 1023 K,W/F= 0.22 g min/ml. The stability test for the 0.2 mol NaCl/PbTiO3 catalyst suggests that the catalyst loses its high activity when most of the NaCI has been removed from the catalyst during the test. However, the same level of activity is recovered when NaCI is added again to the deactivated catalyst. The thermal and temperature-programmed desorption analyses suggest that both high activity and high C2 selectivity for the Nacl-promoted PbTiO3 catalyst can be ascribed to the generation of new basic active sites. These sites must be created through the interaction between NaCl and PbTiO3 on the surface of the catalyst.

Oxygen desorption and oxidation-reduction kinetics with methane and carbon monoxide over perovskite type metal oxide catalysts

Selected perovskite-based, metal oxide catalysts of composition La 1−x Sr xB yB' zO 3 (B: Mn,.Fe; B': Fe or Cu) containing, in some cases, an excess of one or more of the B-position elements (i.e. y+z >1) were investigated for their use in methane oxidation. A flow reactor/mass spectrometer arrangement was used to characterize the supported monolith catalyst samples. The catalysts possess significant activity for methane oxidation and also are able to exchange bulk oxygen in quantities corresponding to several hundred monolayers. Much greater quantities of oxygen could be removed under reducing reaction conditions than by desorption in an inert argon atmosphere. With one catalyst, LaFe 0.84Cu 0.16O 3, oxygen desorption occurred already at 200 ° C; otherwise typical temperatures for desorption onset were 500–600 °C. Lattice oxygen removal under reducing conditions and oxygen uptake by reduced catalysts were both found to exhibit a rather complex temperature dependence. Investigated catalysts with an excess of B-position metals had a greater capacity to exchange oxygen than the stoichiometric perovskites LaMnO 3 and LaFe 0.84Cu 0.16O 3. Reoxidation of the reduced catalysts occurred at lower temperatures than reduction. Oxidation of carbon monoxide consistently occurred at considerably lower temperatures than oxidation of methane. Complete oxidation of methane to carbon dioxide and water was observed under most conditions with little carbon monoxide or higher hydrocarbon formation. Only for strongly reduced catalysts was carbon monoxide production detected.

Partial Oxidation of Hydrocarbons and Oxygenated Compounds on Perovskite Oxides

Abstract Research of perovskite oxide catalysts (AB03) with a rare-earth ion as an A-site and a transition metal ion as a B-site has been concentrated on the complete oxidation of hydrocarbons, particularly related to exhaust control, and revealed that they are potential catalysts for deep combustion of hydrocarbons (1). The complete oxidation activities have been reported to be mainly controlled by the physicochemical property of the B-site metal cations such as the electronic configuration of d-electron (2), the binding energy of B-0 bond (3) and the stabilization energy of the crystal field (4), rather than the relatively small and less important effect of the rare-earth ion of the A-site (5) and also improved by the substitution of other metal cations for A- or B-site (6,7). Although it is difficult to find many investigations on the application of perovskite-type oxides to partial oxidation, in this chapter, the movement to the partial oxidation of hydrocarbons and oxygenated compounds using various ...

Treatment of exhaust gases from a methanol fueled vehicle over perovskite oxide catalysts

As a study on the treatment of exhaust gases from a methanol-fueled vehicle, catalytic oxidation of formaldehyde and methanol on perovskite-type oxides was performed. La0.8Sr0.2MnO3, La0.8Sr0.2CoO3, YBa2Cu3O7 (superconductor), and ErBa2Cu3O7 (superconductor) were used as catalysts. La-based catalysts were prepared by a citrate method and calcined at 650°C, 800°C, and 900°C, respectively. The catalytic activity of La-based catalysts increased with the increase in the surface area that was dependent on the calcination temperature. Superconductive oxides were also prepared by a citrate method and calcined at 920°C. The catalytic activity of ErBa2Cu3O7 was found to be better than that of YBa2Cu3O7. For La-based perovskite calcined at 650°C, the catalytic activity of La0.8Sr0.2MnO3 was higher than La0.8Sr0.2CoO3. Calcining at 800°C and 900°C, however, the catalytic activity of LLa0.8Sr0.2 CoO3 was higher than La0.8Sr0.2MnO3.

Oxidative coupling of methane over Ba2Sb(La0.5Bi0.5)O6 and other perovskite oxide catalysts

Novel perovskite-type oxides Ba2MIIIM′VO6 containing high oxidation-state post-transition elements have been shown to catalyse the oxidative coupling of methane; yields of up to ca. 17% are obtained at 1023 K when the catalyst contains antimony(V).

Application of computer graphics to catalyst design

The suitability of computer graphics for the investigation of the structure and function of heterogeneous catalysts has been demonstrated with supported Perovskite oxide catalysts, supported vanadium oxide catalysts, supported gold catalysts, and acid-base cooperative catalysis in the side-chain alkylation of toluene with methanol on alkali-ion exchanged zeolites. Computer graphics is especially effective for discussing the geometrical factors relevant to catalysis and catalyst formulation.

Effect of carbon dioxide on electrochemical stability of gas diffusion electrodes in alkaline solution

By means of radioisotope (3H and 14C) tracer methods, a study was undertaken to investigate the role of CO2 impurity [10% (m/o)] contained in O2 feed gas on the electrochemical stability of gas diffusion electrodes which performed the oxygen reduction in alkaline solution. The electrodes were prepared by supporting a perovskite oxide catalyst on three kinds of carbon carriers; hydrophilic activated carbon, hydrophobic acetylene black and furnace-type carbon black. For the electrodes with the carriers mixed by activated carbon and acetylene black, a polarization loss of the electrode and a dissolution of CO2 into electrolytic solution were observed during the supply of CO2 to O2 feed gas. Under a low gas flow rate of the feed gas, a reversible polarization responsible to the supply of CO2 was observed in the electrodes with high contents of activated carbon carrier. However, an irreversible fatal polarization loss accompanied with the progressive wetting of the electrode was observed under a high gas flow rate of the feed gas, leading to the decay of three phase equilibrium even when cutting off the supply of CO2. On the other hand, neither the dissolution of CO2 into electrolytic solution nor the wetting of the electrode induced by the introduction of CO2 were detected for the electrode with furnace-type carbon black which was able to construct a compactly packed electrode structure.