Arnfinn G. Andersen

Partial oxidation of methane to synthesis gas over some titanates based perovskite oxides

Ca1−x-xSrxTiO3-based mixed oxide catalysts containing chromium, iron, cobalt or nickel were prepared and used in the oxidation of methane. The catalyst containing cobalt or nickel showed high activity for the synthesis gas production from methane. In the case of nickel containing catalyst, nickel oxide originally separated from the perovskite structure was easily reduced to nickel metal, which showed synthesis gas production activity. In the case of the cobalt containing catalyst, pretreatment with methane was required for high activity. Reduced metallic cobalt was formed from the perovskite structure, which revealed relatively high selectivity for the oxidative coupling of methane, and afforded synthesis gas production. Both the catalysts also catalyzed carbon dioxide reforming of methane and especially both high activity and selectivity were observed over the nickel containing catalyst.

Partial oxidation of methane over aNi/BaTiO3 catalyst prepared by solid phasecrystallization

Ni/BaTiO 3 catalyst has been prepared by solid phase crystallization (SPC) and used successfully for partial oxidation of CH 4 into synthesis gas at 800°C. In the SPC method, Ni/BaTiO 3 catalyst is obtained in situ by the reaction of starting materials with nickel species homogeneously incorporated in the structure. For the starting reagents, materials of two compositional types were employed i.e., perovskite structures BaTi 1-x Ni x O 3- δ (0⩽x⩽0.4) and stoichiometric structures, BaTiO 3 , Ba 2 TiO 4 and BaTi 5 O 11 , with 0.3NiO. The starting materials were tested for oxidation of CH 4 by increasing the reaction temperature from room temperature to 800°C. The catalysts showed the highest activity for synthesis gas formation around 800°C, and the highest value was obtained at a composition of x=0.3 in the former catalysts. Among the latter catalysts, the highest activity was observed over BaTiO 3 ·0.3NiO, which was more active than BaTi 0.7 Ni 0.3 O 3-δ . On the both catalysts, nickel species originally incorporated in the structure were reduced to the metallic state during the reaction. The BaTiO 3 ·0.3NiO catalyst was further tested for 75 hours at 800°C with no observable degradation and negligible coke formation on the catalyst. Thus, Ni/BaTiO 3 prepared in situ from the perovskite precursor, i.e., by the SPC method, was the most active and resistant to coke formation and deactivation during the reaction. This may be due to well dispersed and stable Ni metal particles over the perovskite, where the nickel species thermally evolve from the cations homogeneously distributed inside an inert perovskite matrix as the precursor.

Sustainable Ni/BaTiO3 catalysts for partial oxidation of methane to synthesis gas

Publisher Summary Ni/BaTiO 3 catalyst has been prepared by solid phase crystallization (SPC) method and used successfully for partial oxidation of CH 4 into synthesis gas at 800°C. The partial oxidation of CH 4 , expected to afford synthesis gas, having H 2 /CO ratio of about two, makes methanol synthesis an ideal follow-up process. In the partial oxidation of CH 4 to synthesis gas, coke formation over the catalyst frequently takes place, resulting in catalyst deactivation. Nickel catalysts are highly effective for partial oxidation of CH 4 to synthesis gas, but they are unsatisfactory, with respect to coke formation. From the industrial viewpoint, Ni is preferable as the active species compared to expensive precious metal, such as Rh, Pd, or Ru. Nickel-supported catalysts are conventionally prepared by wet impregnation of different supports. This method is not fully reproducible and may give rise to some unhomogeneity in the distribution of the metal on the surface. Therefore, a new method of catalyst preparation able to produce homogeneous distribution of nickel is proposed. Sustainability and high activity of Ni/(Ca, Sr)TiO 3 in the oxidation of CH 4 to synthesis gas has been described where the Ni catalyst supported on (Ca,Sr)TiO 3 perovskite was prepared by the SPC method. However, the precursor was not homogeneous and contained two types of nickel species; one was dissolved in the Ti site in (Ca, Sr)TiO 3 and another was separated as NiO from the perovskite structure. By controlling the ratio of Ba/Ti in the citrate method mentioned above, Ba 2 TiO 4 , BaTiO 3 , and BaTi 5 O 11 were obtained as a single phase in each composition. The three mixed oxides and TiO 2 were combined with nickel at the ratio of 1/0.3 by the citrate method and tested for the CH 4 oxidation. A summary of the observations in the X-ray diffraction (XRD) patterns for the related compounds before and after the catalytic testing is discussed in this chapter.

Preparation and characterization of CaTiO3-based perovskitic oxides as catalysts for partial oxidation of light hydrocarbons

A series of perovskites of the formula Ca1−xSrxTi1−yMyO3−δ, M=Fe, Co, Cr or Ni,x = 0−1,y = 0−0.6, has been synthesized by a modified sol-gel method using citrate. Several of these materials were proved to be stable under operating conditions in reducing atmospheres of air and hydrocarbons. An outline of the synthesis procedure is given, together with the results of XRD, SEM, BET, TG, DTA and IR characterization before and after catalytic testing. The solubility of Ni and Cr in this perovskite was very limited, and the solubility of Co decreased abruptly above 1173 K. The solubility range of Ca and Sr on alkaline earth sites is 100%.

Partial oxidation of methane to synthesis gas over (Ca,Sr) (Ti,Ni) oxides

Abstract Ni catalysts supported on perovskite were in situ prepared from Ca1-xSrxTi1-yNiyO precursors and were tested in the oxidation of CH4 by increasing reaction temperature from room temperature to 800°C. NiO originally separated from the perovskite structure under sol-gel preparation conditions was reduced to Ni metal during the CH4 oxidation and thus formed Ni metal supported on perovskite showed high activity for synthesis gas production at 800°C. This process involves first the oxidation of a part of CH4 to H2O and CO2 followed by the reforming reaction of CH4 with H2O and CO2. When the catalyst of y = 0.2 was used, high Sr contents afforded high activity for the CH4 oxidation and the highest activity to synthesis gas was obtained with x = 0.2. In the catalysts of x = 0.2, those of y ≥ 0.1 showed high activity for the synthesis gas production, that of y = 0.05 required pretreatment with CH4 for acquiring the activity and a further decrease in the Ni content resulted in no activity. Ni catalyst prepared by impregnation over the perovskite carrier showed a high activity, while those prepared by mixing metal oxides were not active. It is thus most likely that perovskite structure possesses an important role as the carrier in Ni catalysts.

Liquid phases in Li:MgO as studied by thermoanalytical methods, electron microscopy, and electrical conductivity measurements

Abstract The phase relations in parts of the system Mg-Li-O-H-C are reviewed and some features investigated by TG, DTG, DSC, SEM, TEM, and electrical conductivity measurements on a commercial Li:MgO catalyst. Electrical conductivity measurements on samples with varying Li contents are used to monitor the presence of highly conducting surface melts under controlled atmospheres at high temperatures. The measurements indicate that the solubility of lithium in MgO bulk increases with increasing oxygen activity, as predicted by defect theory. The solubility of Li in MgO at 700°C in CO2-rich, oxidizing atmosphere is estimated to be of the order of magnitude of 0.1 mol-% (0.02 wt-%).

Electrical conductivity and defect structure of lithiumdoped magnesium oxide

Abstract The electrical conductivity of sintered samples of lithium-doped magnesium oxide has been studied at various temperatures (

Oxidative coupling of methane over LaCoO3−δ-based mixed oxides

The catalytic activity of LaCoO3−δ-based mixed oxides for the oxidative coupling of methane has been tested by TPR and cyclic reaction. Characterization has been done by XRD, TGA and Mössbauer spectrometry. It is likely that the perovskite-crystal structure containing hypervalent metal ions has an important role and that unique structural oxygen species in the perovskite contribute to the partial oxidation of methane.

Oxidative coupling of methane over some titanates based perovskite oxides

A series of perovskites of the formula Ca1−xSrxTi1−yMyO3−δ (M = Fe or Co,x = 0–1,y = 0–0.6 for Fe,y = 0–0.5 for Co) were prepared and tested as the catalyst for the oxidative coupling of methane. The catalysts were stable under the reaction conditions. The catalysts of high p-type and oxide ionic conductivity afforded the high selectivity. Some catalysts containing Co on B-sites are thermally unstable and decomposed to metal oxide components at high temperature, giving rise to synthesis gas production.

Oxidative dehydrogenation of ethane over some titanates based perovskite oxides

A series of perovskite catalysts have been tested for the oxidative dehydrogenation of ethane. The composition of these catalysts covered CaTi1−xFexO3−δ, with 0 ⩽x ⩽ 0.4, SrTi1−xFexO3−δ, with 0 ⩽x ⩽ 1.0, as well as mixtures of these. The latter catalysts containing more basic Sr metal showed higher selectivity to ethene than the former catalysts containing Ca. A few catalysts with Co on B-sites in the lattice were tested, but lost their stability above 923 K, resulting in a substantial change in the product selectivity. The perovskites gained activity when Fe was introduced in the lattice to form hypervalent ions (Fe4+) which are believed to play a role in the catalytic activity of these materials.