Åse Slagtern

Partial oxidation of methane to synthesis gas using La-M-O catalysts

Abstract Catalytic partial oxidation of methane to synthesis gas was performed over La-M-O, with M = Co, Cr, Ni, Rh. The best system, La-Rh-O, gave 95% conversion with 98% selectivity to carbon monoxide even after 120 h on stream at 800°C. La-Ni-O deactivated after about 17 h on stream, probably due to coke formation. La-(Ni,Rh)-O showed improved stability compared to La-Ni-O. La-Co-O gave mainly carbon dioxide during the first 30 h of the test. Then the activity changed to give mainly carbon monoxide. Some deactivation was observed during the next 50 h test. La-Cr-O produced mainly carbon dioxide. In order to stabilize the small metal clusters formed on the catalyst surface, a second metal will probably have to be included in the perovskite structure.

Catalytic partial oxidation of methane over ni-, co- and fe-based catalysts

Abstract Partial oxidation of methane to synthesis gas has been investigated over Fe-, Co- and Ni-based catalysts in fixed bed reactor in view of a possible application in a fluidized bed reactor. Catalytic testing of the oxidic catalysts show an increasing activity for total oxidation of methane in the following order: Fe2O3>CoO>NiO. After reduction of the metal, the Ni and Co catalysts give equilibrium conversion to synthesis gas. Co is much more easier oxidized compared to Ni at decreasing temperature under experimental conditions and equilibrium is not followed at temperatures below 550°C. Low reforming activity is obtained over the Fe catalyst. Investigations at 1000–1100°C are necessary to further explore Fe as a reforming catalyst.

Characterization of Ni on La modified Al2O3 catalysts during CO2 reforming of methane

Abstract 0.15 wt% Ni/x wt% Ln/Al 2 O 3 ( x=0, 1.7, 8.5 , Ln=rare earth mixture ) catalysts have been tested for life time stability (60–600 h) during CO 2 reforming of methane in a fluidized bed reactor at 800°C and 1 atm with CH 4 : CO 2 : N 2 =2 : 2 : 1 . The catalyst with 1.7% Ln is more active and stable than the unpromoted catalyst and the catalyst with 8.5% Ln. Samples of the catalysts were taken out after different times on stream and characterized using magnetic measurements and Transmission Electron Microscopy (TEM). The characterization results showed that even after prereduction at 1000°C (5% H 2 /He, 2 h), Ni is continuously reduced during testing of the Ln-containing catalysts. This effect is more pronounced at higher Ln loadings (8.5% vs. 1.7% Ln). An increase in Ni particle size during testing was also observed. The results indicate that Ni sintering is initially a major reason for deactivation, while coking becomes increasingly important with longer times on stream (i.e., >60 h). The catalyst with 1.7% Ln has a higher initial Ni dispersion than the catalyst with 0% Ln. The higher activity of the promoted vs. unpromoted catalyst cannot be fully explained by this difference. However, the activity difference between the catalyst promoted with 1.7% or 8.5% Ln may be explained by a lower reduction of Ni for the 8.5% Ln-promoted catalyst.

In situ XRD characterization of LaNiAlO model catalysts for CO2 reforming of methane

In situ XRD studies have been performed on LaNiAlO catalysts for CO2 reforming of methane. Conditions were chosen to get information about catalysts used in fluidized bed reactors. Gas products were monitored by mass spectrometry. Reduction and catalytic properties of model compounds like LaNiO3 and LaNiAl11O19 as well as catalysts containing mixtures of such oxides were studied. Introduction of aluminium into the perovskite structure of LaNi1−xAlxO3 stabilizes the Ni-ions and a higher reduction temperature is necessary to obtain complete reduction to Ni(s). The magnetoplumbite type oxide, LaNiAl11O19, is reduced with even more difficulty. Furthermore, a continuous reduction of nickel is possible during the catalytic testing, stemming from such Ni-containing perovskite and magnetoplumbite type oxides of the catalyst. The reduced catalyst can be regenerated with O2, however, the oxidation of Ni(s) is not complete under the chosen conditions. Treatment of the catalyst in CO2 increases the activity of the catalyst and is probably due to removal of coke and formation of NiO which is immediately reduced during catalytic testing giving redispersed and more available Ni. The results clearly indicate that Ni is the active phase in CO2 reforming of methane. By the methods used, no formation of La2O2CO3 was observed on the tested catalysts and the deactivation due to such compound could not be concluded. The results indicate dissolution of C in Ni under CO2 reforming conditions as a possible reason for deactivation.

Oxidative dehydrogenation of propane in lithium hydroxide/lithium iodide melts

Abstract The reactions of propane with iodine have been evaluated theoretically in the temperature range 700–900 K. These calculations have been compared with test runs with propane/air in lithium hydroxide/lithium iodide melte. Thermodynamic and kinetic considerations show that low temperatures give higher propene selectivities. The experimental results confirm this and indicate that the reaction proceeds by a radical mechanism. A major factor governing propene selectivity is the ratio of nonnal/isopropyl radicals. At the relatively high radical concentrations encountered in the system, benzene is the ultimate product. Optimizing the iodine/hydrogen iodide-catalyzed oxidative dehydrogenation of propane with oxygen for propene or benzene production is feasible.

Hydrogen acceptor and membrane concepts for direct methane conversion

Abstract Condensation of methane in the presence of a hydrogen acceptor (titanium) to ethane and titaniumdihydride gives a thermodynamic conversion of 60% (PCH4 = 1 atm, T = 400 K). Experiments with Ti as the acceptor together with Pt/Sn, Rh or Ni catalysts, give, however, a methane conversion in the range of 1% with coke as the main product. In order to explore the possibility of methane conversion by a membrane concept , titanium and palladium as a hydrogen permeable material have also been theoretically investigated. Assuming diffusion limitation, up to 1.8 g ethane/m2·h (T = 400 K, Δx = 0.03 cm, equilibrium at p = 4 bar) may be produced in the case of palladium. Exploratory experiments show very low conversion of methane with coke as the main product.

Adsorption of lower alcohols from water solutions on high silica zeolites, mesoporous MCM-41 and AIPO4-5

Two dealuminated β-zeolites, zeolite Y and MCM-22 as well as silicalite, MCM-41 and AlPO4-5 have been studied as hydrophobic adsorbents in water solutions. Dealuminated β-zeolite, MCM-22 and silicalite all adsorb alcohols from water solutions. Enhanced adsorption is obtained for alcohols with longer alkyl chains. Adsorption in the practically most interesting 10–80% range of zeolite filling may adequately be described by Langmuir isotherms. The Langmuir adsorption constants are similar for β-zeolite, MCM-22 and silicalite. This indicates that the adsorption is independent of the pore structure for the alcohols tested in this study. The surface silanol density is however important, such that a low SiOH density is required to give lipophilic properties. In line with this, dealuminated zeolite Y, as prepared here, and MCM-41 give only a poor preference for alcohols from water. For the β-zeolite, the dealumination procedure is important for retaining the micropore volume and adsorption capacity of the zeolite. AlPO4-5 shows no potential as an adsorbent for alcohols from water solutions.

Properties of LaCo1−tCrtO3 III. Catalytic activity for CO oxidation

Abstract The catalytic activity for CO oxidation has been studied for samples of the solid-solution series LaCo1−tCrtO3, and NdCoO3 for comparison. The catalytic activity over LaCo1−tCrtO3 generally decreases with increasing chromium content. For samples with t = 0.70 and 0.80, distinct activity changes occur during the reaction, for t = 0.80 representing a permanent deactivation. Samples of LaCo1−tCrtO3 were also studied by XRD, TPR, TG and XPS. Variations in catalytic activity were compared with variations in structural, physical and chemical properties. A rough correlation was found between the starting temperature for reduction during TPR and the temperature required for 5% CO conversion. Furthermore, the activity pattern at 600 K follows the atom percentage of surface oxygen species as seen by XPS. Possible surface reactions on LaCo1−tCrtO3 during the catalytic oxidation of CO are discussed.

Pulse reactor studies of catalysts for the oxidative coupling of methane

Abstract The behaviour of the catalysts MgO, Li/MgO, Li/ZnO and Mn/Na4P2O7/SiO2 are compared using a pulse reactor:. The catalysts are exposed to pulses of different gases, such as air, methane and a methane:air mixture (1:1). There is more interaction from lattice oxygen with the Mn/Na4P2O7/SiO2 and Li/MgO catalysts than with the pure MgO or Li/ZnO.