Unni Olsbye

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.

Study of Pt/alumina catalysts preparation

Abstract Platinum-alumina catalysts were prepared at 20°C by using a method in which hexachloroplatinic anions from solution were adsorbed on θ-alumina in the pH range 1–10 and with contact times between 1 and 24 h. An adsorption maximum was observed at pH around 3–4. From measurements of electrophoretic mobility, the isoelectric point of θ-alumina was determined to be about 8.5. Comparison with literature data indicated that γ- and θ-alumina exhibit similar adsorption properties and that the amount of Pt deposited is controlled by pH and contact time for both systems. The adsorption appears to proceed initially as a physisorption process with relatively strong specific interaction or chemisorption taking over at longer contact times. Pt θ -alumina samples with 0.3 to 2.2 wt% Pt were prepared. Wet calcination at 570°C led to a decrease in the Cl content of the samples, while the Pt content was unaffected.

Partial oxidation of methane to synthesis gas in a fluidized bed reactor

Abstract The partial oxidation of methane to synthesis gas (POX) over N1/AI 2 O 3 catalysts has been studied in a fluidized bed reactor. Flow characterization studies showed that the reaction zone was isothermal, and that the back mixing of gas was negligible. The reaction was rapid, and full O 2 conversion was achieved after 8 ms contact time over 1.5%Ni/Al 2 O 3 at 700°C, with CH 4 /O 2 /N 2 /H 2 O =2/1/2/0.5. The CO selectivity went through a minimum and then increased and approached equilibrium after 48 ms contact time. Simulations of the reaction scheme indicated that the catalyst is active for oxidation of CH 4 , CO and H 2 , as well as for reforming. The simulations further suggested that the reaction rates were diffusion limited.

The influence of rare earth oxides on Ni/Al2O3 catalysts during CO2 reforming of CH4

Abstract Rare earth oxide mixture (Ln 2 O 3 ) and La 2 O 3 give the same effects when used as promotors for Ni/Al 2 O 3 catalysts for the CO 2 reforming of methane to synthesis gas. An optimum in activity and stability was obtained for catalysts promoted with 2–5wt% Ln 2 O 3 . Catalysts promoted with Ln 2 O 3 have increased Ni-support interaction compared to pure Ni/Al 2 O 3 . This interaction is dependent on the calcination temperature used during preparation of the catalysts. Increased interaction gives less reducible catalysts and Ni appears to be continously reduced during catalytic testing even after reduction in H 2 at 1000°C for 2h.