Partial oxidation of methane (POM) was studied over a series of Co/Mg-Al catalysts. Various commercial hydroxides with different Mg/Al ratios were used as precursors of the oxides employed as catalytic supports, as well as MgO prepared in the laboratory. The effects of Co loading, Mg content, and calcination temperature (400-750 ºC) were studied in the POM reaction. The catalytic performance was evaluated at 800 ºC in a fixed-bed tubular quartz reactor under a high space velocity of 300 L N CH4/(gcat•h) and a O2/CH4 molar ratio of 0.5. A very high activity was obtained during 3.5 h on-stream with a 20 % (m/m) Co catalyst prepared with a Mg-Al mixed oxide support having a MgO content of 63 % (m/m). This catalyst gave CH4 conversions (91.3 %) very close to the maximum corresponding to the thermodynamic equilibrium. Such notable performance could be attained with the catalyst precursor subjected to calcination at 500 o C for 6 h and subsequent in situ reduction under H2 flow at 800 ºC for 2 h. Two main types of deactivation were generally observed in most of the samples that suffered either a very rapid cobalt re-oxidation upon their exposure to the POM reaction atmosphere or significant deposition of carbonaceous deposits of different kinds. The characterization of the spent samples by transmission electron microscopy (TEM) revealed the presence of carbon 2 deposits of different nature in the Mg/Al samples having a high MgO content, including filamentous carbon (whiskers), onion-shell like sheets and/or amorphous encapsulating layers. Conversely, no carbon deposits were observed in the spent Co/MgO catalyst, which underwent oxidation of the relatively less dispersed surface Co sites to form clearly defined crystals of Co oxides with particle diameters typically ranging between 25 and 100 nm.
In this work, the production of renewable hydrocarbons was explored by the means of waste cottonseed oil (WCSO) micropyrolysis at 500 °C. Catalytic upgrading of the pyrolysis vapors was studied using α-Al2O3, γ-Al2O3, Mo-Co/γ-Al2O3, and Mo-Ni/γ-Al2O3 catalysts. The oxygen removal efficiency was much lower in non-catalytic pyrolysis (18.0%), whilst γ-Al2O3 yielded a very high oxygen removal efficiency (91.8%), similar to that obtained with Mo-Co/γ-Al2O3 (92.8%) and higher than that attained with Mo-Ni/γ-Al2O3 (82.0%). Higher conversion yields into total renewable hydrocarbons were obtained with Mo-Co/γ-Al2O3 (61.9 wt.%) in comparison to Mo-Ni/γ-Al2O3 (46.6%). GC/MS analyses showed a relative chemical composition of 31.3, 86.4, and 92.6% of total renewable hydrocarbons and 58.7, 7.2, and 4.2% of oxygenated compounds for non-catalytic bio-oil (BOWCSO), BOMoNi and BOMoCo, respectively. The renewable hydrocarbons that were derived from BOMoNi and BOMoCo were mainly composed by olefins (35.3 and 33.4%), aromatics (31.4 and 28.9%), and paraffins (13.8 and 25.7%). The results revealed the catalysts’ effectiveness in FFA decarbonylation and decarboxylation, as evidenced by significant changes in the van Krevelen space, with the lowest O/C ratio values for BOMoCo and BOMoNi (O/C = 0–0.10) in relation to the BOWCSO (O/C = 0.10–0.20), and by a decrease in the presence of oxygenated compounds in the catalytic bio-oils.
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