| Abstract |
New bimetallic calcium-actinide (Th and U) oxides were synthesized and tested as catalysts for the oxidative coupling of methane (OCM) using nitrous oxide as oxidant. The reaction main products were primarily C2 hydrocarbons (C2H4 and C2H6), particularly over the bimetallic calcium-thorium oxide catalyst (CH4 conversion 28\%; C2 selectivity approximate to 153\%; C-2 yield approximate to 15\% at 800 degrees C). The selectivity to hydrocarbons is promoted when thorium replaces uranium on the bimetallic calcium-actinide oxides (at CH4 isoconversion = 15 3\%; C2 selectivity 32\% and 64\% over the bimetallic Ca-U-0 and Ca-Th-0 catalysts at 750 C, respectively), which can be linked to the actinide oxide phase properties. The bimetallic calcium-actinide oxides catalytic performance correlates with their acid-base and conductivity properties (selectivity to hydrocarbons increases with the catalysts basicity and it is higher over p-type conductors, e.g. Th02). The influence of the reaction temperature, gas phase CH4/N2O molar ratio and type of oxidant agent were also studied. In particular, the studies performed either under o(2) or N2O confirm that the use of nitrous oxide improves the selectivity to hydrocarbons. To the best of our knowledge, this is the first time that an OCM study using N2O as oxidant agent is reported over bimetallic Ca-An (An = Th and U) oxides aiming the production of C-2 hydrocarbons. (C) 2014 Elsevier B.V. All rights reserved. |
