Conversion of Methane over Bimetallic Copper and Nickel Actinide Oxides (Th, U) Using Nitrous Oxide As Oxidant

For the first time, bimetallic copper–thorium (Cu–Th–O), nickel–thorium (Ni–Th–O), and nickel–uranium (Ni–U–O) oxides were tested for the conversion of methane using N2O as oxidant. The behavior of the uranium and thorium catalysts is very different: at 10% methane isoconversion (700 °C), the production of C2 hydrocarbons is high over the uranium catalyst (≈80%), but the formation of oxidation products (CO2, CO) prevails over the thorium-based catalysts (≈85 and ≈15% selectivity to CO x and C2). At higher temperature (750 °C), the formation of C2 hydrocarbons remains high over the uranium catalysts (conversion CH4 ≈ 20%, selectivity to C2 ≈ 60%), but the production of syngas is now very high over the thorium-based catalysts (conversion CH4 ≈ 50%, selectivity to CO and H2 ≈ 90% at 750 °C over Ni–Th–O) without formation of C2). This distinct behavior could not be assigned to the catalytic behavior of pure metal oxides or mechanical mixtures of single metal oxides, which is very different from that of the bimetallic oxides and was explained by the differences on the accessibility and acidity of the catalysts surface. The catalytic behavior seems to depend on the actinide element, and the catalyst can be selected accordingly with the products that we want to achieve. To our knowledge, this is the first time that the conversion of methane using N2O as oxidant is reported over 5f block element-based catalysts.