Molybdenum and nickel-molybdenum nitride catalysts supported on MgO-Al2O3 for the dry reforming of methane

Molybdenum and nickel-molybdenum nitride catalysts supported on MgO-Al2O3 were synthesized and tested for methane dry reforming at temperatures of 760-840 degrees C. Two in-situ nitridation procedures involving heating the catalyst in NH3/N-2 or H-2/N-2 gas at a space velocity of 44 s(-1) and 5 degrees C/min heating rate, were assessed and compared with a conventional reduction procedure. The activity of the bimetallic nitride was much higher than that of molybdenum nitride, with a slightly better performance with H-2/N-2-treated catalysts. The nitrides showed deactivation and poor stability at atmospheric pressure. The nitride phase was shown to transition into an oxide/carbide phase during reaction. Furthermore, hydrogen/nitrogen treatment caused partial reduction to occur, which explains the activity improvement in bimetallic Ni-Mo nitrides. Whisker carbon was significantly decreased although carbon formation was observed. The basic support improves coking resistance by enhancing CO2 adsorption. Initial results indicate a unique activation site for both methane and CO2 through a Mars-Van Krevelen mechanism, with a phase transformation followed by a carbide-oxide redox cycle mechanism taking place.