Evidence of water dissociation and hydrogenation on molybdenum carbide nanocatalyst for hydroprocessing reactions

Abstract

Cubic molybdenum carbide, α-MoC_1−x, was used for simultaneous water dissociation and hydrogenation reactions. Hydroprocessing reactions of heavy hydrocarbons under different hybrid environments consisting of water vapor, steam, and hydrogen at 623 K and 7 MPag were carried out and production of CO₂ and olefins was closely followed to track the extent of water dissociation. Nitrogen, as an inert gas, systematically substituted either of the two gases to study the effect of partial pressure on the reaction products. In addition, water activation was verified by isotopically labelling O atoms in water, i.e. using H₂¹⁸O, and then production of heavier isotopes of CO₂ was followed using mass spectrometry. Moreover, the potential effect of the co-presence of hydrogen on water dissociation was investigated by carrying out several flow reaction studies as well as adsorption studies using thermogravimetry/calorimetry coupled with mass spectrometry. While α-MoC_1−x showed outstanding activity and stability for simultaneous water dissociation and hydrogenation, water activation was found to be partially hindered by the co-presence of hydrogen.