Pairwise Parahydrogen Addition Over Molybdenum Carbide Catalysts

Herein, we have shown that the phase composition of molybdenum carbide catalysts has a pronounced effect on the pairwise hydrogen addition selectivity in the gas-phase propyne hydrogenation with parahydrogen. Molybdenum carbide catalysts were prepared using either the Pechini method or temperature-programmed reduction with CH 4 /H 2 carburizing gas mixture. The structures of carbide catalysts were characterized by high-resolution transmission electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. It was found that molybdenum carbide prepared by the Pechini method predominantly contains a face-centered-cubic MoC 1−x phase, while the TPR method yields a hexagonal-close-packed Mo 2 C phase. By varying the gas hourly space velocity of carburizing gas mixture, the defected phase can be produced. Computer modeling for XRD patterns was used to identify the phase composition of Mo 2 C catalysts. All the catalysts were found to be active in pairwise hydrogen addition; however the hcp-Mo 2 C phase exhibits a higher contribution of pairwise H 2 addition providing ~ 150-fold proton NMR signal enhancement.