Add time:07/31/2019         Source:sciencedirect.com

The catalytic performance of Mo2N and K-Mo2N were assessed in hydrogenation of carbon monoxide in the reaction temperature range of 275–325 °C, 7 MPa and 60,000 h−1. The nitrides were synthesized via temperature-programmed treatment of ammonium heptamolybdate (AHM) and K-AHM precursors under continuous NH3 flow. The influence of potassium loading (0.45–6.2 wt.%) on the Mo nitride phase and its resultant effect on the catalytic properties were been investigated. The nitride catalysts were characterized in terms of BET/pore size, powder X-ray diffraction, DRIFTs, CO-TPD-mass, HR-TEM and XPS measurements. The formation of cubic γ-Mo2N and monoclinic K2MoO4 phases were confirmed by XRD and TEM. Platelet morphology with particle size in the range of 5–10 nm was observed for γ-Mo2N. CO-TPD-mass results mainly revealed molecular CO sorption on Mo2N and K-Mo2N surface. The highest total oxygenate selectivity (44%, 300 °C) was observed on 1.3K-Mo2N with a K/Moδ+ surface ratio of 0.06. This is associated with well distributed K in the matrix of γ-Mo2N. Distribution of K was reduced due to K2MoO4 formation at 3 and 6.2 wt.% K loading. DRIFTs results clearly demonstrates greater hydrocarbon formation on unpromoted Mo2N due to (i) CO dissociative hydrogenation (ii) water-gas shift reaction. Further, addition of K to Mo2N significantly improved the oxygenate selectivity by promoting the molecular CO insertion into −CHx intermediate.

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