Abstract
The aim of this work is to understand the catalytic behaviour of Li and Cs promoted Mo2N for CO hydrogenation to hydrocarbons and oxygenates at the reaction conditions 275-325 degrees C, 7MPa, and 30000h(-1) GHSV. Molybdenum nitrides were synthesized via temperature programmed treatment of ammonium heptamolybdate (AHM) and alkali metal (AM) precursors under continuous gaseous ammonia flow. Unpromoted Mo2N and AM-Mo2N catalysts were characterized using BET-pore size, X-ray diffraction, TPD-mass of CO, HR-TEM, and XPS techniques. Nominal loadings of 1, 5, and 10wt% of Li and Cs were selected for these studies. At a 10% CO conversion level, the total oxygenate selectivity of 28, 11, and 6.5% was observed on 5Cs-Mo2N, 5Li-Mo2N, and unpromoted Mo2N, respectively. The decreased oxygenate selectivity for unpromoted Mo2N was mainly associated with CO dissociative hydrogenation on Mo+ sites. On the other hand, improved molecular CO insertion into -CxHy intermediate accelerates the total oxygenate formation on the Cs-Mo-N catalyst. However, during nitridation, crystal structure changes were observed in Li-Mo-N and the obtained oxygenates selectivity was attributed to the Li2MoO4 phases. At lower AM loadings, the active sites corresponding to oxygenates formation were inadequate, and at higher AM loadings, surface metallic molybdenum decreased the total oxygenate selectivity.