Formic Acid as a Bio-CO Carrier: Selective Dehydration with γ-Mo<sub>2</sub>N Catalysts at Low Temperatures
Zhongliang Yu, Akihiro Yoshida, Jin Shi, Tao Wang, Song Yang, Qing Ye, Xiaogang Hao, Abuliti Abudula, Yitian Fang, Guoqing Guan
Abstract
Formic acid (FA) can be considered a bridge between biomass and green fuels, as biomass can be oxidized to FA, followed by FA dehydration to CO for Fischer–Tropsch synthesis. In this work, a series of γ-Mo2N-based catalysts used for FA dehydration was prepared by the facile pyrolysis of a Mo-containing precursor at different temperatures. It was found that the γ-Mo2N-based catalysts exhibited high performance for FA dehydration to CO with a maximum selectivity of ∼99.8%, and the onset reaction temperature over the γ-Mo2N-based catalysts was also much lower (100–200 °C) than those over conventional solid acid catalysts. In particular, the γ-Mo2N obtained at a pyrolysis temperature of 625 °C exhibited the highest activity, which was followed by those of the catalysts obtained at 600, 650, and 700 °C, which was consistent with the acidities of these catalysts. However, the CO selectivity monotonically increased with the increase in the catalyst preparation temperature but decreased with the increase in the FA decomposition temperature. FA conversion decreased when the contact time between the catalyst and the FA was reduced, but conversely, the CO selectivity increased. The enhanced CO selectivity might be ascribed to dehydrogenation having comparatively lower kinetics than that of dehydration, and thus, compared to dehydration, dehydrogenation could be more apparently suppressed by the reduced contact time, resulting in a higher CO selectivity. Moreover, it was found that the γ-Mo2N catalyst had no obvious deactivation for FA dehydration over the 20 h continuous operation period.