Dehydration of Amides to Nitriles over Heterogeneous Silica-Supported Molybdenum Oxide Catalyst

Silica-supported molybdenum oxide (MoO_x/SiO₂) with 4.8 wt% Mo (0.5 mmol g⁻¹) was an effective and reusable heterogeneous catalyst for dehydration of 2-furamide to 2-furonitrile (96 % yield). The catalyst was applicable to the dehydration of various amides including heteroaromatic, aromatic and alkyl amides, providing the corresponding nitriles in high yields (87-97 %). Based on the results of catalyst characterizations (XRD, TEM, UV-vis, Raman) and activity tests, MoO_x species are highly dispersed over SiO₂, and heptamolybdate anion ([Mo₇O₂₄]⁶⁻) and isolated dioxo ((O=)₂MoO₂) were mainly formed on the SiO₂ support of the optimal MoO_x/SiO₂ catalyst. The strong Brønsted acid sites (Mo-OH−Si site) can be formed from the MoO_x species and the adjacent silanol group, and the acid-base pair site (Mo(=O)−OH−Si site) of the strong Brønsted acid site (Mo−OH−Si site) and base site (Mo=O) over MoO_x/SiO₂ catalyst could be the main active site for the dehydration of amides.