Acetonitrile Synthesis from CO, H2, and NH3 over Iron Catalysts

Abstract

The reaction of 1 : 2 : 1 CO : H2 : NH3 at 698-723 K over reduced or prenitrided iron powder is initially active for production of CH3CN, but deactivates quickly due to extensive carbon deposition. Much longer periods of stability are observed over a highly dispersed, prereduced Fe/SiO2 or Fe on carbon catalysts, suggesting the importance of small particle size for resistance to coking. Prereduced Fe/SiO2 catalysts containing only Fe2+ are less active for the nitrile reaction initially than those containing larger particle Fe0 or Fe2N phases, but increase in activity with time on stream. Mössbauer spectroscopy measurements indicate that the nitrided Fe/SiO2 catalyst is converted in minutes to Fe carbide during reaction. Thus little or no bulk nitrogen remains during reaction. Fe0 in supported or unsupported catalysts quickly converts to a carbide during reaction as well. Unlike the unsupported catalyst, which ceases to be active, the supported catalyst always maintains some finite activity. This activity is attributed to the iron particles that are below the size that produces excessive carbon deposition.