Selective hydrogenation of amides using Rh/Mo catalysts

摘要

Rh/Mo catalysts formed in situ from Rh_6(CO)_(16) and Mo(CO)_6 are effective for the liquid phase hydrogenation of CyCONH_2 to CyCH_2NH_2 in up to 87% selectivity, without the requirement for ammonia to inhibit secondary amine formation. Use of in situ HP-FTIR spectroscopy has shown that decomposition of metal carbonyl precursors occurs during an extended induction period, with the generation of recyclable, heterogeneous, bimetallic catalysts. Variations in Mo:Rh content have revealed significant synergistic effects on catalysis, with optimum performance at values of ca. 0.6, and substantially reduced selectivities at ≥1. Good amide conversions are noted within the reaction condition regimes 50-100 bar H_2 and 130-160 °C. Ex situ characterization of the catalysts, using XRD, XPS and EDX-STEM, has provided evidence for intimately mixed (ca. 2-4 nm) particles that contain metallic Rh and reduced Mo oxides, together with MoO_3. Silica-supported Rh/Mo analogues, although active, perform poorly at <150 °C and deactivate during recycle.