Ta organometallic complexes have been studied as HDN models and dispersed, supported Ta is active in reductions and isomerizations, but related HDN catalysts are not known. Here we use highly-dispersed, supported Ta derived from calixarene-Ta(V) complexes in quinoline HDN. Supported Ta is minimally reactive, but has high selectivity to propylaniline and propylbenzene, consistent with (unusual) direct C-N bond hydrogenolysis. Propylbenzene appears neither over catalysts derived from TaCl 5 at any loading, nor from partially reduced catalysts. XAS and FTIR show Ta(V) is stable during reaction. Adding Pd increases propylbenzene yields, especially for Pd-Ta/Al 2O 3. Large enhancements suggest spillover-mediated cooperativity between initial hydrogenation over Pd, followed by hydrogenolysis of subsequent intermediates coordinated to Lewis acidic Ta(V). In model reactions, adsorbed aniline is reduced to cyclohexane over Pd-Al 2O 3, but benzene over Pd-Ta/Al 2O 3, and DRUV-vis spectra are consistent with the formation of Ta imido species, indicating direct C-N bond hydrogenolysis.
ASJC Scopus subject areas
- Chemical Engineering(all)