Pyrrolic nitrogen-doped carbon nanotubes: physicochemical properties, interactions with Pd and their role in the selective hydrogenation of nitrobenzophenone

Abstract

Nitrogen-doped carbon nanotubes (N-CNTs) containing 63%, 73% and 80% pyrrolic-N were synthesized and used to evaluate the influence of pyrrolic nitrogen on the physicochemical properties and catalytic activity of Pd supported on N-CNTs (Pd/N-CNTs). Micrographs of Pd/N-CNTs showed that Pd was located along the defect sites of N-CNTs indicating strong Pd-support interactions. X-ray photoelectron spectroscopy revealed that the abundance of Pd⁰ decreased while that of Pd²⁺ increased as the quantity of pyrrolic nitrogen increased. The Pd²⁺ species were formed as Pd–N coordination complexes, which stabilized Pd²⁺ nanoparticles. Selective hydrogenation of nitrobenzophenone to aminobenzophenone or p-benzylaniline was used to evaluate the catalytic performance of catalysts. Pd/N-CNTs exhibited a higher selectivity towards aminobenzophenone than Pd on carbon nanotubes and Pd on activated carbon. The enhanced selectivity towards nitro-reduction alone, observed with Pd/N-CNTs was attributed to the promoting effect of pyrrolic-N. Hence, Pd/N-CNTs are promising catalysts for the selective reduction of nitro arenes.