Phenol and dihydroxybenzene hydrogenation catalysts based on polyamide dendrimers and rhodium species

Abstract

Heterogeneous catalysts based on rhodium nanoparticles and first- and second-generation poly(amidoamine) (PAMAM) dendrimers crosslinked with hexamethylene diisocyanate have been synthesized. It has been found that catalyst samples with a particle size of 0.88 to 1.96 nm, depending on the PAMAM dendrimer generation, are effective in the hydrogenation of phenol, hydroquinone, resorcinol, and pyrocatechol (85°C, 30 atm O2, 2 h). In phenol hydrogenation, the selectivity for cyclohexanone is 100%. Cyclohexanone has not undergone further transformation under the reaction conditions. The main products of dihydroxybenzene hydrogenation have been trans-cyclohexanediols, with their proportion decreasing in the order: resorcinol > hydroquinone > pyrocatechol. The selectivity has been found to be 100% for 1,3-cyclohexanediol, 97–99% for 1,4-cyclohexanediol, and 33–91% for 1,2-cyclohexanediol. The catalysts based on the second-generation dendrimer have shown a high activity in dihydroxybenzene hydrogenation (TOF of 6600 to 35000 h−1).