On the Use of Calcined Agro-Industrial Waste as Palladium Supports in the Production of Eco-Friendly Catalysts: Rice Husks and Banana Peels Tested in the Suzuki-Miyaura Reaction

Two calcined agro-industrial wastes [rice husk ash (RHA) and banana peel ash (BPA)] with immobilized PdCl2 (Pd/RHA and Pd/BPA, respectively) that were produced at an extremely low cost were found to be efficient catalysts for Suzuki-Miyaura cross-coupling reactions. Iodo- and bromoarenes coupled with aryllboronic acid under eco-friendly conditions (i.e., phosphine-free and with ethanol as the solvent) to give very good product yields. The study of Pd/RHA in the Suzuki-Miyaura reaction showed that the catalyst only promoted the cross-coupling of bromoarenes after no iodoarenes in the reaction medium remained (competition study). Also, the Pd/RHA showed catalytic activity up to the fifth recycling, as evidenced by active soluble Pd found with a new proposed method based on the use of hollow fiber. An Hg(0) poisoning test did not find the presence of unprotected Pd(0) in the system. Thus, it is believed that there is a synergistic catalytic action between Pd supported in Pd/RHA and leached Pd(II). [GRAPHICS] .