Pd-Co catalysts prepared from palladium-doped cobalt titanate precursors for chemoselective hydrogenation of halonitroarenes

Bimetallic Pd-Co catalysts supported on the mixed oxides CoTiO₃-CoO-TiO₂ (CTO) were synthesized via the thermal reduction of Pd-doped cobalt titanates Pd_xCo_1-xTiO₃ and evaluated for the chemoselective hydrogenation of halonitroarenes to haloarene-amines. The nominal Pd mass percentage of the Pd-Co/CTO systems was varied from 0.0 to 0.50. After the thermal reduction of Pd_xCo_1-xTiO₃ at 500 °C for 3 h, Pd was completely reduced and Co was partially reduced, producing a mixture of ionic Co, metallic Co, and TiO₂-rutile species to give the supported bimetallic catalysts. The metallic cobalt content increased with the Pd content of the precursor. The catalytic activity toward 4-chloronitrobenzene increased with the Pd content; however, >0.1 mass% Pd decreased the chemoselectivity toward 4-chloroaniline due to the formation of the hydrodehalogenation product—aniline. The 0.1Pd-Co/CTO system was used as a model catalyst to produce haloarene-amine building blocks for linezolid, loxapine, lapatinib, and sorafenib with >98% conversion, 96% chemoselectivity, and no hydrohalogenation products. Finally, recycling tests of the 0.1Pd-Co/CTO catalyst showed loss of activity and selectivity during the third cycle due to catalyst deactivation. Regeneration treatments, every two catalytic cycles, allowed six operation cycles without loss of chemoselectivity and only a slight decrease in catalytic activity during the last cycle.