Nanoceria-promoted low Pd–Ni catalyst for the synthesis of secondary amines from aliphatic alcohols and ammonia

Abstract

This paper describes the preparation of a series of bimetallic Pd–Ni catalysts supported over nanoceria with very low Ni and Pd loading (<0.5 wt%) for the direct amination of aliphatic alcohols with ammonia. Different metal impregnation methods were used for engineering the interaction between Pd, Ni and nanoceria. The as-prepared catalysts were characterized in detail by combining XRD, H₂-TPR, H₂-TPD, STEM-EDS-SDD and XPS. The sequence of impregnation of both metals and the Pd loading affected to an important extent the catalytic activity by conditioning the crystallite size and the Pd and Ni speciation, as well as the reducibility and reversible H₂ storage properties. By optimizing the preparation protocols, a 0.5wt% Pd–0.5wt% Ni–Pd/CeO₂ formulation prepared by sequential impregnation of the nickel and palladium precursors afforded 80% yield of dioctylamine at almost full conversion [TON = 1160 mmol per mmol (Ni + Pd)_surface] in the direct amination reaction of 1-octanol with ammonia at 180 °C for 2 h. Metal leaching during the reaction could be completely avoided. The high catalytic performance of Pd–Ni induced by nanoceria places this catalyst among the best ever reported catalysts for the synthesis of secondary amines.