Direct amination of 1-octanol with NH3 over Ag-Co/Al2O3: Promoting effect of the H2 pressure on the reaction rate

Abstract

The kinetics of the direct gas-phase amination reaction of 1-octanol with ammonia was studied over a Ag-Co/Al2O3 catalyst. An exhaustive experimental dataset was acquired on a Flowrence unit using a full factorial experimental design, covering the effect and interactions of the 1-octanol, ammonia and hydrogen partial pressures in the range 160–180 °C. An apparent zero order was obtained for both reactants (i.e. 1-octanol and NH3), addressing alcohol dehydrogenation as the rate-determining step of the overall catalytic process. Most interestingly, a non-trivial positive effect of the exogeneous H2 pressure was observed on the 1-octanol conversion, also favoring the formation of the secondary amine. To unveil the promoting role of H2 on the reaction rate, a comprehensive kinetic modeling study was carried out. Based on the observed experimental trends, various kinetic models were proposed relying on an in situ catalytic deactivation-regeneration mechanism of the catalyst surface. Upon statistical discrimination, a robust kinetic model could be obtained, pointing out the adsorbed octylimine intermediate as the most plausible source of deactivation. The kinetic model afford an excellent description of the observed experimental trends at both low and high 1-octanol conversion and provides a sound mechanistic explanation accounting for the unexpected role of H2 on alcohol amination reactions.