Cobalt-catalyzed nitrile hydrogenation: Insights into the reaction mechanism and product selectivity from DFT analysis

Abstract

When primary amines are the desired product of nitrile hydrogenation, the use of cobalt catalysts are commonly recommended. Nitrile hydrogenation using heterogeneous catalysis is an important commercial process for the production of primary, secondary, and tertiary amines. In recent years, modern experimental methods have investigated the detailed mechanism underlying the surface reactions of nitrile hydrogenation. These experimental studies provide new insights, but also raise additional questions. To help resolve these inconsistencies, modern theoretical techniques have been applied by way of periodic plane-wave Density Functional Theory (DFT) calculations to study acetonitrile adsorption and hydrogenation to primary (monoethylamine), secondary (diethylamine), and tertiary amines (triethylamine) over flat Co surfaces, specifically the Co(0001) surface facet. The presented theoretical analysis applies fundamental physical chemistry and reaction engineering principles to better understand surface reaction mechanisms in the kinetically-controlled regime at low surface coverages. Reaction pathways for acetonitrile hydrogenation and the most probable routes for secondary and tertiary amine formations are discussed. The presented first-principles analysis is in line with experimental observations of gas-phase acetonitrile hydrogenation on flat Co surfaces. Key mechanistic findings are discussed in the context of larger alkane nitrile hydrogenation processes, which are ordinarily performed in the liquid phase.