(351c) Building a Microkinetic Model from First Principles for Higher Amine Synthesis on Pd and Co Catalysts

Production of higher amines from lower amine and nitrile feedstock using heterogeneous catalysis is an important industrial process for the production of solvents, agrochemicals, feed and food additives, rubber processing chemicals, surfactants, water treatment chemicals, and pharmaceuticals. 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 Pd and Co surfaces.[1-2] 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 Pd and Co surfaces. Key mechanistic findings are discussed in the context of larger alkane nitrile hydrogenation processes, which are ordinarily performed in the liquid phase.

A microkinetic model based on the elucidated reaction mechanism was developed for higher amine synthesis on Pd- and Co-based catalysts.[3] The reaction network consists of 2 reactants, 4 products, 16 surface species, 6 chemisorption/desorption steps and 12 surface elementary reactions. The rate of every elementary step is obtained using the corresponding DFT reaction enthalpies and activation energies previously calculated. While reaction enthalpies of the surface elementary reactions were maintained fixed in the model, activation energies and chemisorption enthalpies of reactants and products needed further refinement by estimation with experimental data. Pre-exponential factors for the forward and reverse steps were calculated following statistical thermodynamics assumptions. The kinetically relevant elementary steps in the reaction network were identified. Detailed concentration profiles of reactants, products and surface species are obtained as a function of operating conditions. The microkinetic model can successfully describe general trends such as the different amines selectivities observed with Pd and Co catalysts.

[1] Adamczyk, A. J., First-principles analysis of acetonitrile reaction pathways to primary, secondary, and tertiary amines on Pd(111), Surface Science, 682, 84-98, 2019

[2] Lozano-Blanco G., Adamczyk, A.J., Cobalt-catalyzed nitrile hydrogenation: Insights into the reaction mechanism and product selectivity from DFT analysis, Surface Science, Submitted

[3] Lozano-Blanco, G.; Surla, K.; Thybaut, J. W.; Marin, G. B., Extension of the Single-Event Methodology to Metal Catalysis: Application to Fischer-Tropsch Synthesis, Oil & Gas Science and Technology-Revue D’IFP Energies Nouvelles 66 (3), 423-435, 2011