γ-alumina is a widespread support in heterogeneous catalysis, for many processes ranging from biomass conversion to petroleum industries. However, its affinity for water is responsible for its chemical degradation due to rehydration. Thus, oxygenated organic additives are added to improve its stability in presence of liquid water. A better understanding of the interaction of these organic molecules with the support in liquid water is still required to better rationalize the stabilization process of the catalyst. For that purpose, with ab initio molecular dynamics (AIMD) and explicit description of water, we simulate the interaction of alcohols and polyols on the various sites of γ-alumina (110) surface in presence of water, on a large Al128O192(H2O)165 model. Periodic enhanced AIMD simulations have been performed using Density Functional Theory with the CP2K code (PBE-D3 functional, time-step of 0.5 fs, CSVR thermostat, production runs of 10-15 ps). Thermodynamic integration (at 330 K) for the desorption process (Figure 1.b) provides a free energy barrier of 51 kJ/mol for chemisorbed ethanol (μ1 mode, Figure 1.a) and 89 kJ/mol for bridging ethoxy (μ2 mode). Metadynamics and QM/MM simulations have also been performed in order to improve the description of the solvation process and the sampling of liquid water at the interface. The methods proved to be complementary, giving insight into the interaction of alcohols with γ-alumina at the interface with liquid water.

Stability of the γ-alumina support in presence of water in biomass conversion process: adsorption of alcohols investigated by ab initio molecular dynamics

ACS Spring Meeting 2021

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