Unraveling the Deactivation Precipitation Mechanism of Iridium Catalysts in Methanol Carbonylation to Acetic Acid via Dissipative Particle Dynamics.

Iridium catalysts offer superior activity and cost-efficiency over Rh in the low-pressure methanol carbonylation for acetic acid. However, industrial use is limited by deactivation via precipitation, which is difficult to resolve experimentally due to complex variable coupling. This study employs mesoscopic dissipative particle dynamics (DPD) simulations with a chemically accurate coarse-grained model linking molecular interactions to reactor-scale behavior. Microsecond simulations reveal a self-assembly mechanism: phase separation forms a water-in-oil microstructure. Amphiphilic iridium catalyst ligands migrate to the oil-water interface via a hydrophilic-hydrophobic synergy, leading to significant interfacial enrichment. Aggregates form critically at 4000 ppm of Ir or 2 wt % water, with RDF analysis establishing an aggregation criterion. Solvent effects of byproducts (ethanol, propionic acid, C2+ alkyl iodides) on aggregation are assessed, predicting concentration-dependent interfacial deactivation. Furthermore, through density functional theory (DFT) calculations, the interaction mechanism between impurity molecules and iridium active centers was revealed at the electronic level, clarifying the microscopic root of their promotion of aggregation. This multiscale framework decouples variables and provides stabilization strategies via interface engineering and impurity control, establishing a transformative computational platform bridging molecular catalyst design with reactor optimization.