Phase-Equilibrium-Guided Carbonyl Processing of Highly Active Nickel Powders

Nickel powders with large specific surface areas are cost-effective alternatives to noble-metal catalysts for hydrogen-producing reactions, including methane reforming and ammonia decomposition. However, thermodynamic control of nickel carbonyl formation and decomposition is essential for producing catalytically active powders through the Mond process. In this study, we established a thermodynamic framework for carbonyl nickel production by combining Gibbs free-energy analysis, the Clausius–Clapeyron relation, and liquid–gas phase-equilibrium calculations for the reaction Ni + 4CO ↔ Ni(CO)₄. The resulting phase-equilibrium map identified operating windows for selective nickel carbonyl formation and subsequent decomposition. High-pressure carbonylation achieved 99.7% nickel conversion at 200 °C and 50 atm, whereas thermal decomposition at 300 °C and 1 atm yielded 57.9% nickel recovery. Scanning electron microscopy revealed needle-like nickel particles, suggesting a morphology favorable for catalytic applications. Process simulations captured pressure evolution and Ni(CO)₄ phase transitions, supporting rational selection between liquid- and gas-phase operating regimes. These findings indicate that phase-equilibrium-guided carbonyl processing offers a scalable route to high-activity nickel powder catalysts for hydrogen-production technologies.