An In Situ TEM Study of the Influence of Water Vapor on Reduction of Nickel Phyllosilicate - Retarded Growth of Metal Nanoparticles at Higher Rates.

Unavoidable water formation during the reduction of solid catalyst precursors has long been known to influence the nanoparticle size and dispersion in the active catalyst. This in situ transmission electron microscopy study provides insight into the influence of water vapor at the nanoscale on the nucleation and growth of the nanoparticles (2-16 nm) during the reduction of a nickel phyllosilicate catalyst precursor under H 2 /Ar gas at 700 °C. Water suppresses and delays nucleation, but counterintuitively increases the rate of particle growth. After full reduction is achieved, water vapor significantly enhances Ostwald ripening which in turn increases the likelihood of particle coalescence. This study proposes that water leads to formation of mobile nickel hydroxide species, leading to faster rates of particle growth during and after reduction.