Atomistic simulation of the nano-structural evolution of Raney-type catalysts from spray-atomized NiAl precursor alloys during leaching with NaOH solution

Abstract

A model for the nano-structural evolution of Raney-type nickel catalysts (widely used in hydrogenation reactions) from the constituent intermetallic phases present in nickel-aluminium precursor alloys is presented here. Nano-porous nickel catalysts are prepared via a caustic leaching process where the NiAl alloy powder (typically 50-50 at.%) is immersed in concentrated NaOH solution in order to leach away the aluminium present to leave a highly-porous nickel catalyst (often referred to as spongy nickel).The temporal evolution of the nickel catalyst is described by a kinetic Monte Carlo (kMC) method, which captures two dominant processes taking place on leaching with NaOH solution: rapid aluminium dissolution from the crystalline intermetallic phases and surface adatom diffusion of nickel and aluminium. Structural changes from NiAl 3 and Ni 2 Al 3 phases present in the starting alloy are considered on an event-by-event basis. Individual crystallite size, pore diameter and effective surface area are predicted. Finally, a Metropolis Monte Carlo method is used to investigate the surface nature of the as-leached catalyst and compared to concurrent experimental investigations.