  A migration of charged particles relative to a solvent, caused by a gradient
of salt concentration and termed a diffusiophoresis, is of much interest being
exploited in many fields. Existing theories deal with diffusiophoresis of
passive inert particles. In this paper, we extend prior models by focusing on a
particle, which is both passive and catalytic, by postulating an uniform ion
release over its surface. We derive an expression for a particle velocity
depending on a dimensionless ion flux (Damkohler number Da) and show that a
charged region is formed at distances of the order of the particle size,
provided the diffusion coefficients of anions and cations are unequal. When Da
becomes large enough, the contribution of this (outer) region to the particle
velocity dominates. In this case the speed of catalytic passive particles
augments linearly with Da and is inversely proportional to the square of
electrolyte concentration. As a result, they always migrate towards a high
concentration region and in dilute solutions become much faster than inert
(non-catalytic) ones.
