Reaction induced diffusio-phoresis of ordinary catalytic particles

Abstract

In this paper we demonstrate experimentally diffusio-phoresis of plain catalytic particles driven by the macroscopic concentration field that the particles generate by themselves. This introduces a general framework for heterogeneous catalysis where the driving force relies on solute gradients that are generated by a mere uneven distribution of catalytic particles. Whenever an inhomogeneity appears in the particle distribution, the higher particle density region will lower the reactant concentration more than the surrounding environment. This macroscopic concentration gradient propels the particles towards higher reactant concentration by surface driven flows. The nature of this flow originates from osmotic pressure differences and diffusion potentials in the case of charges species. This context of diffusio-phoresis demonstrates an additional transport mechanism for slurry reactors. We investigate the reaction induced particle movement for a photocatalytic degradation reaction using TiO₂ suspensions in a co-flow microchannel. We have analyzed the experimental particle distribution by means of a numerical model that includes diffusio-phoretic movement of the catalytic particles. This model stresses the importance of particle characteristics, like surface potential, reactant and product interaction, and reaction kinetics with respect to the catalyst particle migration.