Many chemical reactions make use of a catalyst, which not only increases the chemical reaction rate but in many cases also dictates the selectivity of a reaction. In heterogeneous catalysis the catalyst is usually present as a solid phase, for example a porous particle with a high surface area. In the case where the active catalytic material is a metal (typically elements of Group VIII or Group IB of the periodic table), the active metal (nano)particle is supported on a carrier to achieve higher dispersion and improved resistance to sintering. A high dispersion means that many of the possible active sites on a metal nanoparticle are available for catalysis, and this typically means that the nanoparticles are very small (~1nm). Recently it has been discovered that the density of the particles can be more significant than the particle size. This effect has been called the “Particle Proximity Effect”[1,2], and has been discussed mainly in relation with the oxygen reduction reaction in fuel cells. The phenomenon may however also play a role in other heterogeneous catalytic reactions.
The first goal of the assignment is to investigate, via a literature search, what is already known about the theory behind the "proximity effect". The second goal is to make a model for simple system of a 1D array of catalyst particles, and study what the effect is of the distance between the particles on the overall reactivity of the system, and the scaling laws related to this problem. In this model, both the reaction kinetics on the particle surface and the reactant/product diffusion around and inbetween the particles will be considered. If time permits, the third goal is to extend the model to a 2D array of catalytic particles.
- M. Nesselberger et al., The effect of particle proximity on the oxygen reduction rate of size-selected platinum clusters, Nature Materials 12 (2013) 919-924.
- J. Speder et al. The particle proximity effect: from model to high surface area fuel cell catalysts, RSC Advances 4 (2014) 14971-14978.
Han Gardeniers; Email: firstname.lastname@example.org