The coupling of reaction and diffusion between neighboring active sites in the catalyst pore leads to the spatiotemporal fluctuation in component concentration

which is very important to catalyst performance and hence its optimal design. Molecular dynamics simulation with hard-sphere and pseudo-particle modeling has previously revealed the non-stochastic concentration fluctuation of the reactant/product near isolated active site due to such coupling

using a simple model reaction of A → B in 2D pores. The topic is further developed in this work by studying the concentration fluctuation due to such coupling between neighboring active sites in 3D pores. Two 3D pore models containing an isolated active site and two adjacent active sites were constructed

respectively. For the isolated site

the concentration fluctuation intensifies for larger pores

but the product yield decreases

and for a given pore size

the product yield reaches a peak at a certain reactant concentration. For two neighboring sites

their distance (

d

) is found to have little effect on the reaction

but significant to the diffusion. For the same reaction competing at both sites

larger

d

leads to

more efficient diffusion and better overall performance. However

for sequential reactions at the two sites

higher overall performance presents at a smaller

d

. The results should be helpful to the catalyst design and reaction control in the relevant processes.