Gas-solid riser flows tend to be characterized by particle clusters that significantly affect the flow, the mass/heat transfer, and the reaction behavior. To account for the effect of such particle clustering on the mass transfer between gas and particles, we use a lattice Boltzmann model with coupled mass transfer to conduct fully resolved simulations for flow past arrays of particles with both homogeneous and heterogeneous structures. We find that the distributions of velocity and concentration among the particle arrays are both affected significantly by particle clustering, and that the computed Sherwood number for either the homogeneous or heterogeneous particle structure increases exponentially with Reynolds number. However, the Sherwood number for homogeneously distributed particles is 3-5 times greater than that for heterogeneously distributed particles. This further supports the case for particle clustering having a serious effect on the mass-transfer efficiency between gas and solid in processes that involve flow past arrays of particles. Finally, the feasibility of using the lattice Boltzmann method with our mass-transfer model to describe the mass transfer in a heterogeneous two-phase gas-solid flow is also discussed. (C) 2017 Elsevier B.V. All rights reserved.