A data-based model of surface states in packed tubes is joined with an intraparticle diffusion-reaction model to describe reactors with significant intraparticle gradients. This modelling approach is demonstrated with steady-state simulations of the partial oxidation of n-butane to maleic anhydride in a packed-tube reactor with spherical particles and a tube/particle diameter ratio of 2.02. The simulation is based on a correlation of heat transport experiments performed in a unique packed-tube gas flow apparatus, and on a kinetic model taken from the literature. An orthogonal collocation scheme, using rounded Hahn polynomial zeros as axial nodes and Jacobi zeros as intraparticle nodes, allows efficient solution of the resulting detailed reactor model.