A 2-D heterogeneous convection reaction model for a gas–solid lamp-in-tube annular photocatalytic reactor is presented. The catalyst (TiO2) is supported on a reticulated-foam monolithic structure placed in the annular space between the UV lamp and the reactor wall. Mass balances for individual species are coupled through the reaction-rate expression that appears in the boundary condition at the fluid–solid interface in heterogeneous catalytic reactor models. The heterogeneous reaction rate is modeled using semiempirical Langmuir-Hinshelwood-Hougen-Watson (LHHW) kinetics with adsorption constants for various species. The local volumetric rate of energy absorption (LVREA) term in the rate expression was computed using a 3-D polychromatic radiation-field model. The overall system of nonlinear partial differential equations was solved using a combination of the Crank-Nicolson method and the globally convergent Newton-Raphson method. The apparent, average quantum yield in the LHHW kinetic rate form is the single adjustable parameter in the model. Isopropanol (IPA) was chosen as the test contaminant to conduct experimental performance measurements for model validation. Model-predicted radial and axial profiles for bulk and surface concentration reveal that the extent to which mass transport influences the operation of a photocatalytic reactor is determined largely by the local magnitude of the LVREA. Similitude in the scale-up of an annular lamp-in-tube heterogeneous photocatalytic reactor is achieved only when the dimensionless radial radiation profile, as well as corresponding magnitudes of a geometric number, the Peclet number, the Stanton number, and the photocatalytic analog of the Damköhler number, are identical.