Catalytic ozone decomposition reaction was used to study the performance of a 76 mm i.d. and 10.2 m high gas-solid circulating fluidized bed (CFB) riser reactor. Optical fiber probes and an ultraviolet (UV) ozone analyzer were used to obtain comprehensive information about local solid holdup and ozone concentration profiles at different axial and radial positions. The operating conditions were at superficial gas velocities of 2-5 m/s and solid circulation rates of 50 and 100 kg/(m(2).s). Axial ozone concentration profiles significantly deviated from the plug-flow behavior, with most conversion occurring in the entrance region or flow developing zone of the riser reactor. Strong correlation was observed between the spatial distributions of solids and ozone; higher local solid holdups cause lower ozone concentrations due to greater reaction. Radial gradients of the reactant (ozone) concentrations increased with the height of the riser, and decreased with increasing superficial gas velocity and solid circulation rate. Contact efficiency, a measure of the interaction between gas and solid phases indicated high efficiency in the flow developing zone and decreased with increasing height in the fully developed region. (C) 2013 Elsevier B.V. All rights reserved.