The transient behavior of catalytic methane steam reforming (MSR) coupled with simultaneous carbon dioxide removal by carbonation of CaO pellets in a packed bed reactor for hydrogen production has been analyzed through a mathematical model with reaction experiments for model verification. A dynamic model has been developed to describe both the MSR reaction and the CaO carbonation-enhanced MSR reaction at non-isothermal, non-adiabatic, and non-isobaric operating conditions assuming that the rate of the CaO carbonation in a local zone of the packed bed is governed by kinetic limitation or by mass transfer limitation of the reactant CO2. Apparent carbonation kinetics of the CaO pellet prepared has been determined using the TGA carbonation experiments at various temperatures, and incorporated into the model. The resulting model is shown to successfully depict the transient behavior of the in situ CaO carbonation-enhanced MSR reaction. The effects of major operating parameters on the transient behavior of the CaO carbonation-enhanced MSR have been investigated using the model. The bed temperature is the most important parameter for determining the amount of CO2 removed by carbonation of CaO, and at temperatures of 600degreesC 650degreesC, 700degreesC and 750degreesC, the CO2 uptake is 1.43, 2.29, 3.5 and 5.09 mol-CO2/kg-CaO, respectively. Simultaneously with the increase in CO2 uptake with increasing temperature, the corresponding amounts of hydrogen produced are 1.56, 2.54, 3.91 and 5.63 mol-H-2/kg-CaO, at the same temperatures as above. Operation at high pressure, high steam to methane feed ratio, and the decreased feed rate at a given temperature are favorable for increasing the degree of the overall utilization of CaO pellets in the reactor bed, and for lowering the CO concentration in the product. (C) 2004 Elsevier Ltd. All rights reserved.