Partially decomposed dolomite is a promising base material for regenerable MgO-based sorbents to capture CO2 from precombustion syngas at high pressures and temperatures. An important characteristic of the sorbent affecting the economic Viability of this class of sorbents is the reactivity and the capacity of the sorbent for CO2 capture. To improve the reactivity of the sorbent, the thermal behavior and the kinetics of partial decomposition of dolomite were studied in the temperature range of 520-610 degrees C in a dispersed-bed reactor. The microstructure and the nature of the solid products were found to be strongly dependent on the CO2 partial pressure near the reacting interface and on the decomposition temperature: A significant increase in the rate of the dolomite decomposition reaction was found in the presence of steam. Steam improves the kinetics of decomposition, modifies the radial distribution of the pores, and improves the connectivity Of the pores inside the dolomite particles, which decreases the diffusion resistance of produced carbon dioxide inside the particle. A shrinking core model with variable product layer diffusivity was used to fit the experimental data and determine the kinetic parameters of the dolomite decomposition reaction. The results indicate that transport of CO2 across the reacting interface. in the porous particle was the main limiting factor in the decomposition reaction at the experimental conditions investigated. The model is shown to provide an excellent fit to the experimental data on partial decomposition of dolomite in the temperature range studied.