Cyclic carbonation and calcination reactions were investigated for capturing CO2 from combustion and gasification processes. Sorbent particles in the size range 600-1400 mum were subjected to multiple capture cycles at atmospheric pressure to obtain a surface mapping of conversion based on calcination and carbonation temperatures. Steam hydration of CaO was utilized to increase both pore area and pore volume to improve long-term conversion to CaCO3 over multiple cycles. The steam hydration improved the long-term performance of the sorbent, resulting in directly measured conversions as high as 52% and estimated conversions as high as 59% after up to 20 cycles. It is estimated that the increase in conversion has improved the economics of the proposed process to the point where commercialization is attractive. It has been shown that when carbonating in the temperature range from 700 to 740 degreesC, calcination temperatures from 700 to 900 degreesC can be used without seriously reducing the conversion of CaO for CO2 capture over multiple cycles. Processes based on this approach are expected to be able to reduce CO2 emissions from coal- and petroleum coke-fired fluidized bed combustors by up to 85%, while avoiding excessive sorbent replacement.