Calcium-looping is a promising CO2-capture technology. The economics and environmental impact of the process are affected by the rapid decay in reactivity of the limestone sorbent, which necessitates a high purge rate from the system to maintain sorbent reactivity. This work investigates techniques to improve long-term reactivity in such a system by doping the limestone with a variety of different dopants. It also demonstrates that the main reason for improvement is that the doping increases the volume of pores around 100 nm in diameter in the calcined material after a significant number of cycles, in comparison to the calcine from an undoped sorbent. Improved reactivity means a lower required purge-rate and fewer potential disposal issues, and less fresh limestone to be used. Doped samples were subject to repeated cycles of carbonation and calcination in a fluidized bed reactor (FBR). The work includes the use of inorganic salts MgCl2, CaCl2, Mg(NO3)2, and the Grignard reagent-isopropylmagnesium chloride...