Enhanced hydrogen (H-2) synthesis in biomass gasifiers using a carbon dioxide (CO2) sorbent is a promising method for the renewable production of a H-2-rich fuel gas. Calcium oxide (CaO) is the most likely sorbent for in situ CO2 capture, because (i) CaO reacts with CO2 in the temperature range suitable for biomass gasification with steam; GO CO2 capture based on a gas-solid absorption reaction is exothermic, providing additional heat to drive the endothermic biomass conversion process; (iii) CaO can be regenerated, producing a pure stream of CO2; and (iv) CaO is derived from a range of inexpensive and abundant precursors (e.g., limestone (CaCO3), dolomite (CaCO3-MgCO3), or calcium hydroxide (Ca(OH)(2))). Characterizing the reactivity of the CaO sorbent is relevant to determine the overall consumption of sorbent and, hence, the cost of the process. In this work, we present a review of the factors that affect sorbent reactivity for enhanced H2 synthesis in biomass gasifiers, including (i) diffusion-inhibited conversion, (ii) diminished reactivity post-sorbent regeneration due to particle sintering; (iii) loss of reactive surface area due to coking; and (iv) competing chemical reactions. In this context, we present experimental results that demonstrate the influence of key parameters on the preparation and characterization of a tailored C02 sorbent derived from precipitated CaCO3. We confirm the fundamental relationship between the morphological structure of CaCO3 and the subsequent reactivity of CaO, specifically demonstrating enhanced C02 capture capacity of CaO derived from mesoporous CaCO3, beyond stoichiometric limitations.