Catalytic effect of water on calcium carbonate decomposition

• The rate of calcium carbonate decomposition increases when steam is applied. • A catalytic effect occurs since the activation energy decreases without by-products formation. • Steam opens a new pathway via formation of surface bicarbonate. • Bicarbonate decomposes in two steps, via surface calcium hydroxide. The search for cheap solutions for carbon dioxide capture in order to prevent global warming is still challenging. Calcium oxide may be a suitable sorbent, but the regeneration process from calcium carbonate requires too high temperatures, causing sintering and decreasing sorption capacity. In this study the effect of steam on the decomposition of the carbonate is investigated. A clear rate-enhancing effect up to a factor of 4 is observed when steam concentrations up to 1.25% are applied during isothermal reactions at temperatures between 590 and 650 °C. This results in a decrease of the apparent activation barrier from 201 to 140 kJ mol −1 , caused by the opening of a new reaction pathway. The kinetics of steam catalyzed decomposition of CaCO 3 is discussed and a simple reaction scheme is proposed, including estimation of kinetic constants. The new pathway proceeds via formation of a stable surface bicarbonate followed by decomposition to surface OH groups, which then decompose by desorbing H 2 O.