Sorption enhanced water gas shift reaction (SEWGS) based on calcium looping is an emerging technology for hydrogen production and CO2 capture. SEWGS involves mainly two reactions, the catalytic WGS reaction and the bulk carbonation of CaO with CO2, and the solid product is CaCO3, and the Ca(OH)(2) may be formed from the reaction of CaO with H2O with the presence of steam in gas phase. The effect of Ca(OH)(2) and CaCO3 on the catalytic WGS reaction and carbonation reaction was studied in a fluidized bed reactor. It was found that the hydrated sorbent and CaCO3 did not show any catalytic reactivity toward WGS reaction at 400 degrees C. When the temperature was increased to 500 degrees C and 600 degrees C, the catalytic reactivity of hydrated sorbent was recovered partially, but this will depend on the steam fraction in gas phase, the recovery of fresh CaO surface from dehydration of Ca(OH)(2) may be the reason of catalytic reactivity recovery. CaCO3 can catalyze the WGS reaction at the high-temperature (> 600 degrees C), this may due to the CaCO3 decomposition and recarbonation processes in which the CaO is transiently formed. The possible mechanism was discussed. Copyright (C) 2012, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.