Sammendrag
CaO is an attractive CO2 acceptor, due to its good kinetics and high capture capacity, even under low CO2 concentration conditions. The major problem associated with CaO acceptors is the loss of CO2 capture capacity during cyclic operations. The declining performance of the CaO acceptors is more pronounced in the presence of steam. In this article we propose a method for fabrication of nano-CaO acceptors coated with a ZrO2 layer to improve the stability. The nano-CaO acceptor was prepared by a thermal decomposition method following coating by a sol–gel, incipient wet impregnation, or hydrolysis process. Thermogravimetric analysis of the cyclic process of CO2 carbonation/decarbonation revealed that the nano-CaO acceptors with sol–gel (CaO-SG) and wet impregnation (CaO-IM) coatings have higher CO2 capture capacity and longer lifetime than the uncoated ones. The capture capacity of CaO-IM declined after 14 cycles, whereas CaO-SG remained stable up to 20 cycles. X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and Raman spectroscopy were used to characterize the coated and uncoated nano-CaO structures. Combined characterization techniques showed that a CaZrO3 layer was formed around the nano-CaO particles by sol–gel coating. Multicycle carbonation/decarbonation processes were performed in the absence and in the presence of steam in CO2 capture kinetics experiments as well as under the sorption-enhanced reforming conditions, and CaO nanoparticles with a surface CaZrO3 layer showed promising cyclic stability.
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