Influence of the Synthesis Method on the Structure and CO2 Adsorption Properties of Ca/Zr Sorbents

Abstract

The influence of the synthesis method has been investigated on the structure and CO2 adsorption properties of Ca/Zr sorbents. For this purpose, Ca/Zr sorbents are synthesized using co-precipitation, sol–gel, and deposition–precipitation methods and compared to our previously reported Ca/Zr sorbent prepared by the flame spray pyrolysis method. Among the various sorbents, the sorbent synthesized by the sol–gel method exhibits excellent adsorption capacity and remarkable multi-cycle stability compared to the sorbent synthesized by the flame spray pyrolysis synthesis method. This interesting and rather useful behavior was a result of surface properties of the sol–gel-synthesized sorbents. X-ray diffraction measurements indicate that the CaO phase was dominant with respect to the CaZrO3 phase in the case of the Ca/Zr sorbent prepared by the deposition–precipitation method. The opposite trend was observed for the sorbents synthesized by the remaining methods. Temperature-programmed desorption measurements show that the basic properties of the sorbents depend upon the synthesis method adopted. O 1s X-ray photoelectron spectroscopy (XPS) spectra confirms the formation of the CaZrO3 phase in the prepared sorbents. Transmission electron microscopy (TEM) measurements show that the Ca/Zr sorbent synthesized by the sol–gel method exhibits smaller crystallites similar to the flame-spray-pyrolysis-synthesized sorbent. TEM–energy-dispersive spectrometry and XPS atomic ratios show that the sol–gel-synthesized Ca/Zr sorbent has more CaO particles over the surface compared to the Ca/Zr sorbent prepared by flame spray pyrolysis and is responsible for the better CO2 capture performance observed.