Evidence for the Predominance of Condensed Phase Reaction in Chemical Looping Reactions between Carbon and Oxygen Carriers

This study investigates the use of metal oxides as an oxygen carrier in chemical looping combustion applications. The initiation and decomposition of C/CuO and C/Fe 2 O 3 are investigated using a time-resolved T-jump/time-of-flight mass spectrometer (T-Jump/TOFMS). Heating of the metal oxide nanopowders produces gaseous O 2, but when mixed with the fuel (carbon), gaseous O 2 forms temporally after the primary combustion product, CO 2 . This indicates condensed phase reaction between the metal oxide and carbon as the predominant reaction mechanism rather than gas phase release of O 2 and subsequent burning of carbon, at least in the initiation phase. In situ heating TEM, and SEM are used to further investigate the reaction. The oxidation rate of carbon in the present experiment is estimated to be 3 to 5 orders of magnitude greater than that predicted using the Nagle Strickland-Constable model. The activation energy of C/CuO, C/Fe 2 O 3, and C/Bi 2 O 3 are determined using the Ozawa iso-conversion method and are found to be 110, 170, and 230 kJ/mol, respectively. The condensed phase nature of this reaction is compared to our previous studies on aluminum nanothermites and is considered to be further evidence toward a reactive sintering initiation mechanism.