Chemical-looping combustion of syngas with nano CuO–NiO on chabazite

To enhance CO2 capture, nanostructured bimetal oxide (i.e., CuO–NiO) dispersed on chabazite were used as an oxygen carrier for the chemical-looping combustion (CLC) of a syngas (CO (35%) and H2 (25%) balanced with N2). At the temperature range of 973–1173K, desired contact times (<4min) for CLC of the syngas with the CuO–NiO/chabazite oxygen carrier can be obtained. Notably, the oxygen carrier possesses a high reactivity in the 5-cycle CLC test. Mainly nano CuO and NiO on chabazite are observed by component-fitted X-ray absorption near edge structure (XANES) spectroscopy. The refined X-ray absorption fine structure (EXAFS) spectra also indicate that during CLC, bond distances of CuO and NiO in the bimetal oxide oxygen carrier are increased by 0.04 and 0.02Å, respectively, suggesting an effective oxygen transfer for the syngas combustion. About 96% of NiO on chabazite are in the nano scale, which can be reduced with the syngas to form nanosize Ni (95%) at 1073K. Notably, about 5% of oxygen are transferred from NiO to Cu, and leads to form Cu2O during CLC. The effective oxygen transport with the bimetal oxide oxygen carries during CLC gives better combustion efficiency than the individual metal oxide at the high temperature range of 973–1073K.