Chemical looping reforming of toluene as a biomass tar model compound over two types of oxygen carriers: 2CuO-2NiO/Al2O3 and CaFe2O4

Abstract Chemical looping reforming/gasification of toluene, the model compound representing biomass tar, was studied by using two oxygen carriers, 2CuO-2NiO/Al 2 O 3 (molar ratio) and CaFe 2 O 4 . Their reaction performances were evaluated in a TG-FTIR and a laboratory-scale fixed bed reactor. The active lattice oxygen of the 2CuO-2NiO/Al 2 O 3 oxygen carrier demonstrated excellent reactivity and completely oxidized toluene to CO 2 at 600–700 °C, while the fixed bed reactor data indicated that 2CuO-2NiO/Al 2 O 3 oxygen carrier could catalyze the cracking of toluene to produce H 2 after loss of lattice oxygen. The CaFe 2 O 4 oxygen carrier exhibited a good performance of chemical looping partial oxidation of toluene to CO and H 2 with a fairly high reactivity. Over CaFe 2 O 4 oxygen carrier, the CO and H 2 dominated reaction products in the temperature range of 800–900 °C except at the startup stage. Catalytic cracking of toluene by CaFe 2 O 4 to produce H 2 was also observed after partial loss of lattice oxygen. Stable performance of CaFe 2 O 4 with high reactivity to syngas (CO and H 2 ) was demonstrated during a 3-cyle test in the fixed bed reactor. After reduction of action with toluene, scanning electron microscopy (SEM) and X-ray diffraction (XRD) indicated that 2CuO-2NiO/Al 2 O 3 was reduced to metallic copper and nickel with the mixture of NiAl 2 O 4 , and CaFe 2 O 4 was reduced to metallic iron and CaO. In summary, two oxygen carriers displayed high toluene conversion at the beginning stage and the conversion of toluene increased to about 100% in the subsequent stage.