## 3 Results and Discussions  
### Enhanced Fuel Conversion by Catalytic Oxygen Carrier  
Initially, the toluene was introduced to the reactor without bed material to carry out the thermal pyrolysis as the reference condition. Without an oxygen carrier, the toluene was primarily converted into H\({}_{2}\) and CH\({}_{4}\) rather than CO or CO\({}_{2}\). The elevated temperature favored the thermal pyrolysis of toluene. Although, the concentration of H\({}_{2}\) and CH\({}_{4}\) was lower than 1% at 900 \({}^{\circ}\)C, and was still very low even at 1000 \({}^{\circ}\)C. The results were in agreement with open literature that the efficient toluene conversion without catalyst would require extremely high operation temperature which would result in extra operation cost [34]. Different oxidized oxygen carriers of LaM (M = Fe, Mn, Co, Cu, and Ni) were used as bed materials for chemical looping conversion of toluene at 900 \({}^{\circ}\)C, and the gas product evolution was shown in Figure 3. The concentration of gas products varied greatly, depending on the material. When LaNi was used, the main reaction could be roughly divided into 3 stages according to the gas concentration. Full oxidation of toluene occurred in stage 1 where CO\({}_{2}\) increased during the first 1 min and CO and H\({}_{2}\) were maintained at a low level. After that, with the lattice oxygen carrier being used up, CO\({}_{2}\) gradually decreased, and some CO was formed. Simultaneously, due to the catalytic effect of Ni on toluene conversion, H\({}_{2}\) concentration increased to the maximum of about 12%. After that, H\({}_{2}\) concentration gradually decreased to 6% with coke formation covering the activity center of the catalyst. It could be seen that the oxidized LaNi would cause full oxidation of toluene. The reduced oxygen carrier would play a catalytic effect on toluene conversion and H\({}_{2}\) yield yet the coke would cause reactivity deterioration. Figure 4 shows the gas composition when different oxygen carriers were used. When LaFe was used, the gas composition changed a lot. A high CO concentration (peaking at about 9%) was observed, and gradually decreased with the oxygen carrier was consumed. During the whole reaction stage, both CH\({}_{4}\) and CO\({}_{2}\) maintained at a low level. H\({}_{2}\) concentration maintained at about 8% during the whole reaction stage without an obvious decrease like the case of LaNi. Meanwhile, although with some decrease, CO concentration maintained till the end of the reaction. It means that the oxygen carrier can continuously provide lattice oxygen for partial oxidation, and mitigate serious coke formation. Overall, compared with LaNi, LaFe was easier to motivate partial oxidation rather than full oxidation, favoring syngas yield. When LaCo was used, a much higher CO\({}_{2}\) concentration (peaking over 12%) than both LaNi and LaFe was observed, and H\({}_{2}\) and CO maintained at a low level during this stage. This indicates that a full oxidation reaction mainly occurred in this stage. Afterward, CO\({}_{2}\) decreased, and CO and H\({}_{2}\) appeared, indicating the occurrence of partial oxidation of toluene. The higher CO concentration than H\({}_{2}\) concentration indicates full oxidation of H\({}_{2}\) into H\({}_{2}\)O. After 4 min, the CO concentration decreased to a low level revealing the exhaust of available lattice oxygen in the oxygen carrier. However, the H\({}_{2}\) concentration was much lower than the case of LaNi and LaFe over the whole reaction stage, and it indicates a lower catalytic effect of LaCo on toluene conversion. Compared with LaCo, the LaMn exhibited similar performance in toluene conversion but with lower complete oxidation ability and higher catalytic performance. Initially, full oxidation of toluene occurred with CO\({}_{2}\) concentration peaking below 4%. After the exhaustion of lattice oxygen, the catalytic pyrolysis occurred, and the H\({}_{2}\) concentration was stable at about 4%.