## 3 Results and Discussions
### LaFe1-xNix Oxygen Carrier
#### 3.2.3 Steam Enhanced Syngas Production
It can be seen that the steam addition promoted C\({}_{1}\) yield to about 80%, and the H\({}_{2}\) yield reached about 220%, depending on the Ni ratio in the oxygen carrier. A reactivity deterioration (decrease in C\({}_{1}\) and H\({}_{2}\) yield) with time was also observed for the LaFe rather than other oxygen carriers. For the Ni tuned oxygen carrier, the C\({}_{1}\) and H\({}_{2}\) yield tended to be stable during the whole reaction stage. It means that the Ni addition could promoted the 2C\({}_{\text{x}}\)H\({}_{\text{y}}\) + 2 xH\({}_{2}\)O = 2 xCO + yH\({}_{2}\). Figure 10: Gas production during chemical looping conversion of toluene using LaFe\({}_{0.4}\)Ni\({}_{0.6}\)O\({}_{3}\) at 900 \({}^{\circ}\)C: (**a**) In the absence of H\({}_{2}\)O, (**b**) In the presence of H\({}_{2}\)O.  
LaFe\({}_{0.6}\)Ni\({}_{0.4}\) was selected to evaluate the effect of S/C, and Figure 12 compares the effect of the S/C ratio on carbon conversion and H\({}_{2}\) production at 900 \({}^{\circ}\)C. With the S/C increasing from 0.8 to 2, both the C\({}_{1}\) yield and H\({}_{2}\) yield exhibited an increasing trend, while coke formation decreased. The C\({}_{1}\) yield, coke formation and H\({}_{2}\) yield were 73.9%, 11.4% and 197.9% at S/C=0.8, and they became 99%, 0.1% and 275.6% at S/C = 2. Although the oxygen carrier would catalyze toluene conversion and steam would further promote toluene conversion, the presence of steam would recovery the lattice oxygen in the oxygen carrier, which means that the lattice oxygen in the oxygen carrier was not consumed as a whole. Therefore, S/C \(<\) 1 was not enough for toluene conversion in theory. It would also result in serious coke formation, and coke yield was 11.4% at S/C = 0.8. With the progress of the reaction, more and more coke covered the active center of the oxygen  
Figure 11: C\({}_{1}\) yield and H\({}_{2}\) yield during chemical looping toluene conversion using different LaFeNi with and without steam at 900 \({}^{\circ}\)C: (**a**) C\({}_{1}\) yield and (**b**) H\({}_{2}\) yield for LaFe, (**c**) C\({}_{1}\) yield and (**d**) H\({}_{2}\) yield for LaFe\({}_{0.6}\)Ni\({}_{0.4}\), (**e**) C\({}_{1}\) yield and (**f**) H\({}_{2}\) yield for LaNi. carrier and reduced its catalytic activity. When S/C was greater than 1.2, the carbon deposition was almost eliminated by steam-reforming, resulting in a significant increase in the total conversion of toluene and H\({}_{2}\) yield. When the S/C exceeded 1.6, the C\({}_{1}\) yield and H\({}_{2}\) yield even reached 96% and 265%, respectively. The further increase in S/C also decreased the residence time of toluene and its conversion. Therefore, S/C=1.6 was further selected to investigate the effect of temperature (800-950 \({}^{\circ}\)C) on C\({}_{1}\) yield, and the results are shown in Figure 13. Since the steam reforming and carbon gasification are both intensively endothermic, and the elevated temperature can stably promote the toluene conversion into C\({}_{1}\). C\({}_{1}\) yield tended to stabilize at about 81% at 800 \({}^{\circ}\)C, and 96% at 900 \({}^{\circ}\)C. Further increase in temperature did not help too much for toluene conversion.