###### Abstract  
Chemical looping biomass gasification is a novel technology converting biomass into syngas, and the selection of oxygen carrier is key for efficient tar conversion. The performance of LaFe\({}_{1\text{-}}\)xNi\({}_{\text{x}}\) as a robust catalytic oxygen carrier was investigated in the chemical looping conversion of toluene (tar model compound) into syngas in a fixed bed. LaM (M = Fe, Ni, Mn, Co, and Cu) was initially compared to evaluate the effect of transition metal on toluene conversion. LaFe (partial oxidation) and LaNi (catalytic pyrolysis) exhibited better performance in promoting syngas production than other oxygen carriers. Therefore, Ni-substituted ferrite LaFe\({}_{1\text{-}}\)Ni\({}_{\text{x}}\) (x = 0, 0.2, 0.4, 0.6, 0.8 and 1) was further developed. The effects of Ni-substitution, steam/carbon ratio (S/C), and temperature on toluene conversion into C\({}_{1}\) and H\({}_{2}\) were evaluated. Results showed that the synergistic effect of Fe and Ni promoted toluene conversion, improving H\({}_{2}\) yield yet with serious carbon deposition. Steam addition promoted toluene steam reforming and carbon gasification. With S/C increasing from 0.8 to 2.0, the C\({}_{1}\) and H\({}_{2}\) yield increased from 73.9% to 97.5% and from 197.7% to 269.6%, respectively. The elevated temperature favored toluene conversion and C1 yield. LaFe\({}_{0.6}\)Ni\({}_{0.4}\) exhibited strong reactivity stability during toluene conversion at S/C = 1.6 and 900 \({}^{\circ}\)C.  
LaFe\({}_{1\text{-}}\)Ni\({}_{\text{x}}\) oxygen carrier; chemical looping; catalytic reforming; toluene; tar model  
gasification technology. Therefore, efficient tar removal or conversion technology is very important for the biomass gasification process. There are two main methods for tar removal, i.e., non-catalytic and catalytic methods. The former involves the use of a wet scrubber [6; 7] or a secondary tar process outside the gasification reactor [8; 9]. The catalytic method mainly includes catalytic cracking and catalytic reforming [10; 11; 12; 13; 14; 15]. It could remove tar during biomass utilization and adjust the gas compositions of biogas. A highly reactive catalyst is the key point for in-situ tar removal. At present, the mainstream catalysts include natural ore (dolomite and olivine) [15; 16], alkali metal [17; 18], transition metal (Ni, Fe, Co et al.) [19; 20; 21; 22; 23] and carbon-based material [24]. Ordinarily, catalysts with a single active component have usually exhibited some shortcomings. For example, Ni catalyst is prone to cause sintering, carbon deposition, and sulfur poisoning. Natural ore with low price often presents low reactivity. The alkali metal and carbon-based catalyst often face the problems of reactivity decay due to deterioration of surface structure during longtime operation. Multicomponent catalysts can make up for the deficiency of single-component catalysts attracting increasing attention [21; 22; 23]. Chemical looping gasification (CLG) is a novel technology that uses lattice oxygen in an oxygen carrier to transfer oxygen from air to fuel to initiate biomass gasification. Figure 1 shows the schematic diagram of CLG performed by redox reaction that could be described by R1-R3. The oxygen carrier is oxidized by air in the air reactor. The oxidized oxygen carrier is used to initiate partial oxidation of biomass to produce syngas in the gasification reactor. The application of oxygen carriers is a key factor for the CLG process, and two main strategies are often used. Method 1 is to use traditional transition metal oxide with a low ratio of oxygen carrier to biomass to prevent excessive oxidation. Most of the research focused on materials of iron ore, Mn, Fe, and et al. [25; 26; 27; 28]. Method 2 is to use an oxygen carrier with low oxidative activity to initiate partial oxidation rather than full oxidation. These kinds of oxygen carriers are often mixed oxides like ferrites or perovskites-based materials [29; 30; 31].