4.1.3. Perovskite Catalysts

Perovskite-type oxides are a kind of composite oxides which have a similar structure with CaTiO3, and can be expressed by ABO3. The common way to modify the perovskite catalysts is replacement of the cation B by B' to tune the redox ability or enhance the stability [1]. With the replacement of the cation B, the crystal lattice would be distortion which leads to the enhancement of redox ability and improvement of stability. The most commonly used perovskite for catalytic combustion of VOCs is LaBO3, in which B can be Co, Fe, Ni, Mn, and Sr (Table 7) [60,97,170,171]. Huang et al. used Sr partially replaced La in LaCoO<sup>3</sup> for catalytic combustion of propyl alcohol, toluene, and cyclohexane [70]. The results showed that the doped LaCoO<sup>3</sup> showed a better catalytic performance than the undoped one, and the modified catalysts were stable in the reaction. R. Spinicci et al. compared the catalytic activity of LaMnO<sup>3</sup> and LaCoO<sup>3</sup> for catalytic combustion of acetone, isopropanol, and benzene [60]. They suggested that LaMnO<sup>3</sup> showed a better performance than LaCoO3. In oxidation of isopropanol, acetone was the intermediate product. The surface oxygen species played a key role in this process. The increase of oxygen pressure is positive for the catalytic combustion of VOCs over these perovskite catalysts. G. Sinquin et al. applied LaMnO<sup>3</sup> and LaCoO<sup>3</sup> for the catalytic combustion of chlorinated VOCs, such as CH2Cl<sup>2</sup> and CCl4. LaMnO<sup>3</sup> showed a better chlorine resistance than LaCoO<sup>3</sup> [97]. Mihai Alifanti et al. supported LaCoO<sup>3</sup> on cerium-zirconium oxides (Ce1-xZrxO2, x = 0–0.3) for the catalytic combustion of benzene and toluene [172]. The results showed that all the supported catalysts showed a better performance than Ce1-xZrxO<sup>2</sup> and 20% loaded LaCoO<sup>3</sup> showed about 10 times higher catalytic activity than LaCoO<sup>3</sup> for toluene oxidation due to its large surface area and good oxygen mobility. S. I. Suárez-Vázquez et al. synthesized SrTi1-xBxO<sup>3</sup> (B = Mn, Cu) for toluene destruction [71]. Mn could replace Ti and enter the perovskite structure, while Cu could not. The Mn doped catalysts showed the highest catalytic activity and can completely decompose toluene to CO<sup>2</sup> at a temperature lower than 350 ◦C. Perovskite also can be prepared from solid waste such as the obsoleting lithium battery. Mingming Guo et al. prepared manganese-based perovskite catalyst from the waste lithium battery for catalytic combustion of toluene, which showed a better catalytic activity than pure manganese perovskite catalyst due to more Mn4<sup>+</sup> ions and lattice oxygen species, as well as high specific surface area [72]. In order to increase the amounts of active sites, Junxuan Yao et al. removed the La ions from LaCoO<sup>3</sup> to obtain the disordered Co3O4. It showed a better catalytic activity for propane combustion than the one prepared by other methods [94]. To further improve the catalytic activity, γ-MnO<sup>2</sup> was calcined on the surface of SmMnO<sup>3</sup> which had a large specific surface area, high Mn4+/Mn3<sup>+</sup> and Olatt/Oads. Compared with SmMnO3, it showed a better catalytic activity and stability (10 vol% water) in the process of catalytic reaction [61]. Jingsi Yang et al. assembled the LaMnO<sup>3</sup> perovskite in MnO<sup>2</sup> and adjusted La/Mn to 15. The redox ability of the catalyst was improved by enhancing the interaction between the active phase and the support [73]. The ratio of citric acid and metal ion (La3+Mn2+) was also tested to find out the best composite of perovskite catalysts. Zakaria Sihaib et al. prepared LaMnO<sup>3</sup> with different ratios. The results show that the catalyst with the ratio of 0.5 to 1.5 has the best catalytic performance and the amount of citric acid affects the specific surface area of perovskite catalyst [74]. Li Wang et al. added Sr into the LaMnO<sup>3</sup> to prepare La0.5Sr0.5MnO3. The amount of Mn4<sup>+</sup> and the oxidation ability of vinyl chloride has been improved after HCl modification [104]. The perovskite catalysts showed a good catalytic activity for combustion of VOCs at low temperature due to their tunable redox property by replacing the B atom. However, they also have some disadvantages, such as low thermal stability. The catalytic activity and stability of perovskite catalysts need to be further improved.








chlorination.

4.1.4. Concentrated Oxidation Catalysts
