4.1.4. Concentrated Oxidation Catalysts decomposed at 250 °C overthe NaX zeolite. The addition of Pt on the zeolite can significantly increase the catalytic activity. The main obstacle for the application of zeolite was the coke that formed during

The low concentration of VOCs can limit the catalytic efficiency of catalysts. Some porous materials were investigated to the concentration and decomposition of VOCs, such as zeolite, γ-Al2O<sup>3</sup> (Table 8, Figure 13) [84,101,173–175]. R. Beauchet et al. tried to decompose the isopropanol and o-xylene mixture over the CsX, NaX, and HY zeolite [173]. O-xylene and isopropanol were totally decomposed at 250 ◦C over the NaX zeolite. The addition of Pt on the zeolite can significantly increase the catalytic activity. The main obstacle for the application of zeolite was the coke that formed during the reaction, which led to the short lifetime. Amir Ikhlaq et al. studied the mechanism and kinetics of decomposition of chlorinated VOCs by ozonation over the γ-Al2O<sup>3</sup> and ZSM-5 zeolite [174]. The results suggest that ozone reacts with the absorbed VOCs on the surface of catalysts. However, the ozonation process will increase the cost in most of the industrial processes. Yuexin Peng et al. supported MnO<sup>2</sup> on the Al-rich <sup>β</sup>-zeolite to degrade toluene [75]. The T<sup>90</sup> is 285 ◦C, which is much lower than the MnO<sup>2</sup> supported on γ-Al2O<sup>3</sup> due to the lattice oxygen species in MnO<sup>2</sup> and absorbed oxygen species on the zeolite. Cu and Co were also used to modify the β-zeolite for the destruction of toluene and trichloroethylene [76]. The modified zeolite showed good stability in the reaction. The catalytic activity is mainly from the supported metal oxides. The suitable acidity and strong oxidation stability can improve the CO<sup>2</sup> selectivity. Dedong He et al. modified the HZSM-5 zeolite with a series of rare earth elements, including La, Ce, Pr, Nd, Sm, Y, and Er, for the catalytic decomposition of CH3SH [91]. Cu was also used to modify ZSM-5 for the combustion of acrylonitrile. The isolated Cu is the active center. The SiO2/Al2O<sup>3</sup> ratio can affect the ion exchange capacity and the catalytic performance of the catalyst. When the ratio is 26, the catalyst shows the best catalytic activity [92]. SBA-15 was used to support MnO<sup>x</sup> for the combustion of toluene and showed good catalytic activity [176]. The La modified HZSM-5 zeolite showed much better activity and stability than HZSM-5 due to the tunable acidity, which can promote the adsorption and activation of the CH3SH molecule and inhibit the formation of coke deposit. The previous researches showed the potential application in the industry. However, to fulfill the requirements of the industry, the concentration-catalysis process to remove VOCs needs more research on lifetime, catalytic efficiency. the reaction, which led to the short lifetime. Amir Ikhlaq et al. studied the mechanism and kinetics of decomposition of chlorinated VOCs by ozonation over the γ‐Al2O3 and ZSM‐5 zeolite [174]. The results suggest that ozone reacts with the absorbed VOCs on the surface of catalysts. However, the ozonation process will increase the cost in most of the industrial processes. Yuexin Peng et al. supported MnO2 on the Al‐rich β‐zeolite to degrade toluene [75]. The T90 is 285 °C, which is much lower than the MnO2 supported on γ‐Al2O3 due to the lattice oxygen species in MnO2 and absorbed oxygen species on the zeolite. Cu and Co were also used to modify the β‐zeolite for the destruction of toluene and trichloroethylene [76]. The modified zeolite showed good stability in the reaction. The catalytic activity is mainly from the supported metal oxides. The suitable acidity and strong oxidation stability can improve the CO2 selectivity. Dedong He et al. modified the HZSM‐5 zeolite with a series of rare earth elements, including La, Ce, Pr, Nd, Sm, Y, and Er, for the catalytic decomposition of CH3SH [91]. Cu was also used to modify ZSM‐5 for the combustion of acrylonitrile. The isolated Cu is the active center. The SiO2/Al2O3 ratio can affect the ion exchange capacity and the catalytic performance of the catalyst. When the ratio is 26, the catalyst shows the best catalytic activity [92]. SBA‐15 was used to support MnOx for the combustion of toluene and showed good catalytic activity [176]. The La modified HZSM‐5 zeolite showed much better activity and stability than HZSM‐5 due to the tunable acidity, which can promote the adsorption and activation of the CH3SH molecule and inhibit the formation of coke deposit. The previous researches showed the potential application in the industry. However, to fulfill the requirements of the industry, the concentration‐catalysis process to remove VOCs needs more research on lifetime, catalytic efficiency.

*Catalysts* **2020**, *10*, 668 32 of 49

materials were investigated to the concentration and decomposition of VOCs, such as zeolite, γ‐Al2O3

The low concentration of VOCs can limit the catalytic efficiency of catalysts. Some porous

**Figure 13.** Scheme of adsorption/oxidation apparatus. Reprinted with permission from [1], 2009, Elsevier Ltd. **Figure 13.** Scheme of adsorption/oxidation apparatus. Reprinted with permission from [1], 2009, Elsevier Ltd.


**Table 8.** Concentrated oxidation catalysts for catalytic combustion of VOCs.
