**2.3 Multistage reactor**

The multistage reactor can be described as a combination of more than one single-stage bed/reactor (**Figure 2(c)**). The multistage reactor gives a more flexible option in the industrialization of the plasma catalysis, attributing to the combination of catalysts with a different function for the expected reaction [38]. Chavade et al. [39] used a four-stage plasma and catalytic reactor system for oxidation of benzene. The results showed that the increase in stage number enhanced benzene conversion and CO2 selectivity. The same result can be found in biogas reforming process using a multistage gliding arc discharge system without catalyst [40]. Harling et al. [41] developed a three-stage reactor for VOCs removal. The combination of plasma and catalyst in series could significantly improve the efficiency of VOCs decomposition. At the same time, the formation of by-product such as NOx was suppressed.
