# Pentane Depletion by a Surface DBD and Catalysis Processing
## 4 Discussion  
A closer analysis of the results in terms of the time scales shown in Table 2 suggests that the catalyst is not directly involved in the decomposition of pentane. In fact, the time scales \(\tau_{5}\) are independent of the presence of the catalyst. At plasma power \(P=16.9\) W, \(\tau_{5}=(5.3\pm 0.8)\) min, and at \(P=44.2\) W, \(\tau_{5}=(1.7\pm 0.2)\) min, suggesting that the pentane decomposition is primarily due to the action of the plasma. In contrast, the role of catalysts is very important for the depletion of the intermediate reaction products, as displayed by the associated time scales and denoted by \(\tau_{\mathrm{x}}\), particularly at lower plasma power. For the latter, the catalytic depletion of intermediates is very efficient, as much as four times faster than that of plasma. Catalysis processing without plasma refers to an experiment where plasma is not switched on, and so only the catalyst (present on the surface of plasma module) is operating. The reactions that the catalyst speeds up are the oxidation of acetylene and propane, which are previously formed by the partial decomposition of pentane, mainly by means of plasma action. At higher powers, the catalyst acts weakly on the depletion of acetylene, but not on propane. The time scale for the production of acetylene is weakly dependent on the catalyst, and at low power, it seems to diminish propane production. These studies support the experimental evidence that catalysis concurs with the depletion of the intermediate reaction products in the plasma reactor, as also reported in the literature [29,30]. In the previous experiments reporting propane abatement, catalysis processing was used without a plasma, which showed very low efficiency. Therefore, the higher efficiency reported here is due to the synergetic effect of the plasma and the catalyst. In fact, our previous study [31] demonstrated a much lower abatement efficiency for propane, performed by catalysis processing and using only UV-A light energy. In the case of TiO\({}_{2}\), we used light with a UV-A range of 340-400 nm and a peak at 370 nm to obtain an efficiency of less than 10% of the abatement after 22 min of application [31,32]. As previously reported in our studies, the UV-A power emitted by our SDBD was very low, from 20 to 600 times less bright in comparison with the typical UV-A lamps used for catalytic processing [33]. Other previous works suggested that introducing a catalyst into a plasma reactor could generate more highly energetic and reactive species, which favor plasma-induced reactions towards the deep oxidation of VOCs. In our case, the study of the kinematical evolution of depletion demonstrates that catalysts do not affect the pentane decomposition. We may conclude that the catalyst does not generate reactive species favoring the decomposition of the pentane, but it is the ability of the plasma state to primarily decompose pentane, thus generating the active intermediate species that could be removed by the catalyst. Catalytic processes are mainly responsible for removing the produced species, such as propane and acetylene, thus shifting the chemical kinetics towards full VOC depletion. Hence, the combination of plasma with catalysis has a great potential to lower the activation temperature of the catalysts, enhance the removal of pollutants, and minimize the formation of undesired intermediate reaction products, all of which may contribute in different ways to the enhancement of the energy efficiency of the plasma process [27]. The results obtained in the present paper show that TiO\({}_{2}\) does not directly affect the removal/conversion of pentane, with the catalyst only having clear effects on the removal of excited species and by-products. The choice of the catalyst deserves further investigation in order to understand if different choices may influence the depletion of pentane.