# Pentane Depletion by a Surface DBD and Catalysis Processing
## 3 Experimental Results
### Pentane Decomposition
However, the observed trend is sufficient to conclude that depletion is happening at a much higher rate. The straight  
Figure 5: Depletion rate of pentane at different concentrations per plasma power: (**a**) \(P=16.9\) W, and (**b**) \(P=44.2\) W. The values for \(\tau_{5}\) (representing the slopes of the plotted straight lines) are summarized in Table 1 together with the estimated errors. The latter values were obtained by taking the highest and lowest slopes consistent with the data. The experimental uncertainties in the measured values, at about 10%, are roughly the size of the symbols shown. line shown, with a slope given by \(\tau_{5}=0.7\) min, is consistent with the available data. Notice that we only have one parameter in the model, i.e., \(\tau_{5}\), and three times more data to fit it. Some deviations from the fit could be due to the presence of complex processes related to the generation of intermediate reaction products, as discussed below. Quantitatively, pentane decomposition, denoted by \(D_{5}\), is evaluated as follows:  
\[D_{5}(\%)=100\ \frac{[C_{5}H_{12}]_{0}-[C_{5}H_{12}]_{i}}{[C_{5}H_{12}]_{0}}, \tag{2}\]  
where \([C_{5}H_{1}2]_{0}\) is the pentane concentration before treatment, and \([C_{5}H_{1}2]_{i}\) is the pentane concentration after treatment time \(t\). In Table 1, the pentane decomposition \(D_{5}\) and the time scale for decomposition \(\tau_{5}\) are reported for \(t\) = 5 min in the absence and presence of the catalyst. As one can see for 44.2 W plasma power, pentane decomposition occurs in less than 2 min, and the depletion time scale \(\tau_{5}\) decreases with decreasing pentane concentrations, from 1.7 min (1200 ppm) to 0.7 min (300 ppm). Catalysis does not seem to compete with plasma at a high power level, and \(D_{5}>95\%\). At the lower plasma power and for high pentane concentrations, neither the plasma nor the catalyst is able to completely abate pentane. At the lowest concentration, \(D_{5}\) becomes larger than 95% in the presence of the catalyst. Indeed, the catalyst helps the depletion at low initial concentrations, while it does not greatly affect the depletion at higher concentrations. This can be explained by assuming that at high concentrations, the catalytic sites are saturated; therefore, the plasma controls the chemical kinetics. We also estimated the pentane decomposition efficiency after 1 min of plasma treatment, displayed in Figure 6. The efficiency is estimated as the ratio between the amount in grams of the decomposed pentane to the applied energy in kWh. The efficiency increases with the pentane concentration, and the catalyst does not seem to play any relevant role in pentane decomposition, even at low concentrations. The increase in efficiency with pentane concentration demonstrates that for these plasma parameters, plasma processing occurs in the gas phase. These results are comparable to the efficiencies found in the NTP devices [10; 27]. \begin{table}
\begin{tabular}{c c c c c} \hline
**Power (W)** & **Starting C\({}_{5}\)H\({}_{12}\) (ppm)** & **Catalyst** & \(D_{5}\) **(\%)** & \(\tau_{5}\) **(min)** \\ \hline \multirow{8}{*}{16.9} & \multirow{3}{*}{300} & No & 87 & 2.5 \(\pm\) 0.3 for \(t\) \(<\) 2 min, 1.8 \(\pm\) 0.1 for \(t\)\(>\) 2 min \\ \cline{3-5}  & & Yes & \(>\)95 & 2.5 \(\pm\) 0.3 for \(t\)\(<\) 2 min, 1.8 \(\pm\) 0.1 for \(t\)\(>\) 2 min \\ \cline{2-5}  & & No & 55 & 4.8 \(\pm\) 0.5 \\ \cline{2-5}  & & Yes & 75 & 4.8 \(\pm\) 0.5 for \(t\)\(<\) 2 min, 2.6 \(\pm\) 0.2 for \(t\)\(>\) 2 min \\ \cline{2-5}  & & No & 58 & 5.3 \(\pm\) 0.8 \\ \cline{2-5}  & & Yes & 60 & 5.3 \(\pm\) 0.8 \\ \hline \multirow{8}{*}{44.2} & \multirow{3}{*}{300} & No & \(>\)95 & 0.7 \(\pm\) 0.1 \\ \cline{2-5}  & & Yes & \(>\)95 & 0.7 \(\pm\) 0.1 \\ \cline{2-5}  & & No & \(>\)95 & 1.0 \(\pm\) 0.1 \\ \cline{1-1} \cline{2-5}  & & Yes & \(>\)95 & 1.0 \(\pm\) 0.1 \\ \cline{1-1} \cline{2-5}  & & No & \(>\)95 & 1.7 \(\pm\) 0.2 \\ \cline{1-1} \cline{2-5}  & & Yes & 60 & 1.7 \(\pm\) 0.2 \\ \hline \end{tabular}
\end{table}