## 3 Results and Discussion
### The Performance Comparison between Commercial and Newly Prepared AC-CoPcS Catalysts  
The same optimization method of the operation parameters was applied to the commercial AC-CoPcS catalyst, and the optimum parameters are listed in Table 3. The best catalyst dosage of  
Figure 10: The effect of oxygen pressure on \(\mathit{CPP}_{\mathrm{SMM}}\), \(\mathit{Yield}_{\mathrm{DMDS}}\), and \(\mathit{Purity}_{\mathrm{DMDS}}\) using the AC-CoPcS catalyst. Experimental conditions: SMM (18.0 wt%) 450 g, \(\mathit{RR}=600\) r/min, \(\mathit{C}_{\mathrm{ca}}=888.9\) ppm, \(t=60\) min, \(\mathit{T}_{\mathrm{re}}=65\)\({}^{\circ}\)C.  
Figure 9: The effect of reaction temperature on \(\mathit{CPP}_{\mathrm{SMM}}\), \(\mathit{Yield}_{\mathrm{DMDS}}\), and \(\mathit{Purity}_{\mathrm{DMDS}}\) using the AC-CoPcS catalyst. Experimental conditions: SMM (18.0 wt%) 450 g, \(\mathit{RR}=600\) r/min, \(\mathit{C}_{\mathrm{ca}}=888.9\) ppm, \(t=60\) min, \(P\)(O\({}_{2}\)) = 0.9 MPa.  
commercial AC-CoPcS of 1333.3 ppm is much larger than the newly prepared one of 888.9 ppm, which will cost more for industrial application. The performance comparison experiment between the commercial and new AC-CoPcS catalysts was conducted under their optimum parameters, and the result is summarized in Table 3. When compared with commercial AC-CoPcS, the newly prepared AC-CoPcS catalyst shows higher _CPP_\({}_{\text{SMM}}\) and _Yield_\({}_{\text{DMDS}}\) of 98.7% and 86.8% than the commercial one of 97.4% and 85.6%. However, the purity of the DMDS product using both the commercial and new AC-CoPcS catalysts are particularly high, 99.7% and 99.8%, respectively.  
The most important advantage of the supported catalyst is its reusability. The reuse performance of the commercial and newly prepared AC-CoPcS catalyst is shown in Figures 11 and 12. As can be seen in the figures, _CPP_\({}_{\text{SMM}}\) and _Yield_\({}_{\text{DMDS}}\) decrease with the increase of reuse times of the two catalysts. For the new AC-CoPcS catalyst, it can be reused seven times, and for the first four times of reuse the _CPP_\({}_{\text{SMM}}\) and _Yield_\({}_{\text{DMDS}}\) only reduce from 98.7% and 86.8% to 92.0% and 72.7%, respectively. However, the significant decrease of the _CPP_\({}_{\text{SMM}}\) and _Yield_\({}_{\text{DMDS}}\) occurs at the fifth reuse of the new catalyst of 78.2% and 46.6%, and the _CPP_\({}_{\text{SMM}}\) and _Yield_\({}_{\text{DMDS}}\) is only 26.2% and 8% for the seventh reuse. The reuse performance of the commercial AC-CoPcS catalyst is slightly worse than the former one. It can only be reused five times. The _CPP_\({}_{\text{SMM}}\) and _Yield_\({}_{\text{DMDS}}\) decrease from 97.4% and 85.6% to 90.2% and 71.3% for the second reuse, but decrease to 70.8% and 33.9% for the third reuse. As a result, the new and commercial AC-CoPcS catalysts can be properly reused four and two times, respectively, which still can achieve relatively high _Yield_\({}_{\text{DMDS}}\) and _CPP_\({}_{\text{SMM}}\) of more than 70% and 90%. It is worth mentioning that the reuse times have little effect on the _Purity_\({}_{\text{DMDS}}\). The _Purity_\({}_{\text{DMDS}}\) of all the DMDS product remains above 99.3%. The decrease of catalytic performance of AC-CoPcS catalyst with the increase of reuse times can be attributed to the following reasons: Firstly, the more times AC-CoPcS catalyst is reused, the greater loss of its active components during the reaction process of high temperature and high pressure; secondly, the SMM reagent, DMDS product, or even the byproduct produced in the reaction may be absorbed by the AC carrier, which can block up the micropores of the AC, preventing the reagents and catalyst from contacting with each other; and, thirdly, the mechanical strength of the AC carrier will also drop, resulting in its hole collapse, which also reduces the connection of active spots of the catalyst with the reagents [30].