Non-thermal plasma technology has great potential in reducing polycyclic aromatic hydrocarbons (PAHs) emission. But in plasma-alone process, various undesired by-products are produced, which causes secondary pollutions. Here, a dielectric barrier discharge (DBD) reactor has been developed for the oxidation of naphthalene over a TiO 2 /diatomite catalyst at low temperature. In comparison to plasma-alone process, the combination of plasma and TiO 2 /diatomite catalyst significantly enhanced naphthalene conversion (up to 40%) and CO x selectivity (up to 92%), and substantially reduced the formation of aerosol (up to 90%) and secondary volatile organic compounds (up to near 100%). The mechanistic study suggested that the presence of the TiO 2 /diatomite catalyst intensified the electron energy in the DBD. Meantime, the energized electrons generated in the discharge activated TiO 2 , while the presence of ozone enhanced the activity of the TiO 2 /diatomite catalyst. This plasma-catalyst interaction led to the synergetic effect resulting from the combination of plasma and TiO 2 /diatomite catalyst, consequently enhanced the oxidation of naphthalene. Importantly, we have demonstrated the effectiveness of plasma to activate the photocatalyst for the deep oxidation of PAH without external heating, which is potentially valuable in the development of cost-effective gas cleaning process for the removal of PAHs in vehicle applications during cold start conditions.
The aim of this work was to study the supercritical water (SCW) regeneration of phenol-saturated activated carbon (AC) with the H2O2 and alkali metal catalyst (Na2CO3, NaOH, K2CO3, and KOH) addition. The results showed that SCW could effectively regenerate AC in the 385–425°C range without any additives, but large and small amounts of phenol and dibenzofuran were present in the liquid phase, respectively, which would result in secondary pollution. The H2O2 addition enhanced the decomposition of phenol and increased the CO2 yield. With the addition of H2O2 and an alkali metal catalyst, SCW further decreased the phenol and dibenzofuran yields but increased the H2 and CO2 yields. Active component-supported (Cu-Ce-O, Fe-Ce-O, Ni-Zn-Pt, and Ni-Co-Pt) AC adsorbents might have decomposed some of the phenol during the phenol adsorption process, which resulted in relatively small amounts of phenol adsorbed on the AC and a decrease of the liquid (phenol and dibenzofuran) and gaseous (H2 and CO2) yields. SCW regeneration increased the surface area and pore volume of the AC and raised the adsorption capacity. The H2O2 and alkali metal catalyst addition can be used to achieve the rapid, efficient, and harmless regeneration of AC in SCW at a lower temperature (385°C).
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