| Research Abstract |
We have previously reported on a decomposition system of organic wastes by use of thermally-excited holes in TiO_2 at high temperatures. An appealing feature of our system is to make use of a great number of holes formed, for example, at 350 ℃ for oxidation of organic wastes. In the present investigation, we aim at applying this technology to complete decomposition of benzene, toluene and particulate matter (PM) included in the exhaust of diesel engines. Special attention has been paid to the adsorption process of benzene and toluene onto the surface of TiO_2, as well as to their subsequent decomposition, as studied by thermal analysis, Raman, and ESR spectra in consideration of the specific surface of TiO_2 powders. Both benzene and toluene are found to completely decompose into H_2O and CO_2 at about 350 ℃, via fragments of ethylene, butane, propane, and butadiene. On the other hand, PM appears more difficult to decompose due to its powdered form. However, PM was finally confirmed to be decomposed when the mixture of PM and TiO_2 was heated under pressure of about 280 N/m^2 at about 350 ℃.
In view of the practical use of the present system, fixation of TiO_2 powders onto a support in the form of, for example, honeycomb seems to be the core technology. To realize this, we have tried in the present investigation to prepare TiO_2 on Ti-wires by direct oxidation at 800 ℃ in air, or to coat wires of heating element (Ni-Cr etc.) with TiO_2 powders of the anatase form by means of electrophoretic deposition. Both methods are found to be effective, and we have confirmed the formation of the rutile and anatase forms by Raman spectra, respectively. On the basis of the T1O_2-coated wires thus prepared, we have carried out decomposition experiments of polycarbonate as well as benzene and toluene in the presence of oxygen. We have confirmed that the compounds have completely been decomposed into H_2O and CO_2.
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