Complete decomposition of benzene, toluene and particulate matter (PM) contained in the exhaust of diesel engines by means of thermally-excited holes in TiO<sub>2</sub> at high temperatures

Abstract

Titanium dioxide was once extensively investigated as a photoconductor for the electrophotographic photorecptor at its incunabula. Nowadays, it has attracted attention as a material for photocatalyzers, solar cells as well as their related areas. We report here another application of titanium dioxide. Our motivation is to make use of thermally-generated holes for decomposition of organic compounds. We have previously reported on a decomposition system of organic wastes by use of thermally-excited holes in TiO2 at high temperatures (about 350-500 °C). In the present investigation, we aim at applying this technology to complete decomposition of benzene, toluene and particulate matter (PM) contained in the exhaust of diesel engines. Special attention has been paid to the adsorption process of benzene and toluene onto the surface of TiO2, as well as to their subsequent decomposition, as studied by thermal analysis, Raman and ESR spectra in consideration of the specific surface of TiO2 powders. Both benzene and toluene are found to completely decompose into H2O and CO2 at about 350 °C, via fragments of ethylene, butene, propene 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 TiO2 was heated under pressure of about 280 N/m2 at about 350 °C.