Investigation on titania synthesis for photocatalytic NOx abatement
Various TiO2 have been synthesized by hydrolysis of a TiOSO4 precursor changing the precipitation agent (NaOH and NH4OH), the pH of aging (acid, neutral or basic) and the temperature of calcination. Characterization by X-ray diffraction, N2 physisorption, ionic chromatography and high-resolution transmission electron microscopy (HR-TEM) has been carried out in order to investigate the structural, physical, and chemical properties of the titanium oxide and their correlation with the catalytic activity. The catalytic behaviour of the investigated systems was tested in the photocatalytic abatement of NOx in gas phase both in the UV and visible region, using a lab made reactor equipped with a chemiluminescence analyzer. A close correlation between photoactivity and physical properties has been found. The samples characterized by high surface area (>100m2/g) and the presence of anatase as the only TiO2 polymorph exhibit the best performances. Moreover, a significant increase of the catalytic activity has been obtained for materials synthesized in acid condition and calcined at lower temperature. The differences in the activity will be discussed in relationship with the textural properties of the various samples.
Over the last years, the sensitivity about the problems related to environmental pollution has greatly increased and the design of new systems for pollution abatement has been encouraged. Heterogeneous photocatalysis has shown a high efficiency in the photooxidation of many organic pollutants present either in the air or in liquid effluents. It allows pollution abatement under mild conditions (room temperature and atmospheric pressure) and avoids the use of noxious metal species that are often present in the classic catalytic depollution processes.
Among the various materials available, semiconductors seem to be the best choice and, in particular, TiO2 has been widely used because of its high photocatalytic activity, non-toxicity,