PREPARATION OF SELECTIVE CATALYTIC REDUCTION CATALYSTS VIA MILLING AND THERMAL SPREADING

New catalyst preparation methods which avoid the formation of waste wa ter are desirable for environmental reasons, especially in the case of catalysts produced in amounts as large as those in the DeNO(x) sector . Thermal spreading has recently been applied in the preparation of ti tania-supported tungsten and molybdenum monolayer catalysts. In this p aper we compare catalysts which are prepared via ball milling of mixtu res of the individual precursor oxides with subsequent thermal spreadi ng to catalysts which are prepared by a conventional coprecipitation p rocess, Titania (anatase) was milled in the presence of either tungste n trioxide or molybdenum trioxide and these mixtures were subsequently calcined in a stream of oxygen which contained water vapor. After cal cination, no crystalline WO3 or MoO3 was detected by XRD or DRIFTS, in dicating a good dispersion of the active oxides, The overtones of tung sten and molybdenum oxygen double bond vibrations, which are represent ative for the formation of surface polyoxo compounds, were detected wi th DRIFT spectroscopy for samples prepared either by coprecipitation o r via ball milling. The intensity distribution of the hydroxyl groups for ball mill prepared samples was different from the distribution for coprecipitated samples. When the physical mixtures were milled for se veral hours, the anatase was transformed into rutile as shown by X-ray diffraction, Furthermore, a decrease in surface area and changes in t he pore size distribution were observed in correlation with the millin g. (C) 1997 Elsevier Science B.V.