III International Conference

PP-II-7resolution of around 200 µm. Measurements can be done both in the wet and in the dry stageof the preparation process thanks to the measuring cell. The set-up (shown in Figure 1)consists of a UV-Vis probe containing 7 optical fibres (Ø=100 µm), six of them connected toa light source and the other one to a detector. A step motor allows the movement of themeasuring cell (x, y directions) and the probe (z direction) [1].Results In the case of Pd II /Al 2 O 3 catalysts the impregnation step was monitored. The ligandto-metal-charge-tranfertransition at 280 nm and the Pd II d-d band at 474 nm of [PdCl 4 ] 2-complexes were measured. The latter band shifted to shorter wavelengths with aging time,indicating a change in the coordination sphere of the metal ion. Moreover, both bands remainedwith time in the outer rim of the pellet. Pd II distribution could be modified by adding excess ofNaCl to the impregnation solution giving a Pd II egg-yolk distribution after 4 days of aging.The influence of the drying temperature was studied on [Ni(en) 3 ] 2+ /Al 2 O 3 pellets. UV-Visspectra, collected after drying at room temperature, showed two Ni 2+ d-d transitions bands at549 and 890 nm, present in all the positions inside the pellet indicating a uniform distributionof [Ni(en) 3 ] 2+ (Figure 2a). Drying at 60 °C yielded a shift of the bands to longer wavelengthsfrom the edge to the core of the pellets (Figure 2b). The shift of the bands indicated that agradual change in the coordination sphere of Ni 2+ occurred from the outer part of the pellet tothe core, in which ethylenediamine groups were partly substituted probably for hydroxylligands from the support [2].0.5(a)0.5(b)Abs0.25Abs0.250250 350 450 550 650 750 850 950 1050Wavelength/nm0250 350 450 550 650 750 850 950 1050Wavelength/nmFigure 2. UV-Vis spectra collected along the cross-section of an impregnated pellet with0.5 M [Ni(en) 3 ] 2+ , after 2 h of aging followed by drying at room temperature (a) and at 60 °C (b).Conclusions Spatially resolved UV-Vis micro-spectroscopy enables studying thephysicochemical processes involved during catalyst preparation. It allows monitoring both thewet and dry steps, giving information of the metal ion surroundings and how this can bemodified. Thus, this technique helps to understand catalyst preparation processes which is ofprime importance for the design of industrial catalysts.References1 Van de Water, L.G.A., Bergwerff, J.A., Nijhuis, T.A., de Jong, K.P. and Weckhuysen, B.M.,J. Am. Chem.Soc. 127 (2005) 5024.2 Espinosa Alonso, L., de Jong, K.P. and Weckhuysen, B.M., in preparation.172