Abstract
Abstract The effect of Zn location and reduction temperature have been studied on pure and Zn-modified MCM-41 supported Pt catalysts. Experimental results show that incorporation of Zn into the siliceous framework of the MCM-41 material introduces structural oxidized Zn centres with a high stability towards a reduction treatment even at high temperatures. XP spectra confirm the high stability of these Zn species although, at the highest reduction temperature (723 K), a high mobility of the doping cations from structural positions to the inner wall of the mesopores is observed. Catalytic studies in the chemoselective hydrogenation of crotonaldehyde show that the presence of Zn produces an important decrease in the catalytic activity of the Pt nanoparticles, in accordance with Pt dispersion measurements. However, the presence of Zn improves the selectivity towards the formation of crotyl alcohol. Compared with a conventional impregnated PtZn/MCM-41 catalyst, structural Zn centres in the doped Pt/ZnMCM-41 catalysts exhibit a higher polarizing/activation of the carbonyl double bond giving rise to a higher yield to crotyl alcohol, the product of interest. Additionally, these Zn-modified MCM-41-based Pt catalysts show an excellent behaviour in an important industrial reaction such as the dehydrogenation of iso-butane to iso-butene, with a selectivity of 100%, which remains stable with time on stream.
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