Pt, Pt-Fe, AND Pt-Sn NANOPARTICLES DEPOSITED OVER GRAPHITIC CARBONS AND THEIR PROPERTIES FOR THE SELECTIVE HYDROGENATION OF CITRAL.

JULIETA P. STASSI; PATRICIA D. ZGOLICZ; OSVALDO A. SCELZA; SERGIO R. DE MIGUEL

Cancún

Congreso; XXI INTERNATIONAL MATERIALS RESEARCH CONGRESS; 2012

Today, many researches on carbonaceous materials as catalytic supports have an important impact in different scientific and technological fields. These materials display different physico-chemical properties that make them attractive as catalytic materials for different applications. An example of that is the development of metallic catalysts supported on carbons for selective hydrogenation reactions of a,b-unsaturated aldehydes to different fine chemical products like unsaturated alcohols (UA). In this sense, there is an increasing interest in the use of graphitic materials in selective hydrogenation due to their particular properties, which would allow the tailoring of nanostructured catalysts with adequate metallic phases to obtain a better activity and selectivity compared with classic supports. In this work, the catalytic behavior of Pt-based catalysts supported on carbon nanotubes (CN) and Vulcan granular carbon (CV) in selective hydrogenation of citral (3,7-dimethyl-2,6-octadienal) in liquid phase at 70ºC and atmospheric presion was studied. Since in this substrate type, the hydrogenation of C=C double bond is thermodynamically favored, the addition of a second metal (Sn or Fe) to the active metal (Pt) to favor the hydrogenation of carbonyl groups was investigated. The mono and bimetallic catalysts (PtSn or PtFe/carbon) were prepared, characterized by different techniques (test reactions (cyclohexane dehydrogenation and cyclopentane hydrogenolysis), H2 chemisorption, TPR, XPS, and TEM) and evaluated in the hydrogenation reaction. Besides, other factors such as the presence of electronic effects of the support, size and morphology of the metallic particles, were studied to relate the characteristics of the metallic phase with the catalytic behavior. Results indicate, for both supports, that the addition of a promoter (Sn or Fe) is necessary to obtain high selectivities to UA. In the case of PtSn catalysts, it can be concluded from TPR and XPS results that an important fraction of Sn is co-reduced with Pt, which also could produce alloyed species according to test reactions results, thus producing both a geometric and electronic effect over the metallic phase that promote the carbonyl group hydrogenation. Besides, supports seem to have a role on metal-carbon interaction: a Pt/Sn molar ratio 1:1 seems to be adequate to obtain the highest selectivity to UA in PtSn/CV (88% at 95% citral conversion) while the same ratio inhibits the catalytic activity in PtSn/CN catalysts due to poisoning of active sites. In the case of PtFe catalysts, TPR and XPS results would indicate that in both supports, a fraction of ionic species remains over the support and another fraction is near Pt species producing mainly a geometric effect. In addition, PtFe/CV catalysts seem to have a fraction of zerovalent Fe, thus showing the highest selectivity to UA (95% at 95% citral conversion for PtFe2.5%wt/CV).