Conversion of cis-2-butene-1,4-diol to hydrofurans on Pd/SiO2 and Pt/SiO2 catalysts under mild conditions: a FT-IR study

The gas-phase interaction of cis-2-butene-1,4-diol (C-2-OL) with silica supported Pd and Pt nanoparticles has been studied using infrared spectroscopy at room temperature. Samples were prepared according to standard recipes and characterized through TEM and the IR spectroscopy of adsorbed carbon monoxide at room temperature. Whereas the reaction with hydrogen of C-2-OL in ethanol solutions yields hydrogenated products through a complex network, and no reaction takes place in the absence of hydrogen, in the present case C-2-OL is converted first to 2,5-dihydrofuran (2,5-DHF) and water. This step occurs on the silica support at room temperature, probably through the intermediacy of the surface species –Si–O–CH2–CH CH–CH2–OH. The presence of Pd nanoparticles allows, at ca. 100 ◦C, the subsequent isomerization of 2,5-DHF to 2,3-dihydrofuran (2,3-DHF). The same reaction requires a higher temperature(ca. 150 ◦C) with the Pt catalyst. At higher temperatures, the expected dehydrogenation of both 2,5- and 2,3-DHFs to furan takes place. On the support alone at 350 ◦C 2,5-DHF is converted to furan, and 2,3-DHF to carbonyl-containing species (as suggested in the literature), through thermal reactions.