Hydrogenation of 2-butyne-1,4diol on supported Pd-catalysts obtained from LDH precursors

The semi-hydrogenation of 2-butyne-1,4-diol has been performed with supported Pd catalysts (0.2–0.3 wt% Pd) obtained from layered double hydroxides (LDH) precursors. The catalysts have been prepared by three different routes: (i) impregnation with Pd(acac)2 of a Mg(Al)O support (Pd/Mg(Al)O-imp), (ii) coprecipitation of a multicationic Pd/Mg/Al LDH (Pd/Mg(Al)O-cop), and (iii) synthesis of a Pd colloid Mg/Al LDH nanocomposite (Pd/Mg(Al)O-nc). After calcination at 723 K and reduction at 483 K the catalysts exhibit specific surface areas ranging from 180 to 280 m2 g_1 and a predominant basic character. The Pd particles have a good dispersion in the three catalysts, especially for Pd/Mg(Al)O-imp with a narrow distribution in size centered at ca. 2 nm. Both activities and selectivities to 2-butene-1,4-diol range as follows: Pd/Mg(Al)O-imp > Pd/Mg(Al)O-nc > Pd/Mg(Al)O-cop in agreement with the dispersion of the samples. Rehydration of the catalysts increases the activity but decreases the selectivity to 2-butene-1,4-diol. Formation of butane-1,4-diol, occurs by consecutive hydrogenation of 2-butene-1,4-diol as well as direct hydrogenation of 2-butyne-1,4-diol through a carbyne. species.