Supported palladium catalysts for the selective conversion of cis-2-butene-1,4-diol to 2-hydroxytetrahydrofuran: effect of metal particle size and support

Palladium catalysts on different supports (SiO2, Al2O3, TiO2, ZrO2, MgO and ZnO) have been tested in selective liquid phase conversion of cis-2-butene-1,4-diol affording also, when hydrogenated, 2-hydroxytetrahydrofuran. The metal particle size was determined by TEM. The acidic properties of the catalysts were studied by FT-IR spectroscopy using pyridine as probe molecule. The influence of some preparative variables, such as the particle size, the support, the partial hydrogen pressure, on the catalytic behaviour of palladium catalysts has been investigated. TEM measurements indicated that Pd particles diameter observed was in the range 2.5-10 nm. No significant variation of TOF and selectivity values with the metal particle size was observed in this range. Moreover, the activity and the selectivity towards reaction products were found to be strongly dependent on the acid-base characteristics of the support. The acid systems have been found more active and selective to isomerisation and hydrogenolysis products than the basic ones. No hydrogenolysis reaction was observed on basic supports. Among the examined catalysts, Pd/TiO2 resulted the most selective to 2-hydroxytetrahydrofuran. A maximum yield to this compound of about 74% was, in fact, obtained at 0.01 MPa of H2 pressure.