Selective hydrogenation (semi-hydrogenation) reactions of alkynes rely on Pd-based catalysts to provide the correct pathway to favour formation of double bonds and avoid full hydrogenation to single bonds. Here, we present the preparation and characterisation of “Pd 3In”/TiO 2 nanocatalysts, which show improved activity and selectivity compared to pure Pd catalysts, towards the liquid phase semi-hydrogenation of 2-methyl-3-butyn-2-ol (MBY) to 2-methyl-3-buten-2-ol (MBE), a fundamental step in the preparation of pharmaceuticals, and other industrially produced substances, as well as a model reaction for the semi-hydrogenation of alkynes. For both the supported and unsupported “Pd 3In” alloys (later re-defined as Pd 3−xIn 1+x), we stabilised two new cubic polymorphs with a Pd-like structure, instead of the tetragonal structure as reported so far in the literature. The stabilisation of these new polymorphs was made possible by using a solution-based synthesis and, thanks to the use of different solvents, the reaction was carried out at different temperatures and the Pd/In ratio could be tuned. The same synthetic approach was adapted to prepare two “Pd 3In”/TiO 2 catalysts by adding the TiO 2 support to the reaction mixture, in a practical one-step, one-pot reaction. HREM and X-Ray maps show that the cubic crystal structure of “Pd 3In” is maintained when prepared in the presence of the support, however, the support seems to influence the Pd/In ratio.
Bibliographical noteFunding: FP7 Research for the Benefit of SMEs. Grant Number: FP70NMP-2012-SMALL-6
- selective hydrogenation