Palladium nanoparticles stabilized in block-copolymer micelles for highly selective 2-butyne-1,4-diol partial hydrogenation

Pd nanoparticles (2 nm) stabilized in the micelle core of poly(ethylene oxide)-block-poly(2-vinylpyridine) were studied in partial hydrogenation of 2-butyne-1,4-diol. Both unsupported micelles (0.6 kg Pd/m3) and supported ones on g-Al2O3 (0.042% Pd) showed nearly 100% selectivity to 2-butene-1,4-diol, with up to 94% conversion. The only side product obsd. was butane-1,4-diol. The catalysis was ascribed to the surface of Pd nanoparticles modified by pyridine units of micelles and alkali reaction medium (pH of 13.4). The TOF [turnover frequency] over unsupported and supported catalysts was 0.56 and 0.91 s-1 (at 323 K, 0.6 MPa H2 pressure, solvent 2-propanol/water = 7:3), resp. Reaction kinetics fit the Langmuir-Hinshelwood model assuming weak hydrogen adsorption. Expts. on catalyst reuse showed that Pd nanoparticles remain inside the micelle core, but the micelles desorbed by less then 5% during the catalytic run. [on SciFinder (R)]