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 2-butyne-1,4-diol partial hydrogenation. Both unsupported micelles (0.6 kgPd/m3) and supported ones on γ-Al2O3 (0.042 wt.% Pd) showed nearly 100% selectivity to 2-butene-1,4-diol up to 94% conversion. The only side product observed was 2-butane-1,4-diol. The catalysis was ascribed to Pd nanoparticles' surface modified by pyridine units of micelles and alkali reaction medium (pH of 13.4). TOFs over the unsupported and supported catalysts were found to be 0.56 and 0.91 s−1 (at 323 K, 0.6 MPa H2 pressure, solvent 2-propanol/water = 7:3), respectively. Reaction kinetics fit the Langmuir-Hinshelwood model assuming weak hydrogen adsorption. The experiments on the catalyst reuse showed that Pd nanoparticles remain inside the micelle core, but the micelles slightly desorbed (less then 5%) during the catalytic run.