Selective hydrogenation of 2-methyl-3-butyne-2-ol in a wall-coated capillary reactor with a Pd25Zn75/TiO2 catalyst

Continuous flow capillary microreactors with embedded monometallic (Pd) or bimetallic (Pd25Zn75) catalysts have been tested in the selective hydrogenation of alkyne reagents. The catalysts were prepared in two steps. At first, polymer-stabilized metal nanoparticles (either Pd or Pd25Zn75) were prepared by the reduction by solvent method. Then, a solution of colloidal nanoparticles with a desired concentration was added into a titania sol, which was destabilized by solvent evaporation during dip-coating of the inner wall of a fused silica capillary with an internal diameter of 250 µm. The wall-coated microreactors were tested in the hydrogenation of 2-methyl-3-butyne-2-ol (0.011-0.45 M solution in methanol) in the 328-337 K temperature range. The highest selectivity towards the alkene product of 90% was obtained at 99.9% conversion on the Pd25Zn75/TiO2 catalyst. The selectivity was further increased to 97% by addition of pyridine into the reactant solution. No deactivation of the wall-coated catalysts was observed during one month of continuous operation at 333 K