Reactant-Selective Hydrogenation over Composite Silicalite-1-Coated Pt/TiO₂ Particles

Abstract

Silicalite-1 coatings were synthesized on spherical Pt/TiO2 particles with a diameter of 0.5 mm from an aqueous solution of fumed silica, tetrapropylammonium hydroxide (TPAOH), and ethanol under hydrothermal conditions. SEM images show that the surface of the Pt/TiO2 particles was fully covered by intergrown silicalite-1 crystals with a crystal size of 5 × 2 × 15 μm. From the cross section of crushed silicalite/Pt/TiO2 particles, the estimated thickness of the silicalite-1 layer was about 40 μm. The compactness of the layer to act as a membrane was demonstrated by catalytic tests of the silicalite-1/Pt/TiO2 particles. The hydrogenation of a mixture of linear 1-hexene (1-Hex) and dibranched 3,3-dimethylbut-1-ene (3,3-DMB) (in a molar ratio of 1-Hex to 3,3-DMB of 1:1.68) was performed using a fixed-bed reactor with a continuous flow system. The composite silicalite-1/Pt/TiO2 catalyst showed 1-Hex/3,3-DMB hydrogenation selectivities of 12−20 at 50 °C and 18−30 at 100 °C due to the selective permeation of 1-Hex into the Pt/TiO2 particles through the silicalite-1 layer. Deactivation of the catalyst was also reduced, probably by protection against poisoning impurities in the feed. This work demonstrates the feasibility of the application of catalyst particles coated with a permselective membrane to achieve reactant selectivities on a particle level.