Silicalite-1 coating on Pt/TiO2 particles by a two-step hydrothermal synthesis

Silicalite-1 membranes were synthesized on spherical Pt/TiO2 particles by a two-step synthesis, which includes consecutive hydrothermal syntheses with and without stirring synthetic solutions in order to control the rates of nucleation and crystal growth. The silicalite-1-coated Pt/TiO2 particles (silicalite-1/Pt/TiO2) were composed of a thinner silicalite-1 layer with smaller crystals than the one synthesized by a one-step synthesis, which had been previously reported. The silicalite-1/Pt/TiO2 shows higher activity for hydrogenation of a mixture of linear 1-hexene (1-Hex) and dibranched 3,3-dimethylbut-1-ene (3,3-DMB) than the previous results because of its thinner effective membrane thickness. Hydrogenation selectivities of 1-Hex/3,3-DMB were very high (20-35 at 323 K and 22-70 at 373 K) due to the selective permeation of the reactant 1-Hex into Pt/TiO2 particles through the silicalite-1 layer. These high selectivities indicate that the membrane quality was improved by the two-step synthesis. Permeances of 1-Hex and 3,3-DMB through the silicalite-1 membrane coating could be determined by an integral reactor analysis assuming permeation control in the reaction performance of the coated particle.