ZSM-5 structured catalysts coated with silicalite-1

Abstract Alumina beads were coated with ZSM-5 films ranging from 150 nm to 2300 nm in thickness. The ZSM-5 coated alumina beads were subsequently hydrothermally treated in a silicalite-1 synthesis solution in two steps whereupon a dense silicalite-1 film was formed on top of the ZSM-5 film. The materials were tested with two probe reactions and the reactivity was compared before and after coating with silicalite-1. As expected, the para-xylene (pX) isomerization reactivity showed no change for samples with and without the top layer of silicalite-1 for equal amounts of zeolite. Surprisingly, the triisopropylbenzene (TIPB) conversion did not decrease after the silicalite-1 film was introduced. As measured by XPS, the aluminum concentration at the surface of the uncalcined silicalite-1 film surface was lower compared to that at the surface of the calcined ZSM-5 film. However, after calcination the concentration of aluminum was higher at the silicalite-1 film surface than at the ZSM-5 film surface. These results suggest that aluminum migrates from the ZSM-5 film into the silicalite-1 film during calcination and testing which results in an active top layer.