The Interplay between Mo Loading and Calcination Temperature over the Hierarchical ZSM-5/Alumina Composite for the Cross-Metathesis Reaction

Thermal treatment and metal loading levels are key factors impacting the distribution and transformation of active sites in supported catalysts. Zeolite-alumina extrudate-derived catalysts receive limited attention due to the complexity arising from the competition in the anchoring and transformation of supported metal/metallic species. In this work, we investigated the intersecting impacts of Mo loading and calcination temperature on the performance of hierarchical MFI zeolite-alumina extruded catalysts in the cross-metathesis reaction between ethene and 2-butene. The response of metathesis activity to alterations in calcination temperature significantly depended on the Mo loading. At the lower Mo loading level, enhanced performance in the cross-metathesis reaction was achieved as the elevated calcination temperature stimulated the thermally driven migration of the dispersed Mo-oxo species from Al₂O₃ component toward zeolite micropores. Nevertheless, the metathesis activity suffered from rapid decay at a higher Mo loading level, especially at elevated temperatures, on account of the formation of Al₂(MoO₄)₃ species. The negative role of Al₂(MoO₄)₃ species in the metathesis reaction was further corroborated by a designed experiment, wherein the stability and durability of the catalyst were restored after the removal of Al₂(MoO₄)₃ species through acid leaching.