Impact of Calcination Temperature on Tungsten-based Composite Catalysts for Olefins Metathesis

The thermal treatment is one of the key procedures for the distribution and transformation of active sites for the supported metal oxide catalysts. However, the underlying impacts of thermal treatment on composite supported catalysts receives limited attention due to the additional complexity of the composite support. In this work, the progressive gradient in the metathesis activity, as the function of enhanced calcination temperature, has been observed for the tungsten-based catalysts supported on the hierarchical ZSM-5 zeolite-alumina composite. The metathesis activity, reflected by ethene conversion, undergoes a stepwise growth from 24.2 % to 38.9 % along with the enhanced calcination temperature from 723 K to 923 K. The supported W-oxo species share high similarity in structural states except their interaction with the Bronsted acidic bridge hydroxyl groups in zeolite. The density of bridge hydroxyl groups is reduced as the function of enhanced calcination temperatures, which reflects the intensified anchoring of surface W-oxo species. It should be noted that such dependence is not observed for their counterparts based on microporous ZSM-5 zeolite-alumina. These sharp comparisons highlight the critical routes of thermal migration of W-oxo species along the intrazeolite-alumina interface in the evolution of active sites for the olefins cross-metathesis reaction. The stepwise growth in the metathesis activity, as the function of enhanced calcination temperature, has been observed for the hierarchical zeolite-alumina composite supported tungsten-based catalysts, which is associated with the promoted thermal migration of W-oxo species. Such thermal-driven alternation primarily rests with the presence of zeolitic intracrystalline mesoporosity as the access for the migration of W-oxo species from alumina to zeolite micropore along the intrazeolite-alumina interface.image