Alkaline treatment of template containing zeolites: Introducing mesoporosity while preserving acidity

作者：van Laak Adri N C; Zhang Lei; Parvulescu Andrei N; Bruijnincx Pieter C A; Weckhuysen Bert M; de Jong Krijn P; de Jongh Petra E^*

来源：Catalysis Today, 2011, 168(1): 48-56.

DOI：10.1016/j.cattod.2010.10.101

• Template
• Zeolites
• Mesoporosity
• Desilication
• Catalysis

Alkaline treatment (desilication) is an effective treatment to increase mesoporosity. However, the concomitant decrease in Si/Al ratio affects the strengths of the acidic sites and hence catalytic activity and selectivity. Therefore instead we subjected template containing zeolites to 1 M NaOH to induce additional porosity. All zeolites tested (ZSM-5, ZSM-12 and Beta) consisted of small crystallites (30-200 nm) that were agglomerated into larger particles between 1 and 5 mu m. Mesopore formation occurred by slowly removing outer layers of individual crystallites, thereby preserving the Si/Al ratio as well as the crystallinity. Inter-crystalline mesopores were formed for all zeolites, but the treatment was most effective for zeolites with small crystallites. The external surface area of ZSM-5 was increased from 90 to 149 m(2) g(-1) and for zeolite Beta from 70 to 158 m(2) g(-1). The catalytic performance was tested at 413 K for 3 h for etherification of 1,2-propylene glycol with 1-octene to form octyl-ether. For ZSM-5, conversion increased from 1.2% to 5.6% upon alkaline treatment in the presence of a template, while only to 5% for the template-free treated sample with a significantly higher external surface area (205 m(2) g(-1)). The parent zeolite Beta was significantly more active (30% conversion, 88% selectivity), which can be ascribed to its larger pore size. Nevertheless also in this case alkaline treatment in the presence of the template significantly increased the activity to 40% conversion with similar selectivity. As only the mesoporosity was changed upon alkaline treatment it suggests that the etherification of 1,2-propylene glycol with 1-octene is affected by intra-crystalline diffusion. Our work illustrates the possibilities to use alkaline treatment of templated zeolites to decouple accessibility changes from acidity, and to gain further insight in zeolite catalysis.

• 出版日期2011-6-20