Acid Treatment for Regulating Hf Sites of the Hierarchical Hf-B-BEA Zeolite, Thereby Boosting Its MPV Reaction Performance

Catalystengineering plays a key role in bridging gaps betweenthe structure of the Lewis acid center and its corresponding catalyticperformance. In this regard, work that has been done in tuning activesites of Hf-containing zeolites, which hold promising catalytic activityfor a variety of hydrogen-shift reactions, is far from complete. Herein,a Hf-B-BEA catalyst was rapidly prepared (within hours) by a hydrothermalsemi-reconstruction strategy, involving partial framework etchingof parent B-BEA and Hf grafting during the reassembling process. Then,an acid treatment was performed for expelling the boron atoms fromthe framework; more importantly, Hf migration into the silanol nestswas triggered. The acid treatment worked powerfully as the drivingforce for transforming the semi-framework Hf into well-defined tetrahedrallycoordinated framework Hf, thus endowing Lewis acidity of the obtainedHf-BEA. Consequently, this operation greatly boosted the Meerwein-Ponndorf-Verleyreduction performance of Hf-BEA, which was almost inactive over thepristine Hf-B-BEA. The rational regulation of Hf sites provides newconcepts in designing Hf-containing zeolites and understanding thestructural-activity relationship.