Defect-Guided Synthesis of Hierarchical Sn-B-Beta Zeolite with Highly Exposed Sn Sites

Abstract

Selectively anchoring active centers on the external surface for forming highly exposed acid sites is a highly desirable but challenging task in zeolite catalyst synthesis. Herein, a defect-guided etching-regrowth strategy is rationally designed for facilely positioning Sn Lewis acid sites on the outer surface of the Sn-B-Beta while fabricating a bifunctional hierarchical structure. The synthesis was conducted by hydrothermal treatment of the as-made B-Beta (uncalcined), which has intrinsic defects of the BEA structure, with Sn source and basic organic structure directing agent (SDA). Under a moderate SDA concentration, with blocked micropore channels, such SDA-triggered etching-regrowth will proceed along the defect defined pathway, which ensures Sn selectively anchored on the external surface. Moreover, this methodology has exclusively introduced tetrahedrally coordinated framework Sn with open Sn sites as the predominated species. Mono- and disaccharide isomerizations in ethanol over different Sn-Beta catalysts proved the prominent advantages of the hierarchical structure with highly exposed and synergetic acid sites.

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

“…N 2 adsorption−desorption (Figure 1C,D) was performed for studying the structural evolution during the treatment process. Consistent with a reported result, 27 the pristine B-BEA mother sample has modest mesoporosity. Surprisingly, after a very short hydrothermal treatment (2 h, Figure S3), the mesoporosity significantly increased in terms of the external surface area and mesopore volume (Table 1).…”

“…The synthesis of parent B-BEA was performed according to a reported recipe . The synthesis of Hf-B-BEA was achieved by hydrothermal treatment of the as-synthesized B-BEA with a chemical composition of 1.0 SiO 2 :1/150 Hf 4+ :0.0075–0.48 TEAOH:30 H 2 O.…”

“…The synthesis of parent B-BEA was performed according to a reported recipe. 27 The synthesis of Hf-B-BEA was achieved by hydrothermal treatment of the as-synthesized B-BEA with a chemical composition of 1.0 SiO 2 :1/ 150 Hf 4+ :0.0075−0.48 TEAOH:30 H 2 O. As a typical run, 0.0142 g of HfCl 4 was dispersed in ethanol and 4 g of 0.4 M TEAOH solution was dropwise added to the above mixture under intense stirring.…”

“…Hf-B-BEA is selected here owing to the fact that its Beta topology is ubiquitously used to host Lewis acid sites due to its three-dimensional large-micropore system and the broad range of its framework composition. 26 For avoiding the use of toxic fluoride anions, a hydrothermal treatment post-synthetic strategy, which has been successfully employed for fabrication of bifunctional hierarchical Sn-B-BEA, 27 was introduced here. This synthesis was conducted upon an as-synthesized B-BEA, which is rich in intrinsic defects; thus, most hetero-atoms were anchored on the eroded outer surface along the defects under the guidance of the organic-structure-directing agent.…”

Rapid Synthesis of Si-Rich SSZ-13 Zeolite under Fluoride-Free Conditions

“…Zeolites, as an important class of silica-based porous materials, have been widely used as catalysts and adsorbents in the chemical industry due to their large micropore volume, high surface area, uniform micropore distribution, and excellent stabilities. − Currently, more than 20 types of zeolites have been industrialized and thus created great economic and social benefits . Among them, aluminosilicate SSZ-13 zeolite is a typical example because of the excellent performance in the selective catalytic reduction of NO x with NH 3 (NH 3 -SCR) reaction. − …”