Rational Positioning of Metal Ions to Stabilize Open Tin Sites in Beta Zeolite for Catalytic Conversion of Sugars

Via hydrothermal synthesis of Sn-Al gels, mild dealumination and ion exchange, a bimetallic Sn-Ni-Beta catalyst was prepared which can convert glucose to methyl lactate (MLA) and methyl vinyl glycolate (MVG) in methanol at yields of 71.2 % and 10.2 %, respectively. Results from solid-state magic-angle spinning nuclear magnetic resonance, X-ray photoelectron spectroscopy, transmission electron microscopy, spectroscopic analysis, probe-temperature-programmed desorption, and density functional theory calculations conclusively reveal that the openness of the Sn sites, such as by the formation of [(SiO)₃ -Sn-OH] entities, is governed by an adjacent metal cation such as Ni²⁺ , Co²⁺ , and Mn²⁺ . This relies on the low structure-defective pore channel, provided by the current synthesis scheme, and the specific silica hydroxyl anchor point is associated with the incorporation of Sn for additional and precise metal ion localization. The presence of metal cations significantly improved the catalytic performance of Sn-Ni-Beta for glucose isomerization and conversion to MLA of sugar compared with Sn-Beta.

Catalytic Performances of Sn-Beta Catalysts Prepared from Different Heteroatom-Containing Beta Zeolites for the Retro-Aldol Fragmentation of Glucose

Beta zeolites with different heteroatoms incorporated into the lattice at two loadings (Si/M = 100 or 200, where M = Al, Fe, Ga, B) were hydrothermally synthesised and used as starting materials for the preparation of Sn-Beta using Solid-State Incorporation. 119Sn CPMG MAS NMR showed that various Sn species were formed, the distribution of which depended on the identity of the initial heteroatom and the original Si/M ratio. The final Sn-Beta materials (with Si/Sn = 200) were explored as catalysts for the retro-aldol fragmentation of glucose to α-hydroxy-esters in the continuous regime. Amongst these materials, B-derived Sn-Beta was found to exhibit improved levels of selectivity and stability, particularly compared to Sn-Beta catalysts synthesised from commercially available Al-Beta materials, achieving a combined yield of methyl lactate and methyl vinyl glycolate > 80% at short times on the stream. Given that B atoms can be removed from the Beta lattice in mild conditions without the use of highly concentrated acidic media, this discovery demonstrates that B-Beta is an attractive starting material for the future post-synthetic preparation of Lewis acidic zeolites.

Double active BEA zeolite/silver tungstophosphates - Antimicrobial effects and pesticide removal

Novel composites of BEA zeolite and silver tungstophosphate were prepared by different procedures: two-step impregnation, ion-exchange, and as physical mixtures with varying component mass ratios. Composites were characterized using Atomic force microscopy, Infrared, Raman and Atomic absorption spectroscopy, and results were related to adsorption properties and antimicrobial efficiencies of the composites. Prepared samples were tested as antimicrobial agents for fungal and different bacterial strains, as well as for adsorbents for pesticide nicosulfuron in aqueous solutions by using High-performance liquid chromatography. Experimental conditions for batch adsorption testing were optimized in order to efficiently eliminate nicosulfuron from aqueous solutions, while enabling antimicrobial activity of these advanced materials. Antimicrobial efficiency of composites was verified, and indicated that silver ion persistence in the solid phase is of utmost significance for the antimicrobial activity. Spectroscopic investigation revealed interaction of the silver tungstophosphate active phase and the zeolite framework, giving evidence of uniform distribution of active sites in the synthesized materials that proved to be essential for adsorption application. The best obtained adsorption capacity, as well as highest antimicrobial efficiency, is found for composite samples prepared by two-step impregnation with (BEA: silver tungstophosphate) mass ratio 2:1. The amount of nicosulfuron removed from water suspension was 38.2 mg per gram of composite, and the minimum inhibitory concentration determined for all investigated gram-negative bacteria was 125 μg mL^-1.