PII.006 Acidity evaluation of H-[Al]-RUB-18 by solid-state 31P-NMR spectroscopy of adsorbed TMPO in the absence and presence of water

Resumo

In this work, the lamellar Na-[Al]-RUB-18 (with Si/Al molar ratios = 15, 30, ∞) was synthesized and characterized by XRD, XRF, TG/DTG, FTIR, and ²⁹Si- and ²⁷Al-RMN. The acidic properties in the presence and absence of water were determined on the acidic materials by ³¹P-MAS-RMN of adsorbed trimethylphosphine oxide (TMPO) as probe molecule, evaluating the nature (LAS/BAS), strength and concentration of the active sites. The synthesis of Na-RUB-18 yielded materials with a Q³/Q⁴ sites ratio = 2, indicating more structural defects due to the larger concentration of -SiOH/-SiO^- groups and implying the incorporation of Al_Td and Al_Oh species in different proportions into its structure. By ³¹P-MAS-RMN, the Brønsted acid sites were identified in different concentrations. A lower amount of TMPO yielded signals above 50 ppm, whose intensity increased considerably when adsorption occurred in the presence of water, suggesting that the interaction of TMPO with the structure is easier in the presence of water. This work initiates the groups’ efforts to create a consistent protocol of acidity analysis in lamellar solids that is comparable to the existing ones for zeolites.