Multinuclear solid-state NMR characterization of the Bronsted/Lewis acid properties in the BP HAMS-1B (H-[B]-ZSM-5) borosilicate molecular sieve using adsorbed TMPO and TBPO probe molecules

abstract

The acid properties of a dehydrated borosilicate, HAMS-1B (H-[B]-ZSM-5), including the acid types, strengths, location, and quantities are investigated by means of trialkylphosphine oxides through multinuclear ID/2D MAS NMR experiments. B-11 DQF-STMAS combined with H-1 MAS NMR studies revealed B-OH and distinct Si-OH protons associated with trigonal boron. P-31 NMR spectra of TMPO-treated HAMS-1B reveal three Bronsted and three Lewis acid sites. We have found a number of limitations applying the TMPO/TBPO method to identify internal/external acidity. Therefore, we propose a new approach to unambiguously discriminate external/internal acid sites by treating a pore-free and pore-blocked HAMS-1B zeolite. This method provided unique structural insight regarding the identification of boron species/coordinations associated with Bronsted/Lewis acid sites. Additionally, ICP analysis in tandem with solid-state NMR enabled full assignment of the detected internal/external acid species and the study of their acid strength. Moreover, we identify the nature of TMPO complexes arising from Bronsted/Lewis interactions. (C) 2014 Elsevier Inc. All rights reserved.

keywords

BORON-SUBSTITUTED ZSM-5; ISOMORPHOUS SUBSTITUTION; P-31 NMR; TRIMETHYLPHOSPHINE OXIDE; THEORETICAL CALCULATION; DEHYDRATED ZEOLITE; CHEMICAL-SHIFT; SITES; SPECTROSCOPY; BORALITES

subject category

Chemistry; Engineering

authors

Wiper, PV; Amelse, J; Mafra, L

our authors

acknowledgements

We are grateful to the Fundacao para a Ciencia e a Tecnologia (FCT) - Portugal, Fundo Social Europeu and Fundo Europeu de Desenvolvimento Regional (FEDER) for general funding. The authors also thank the Associate Laboratory CICECO (PEst-C/CTM/LA0011/2013), the University of Aveiro, and COMPETE programs for financial support. Dr. Charles Cameron, BP Head of Downstream Technology is greatly acknowledged for generous funding for the postdoctoral grant attributed to P.V.W., and BP Amoco Chemical Company (Naperville, USA) is acknowledged for providing additional funds for equipment, expendables, and additional NMR spectrometer time. We also acknowledge the Portuguese NMR Network (RNRMN) for funding. LM thanks FCT for the awarded consolidation grant (IF/01401/2013).

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