Boron removal and reinsertion studies in B-10-B-11 exchanged HAMS-1B (H-[B]-ZSM-5) borosilicate molecular sieves using solid-state NMR

abstract

Novel atomic-level insight in boron removal and reinsertion into the framework of a HAMS-1B (H-[B]-ZSM-5) borosilicate molecular sieve was obtained by a combination of wet chemistry and one-/twodimensional B-11 solid-state NMR (SSNMR) spectroscopy. Uncalcined HAMS-1B shows only tetrahedral boron. However, three boron species are observed in B-11 SSNMR spectra of as-prepared and then calcined HAMS-1B: tetrahedral framework boron (B-[4](fr)), trigonal framework boron (B-[3](fr)), and non-framework trigonal boron (B-[3](NF)). A picture has emerged as to the origins of these three species. Trigonal boron species are formed via hydrolysis by reaction with the water formed from water release and water formed by oxidation and removal of the template during calcination. The trigonal boron species are readily removed from the framework by slurrying in water or mild acid solutions. Tetrahedral boron remains at a concentration about equal to that in the calcined sieve not slurried, indicating that it is more difficult to remove. The extent of boron removal and reinsertion is pH dependent. We demonstrate that boron is removed to a greater extent at low pH and can be reinserted when pH is increased. Boron reinsertion into the framework is proven by B-11 SSNMR on a series of B-10-B-11 exchanged borosilicate zeolites. We found that when boron is reinserted it enters at higher concentrations (similar to 40% more) as tetrahedral boron, not trigonal boron, thus reversing partial hydrolysis and removal during calcination. (C) 2015 Elsevier Inc. All rights reserved.

keywords

ZEOLITES; SPECTROSCOPY

subject category

Chemistry; Engineering

authors

Hough, A; Routh, AF; Clarke, SM; Wiper, PV; Amelse, JA; Mafra, L

Groups

G1 - Porous Materials and Nanosystems

Projects

CICECO - Aveiro Institute of Materials (UID/CTM/50011/2013)

Variable pressure solid-state NMR methods to study gas-surface interactions in nanoporous sorbent materials for industrial post/pre-combustion CO2 capture (PTDC/QEQ-QAN/6373/2014)

acknowledgements

AH gratefully acknowledges funding for her Master's Degree at Cambridge University from the Kinetics and Catalysis division of the BP Distributed Research Laboratory (DRL). PVW gratefully acknowledges generous funding from BP Amoco Chemical Company for a postdoctoral stipend plus operating expenses via a special grant from Dr. Charles Cameron, Head of Technology, Downstream, BP, P.L.C. We thank the support from the Univ. of Aveiro and CICECO-Aveiro Institute of Materials (Ref. FCT UID/CTM/50011/2013), financed by national funds through the FCT/MEC and when applicable co-financed by FEDER under the PT2020 Partnership Agreement. The Portuguese NMR Network (RNRMN) is also acknowledged for financial support. We also acknowledge the Portuguese NMR Network (RNRMN) for funding. LM greatly thank FCT for the awarded development grant (IF/01401/2013) and R&D research project PTDC/QEQ-QAN/6373/2014.