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

Abstract

Boron removal from and reinsertion into the framework of a HAMS-1B (H-[B]-ZSM-5) borosilicate molecular sieve was studied by a combination of wet chemistry and 11 B solid-state NMR (SSNMR) spectroscopy. Uncalcined HAMS-1B shows only tetrahedral boron. However, three boron species are observed in the NMR spectra of as-prepared and then calcined HAMS-1B-3: tetrahedral framework boron ( [4] B fr ), trigonal framework boron ( [3] B fr ), and nonframework trigonal boron ( [3] B 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. [3] B NF is confirmed to be due to free boric acid formed by complete removal of boron from the framework. 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, indicating that it is more difficult to remove. The extent of boron removal and reinsertion is pH dependent. 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 11 B SSNMR of a series of 10 B-11 B exchanged borosilicate zeolites. Surprisingly, when boron is reinserted it enters as tetrahedral boron, not trigonal boron, thus reversing the partial hydrolysis and removal during calcination.

Boron Nitride and Oxide Supported on Dendritic Fibrous Nanosilica for Catalytic Oxidative Dehydrogenation of Propane

“…The signal at ~15 ppm is assigned to tri-coordinated BO3 environments. 12,13,44,46,[49][50][51][52][53] The signal at ~0 ppm is assigned to tetra-coordinated (B IV ) BO4…”

“…The signal at ~15 ppm is assigned to tri-coordinated BO3 environments. 12,13,44,46,[49][50][51][52][53] The signal at ~0 ppm is assigned to tetra-coordinated (B IV ) BO4 environments. 44,46,49,50,54 The spectra of DFNS/BN after catalysis and as-prepared DFNS/B2O3 appear to be relatively similar.…”

Quantification of Brønsted Acid Sites in Zeolites by Water Desorption Thermogravimetry

“…This sample has a non‐framework B content of ca. 20 % as determined by 11 B MAS NMR , . Thus, the corrected number of waters per framework B is around 1.6.…”

Anchoring boron atoms to the specific tetrahedral sites of borosilicate MFI by imidazolium-based molecules

“…As indicated by the 11 B MAS NMR spectra, the as-synthesized borosilicate MFI zeolites showed a single resonance at a chemical shift of around −4 ppm 29,39,40 (Fig. 2), suggesting that the boron species were incorporated in the zeolite framework with the tetrahedral coordination status.…”

“…Interestingly, the boron species in the zeolite framework is highly replaceable and can be selectively replaced by Al (ref. 27–29) or other heteroatoms 30 in an acid medium. In particular, compared with conventional aluminosilicate zeolites, the boron-containing zeolite framework with appropriate acidity and defective coordination status of boron is more suitable for some specific reactions, for instance, conversion of methanol to hydrocarbons 31 and oxidative dehydrogenation of propane.…”