Tracking the solid-state incorporation of Sn into the framework of dealuminated zeolite beta, and consequences for catalyst design

Abstract

Sn-Beta has emerged as a state-of-the-art catalyst for a range of sustainable chemical transformations. Conventionally prepared by bottom-up hydrothermal synthesis methods, recent research has demonstrated the efficiency of several top-down...

Evaluating the Role of Anharmonic Vibrations in Zeolite β Materials

“…Studies in the literature have compared experimental IR spectra and VDOS from aiMD simulation to characterize the adsorption of alcohol in H-ZSM-5; however, there is little consideration for the role of anharmonic effects on the simulated vibrational modes. In order to understand the full impact of anharmonicity for the Sn-β system, we consider the DRIFTS spectrum of Sn­(II) acetate adsorbed on deAl-β (Figure ), which is a key step in SSI, as described in previous work . Subsequently, we compare the DRIFTS spectrum with calculated IR frequencies obtained using (i) the harmonic model (finite-difference method) and (ii) the aiMD approaches detailed here.…”

“…A combination of in situ and ab initio spectroscopic studies have been vital in characterizing the mechanism and intermediates during SSI, with a comparison between infrared spectra and vibrational simulation highlighting key stages such as a change in Sn(II) acetate coordination upon grinding, from bidentate to monodentate, and the formation of acetic acid. 14 When performing ab initio vibrational simulations of materials, the calculations often rely on a harmonic approximation, where the potential energy surface (PES), V(R), around the equilibrium positions, R 0 , is approximated via a second-order Taylor expansion, i.e., by a parabolic potential…”

“…Recently, the demonstration of solid-state incorporation (SSI) for synthesizing Sn-β has addressed limitations in wet synthesis that hinder scale-up, such as high temperatures and pressures and strong acids. − SSI is a “top-down” synthetic approach where readily available zeolite BEA (H-β) undergoes dealumination with a strong acid, creating vacancies in the framework (silanol nests) at the sites previously occupied by Al. The dealuminated framework (deAl-β) then undergoes mechanochemical grinding with a Sn precursor (Sn­(II) acetate), which induces interaction with the framework, and subsequent heating and cooling steps further incorporate Sn into the BEA framework to form the final catalyst (Sn-β, Figure B).…”

“…The dealuminated framework (deAl-β) then undergoes mechanochemical grinding with a Sn precursor (Sn­(II) acetate), which induces interaction with the framework, and subsequent heating and cooling steps further incorporate Sn into the BEA framework to form the final catalyst (Sn-β, Figure B). A combination of in situ and ab initio spectroscopic studies have been vital in characterizing the mechanism and intermediates during SSI, with a comparison between infrared spectra and vibrational simulation highlighting key stages such as a change in Sn­(II) acetate coordination upon grinding, from bidentate to monodentate, and the formation of acetic acid …”

“…Figure 8. Top: Simulated VDOS (300 K) for framework-bound Sn(II) acetate (blue line) and for bound Sn(II) acetate/deAl-β (faded blue line).Bottom: Experimental DRIFTS spectra for Sn(II) acetate/deAl-β mixture (red line) and simulated IR frequencies using finite-difference method for framework-bound Sn(II) acetate (green triangles) replotted from ref[14].…”