DFT Study of Closed and Open Sites of BEA, FAU, MFI, and BEC Zeolites Substituted with Tin and Titanium

Abstract

DFT with long-range corrections and ONIOM along with a polarizable-continuum model were used to analyze zeolites BEA, FAU, MFI, and BEC substituted with Sn and Ti. The preferential substitution sites for Ti and Sn in the different frameworks are reported. The Lewis acidities were measured through the NH 3 binding energies and through the charge transfer of NH 3 upon adsorption. The deprotonation energies of the open sites, which are proportional to the Brønsted acidities, and the hydrolysis energies are also reported. We also present the properties of BEA with a single and a double Sn-substitution to compare the active sites obtained with two methods commonly employed for the synthesis of Sn−BEA. Among the zeolites analyzed in this study, Sn−BEA with a double Sn-substitution has the highest Lewis acidity. The formation of open sites through the hydrolysis of Sn−BEA, Sn−FAU, and Ti−FAU is energetically favorable, but it is not favorable in MFI or Ti−BEA. On the basis of the deprotonation energies, the open sites of Sn−BEA have a strong Brønsted acidity, comparable to Al−BEA or Al−MFI. We also demonstrate that the VDW forces in the binding energies of NH 3 on MFI are more significant than in the other zeolite frameworks and that these forces decrease with increasing pore size.

Cluster model DFT study of lactic acid dehydration over Fe and Sn-BEA zeolite

“…To date, most of the theoretical groups substituted tin inside the zeolite framework. [4][5][6][7][8][9][10] However, in the case of our studies, lactic acid was not stabilized above any zeolite frame-centers (neither Si, Al nor Sn in positions presented at Fig. 4a-b).…”

“…Metal substituted BEA and MFI have been the most studied zeolites, especially for reactions where Lewis acidity is required. [4][5][6][7] Many groups have already been investigated, such as zeolites substituted with tin and other metals. The activity of Sn-BEA in the conversions of glucose to fructose has been significant, while the same reaction has not been noted over Sn−MFI.…”

Synthesis of a novel polyester building block from pentoses by tin-containing silicates

“…Recent work aimed at elucidating the catalytic functioning of Sn-Beta includes DFT calculations, FT-IR, TPR and 119 Sn-NMR spectroscopy. [39][40][41][42][43][44] Despite it being a crystalline material, the preparation method oen greatly inuences the catalytic performance. Two principally different preparation methods are normally used, direct synthesis under hydrothermal conditions using hydrouoric acid as mineralising agent [Sn-Beta (HT)] and synthesis by post treatment of a dealuminated Beta zeolite with a tin source [Sn-Beta (PT)].…”

Active Sites of M(IV)-incorporated Zeolites (M = Sn, Ti, Ge, Zr)

“… 48 demonstrated that Ti(IV) sites adjacent to Si vacancies [(OSiO 3 ) 3 TiOH] are more reactive; that is, the epoxidation processes are significantly accelerated by defects. The two Ti(IV) species [i.e., Ti(OSiO 3 ) 4 and (OSiO 3 ) 3 TiOH] were identified in TS-1 zeolite 49 , 50 and Sn(IV) analogues were proposed for Sn-BEA zeolite 51 – 53 . Defects in Sn-BEA zeolite were reported to play a significant promoting effect during the transformation of cellulosic biomass 54 – 60 .…”