Pillaring of layered zeolite precursors with ferrierite topology leading to unusual molecular sieves on the micro/mesoporous border

Abstract

Layered zeolite materials with FER layer topology can produce various condensed and expanded structures including zeolite frameworks, FER and CDO, their interlayer expanded forms (IEZ), and organic-intercalated and pillared derivatives. This work concerns pillaring of the surfactant-swollen derivative with a gallery height of ca. 2.5 nm between layers by treatment with tetraethylorthosilicate (TEOS) at room and elevated temperatures. The materials obtained at 100 °C and higher showed unusual properties including 2 nm pores on the micro/mesoporous border and disordered layer packing indicated by the absence of distinct low angle interlayer peaks at d-spacing >3 nm (∼3° 2θ Cu Kα radiation) in the X-ray diffraction pattern (XRD). TEOS treatment at room temperature produced a pillared molecular sieve with the expected mesoporous characteristics, namely a pore size of around 3 nm and a high intensity low angle (001) peak at 2.3° 2θ, and a d-spacing of 3.8 nm, in the XRD. The characterization aiming to elucidate the nature of the obtained unusual products included gas adsorption isotherms, aberration corrected (C-corrected) Scanning Transmission Electron Microscopy (STEM) studies and Si solid state NMR. BET surface area values decreased with the temperature of TEOS treatment from approximately 1200 m g to ∼900 and 600 m g, at room temperature, 100 °C, and 120 °C, respectively. The Si solid state NMR revealed the presence of both Q ((SiO)SiOX, X = H or minus charge) and Q ((SiO)Si) centers giving separated signals up to the pillaring step. After pillaring at 100 °C and calcination, the nominal intensity ratios Q : Q were 2.17 and 2.61 but the signals were merged into one broad peak indicating the structural heterogeneity of Si-O coordination. The microscopy showed the presence of FER layers in the samples but the overall structure and composition were not well-defined. The observed unusual disorganization and possible partial degradation of layers during pillaring may result from the combination of high temperature, alkalinity (surfactant hydroxide) and siliceous composition of the layers. The obtained pillared products are of interest for the preparation of larger pore catalysts and sorbents or controlled drug delivery.

Two-Dimensional Zeolite Materials: Structural and Acidity Properties

“…Derivatives of 2D layers with the CDO zeolite topology are currently being explored. As shown in Table 3, interlayer-expansion by the silyation [115,116,118,119,125] and pillaring [33] of PLS-1 has led to COD zeolites with expanded and pillared structures.…”

“…Materials 2020, 13, 1822 11 of 52 [115,116,118,119,125] and pillaring [33] of PLS-1 has led to COD zeolites with expanded and pillared structures. HPM (nanostructured hybrid biohybrid and porous materials)-2 is a new layered organosilicate containing 2D layers with an MTF topology, yielding zeolite MTF by calcination [100].…”

“…ZSM-55 has 2D FER layers, and it condenses to the CDO topology upon calcination. The pillaring of ZSM-55 was done recently, and it produced an ordered pillared FER at room temperature, as well as a structure with disorganization and partial layer degradation at high temperature (373 K) [33]. The interlayer expansion of FER layers by silylation formed new zeolite structures with larger 12-MR micropores [115,163] and 14 × 12 MR [164] materials, as noted by Wu et al Due to the prominent 8-MR pore structure within 2D FER layers and the diversification of 2D derivatives and compositions, 2D FER zeolites have been proven to be efficient catalysts for different reactions.…”

“…Therefore, 2D layered zeolite precursors can be post-modified via intercalation, exfoliation, pillaring, etc. to make delaminated [13][14][15][16][17][18][19][20][21][22][23][24] and pillared [14,[25][26][27][28][29][30][31][32][33][34][35][36] structures. These materials contain hierarchical micro-and mesoporosity within and between adjacent single-unit-cell or near single-unit-cell thick (~2-3 nm) nanosheet layers.…”

Detemplated and Pillared 2-Dimensional Zeolite ZSM-55 with Ferrierite Layer Topology as a Carrier for Drugs

“…Piracetam and ciprofloxacin solutions were contacted with two forms of ZSM-55: acid treated detemplated material with layers connected by weak hydrogen bonds and the expanded pillared form with interlayer pores generated by silica props (pillars) introduced by the standard pillaring with TEOS (tetraethylorthosilicate) and calcination [14]. The scheme of ZSM-55 modification is presented in Figure 2.…”