Modification of MOR by desilication treatments: Structural, textural and acidic characterization

Abstract

The effect of several desilication experimental parameters (base concentration, temperature and time) on the characteristics of MOR zeolite was studied. The samples were characterized by X-ray diffraction, Al-27 and Si-29 MAS-NMR, chemical analysis, and FTIR (framework vibration region). The textural characterization was made by N-2 adsorption and the acidity was evaluated by pyridine adsorption followed by FTIR and by the catalytic model reaction of n-heptane cracking. The alkaline treatments promoted the Si extraction from the zeolite framework, without considerable loss of crystallinity and, as it was envisaged, an important increase of the mesoporous structure was attained. A linear correlation between the number of framework Si per unit cell. N-Si and the asymmetric stretching wavenumber, nu(i), was observed. The acidity characterization shows that the desilicated samples exhibit practically the same acid properties than the parent HMOR zeolite. The optimum desilication conditions were those used to obtain sample M/0.2/85/2, i.e., sample treated with 0.2 M NaOH solution at 85 degrees C for 2 h. (C) 2010 Elsevier Inc. All rights reserved.

Mesopore modification of beta zeolites by sequential alkali and acid treatments: Narrowing mesopore size distribution featuring unimodality and mesoporous texture properties estimated upon a mesoporous volumetric model

“…4a, the NaB(ht) prepared by hydrothermally alkali etching displays the type I isotherm proceeding with an flat and extended hysteresis loop, evidencing the presence of micropores and supermicropores less than 2 nm [10,38], in agreement with the quite weak mesopore distribution observed in Fig. 4b.…”

“…[9][10][11] in relevant acid and alkaline media. The more detailed investigations on fundamental aspects of hierarchical zeolite post-synthesis have involved the partial restructuring of dissolved zeolitic fragments in the presence of quaternary ammonium cations [12].…”

Full Compositional Flexibility in the Preparation of Mesoporous MFI Zeolites by Desilication

“…Previous studies varying alkalinity have primarily focused on individual zeolites of Si/Al ratios within or near the preferred range , adjusting according to either framework structure or morphology. 7,12,19,[33][34][35][36] Herein, we provide further insight into the mechanism of mesopore formation in basic media enabling full compositional flexibility in the preparation of hierarchical zeolites. Exploring the entire range of Si/Al ratios in MFI (10-1000), we probe the influence of base concentration on the properties of the treated zeolites.…”

Alkaline–acid treated mordenite and beta zeolites featuring mesoporous dimensional uniformity

“…Independent of topological structures of initial zeolites, adsorption plateaus presenting in the p/p 0 region below 0.45 evidently upwards deviate from type-I isotherms, implying both slight degradation of intrinsic microporous structures and evolution of extrinsic supermicropores between ca. 0.7 and 2 nm [12]. This probably originated from the predominantly hydrothermal alkali etching, which was promoted by alkali leaching in superior mass transfer.…”