Organosilane-Assisted Synthesis of Hierarchical MCM-22 Zeolites for Condensation of Glycerol into Bulky Products

Abstract

Hierarchical micro-mesoporous MCM-22 zeolites were synthesized using hexamethyleneimine and organosilanes as structure directing agents, which enabled the formation of hierarchical zeolites with mesopores created by the voids left by the organosilanes after thermal treatment, without loss of the intrinsic microporosity of the zeolite. The addition of organosilanes to the synthesis medium reduced the incorporation of aluminum atoms into the zeolite framework, making the hierarchical zeolites more hydrophobic than the microporous MCM-22 reference material. Measurements of the contact angles between water droplets and the zeolites pressed into wafers confirmed the distinct hydrophobic character of the samples. The zeolites were used as catalysts for the liquid-phase condensation of glycerol with acetone. Diffusion of the bulky products in the purely microporous zeolites was hindered due to steric constraints. On the other hand, the hierarchical zeolites showed improved catalytic performance in the glycerol condensation reaction, due to greater access to the active acid sites and increased hydrophobicity, which helped in removing water formed in the reaction from the zeolite cavities. The zeolite synthesized with the organosilane bearing 12 carbon atoms in the alkyl chain provided glycerol conversion of 83% in 2 h, while limited conversion of 19% was obtained over the purely microporous sample. In addition to the satisfactory catalytic results observed in the glycerol condensation reaction, the one-pot synthesis procedure employed was simple and allowed the creation of hierarchical zeolites with narrow mesopore size ranges and excellent potential for the conversion of platform molecules derived from biomass sources.

Evolution of Structure and Active Sites during the Synthesis of ZSM-5: From Amorphous to Fully Grown Structure

“…The global Si/Al molar ratios were determined by chemical analyses of the calcined samples using an Optima 8000 ICP-OES spectrometer. The H-form samples were acid digested, as described by Rodrigues et al 20 The suspension was kept at 150 °C for 1 h. Finally, the remaining sample was diluted with 100 mL of deionized water and analyzed.…”

“…Because of its high kinetic diameter (Table S1, 0.63 nm), solketal can hardly fit through fully grown zeolite pores. In a previous study of micro/mesoporous zeolites synthesized through the use of organosilanes as mesopore structuredirecting agents, Rodrigues et al 20 and Vieira et al 59 showed that hierarchical zeolites are more active than their purely microporous counterparts in reactions involving bulky molecules.…”

Controlled direct synthesis of single- to multiple-layer MWW zeolite

“…the methoxysilyl moiety can incorporate into MWW layers via covalent bonds with growing crystals while the bulky hydrophobic tail can restrict the ordered stacking of MWW layers along the c -axis. Although the strategy is seemingly simple, unfortunately only multilayered MWW nanosheets (15–60 nm) can be synthesized by using HMI and amphiphilic organosilane as dual-SDAs [ 33 , 34 ]. By using similar organosilane as co-SDA, comparable results are obtained in the cases for synthesizing Ti-MWW [ 35 ] and SAPO-34 zeolite nanosheets [ 36 ].…”

A Lamellar MWW Zeolite With Silicon and Niobium Oxide Pillars: A Catalyst for the Oxidation of Volatile Organic Compounds

“…The Pil‐Nb‐4.5 material shows steep adsorption between 0.12 and 0.4 of the p/p 0 region that was created by pillaring and is due to capillary condensation occurring in the mesopores. For the other pillared materials, the N 2 adsorption at low pressures is mainly due to the presence of micropores, while the MCM‐22 zeolite possesses a type I isotherm typical of materials with micropores …”