Tuning the Catalytic Performance of Novel Composites Based on ZIF‐8 and Nafen through Dimensional and Concentration Effects in the Synthesis of Propylene Glycol Methyl Ether

Abstract

Zeolitic imidazolate framework (ZIF‐8, Zn(2‐meIm)2) and composites based on ZIF‐8 and alumina nanofibers (NafenTM), i.e. ZIF‐8/Nafen, were demonstrated to be efficient heterogeneous catalysts for the reaction of methanol with propylene oxide to produce propylene glycol methyl ether (PGME), which is a member of the family of glycol ether solvents used for a wide variety of consumer products and industrial applications. Both the reaction rate and the selectivity toward PGME were found to decrease with increasing crystal size of the ZIF‐8 material, which was related to the change in the number of basic sites and their accessibility. The investigation of ZIF‐8/Nafen composites revealed the dependence of their catalytic performance on the amount of the ZIF‐8 component. In particular, the activity was affected by the crystal size of the ZIF‐8 material and the nature of acid‐base sites in its framework.

Effect of MAF-6 Crystal Size on Its Physicochemical and Catalytic Properties in the Cycloaddition of CO2 to Propylene Oxide

“…The observed characteristic diffraction peaks of RHO structure with crystalline peaks at diffraction angles (2θ) 5.90 • , 7.28 • , 8.44 • , and 9.44 • displayed similar XRD patterns of MAF-6 reported in the literature [43][44][45]. The average crystal size of MAF-6 samples was calculated from X-ray spectra using the Debye-Scherrer equation (Equation (1)) [46,47]: attributed to the Zn-O stretching mode due to the interaction between the Zn 2+ ions of MAF-6 and the oxygen atom of alcohol [37,39]. The change in the character of bands in the region of 770-790 cm −1 (OH out-of-plane bend) (Figure 3) and 1300-1330 cm −1 (OH inplane bend) (Figure S5, Supporting Information) point also to this interaction.…”

“…Moreover, molecules of alcohol can be incorporated in the as-synthesized MAF-6 structure and act as a space-filling molecule as kinetic diameters of alcohols (MeOH 3.8 Å, EtOH 4.30 Å and n-PrOH 4.7 Å [48] are smaller in comparison with the pore size of MAF-6 (theoretical pore size: 7.6 Å [49]). Note that the effect of particle size on the textural properties was demonstrated for ZIF-8 [37,50,51]. It was also found that the external surface decreases, while microporosity increases with increasing crystal size.…”

“…MAF-6 and the oxygen atom of alcohol [37,39]. The change in the character of bands in the region of 770-790 cm −1 (OH out-of-plane bend) (Figure 3) and 1300-1330 cm −1 (OH inplane bend) (Figure S5, Supporting Information) point also to this interaction.…”

“…At the same time, this band splits to 418 and 434 cm −1 in spectra of MAF-6(M) and MAF-6(S), respectively. We can suggest that band at 434 cm −1 is attributed to the Zn-O stretching mode due to the interaction between the Zn 2+ ions of MAF-6 and the oxygen atom of alcohol [37,39]. The change in the character of bands in the region of 770-790 cm −1 (OH out-of-plane bend) (Figure 3) and 1300-1330 cm −1 (OH in-plane bend) (Figure S5, Supporting Information) point also to this interaction.…”

“…We have recently studied the effect of ZIF-8 particle size (50-800 nm) in a hexagonal shape on their catalytic efficiency in the synthesis of propylene glycol methyl ether (PGME) from PO and methanol [37,38]. A pronounced size effect on the reaction rate and selectivity toward PGME was found to decrease along with the growth of the ZIF-8 crystal size.…”