Zeolitic Imidazolate Frameworks ZIF-8 and MAF-5 as Highly Efficient Heterogeneous Catalysts for Synthesis of 1-Methoxy-2-propanol from Methanol and Propylene Oxide

Abstract

Herein, we demonstrated that zinc zeolitic imidazolate frameworks (ZIFs) based on 2-methylimidazole (ZIF-8) and 2-ethylimidazole (MAF-5 or ZIF-14) linkers could be used as effective heterogeneous catalysts for catalytic synthesis of 1-methoxy-2-propanol (1-MP) that is widely used in industry due to its negligible toxicity as an ecofriendly solvent and as an intermediate for the synthesis of different chemicals. Application of these materials decreased the reaction temperature to 110 °C. 1-MP was found to be the major product, with 92.1–93.8% selectivity. The activity of MAF-5 was higher than that of ZIF-8. This difference can be explained by the high basicity of MAF-5. MAF-5 and ZIF-8 materials showed good reusability for 5 cycles in catalysis, which indicates their high potential for catalytic applications. Compared with reported catalysts, the studied ZIFs, especially MAF-5, showed not only the highest conversion of PO but also the highest selectivity for 1-MP under similar reaction conditions

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.…”

“…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.…”

“…Synthesis and Characterization of MAF-6 and MAF-5 MAF-5 was synthesized at room temperature with 2-EIM/Zn 2+ molar ratio of 2.0 in methanol solution. A combination of physicochemical methods points to the formation of the MAF-5 structure with high crystallinity [39]. SEM images, XRD pattern and textural characteristics are shown in Figures S1-S3 (Supporting Information) and Table 3.…”

“…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.…”

“…Note that reaction rate and selectivity towards PGME depended also on the type of ZIFs (Table S1, Supporting Information) and decreased in the following order: MAF-5 (ZIF-71) > MAF-6 (ZIF-14) > ZIF-8. This correlation was caused by the increasing channel size and decreasing surface basicity of ZIFs [38,39].…”