Abstract
In the work, a series of new 12-tungstophosphoric acid (HPW) encapsulated MOF 199 catalysts were synthesized by simple and convenient one step method. The structural and textural properties of the synthesized catalysts were fully characterized by using different techniques such as FTIR, XRD, N(2)adsorption-desorption, TEM and SEM. The acidic properties were also studied by using nonaqueous potentiometric titration and FTIR spectra of chemisorbed pyridine techniques. The efficacy of the newly synthesized acid catalysts was tested in the production of 3,4-dihydropyrimidin-2(1H)-one through three-component coupling based Biginelli reaction and biodiesel production through stearic acid esterification reaction. The obtained results indicate that the MOF 199 preserves its structure without any noteworthy changes after the fruitful incorporation of HPW crystals within its cavities. Furthermore, an extraordinary improvement in both Lewis and Bronsted acid sites is observed as a result of the HPW encapsulation process. The catalytic activity results showed that the catalyst displayed excellent performance, where 98.3% of 3,4-dihydropyrimidin-2(1H)-one was obtained over 0.02 g of 50HPWMOF 199 after 2 h at 80 degrees C using benzaldehyde: ethyl acetoacetate: urea molar ratios of 1:1:1.5. Additionally, 94.1% conversion of stearic acid was observed after 3 h over 0.05 g of 50HPWMOF 199 at similar to 80 degrees C using stearic acid: ethanol molar ratio of 1:8. Moreover, the catalysts also demonstrated excellent reusability in the investigated organic reactions which can be used many consecutive eras without meaningful loss of their catalytic performance. The achieved high catalytic performance of the synthesized catalysts in the Biginelli and esterification reactions are attributed to uniform HPW distribution inside MOF 199 cavities as well as the Lewis acidity property of MOF 199. The results also demonstrated that the incorporation of HPW crystals within MOF 199 cavities through the encapsulation process is more efficient than the impregnation method.