Study on the HPA immobilisation on Al-SBA-15 support over Brønsted groups

In this article, a significant aspect of Brønsted groups in the preparation of HPA/Al-SBA-15 catalyst by immobilising heteropoly acid H₃PW₁₂O₄₀ (HPA) to mesoporous Al-SBA-15 support was studied. The crucial factors affected the preparation such as functional groups formed on the support, the use of HPA type for the immobilisation (commercial catalyst or in-situ synthetic HPA), and Si/Al molar ratio of Al-SBA-15 were systematically investigated. The prepared catalysts were tested their performance in polar reagent reactions (fructone synthesis was chosen as an example) to show the effect of HPA after the immobilisaton. Here we tested the HPA content (by Energy-dispersive X-ray method), acidity (by temperature-programmed desorption of ammonia method) and the ethyl acetoacetate conversion in fructone synthesis to prove this concept. The other characterisation methods such as small angle x-ray scattering, Fourier-transform infrared spectroscopy, specific surface area and pore volume also showed the properties change of materials before and after HPA immobilisation. It was shown that the HPA/Al-SBA-15 sample prepared by using HPA commercial catalyst and NH₄ ⁺ ion-exchanged Brønsted groups of mesoporous Al-SBA-15 support (Si/Al molar ratio of 15) showed the highest acidity and catalytic activity (ethyl acetoacetate conversion of 93.49 wt%) in comparison to HPA commercial catalyst as well as to the other catalysts. In addition, this catalyst also showed good catalytic stability after five reaction cycles with slightly reduction of activity, suggesting the prospect of employing HPA/Al-SBA-15 catalyst for organic synthesis of polar compounds.