Mesoporous H-AlMCM-48: highly efficient solid acid catalyst Original Research Article

Mesoporous cubic Na-AlMCM-48 molecular sieve catalyst with a Si/Al (molar) ratio of 60 was synthesized hydrothermally and characterized by various analytical and spectroscopic techniques. 27Al MAS-NMR results indicate that the presence of aluminum in tetrahedral framework (Brönsted acid site) in both as-synthesized and calcined samples. However, in the case of the latter, a small amount of aluminum was found to be in octahedral coordination. This observation is well supported by NH3-TPD studies over protonated catalyst (H-AlMCM-48), where desorption profile at higher temperature shows features characteristic of Lewis acid sites. Further, these studies also indicate that the presence of high concentration of moderate-to-strong Brönsted acid sites at lower temperature, which are more suitable for the para-selective tertiary-butylation reaction of phenol. Hence, in the present investigation, the reaction was carried out H-AlMCM-48, which however showed much higher activity as compared to the hexagonal H-AlMCM-41. In addition, it was also found that the former does not get deactivated owing to three-dimensional pore system while the latter is susceptible to deactivation on account of one-dimensional pore system.