Heteroatoms of Al and Ti are effectively introduced into the framework of ordered mesoporous silica materials (designated as MAS-7 and MTS-9, respectively) in strong acidic media (pH < 0) by a two-step procedure. MAS-7 shows high catalytic activities for the cracking of both small (cumene) and bulky (1,3,5-triisopropylbenzene) molecules because it combines the advantages of both zeolites (strong acidity) and mesoporous materials (large pores). In contrast, Al-SBA-15 samples prepared from both "post-synthesis" and "direct synthesis" present much lower catalytic activities than MAS-7. Furthermore, MTS-9 exhibits very high catalytic activity in phenol hydroxylation by H 2 O 2 , giving the phenol conversion of 26%, comparable to TS-1.
We report a strategy of combining a Brønsted acid metal-organic framework (MOF) with Lewis acid centers to afford a Lewis acid@Brønsted acid MOF with high catalytic activity, as exemplified in the context of MIL-101-Cr-SO3H·Al(III). Because of the synergy between the Brønsted acid framework and the Al(III) Lewis acid centers, MIL-101-Cr-SO3H·Al(III) demonstrates excellent catalytic performance in a series of fixed-bed reactions, outperforming two benchmark zeolite catalysts (H-Beta and HMOR). Our work therefore not only provides a new approach to achieve high catalytic activity in MOFs but also paves a way to develop MOFs as a new type of highly efficient heterogeneous catalysts for fixed-bed reactions.
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