Facile Synthesis of Zeolite Beta with Hierarchical Micromesoporosity Promoted by Citric Acid: Strategy and Working Mechanism

The introduction of mesoporosity is of great importance because mass-transportation limitations within microporous systems hinder their catalytic performance. The direct formation of mesoporosity in zeolite is generally achieved through the use of an additional and expensive organic template, which limits its industrial applications. In this investigation, we reported a facile procedure for synthesizing zeolite Beta with micromesoporosity, in which tetraethylammonium hydroxide (TEAOH)/crystal seeds (CS) worked as the micropore-directing agents, assisted by simple citric acid (CA) containing hydroxyl carboxylic groups. The working mechanism of TEAOH/CS/CA was proposed on the basis of various characterization methods. Oxalic acid was employed as an additional template to further elucidate the formation mechanism of the mesopores. The formation mechanism is proposed that CA with hydroxyl carboxylic groups can interact with aluminosilicate and TEAOH simultaneously to form a semimicelle, leading to the final mesostructure. The resultant mesoporous material was tested in the esterification reaction of benzyl alcohol and acetic acid. Improved activity and selectivity were observed as a result of the introduction of intracrystalline mesopores, suggesting the superiority of the CA-assisted zeolite Beta. This novel procedure provides a simple procedure for obtaining zeolite Beta with hierarchical pores, which can enable the economic and environmentally friendly production of hierarchical zeolites for industrial applications.