Green catalysis for the production of n-butyl acetate over phosphotungstic acid-encapsulated metal-organic framework UiO-67 catalyst: Catalyst preparation, characterization and reaction kinetics
Tianlin Ma, Chengcheng Song, Hongliang Chen, Manyun Yin, Chunyang Su, Ningfei Guo, Yang Yao, Mingming Yu, Yujie Wang, Gangling Chen, Zhi Yun
Abstract
In the present study, a composite of Keggin-type phosphotungstic acid encapsulated in sized-matched metal-organic framework UiO-67 (HPW@UiO-67) was successfully fabricated via a facile hydrothermal synthesis method and utilized for the preparation of n -butyl acetate. The as-synthesized composite catalyst was comprehensively characterized using FT-IR, PXRD, ICP-OES, N 2 adsorption-desorption, SEM, TEM, NH 3 -TPD, TGA-DTG and XPS techniques. The characterization results confirmed that HPW was successfully immobilized in metal-organic framework without changing the structure of UiO-67. The asprepared HPW@UiO-67 catalyst exhibited higher esterification activity compared to the UiO-67 catalyst due to its suitable surface area and total volume, high dispersion of phosphotungstic acid and high total acidity. The kinetic study indicated that the process followed the second-order kinetic with the activation energy E a = 53.1 kJ/mol. The catalyst exhibited good recovery and catalytic performance in the reuse study, maintaining the conversion of acetic acid above 63.1% after four reaction cycles. Moreover, the reaction mechanism for the synthesis of n -butyl acetate via esterification over HPW@UiO-67 was proposed.