Efficient esterification over hierarchical Zr-Beta zeolite synthesized via liquid-state ion-exchange strategy

The eco-friendly zeolite-based solid acid catalysts constitute an important alternative to the liquid acid catalyst for the production of plasticizer tributyl citrate (TBC), due to their non-corrosive, high hydrothermal stability and easiness to recycle. Herein, a simple acid treatment to the H-Beta zeolite and subsequent incorporation of ZrIV ions into the vacated Al sites were conducted by liquid-state ion-exchange of ZrO(NO3)(2) aqueous solution. The ZrIV ions were incorporated into the framework by the expand of the unit cell size, verified by XRD patterns, the emerging new band at similar to 198 nm on UV-vis spectra, the enhanced binding energies of the Zr 3d5/2 and Zr 3d3/ 2 on XPS spectra, as well as the variations of isolated terminal silanol groups (Si-OH) by FTIR and the change of integrated intensity ratio of Q(3)/Q(4) by 29Si MAS NMR. It was illustrated that the Lewis acid sites was the main active sites for esterification reaction and the produced abundant mesopores in the Zr-Beta-x catalysts would facilitate the transportation of TBC. The maximum conversion of citric acid as high as 80 % was obtained on Zr-Beta-128 (SiO2/ZrO2 molar ratio = 128) catalyst with the highest Lewis acid amount. Furthermore, the Zr-Beta-128 zeolite exhibited high stability without any detectable deactivation after 6 cycles with the 100 % selectivity to TBC. The efficient Zr-Beta catalyst could supply a novel possibility for the development of an environmentally -friendly solid acid catalyst with good performance for the TBC production.

Automated summary

Zeolite-based solid acid catalysts are a promising alternative to liquid acid catalysts for producing eco-friendly plasticizer tributyl citrate (TBC), due to their non-corrosive nature, high hydrothermal stability, and recyclability.