Engineering zirconium-based UiO-66 for effective chemical conversion of -xylose to lactic acid in aqueous condition

• Published in: Chemical communications (Cambridge, England) Vol. 56; no. 58; pp. 819 - 822
• Main Authors: Ponchai, Panyapat, Adpakpang, Kanyaporn, Thongratkaew, Sutarat, Chaipojjana, Kawisa, Wannapaiboon, Suttipong, Siwaipram, Siwarut, Faungnawakij, Kajornsak, Bureekaew, Sareeya
• Format: Journal Article
• Language: English
• Published: 21.07.2020
• ISSN: 1359-7345; 1364-548X
• DOI: 10.1039/d0cc03424j

Utilizing metal-organic frameworks (MOFs) as heterogeneous catalysts is an interesting and important application due to their well-controlled catalytic sites and well-defined porous structures. In this study we apply, for the first time, Zr-based UiO-66 for the catalytic hydrothermal conversion of d -xylose to lactic acid (LA). The reactions are catalyzed by the coordinatively unsaturated Zr 4+ , as Lewis acid sites, and the hydroxide ion (OH − ) located at the defect sites. The catalytic performances of UiO-66 catalysts synthesized through a modulator-free approach (UiO-66) and an acetic acid modulator-assisted approach (UiO-66(AA)) are distinct due to the different concentrations of local defects. The UiO-66 catalyst possessing a higher defect concentration exhibits a superior LA yield of 1.17 mol from 1 mol of xylose. However, the UiO-66(AA) catalyst with higher crystallinity shows better selectivity for LA over furfural, a side product from the competitive pathway. The enhanced LA yield and excellent selectivity can be achieved by the removal of AA from UiO-66(AA) resulting in a novel MOF catalyst (UiO-66(AA)*) which provides more accessible catalytic sites with retained crystallinity. This work highlights that the structural engineering of MOF catalysts is crucial for the fine-tuning of their catalytic properties. Local defects and crystallinity of UiO-66 were systematically engineered, yielding an effective catalyst for lactic acid production from d -xylose via a hydrothermal reaction.