Systematic Modification Of Uio-66 Metal-Organic Frameworks For Glucose Conversion Into 5-Hydroxymethyl Furfural In Water

Metal organic framework UiO-66 is studied as an adaptable heterogeneous catalyst for glucose conversion. UiO-66 was modified by; i) partial linker substitution, ii) particle size modulation and iii) linker defects. We studied the effect of crystallinity and functional groups on the glucose conversion and product yields. The main products are: i) fructose from the isomerisation of glucose, ii) mannose from the epimerisation of glucose and iii) 5-hydroxymethyl furfural from the dehydration of fructose. We found that defective and nano crystalline UiO-66 catalyst performs best for isomerisation. When 50 % of the linkers of UiO-66 are replaced by a sulfonate-containing linker, the catalyst shows higher isomerisation activity than other UiO-66 catalysts. Naphthalene-dicarboxylate linkers were introduced to induce hydrophobicity and this catalyst further increased isomerisation activity showing 31 % fructose selectivity. Finally, the promising catalysts were tested in a flow reactor and a bifunctional mixed linker catalyst possessing both hydrophobic and acidic functional groups is shown to be stable in a time-on-stream study.