**Replacement of Chromium by Non-Toxic Metals in Lewis-Acid MOFs: Assessment of Stability as Glucose Conversion Catalysts**

**Ralentri Pertiwi 1,2,3,**†**, Ryan Oozeerally 1,**†**, David L. Burnett 2, Thomas W. Chamberlain 1,2, Nikolay Cherkasov 1, Marc Walker 4, Reza J. Kashtiban 4, Yuni K. Krisnandi 3, Volkan Degirmenci 1,\* and Richard I. Walton 2,\***


Received: 16 April 2019; Accepted: 6 May 2019; Published: 9 May 2019

**Abstract:** The metal–organic framework MIL-101(Cr) is known as a solid–acid catalyst for the solution conversion of biomass-derived glucose to 5-hydroxymethyl furfural (5-HMF). We study the substitution of Cr3+ by Fe3<sup>+</sup> and Sc3+ in the MIL-101 structure in order to prepare more environmentally benign catalysts. MIL-101(Fe) can be prepared, and the inclusion of Sc is possible at low levels (10% of Fe replaced). On extended synthesis times the polymorphic MIL-88B structure instead forms.Increasing the amount of Sc also only yields MIL-88B, even at short crystallisation times. The MIL-88B structure is unstable under hydrothermal conditions, but in dimethylsulfoxide solvent, it provides 5-HMF from glucose as the major product. The optimum material is a bimetallic (Fe,Sc) form of MIL-88B, which provides ~70% conversion of glucose with 35% selectivity towards 5-HMF after 3 hours at 140 ◦C: this o ffers high conversion compared to other heterogeneous catalysts reported in the same solvent.

**Keywords:** Metal–organic framework; Lewis acid; fructose; 5-hydroxymethyl furfural; biomass
