Sn-modified Zr-UiO-66 metal-organic frameworks for dihydroxyacetone conversion into lactic acid

Abstract

Dihydroxyacetone is a valuable waste-valorization compound, which is a main intermediate in lactic acid production from different recyclable sources. In the present work, the Sn incorporation into the Zr-based metal-organic framework is used to increase its acidity and facilitate dihydroxyacetone conversion to lactic acid through the minimization of side reactions. Three series of Sn-modified metal-organic frameworks with different synthetic conditions and Zr/Sn molar ratio are prepared and characterized by low-temperature nitrogen adsorption, XRD, XRF, TGA, FTIR of adsorbed CO, and NH3-TPD methods. The nature of the Sn species depends on both the Sn precursor and water amount in the liquid phase during the synthesis allowing the control of the SnClx hydrolysis. The Sn addition leads to an increase in the acidity of the MOF and mostly depends on the nature of the Sn species rather than the Sn loading. An insertion of the tin species directly inside the UiO-66 structure results in an almost quantitative yield of the target products. The material retains its structure after catalysis, but the deposition of the polycondensation products on the MOF surface slightly decreases the selectivity at consecutive runs.