Porous Organic Zirconium Phosphonate as Efficient Catalysts for the Catalytic Transfer Hydrogenation of Ethyl Levulinate to -Valerolactone without External Hydrogen

Organic hybrid zirconium phosphonate materials (ZrATMP, ZrEDTMPS, ZrDTPMPA, and ZrHEDP) were synthesized through reaction of organic phosphonic acid sodium salt and ZrOCl2 in water, which exhibited high catalytic activity on the conversion of ethyl levulinate (EL) to -valerolactone (GVL) in the presence of isopropanol. The obtained catalysts were characterized by FT-IR, TGA, XRD, BET, XPS, ICP-AES, SEM, TEM, NH3-TPD, and CO2-TPD. The results demonstrate that the number of acid sites and basic sites between the layers of the catalysts play a very important role in promoting the conversion of EL to GVL and that the functional groups that exist in phosphates could regulate the number of acid and basic sites. Meanwhile, the catalysts could be easily separated from the reaction system and reused at least five times without any obvious decrease in activity or selectivity.