Polyoxometalate catalysts for biomass dissolution: understanding and design

The use of polyoxometalate catalysts for selective delignification of biomass presents a possible route toward using ionic liquids (ILs) to efficiently obtain high-molecular weight biopolymers from biomass. Rapid progress in this area will depend on recognizing and using the link with already well-developed inorganic chemistry in ILs pursued outside the field of biomass processing. Here, we use crystal structures determined from single crystal X-ray diffraction to better understand the behavior of [PV2Mo10O40](5-), a polyoxometalate catalyst known for its ability to promote selective delignification of biomass in the IL 1-ethyl-3-methylimidazolium acetate ([C(2)mim][OAc]). The crystal structure of [C(2)mim](5)[PV2M10O40] . THF shows the formation of cationic shells around the anions which are likely representative of the interactions of this catalyst with [C(2)mim][OAc] itself. The reaction of NH4VO3 with [C(2)mim][OAc] is explored to better understand the chemistry of vanadium(V), which is critical to redox catalysis of [PV2Mo10O40](5-). This reaction gives crystals of [C(2)mim] 4[V4O12], showing that this IL forms discrete metavanadates which are obtained from aqueous solutions in a specific pH range and indicating that the basicity of [OAc]-dominates the speciation of vanadium (V) in this IL.