One-pot conversion of cellobiose to mannose using a hybrid phosphotungstic acid–cerium oxide catalyst†
A hybrid catalyst composed of phosphotungstic acid coated cerium oxide nanoparticles was demonstrated to catalyze the one-pot conversion of cellobiose, the disaccharide unit of cellulose, to a monosaccharide mixture of glucose and mannose. A high % conversion of cellobiose (up to 99%) was achieved resulting in a yield of mannose up to 15.8%. The yield of mannose from a glucose starting material was 22.8%, exceeding those of previous cerium-based glucose epimerization catalysts. The components of the hybrid material were revealed to function synergistically via a two-step process. Cellobiose was hypothesized to be first hydrolyzed to glucose, which was subsequently epimerized to mannose by the cerium ions leached from the catalyst. The 13C NMR spectroscopic study suggested that the epimerization likely occurred by way of a 1,2-carbon shift reaction mechanism.