Cellulose conversion to 5-hydroxymethylfurfural via a simple and efficient phosphate-doped hafnium oxide catalyst

The efficient catalytic conversion of cellulose to 5-hydroxymethylfurfural (HMF) can provide a valuable reference for the high-value utilization of biomass. In this work, a series of simple phosphate-doped hafnium oxide catalysts (x-P-HfO2) were prepared, and their physicochemical properties were analyzed by ICP-OES, XRD, XPS, FTIR, SEM-EDX, N2 adsorption-desorption isotherms, NH3-TPD and Py-FTIR characterizes. Detailed evaluation of the reaction conditions demonstrated the ideal catalytic performance of the x-P-HfO2 catalysts, and the HMF yield from cellulose reached a satisfactory 61% in the water(NaCl)/tetrahydrofuran biphasic reaction system. Based on the captured intermediates and detected by-products, possible catalytic pathways are summarized. Meanwhile, the hydrothermal stability of the catalyst was also investigated, and the reason for its performance degradation after five cycles was determined to be the loss of useful Brønsted active sites. In addition, the effects of the phosphating and sulfating modification approaches on the catalyst activity were also compared, verifying that the introduction of phosphate is more conducive to the catalyst expressing high activity for the formation of HMF from cellulose.