Fabrication of supported Au-CuOx nanohybrids by reduction-oxidation strategy for efficient oxidative esterification of 5-hydroxymethyl-2-furfural into dimethyl furan-2,5-dicarboxylate
5-Hydroxymethyl-2-furfural (HMF) is a key platform molecule for biomass utilization. The HMF derivative 2,5-furandicarboxylic acid (FDCA) by oxidation of HMF is a promising alternative for terephthalic acid as a monomer in polyethylene terephthalate. However, due to the facile purification of dimethyl furan-2,5-dicarboxylate (DMFD), an oxidative esterification derivative of HMF, is more desirable. In this work, supported Au–Cu bimetallic catalysts with Au–CuO x ( x = 0–1) nanohybrids were prepared by a reduction–oxidation pretreatment strategy. The as-prepared catalysts were used for the oxidative esterification of HMF into DMFD under base-free conditions using oxygen as sole oxidant. Activity tests showed that the optimized Au–Cu/γ-Al 2 O 3 catalyst displayed a remarkably high DMFD yield of up to 98% and a turnover frequency (TOF) value of 243 h –1 , whereas the monometallic Au and Cu catalysts exhibited poor performance. Various characterizations confirmed the strong interaction between Au nanoparticles and CuO x species, and their synergistic effect on the enhanced performance of HMF oxidative esterification. The reduction–oxidation pretreatment promoted the dispersion of CuO x and intensified the interaction of Au nanoparticles with CuO x . A plausible reaction mechanism for the oxidative esterification of HMF over Au–Cu/γ-Al 2 O 3 was proposed. This work provided new insights into the effect of reduction–oxidation pretreatment on the fabrication of supported Au–CuO x nanohybrids for the production of DMFD by HMF oxidative esterification.
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