(585bb) Base-Free Aerobic Oxidation of 5-Hydroxymethylfurfural to 2, 5-Furandicarboxylic Acid over Nanoscale Pt Catalysts Prepared By Atomic Layer Deposition
Pt/ZrO2 catalysts synthesized by atomic layer deposition (ALD), incipient wetness impregnation (IW) and co-precipitation (CP) were employed for aerobic oxidation of 5-hydroxymethylfurfural (5-HMF) to produce 2, 5-furandicarboxylicacid (2, 5-FDCA) in aqueous phase without using alkali or acid. Under a mild reaction condition (T = 100 oC, PO2 = 0.4 MPa, time = 12 h), the Pt/ZrO2 synthesized by ALD of 30 Pt deposition cycles gave a complete 5-HMF conversion and 2, 5-FDCA yield of 97% compared with the Pt/ZrO2 synthesized by IW method (a 2, 5-FDCA yield of 9.4 %) and CP method (a 2, 5-FDCA yield of 3.9 %) with the same Pt loading of 3.23 wt%. The three catalysts were characterized by ICP, XRD, TEM and CO-TPD, and the results indicated that high Pt dispersion and uniform Pt particle size distribution on the ZrO2 surface were obtained by ALD and the performance of C=O adsorption was strong. While the growth of Pt particles synthesized by incipient-wetness impregnation was not controllable resulting in the metal particles non-uniformed and the performance of C=O adsorption was weak. The Pt particles synthesized by co-precipitated were wrapped in the ZrO2 and the catalytic activity of the Pt are completely eliminated due to the difficulty of accessing the Pt active surface for reactant and intermediate products. The ALD produce uniform Pt particles to ensure the unitive active sites for the aerobic oxidation of HMF to FDCA. As the deposition cycles of Pt for Pt/ZrO2 (ALD) increased, the average size of the Pt nanoparticle increased but the dispersion did not change, and the Pt/ZrO2 with ALD 30 deposition cycles exhibited the highest TOF. This work has high commercial value for developing efficient heterogeneous catalysts using the cheap and available metals oxide that with low surface area but with high catalytic active which have potential applications in many heterogeneous reactions and maximize the atom efficiency of noble metals.