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Supported Ir, Pd, Rh and Ru catalysts were examined for the conversion of glucose and cellulose in water in the presence of hydrogen. The catalysts were prepared by incipient wetness impregnation of a BEA zeolite (SiO2/Al2O3 = 21.6, Ssp = 739 m2/g) with acetylacetonate metal precursors. Among these catalysts, Ru-BEA was found to be the most active for the conversion of cellulose, while Ir-BEA was found to be the most selective for the formation of sorbitol. Thus, the highest yield to sorbitol was found in the presence of 3 wt%Ru/BEA catalyst irrespective of the raw material nature (glucose or cellulose). It corresponded to a value of 22% for the conversion of the commercial cellulose, and of 72.8% for the conversion of glucose. The Ru-BEA catalyst was followed by the 3 wt%Ir-BEA that led to a yield of 55.3% for glucose and 22% for cellulose but to a much higher selectivity, i.e. over 99.9% for glucose and 89.2% for cellulose. While the high selectivity of Ir to sorbitol was correlated with the d-band width of the metal, the high activity of Ru for the cellulose conversion was assigned to the generation of H+ and [Ru(H2O)5OH]2+ as Bronsted acids by Ru species in water. Finally, the addition of pure nanoscopic hydroxylated SnF4 to the 3 wt%Ir-BEA catalyst led to a conversion of cellulose of almost 99% after only 3 h with a selectivity to sorbitol of 72.5%. |
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