| Boron or phosphorus modified Cu/Al2O3catalysts were prepared by thesuccessive impregnation method. The physicochemical properties of the catalystswere studied by means of N2adsorption-desorption, XRD, FT-IR, UV-Vis, H2-TPR,NH3-TPD, dissociative N2O adsorption-second H2-TPR and XPS. The effect of theboron or phosphorus contents and the impregnation sequence on the structure and theperformance of the catalysts for the hydrogenolysis of glycerol to1,2-propanediol wasdiscussed.The results indicated that the addition of boron or phosphorus to Cu/Al2O3enhanced the acidity and Cu dispersion, especially when boron and phosphorusspecies were impregnated prior to Cu. Also, there was a strong interaction between Cuand boron or phosphorus species. However, the strong interaction leads to thecoverage of Cu atoms with the B or P species with high contents. The coverage maybe more serious when the B or P species were added after Cu to the catalyst.In the hydrogenolysis of glycerol, the addition of boron or phosphorus prior toCu remarkably promoted the performance of Cu/Al2O3. Also, with the increase of Bor P content, the performance of the modified catalysts increased. Under theconditions of220℃,3.0MPa, WHSV of2.0h-1and the H2/glycerol molar ratio of20,Cu/1.0B-Al2O3gave the glycerol conversion of96.84%and the1,2-propanediolselectivity of96.45%. Cu/4P-Al2O3gave the glycerol conversion of95.0%and the1,2-propanediol selectivity of97.2%. We suggest that the promotion effect of boron orphosphorus on the performance of Cu/Al2O3is attributed to the increase of catalystacidity as well as the strong interaction between Cu and B or P species. Thedehydration of glycerol to acetol occurred on the acid sites as well as the Cu sites. Thestrong interaction between Cu and P or B species led to the increase of the surfaceCu+/Cu0ratio. Cu0sites dissociatively absorbed H2molecules, while the Cu+sitescould activate the keto-groups. The synergistic effect between Cu0and Cu+maypromote the hydrogenation of acetol. |
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