Selective dehydration of glycerol on copper based catalysts

Glycerol is produced in large quantities as a byproduct of biodiesel, and among others hydroxyacetone (acetol) is an important commodity obtained from glycerol. Metallic Cu has been identified as active site for the dehydration of glycerol to hydroxyacetone and acid and metal sites are known to influence the catalytic performance. In this study, dehydration of glycerol over 5 wt.% copper supported on γ-Al₂O₃, ZrO₂ and SiO₂ was investigated. Catalysts were characterized by N₂ physisorption, H₂-TPR, NH₃-TPD, N₂O chemisorption, XPS, XRD, FTIR of pyridine adsorption. Cu/ZrO₂ exhibited the highest hydroxyacetone yield at 20 % of glycerol conversion and the highest apparent reaction rate. The superior activity of Cu/ZrO₂ was attributed to the highly acidic, both Lewis and Brönsted acidic, nature of the support and positive roles of the interfacial sites. The Weisz-Prater (WP) criterion was applied to confirm the absence of intraparticle diffusion limitations. It was assumed spherical particles and first order reaction. The WP value obtained in the worst scenario was less than 0.3 ensuring no diffusion limitation. Complementary DFT study indicates that both glycerol and hydroxyacetone interact significantly stronger on Cu/γ-Al₂O₃ and Cu/ZrO₂ compared to metallic Cu, suggesting that the active sites are at the interface of Cu particles and the acidic support.