Coke-tolerant SiW₂₀-Al/Zr₁₀ catalyst for glycerol dehydration to acrolein

Glycerol dehydration to acrolein over a series of supported silicotungstic acid catalysts (SiW_x-Al/Zr_y) was investigated. Characterization results showed that the final catalyst had high thermal stability, a large pore diameter, strong Lewis acidic sites, and a large specific surface area. X-ray photoelectron survey spectra clearly showed peaks attributable to W (W 4f = 35.8 eV), Al₂O₃ (Al 2p = 74.9 eV), and ZrO₂ (Zr 3d = 182.8 eV). The highest acrolein selectivity achieved was 87.3% at 97% glycerol conversion over the SiW₂₀-Al/Zr₁₀ catalyst. The prepared catalysts were highly active and selective for acrolein formation even after 40 h because of the presence of high concentrations of Lewis acidic sites, which significantly reduced the amount of coke on the catalyst surface. Response surface methodology optimization showed that 87.7% acrolein selectivity at 97.0% glycerol conversion could be obtained under the following optimal reaction conditions: 0.5 wt% catalyst, reaction temperature 300 °C, and feed glycerol concentration 10 wt%. Evaluation of a mass-transfer-limited regime showed the absence of internal and external diffusions over pellets of diameter d_P < 20 μm. These results show that glycerol dehydration over a strong Lewis acid catalyst is a promising method for acrolein production.