Effect of surface acidity-basicity balance in modified Zn_xZr_yO_z catalyst on its performance in the conversion of hydrous ethanol to hydrocarbons

Zn_xZr_yO_z and modified M_uZn_xZr_yO_z (M = Si, W, Sc, Mg)/ Zn/(W-Zr) catalysts were studied in conversion of hydrous (4 wt% H₂O) ethanol at P =15 bar, T = 450 °C and WHSV = 0.8-7.9 h^-1. The basicity of the catalysts changed from 0.015 to 0.66 mmol/g and the acidity from 0.07 to 0.24 mmol/g resulting in a wide range of basicity/acidity ratio (R) of 1.3 to 7.3. Measurements of the catalysts activity, selectivity and stability indicate a strong dependency on the R-value. The yield of organic liquid C₅-C₁₁ increased from 17 wt% to 59 wt% while the yield of light olefins C₂-C₄ decreased from 60 wt% to 14 wt%, as R increased from 1.3 to 7.3. The content of C₅-C₁₁ iso-olefins and aromatics in organic liquid on Zn_xZr_yO_z (R = 3.9), W_uZn_xZr_yO_z (R = 2.0) and Mg_uZn_xZr_yO_z (R = 7.3) increased significantly with the residence time. Zn_xZr_yO_z was stable up to 360 h on stream, while the activity and selectivity of Mg_uZn_xZr_yO_z and W_uZn_xZr_yO_z altered after 90 h on stream due to coke deposition blocking the acid and basic sites. It was proposed a comprehensive scheme of ethanol transformations routes consistent with the measured effects of the residence time, catalysts R-value and time on stream on the products distribution.