Gas-phase hydrodeoxygenation of phenol over Zn/SiO₂ catalysts: Effects of zinc load, temperature, weight hourly space velocity, and H₂ volumetric flow rate

The hydrodeoxygenation (HDO) of phenol catalyzed by Zn/SiO₂ under atmospheric H₂ pressure was investigated in a continuous fixed bed reactor. The effects of several process parameters (zinc load, reaction temperature, weight hourly space velocity (WHSV), and H₂ volumetric flow rate) were evaluated to optimize process conditions. Phenol was selected as a stable model component for lignin degradation products in fast pyrolysis bio-oil. Silica-supported zinc catalysts were prepared with different loadings of the active metal (0.5%, 1%, 2%, 3%, and 4%) and assessed using characterization techniques such as XRD, ICP-OES, BET, H₂-TPR/TPD, and FESEM–EDX. Reaction products including benzene, cyclohexene, and cyclohexane were identified through GC/FID analysis. Experimental results revealed that process yield increased with reaction temperature, metal loading, and WHSV. The selectivity percentages of the products were slightly changed by varying process parameters. Moreover, H₂ volumetric flow rate exerted a negligible effect on product yield and selectivity.