Hydrogenolysis of glycerol over ZSM-5 supported ruthenium and copper catalysts: Structural study and effects in reaction

Abstract

HZSM-5 supported bimetallic Ru-Cu catalysts were investigated with the objective of converting glycerol from biodiesel production into propanediols through the hydrogenolysis reaction. Two zeolites were used as supports, one with a SiO2/Al2O3 molar ratio of 80 and another with a ratio of 23. Physisorption analysis showed high specific area for the solids with values in the range of 400 m2 g−1, that enabled the metals to be incorporated as nanoparticles undetectable by XRD. Monometallic Ru catalysts displayed Ru0 species after reduction and RuO2 species duo to passivation, as evidenced by XPS analysis. Monometallic copper catalysts contained Cu0 and Cu+ species verified by XPS and DRIFTS after reduction and passivation, Cu2+ species were not found. As for the Ru-Cu bimetallic catalysts, Ru was added by impregnation of Cu/HZSM-5 and covered the copper nanoparticles as XPS analysis showed an increase in Ru/Cu molar ratio at the surface for both bimetallic catalysts. The XPS analysis showed increased Ru/Cu ratio at the surface for both bimetallic catalysts (1.95 and 2.94 for Ru-Cu/HZSM-5–80 and Ru-Cu/HZSM-5–23, respectively), furthermore no electronic effects between the two metals were observed indicating that the interaction between Ru and Cu consists in Ru diluting Cu. Chemisorption analysis show increase in CO adsorption for the bimetallic catalysts duo to the joint adsorptive capacity of Ru and Cu+, increasing from 141.4 µmol g−1 to 147.8 µmol g−1 for Ru-Cu/HZSM-5–80, and from 155.2 µmol g−1 to 198.5 µmol g−1 for Ru-Cu/HZSM-5–23, although the species adsorbed are thermally unstable compared to the monometallic adsorption, as shown by DRIFTS analysis. The activity of Ru catalysts was the highest (33 % and 32 % for catalysts supported on ZSM-5–80 and ZSM-5–23, respectively), but there was the formation of degradation products such as ethylene glycol. Copper catalysts showed moderate activity (11 % and 8 % for catalysts supported on ZSM-5–80 and ZSM-5–23, respectively) with good selectivity towards propanediols (22 % and 23 % for 1,2-PDO at isoconversion) duo to Cu0 and Cu+ interaction. Bimetallic catalysts Ru-Cu catalyst showed an improvement in selectivity to propanediols (36 % and 54 %) due to the interaction between Ru and Cu with low activity and reaction’s TOF (0.71 and 0.80 ×10−3 s−1).