Hydrogen production via steam reforming of glycerol over Ce-La-Cu-O ternary oxide catalyst: An experimental and DFT study

Abstract

In this study, Ce-La-xCu-O catalysts with distinct Cu contents were fabricated through two different microwave methods; conventional microwave (MW) method and enhanced microwave method, where air cooling (AC) during heating was applied and studied for glycerol steam reforming. The characterization of catalysts reveals that the synthesis methods (MW and AC) influence mainly on the degree of Cu incorporation into the Ce-La-O fluorite lattice, thus leading to one or two phases system. In glycerol steam reforming, MW catalysts showed improvement in glycerol conversion (X) and glycerol conversion to gaseous products (Xgas) with an increase of temperature from 400 to 750 °C; a higher tradeoff between total conversion X (93–94%) and Xgas (89–93%) was attained at 750 °C. The H2 yield over MW catalysts was attained in the range of 3.8–5.0 mol/mole of glycerol. Interestingly, Ce-La-10Cu-O (AC) catalyst exhibits higher glycerol conversion, conversion to gaseous products and higher yield of H2 (5.3 mol/mole of glycerol) as compared to MW catalyst. Moreover, the Ce-La-10Cu-O (AC) catalyst exhibited high stability and deactivated at slower rate. The improved performance of AC catalyst can correlate to a more homogeneous Cu incorporation into Ce-La-O mixed oxide thus forming more accessible active sites to reactants which overall impact on the catalytic performance. DFT calculations showed that doping ceria (111) surface greatly facilitates the adsorption of glycerol compared to the undoped ceria surface by tuning the adsorption energy and the surface-glycerol distance, to −1.42 eV and 1.09 Å, respectively, and by shifting the Fermi level into the valence band (p-type doping), enhancing with the latter the glycerol chemisorption.