Ni/Y₂O₃–ZrO₂ catalyst for hydrogen production through the glycerol steam reforming reaction

In the study presented herein, the catalytic activity and stability of a Ni catalyst supported on Y₂O₃–ZrO₂ was examined for the first time in the glycerol steam reforming reaction and compared with a Ni/ZrO₂. The addition of Y₂O₃ stabilized the ZrO₂ tetragonal phase, increased the O₂ storage capacity of the support and the medium strength acid sites of the catalyst, and although the Ni/Zr catalyst had a higher concentration of basic sites, the Ni/YZr presented more stable monodentate carbonates. Moreover, the Ni/YZr had substantially higher Ni surface concentration and smaller Ni particles. These properties influence the gaseous products’ distribution by increasing the H₂ yield and selectivity and preventing the transformation of CO₂ to CO, by inhibiting the reverse water gas shift (RWGS) reaction from taking place. For both catalysts the main liquid products identified were allyl alcohol, acetaldehyde, acetone, acrolein, acetic acid and acetol; these were subsequently quantified. The time-on-stream experiments showed that the Ni/YZr was more stable during reaction and had a higher H₂ yield after 20 h (2.17 in comparison to 1.50 mol H₂/mol C₃H₈O₃, for the Ni/Zr). Extensive investigation of the carbon deposits showed that although lower amounts of coke were deposited on the Ni/Zr catalyst, these structures were more graphitic in nature and had fewer defects, which means they were harder to oxidize. Moreover, transmission electron microscopy (TEM) analysis showed that sintering of Ni nanoparticles during the reaction was significant for the Ni/Zr catalyst, as the mean particle diameter increased from an initial value of 48.2 to 67.9 nm, while it was almost absent on the Ni/YZr catalyst (the mean particle diameter increased from 42.1 to 47.4 nm).