Enhanced glycerol steam reforming using Ni-doped CaZrO₃, SrZrO₃, and BaZrO₃ perovskite oxides

This study investigates the catalytic activity and time-on-stream stability of Ni catalysts supported on CaZrO₃, SrZrO₃, and BaZrO₃ perovskite oxides for the glycerol steam reforming (GSR) reaction, which aims to convert the crude glycerol obtained from the transesterification of vegetable and microalgae oils (during bio-diesel production) into hydrogen gas. We employed XRD, N₂ physisorption, H₂-TPR, H₂ pulse chemisorption, CO₂-TPD, Raman, TPO, and TEM/HAADF-STEM to examine the surface and bulk properties of the catalysts before and after the reaction. Regarding catalytic activity evaluation, the Ni catalysts supported on CaZrO₃ and SrZrO₃ can effectively eliminate all liquid products (acetol, acetone, allyl alcohol, acetaldehyde, and acetic acid) at reaction temperatures higher than 500 °C, converting all glycerol to gaseous products (>6 mol H₂/mol of glycerol for the best performing Ni/SrZrO₃). This is due to a higher Ni dispersion, increased availability of active sites for the dissociation of C₃H₈O and H₂O molecules, and a more favorable and stronger Ni-support interaction. Notably, the activity of Ni supported on SrZrO₃ is among the highest reported in the literature. Furthermore, due to its unique Ni-support interaction, the Ni catalyst supported on SrZrO₃ demonstrated remarkable catalytic stability. Apparently, some Ni²⁺ cations are solubilized into the perovskite lattice following high-temperature calcination. After being incorporated into the perovskite lattice, these cations then migrate to the surface via the exsolution process upon high-temperature reduction. During the glycerol steam reforming reaction, this helps prevent carbon growth on the exposed metallic Ni surface, thereby prolonging the catalyst lifetime and ensuring reliable H₂ production during long-term operation and under harsh reaction conditions.