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.