Cr and CeO₂ promoted Ni/SBA-15 framework for hydrogen production by steam reforming of glycerol

Ni/SBA-15 meso-structured catalysts modified with chromium and CeO₂ (Ni-Cr-CeO₂/SBA-15) were utilized to produce hydrogen from glycerol steam reforming (GSR). The catalysts were synthesized by a one-pot hydrothermal process and extensively characterized by analytical techniques such as N₂ adsorption-desorption (BET), H₂-temperature programmed reduction (H₂-TPR), powder X-ray diffraction (PXRD), inductively coupled plasma-optical emission spectrometry (ICP-OES), and transmission electron microscopy (TEM). The low-angle XRD reflections affirmed that the catalysts were crystalline and possessed a 2D-ordered porosity. The BET results depicted that all the catalysts exhibited a good surface area ranging from 633 to 792m²/g, and the pore sizes were consistently in the mesoporous range (between 3 and 5 nm). TEM analysis of both calcined and spent catalysts revealed that the metal active sites were embedded in the hybrid CeO₂-SiO₂ support. Overall, the Ni-based catalysts exhibited higher glycerol conversion -12Ni-SBA-15-99.9%, 12Ni3CeO₂-SBA-15-89.4%, and 8Ni4Cr3CeO₂-SBA-15-99.7%. Monometallic 12Ni/SBA-15 performed exceptionally well, while 12Cr/SBA-15 performed poorly with the highest 71.48% CO selectivity. For short-term GSR reactions, CeO₂ addition to 12Ni/SBA-15 did not have any effect, whereas Cr addition resulted in a 32% decrease in H₂ selectivity. The long-term stability studies of 12Ni-SBA-15 showed H₂ selectivity of ~ 64% and ~ 98% glycerol conversion. However, its activity was short-lived. After 20-30 h, the H₂ selectivity and conversion dropped precipitously to 40%. The doping of mesoporous Ni/SBA-15 with Cr and CeO₂ remarkably enhanced the long-term stability of the catalyst for 12Ni3CeO₂-SBA-15, and 8Ni4Cr3CeO₂-SBA-15 catalyst which showed ~ 58% H₂ selectivity and ~ 100% conversion for the entire 60 h. Interestingly, Cr and CeO₂ seem to improve the shelf-life of Ni-SBA-15 via different mechanistic pathways. CeO₂ mitigated Ni poisoning through coke oxidation whereas Cr bolstered the catalyst stability via maintaining a well-defined pore size, structural rigidity, and integrity of the heterogeneous framework, thereby restricting structural collapse, and hence retard sintering of the Ni active sites during the long-term 60 h of continuous reaction. Hydrogen generation from renewable biomass like glycerol could potentially serve as a sustainable energy source and could substantially help reduce the carbon footprint of the environment.