A critical and systematic review of sustainable hydrogen production from ethanol/bioethanol: Steam reforming, partial oxidation, and autothermal reforming

The emerging study of hydrogen energy is receiving substantial attention in the scientific community due to its efficiency in approaching net zero and environmental sustainability. Meanwhile, bioethanol is a sustainable and carbon–neutral fuel for hydrogen production. This research aims to assess various ethanol reforming routes, including ethanol steam reforming, partial oxidation, and autothermal reforming, and evaluate the differences in hydrogen production as a function of catalyst physicochemistry and experimental parameters. For all three techniques, 75 % hydrogen selectivity is attained at 400 °C. In the ethanol steam reforming, non-noble metals (Co and Ni) are more reactive than noble metals (Rh and Ru). However, the sequence of hydrogen selectivity is featured by Rh > Ir > Ru > Pt > Ni > Co in autothermal reforming of ethanol. The partially filled d-orbitals of various transition metals can uptake or provide electrons to various reagents, thereby controlling reaction activity. Non-noble metals are inexpensive, making these catalysts appealing for a variety of reforming processes. The small crystal size <10 nm and the large Brunauer-Emmett-Teller surface area of the metal-support particles regulate the dispersion and reactivity of the catalyst. Hydrogen selectivity is lower in partial oxidation and autothermal reforming, while CO and CO2 exhibit no specific selectivity trend. The reactivity of intermediate reactions such as dehydrogenation and decarbonylation positively correlated with the reaction temperature and the steam/oxygen/ethanol ratio, which regulates syngas product distributions. Overall, this review provides a vision for sustainable hydrogen production and decarbonization to achieve the net zero target.