Clean hydrogen (H₂) is highly desirable for the sustainable development of society in the era of carbon neutrality. However, the current capability of water electrolysis and steam methane (CH₄) reforming to produce green and blue H₂ is very limited, mainly due to the high production cost, difficult scale-up technology, or operational risk. Here, we propose the direct catalytic decomposition of diesel using a nano-Fe-based catalyst to produce the so-called “jadeite H₂,” while simultaneously fixing the carbon from the diesel in the form of carbon nanotubes (CNTs). Efforts are made to understand the suppression mechanism of the CH₄ byproduct, such as by tuning the catalyst type, space velocity, and reaction time. The optimal green index (GI)—that is, the molar ratio of H₂/carbon in a gaseous state—of the proposed technology exceeds 42, which is far higher than those of any previously reported chemical vapor deposition (CVD) method. Moreover, the carbon footprint (CFP) of the proposed technology is far lower than those of grey H₂, blue H₂, and other dehydrogenation technologies. Compared with most of the technologies mentioned above, the energy consumption (per mole of H₂) and reactor amplification of the proposed technology validate its high efficiency and great practical feasibility.