CO 2 -Free Production of Hydrogen by Catalytic Pyrolysis of Hydrocarbon Fuel

All conventional options of hydrogen production from hydrocarbon fuel (primarily natural gas, NG), e.g., steam reforming (SR), partial oxidation, and autothermal reforming, involve CO 2 production at some point in the technological chain of the process. Therefore, the main problem remains: how to produce hydrogen from hydrocarbon fuels without CO 2 emission. The capture of CO 2 from the SR process streams and its sequestration (underground or ocean disposal) are actively discussed in the literature. However, this method is energy intensive, poses uncertain ecological consequences, and still does not completely eliminate CO 2 emission. Another approach is to decompose hydrocarbon fuels into hydrogen and carbon. The thermal decomposition of NG is a technologically simple one-step process without energy and material intensive gas separation stages and shows the potential to be a CO 2 -free hydrogen production process. The experimental results of the thermocatalytic decomposition of gaseous (methane and propane) and liquid (hexane, gasoline and diesel fuel) hydrocarbons over metal-oxide and carbon-based catalysts are presented. Although transition metal catalysts produce gas with high initial hydrogen concentration, their activity rapidly drops because of the surface deposition of carbon. Carbon-based catalysts offer certain advantages over metal catalysts, since there is no need for the carbon separation from the catalyst. Catalytic pyrolysis of light liquid hydrocarbons, including gasoline, over activated carbon yields hydrogen-rich gas (40−50 vol % H 2 ). The decomposition of methane in binary mixtures with saturated and unsaturated hydrocarbons was also studied. It was found that the addition of small amounts of unsaturated hydrocarbons (e.g., acetylene) to methane noticeably increases the steady-state concentration of hydrogen in the effluent gas. The studied process can be the basis for the development of compact catalytic units for on-site production of hydrogen/methane blends from NG and liquid hydrocarbon fuels at gas refueling stations. The concept can also be used for a CO 2 -free production of hydrogen for fuel cell applications.