In situ hydrogen generation in subsurface reservoirs of fossil fuels by thermal methods: Reaction mechanisms, kinetics, and catalysis

In situ hydrogen generation (ISHG) from fossil fuels in subsurface reservoirs has emerged as a promising way to lower greenhouse gas emissions. This process can be realized within reservoirs through various methods, typically under high-temperature and high-pressure conditions. Multiple reaction pathways, including steam reforming, partial oxidation, pyrolysis, autothermal reforming, dehydrogenation, and gasification, can simultaneously occur inside reservoirs depending on the applied thermal technologies. Achieving the desired reaction pathways, reaction rates, and product yields requires careful selection and control of suitable processes. This review thoroughly discusses the methods and technologies employed in ISHG, along with associated reaction pathways and kinetics. Special emphasis is given to catalyst design and the strategic use of catalysts to optimize specific reactions. The potential of ISHG technology is finally discussed, highlighting the technical challenges that must be addressed to verify the feasibility of ISHG as a viable and competitive process. By enhancing the understanding of the science behind ISHG, this comprehensive review aims to pave the way for the development of innovative technologies that can revolutionize the energy landscape while mitigating the impacts of climate change.