Hydrogen generation using methanol steam reforming – catalysts, reactors, and thermo-chemical recuperation

Abstract

Hydrogen is a promising replacement for fossil fuels since it can be produced using renewable resources. However, hydrogen storage and transportation are the two significant barriers to the implementation of hydrogen-fuelled energy systems. Nevertheless, this issue can be solved by producing hydrogen on-board by methanol steam reforming. Methanol has a higher hydrogen/carbon ratio when compared to other hydrocarbons and it can be obtained from renewable sources such as biomass and stored and carried on-board. Further, the addition of hydrogen/hydrogen-rich reformates as secondary fuel can significantly improve the efficiency of internal-combustion engines and reduce emissions. In methanol-reformation, the type of catalyst and reactor design affect hydrogen yield and selectivity. This review focuses on the recent advancements in developing catalysts and reactors for methanol steam reforming and integration of methanol-reformers with internal-combustion engines for on-board production of hydrogen and its utilization as a secondary fuel. Different catalysts and their synthesis methodologies, promotors, and additives adopted for methanol reformation are compared. The applicability of novel catalysts such as spinels, perovskites and metal-organic frameworks is scrutinised. Moreover, the active sites involved, and mechanistic pathways are investigated. Additionally, the merits and demerits of conventional fixed-bed reactors, and the structural features and the benefits of micro-reactors studied are critically analysed. The integration of a methanol-reformer with an internal-combustion engine exhaust through a heat exchange system, a technique known as thermo-chemical recuperation and the influence of hydrogen-rich reformates on engine performance, thermal efficiency and emissions are deliberated.