Structured catalysts for natural gas reforming

Hydrogen is a zero-carbon energy carrier for the deployment of fuel cell technologies in distributed energy systems and offers great potential in the transition toward a low-carbon economy. In addition to improved energy efficiency, hydrogen fuel cells can improve air quality with negligible emission of harmful particulates and nitrogen oxides. Hydrogen can be produced from a variety of feedstocks, such as non-renewable and renewable resources using electrolysis and reforming processes. Methane is the main component of large distributed renewable (e.g., biomethane, biogas) and nonrenewable (e.g., natural gas, shale gas) feedstocks, and up to now the reforming of methane is the most suitable and easy way to produce hydrogen. Methane steam reforming (MSR) is a mature technology, dominant at an industrial scale supplying 40% of world’s hydrogen, with benefits of higher hydrogen yield and concentration in the product stream as compared to other reforming technologies. MSR is a highly endothermic reaction, requiring a large amount of heat at temperatures up to 1000 °C25 for attractive equilibrium conversion, which makes a high-temperature catalytic combustor desirable. The scaled-down version of industrial reformers shows poor performance and responds slowly to throughput variation, mainly because of heat transfer limitations between the flame and the catalyst pellet, and also due to mass transfer limitations. By improving transport limitations, microreactor technology and structured catalysts provide unique opportunities to realize compact and modular steam reformers. In fact, the improved heat and mass transport rates lead to 1−3 times higher throughput of hydrogen. This review will highlight the emerging technologies in terms of structured reactors for the production of syngas via MSR.