Steam Reforming of Methanol for Hydrogen Production: A Critical Analysis of Catalysis, Processes, and Scope

The hydrogen economy is being pursued quite vigorously since hydrogen is an important and green energy source with a variety of applications as fuel for transportation, fuel cell, feedstock, energy vector, reforming in refineries, carbon dioxide valorization, biomass conversion, etc. Steam reforming of alcohols is a well-established technique to obtain syngas. Methanol is viewed to be a lucrative alternative for fossil fuels, due to its flexibility in being generated from multiple sources, high energy density, and low operating temperatures. The catalysts used for reforming govern the methanol conversion rate and the ratio of gaseous products, i.e., H2, CO, and CO2. Group VIII–XII metals have been widely utilized for methanol steam reforming as they have a higher hydrogen yield. Several other catalysts and novel techniques have been developed and used to date. Quite a few strategies to enhance the performance of catalysts and reduce deactivation have been discussed. This review focuses on the metallic catalysts, mainly Cu, Pd, Zn, with different formulations and compositions for steam reforming of methanol (SRM). Active catalyst components, supports, and their interactions, along with different promoters, are reviewed, and their performances are critically analyzed. The various reaction mechanisms and reaction pathways have been identified and elaborated. A fundamental understanding of the functionality and structure of catalysts is required no matter which alcohol is used as a feedstock, and some general inferences can be obtained from polyhydroxyl feed for the steam reforming of methanol, which is the subject matter of this review. Particularly, the role of copper as a component in mono and multimetallic systems and the nature of support must be studied fundamentally to get high hydrogen yields. It is important to determine how metal support interactions, including oxygen transfer from reducible oxides to the metal site, influence the catalyst activity, selectivity, and stability. Further, the mechanism by which alloying affects the selectivity in multimetallic catalysts must be understood by using high-end characterizations.