Advances in Homogeneous Catalysis for Low Temperature Methanol Reforming in the Context of the Methanol Economy

The Methanol Economy is a concept that was championed by the late professor and Nobel laureate George A. Olah. Methanol can act not only as a convenient fuel and energy carrier but also as a raw material for numerous chemicals and products. While methanol is still predominantly produced from fossil fuels, it can be made from any carbon source including biomass and CO2. The capture and recycling of CO2 to methanol offers a pathway to a sustainable carbon neutral cycle that would be an anthropogenic equivalent to nature's own carbon cycle. The required energy would come from renewable as well as nuclear sources (fission and hopefully fusion in the future). While methanol can be used directly as a fuel for example in internal combustion engines, stoves, turbines as well as direct methanol fuel cells, it can also act as a convenient hydrogen carrier. Hydrogen is the preferred fuel for fuel cells. Storing hydrogen in the form of methanol avoids the cumbersome, expensive and potentially dangerous storage of hydrogen at very high pressures or under cryogenic conditions. When needed, the hydrogen can be easily liberated by methanol reforming with water. Until now, most reforming reactions were based on heterogeneous catalysts operating at relatively high temperatures and pressures. However, in order to lower the reaction temperature and improve its selectivity, homogeneous catalysts for methanol reforming have over the past few years gained much interest. Early results are promising with TON already in excess of 300,000. In this review, the homogeneous catalysts studied and reported so far will be presented and discussed. The possibility to improve the activity of these catalysts for methanol reforming by in depth mechanistic studies and rational design of the catalyst on the molecular level is particularly intriguing.