The Science
Transforming carbon monoxide into an energy dense liquid fuel such as methanol is hard to accomplish in a single step. Researchers instead use multi-step reactions. Recently, scientists improved this multi-step process. They used simple and recyclable organic substances similar to those found in nature to handle reduction—the transfer of protons and electrons as part of the transformation process. The researchers also identified two key substances that form partway through the transformation of carbon monoxide to methanol. When coupled with an additional ruthenium complex for converting carbon dioxide (CO2) to carbon monoxide (CO), these advances provide for a domino-style cascade of reactions for generating fuel.
The Impact
This study contributes to the ways in which scientists can activate stable and abundant molecules to generate liquid fuels. Carbon dioxide is a stable molecule and its reduction to liquid fuels is challenging. Cascade reaction schemes capitalize on the use of multiple catalysts that carry out such complex transformations. In the next steps for this research, scientists will use solar energy to make this process renewable, opening up new possibilities in solar driven fuel formation.
Summary
Cascade catalysis is a promising strategy for upgrading CO2 into value-added fuels. This research, carried out at the University of North Carolina at Chapel Hill and Brookhaven National Laboratory, two of the institutions in the Center for Hybrid Approaches in Solar Energy to Liquid Fuels (CHASE), showed that simple organic hydride donors reduce CO to methanol (CH3OH). The researchers proposed a catalytic cycle and found that the unique reactivity of two key intermediates is important. The use of organic hydride species to shuttle the protons and electrons to CO was critical, as previous research has shown that such reactivity cannot be realized by sequential electron and proton transfers. The organic hydrides utilized share some commonalities with those found in natural photosynthetic CO2 fixation that may be regenerated for sustainable methanol generation.
CHASE carried out X-ray absorption spectroscopic measurements at the National Synchrotron Light Source II, a Department of Energy Office of Science user facility operated by Brookhaven National Laboratory, to study the nature of the ruthenium in each of the three reaction steps. Taken together with mechanistic and isotopic labelling studies, the advanced mechanistic details highlight the importance of collaborative research made possible by the user facilities found only at national labs. The insights gleaned from these studies are being used to investigate the next generation of catalysts for methanol synthesis.
Funding
This work was solely supported as part of CHASE, an Energy Innovation Hub Awardee funded by the Department of Energy Office of Science, Office of Basic Energy Sciences. The XAS measurements were done at the National Synchrotron Light Source II, a user facility operated for the DOE Office of Science by Brookhaven National Laboratory.
