Sustainable SMR
In the pursuit of lowering greenhouse gas emissions, hydrogen has gained much attention as a potentially “clean” energy source. Typically, hydrogen is produced by steam methane reforming (SMR), a process which itself produces greenhouse gases. Efforts to lower the carbon footprint of hydrogen production include producing “green” hydrogen via electrolysis, using carbon capture with SMR to produce “blue” hydrogen, as well as increasing the efficiency of the SMR process (see Methane Reforming: Solving the Hydrogen Blues, Chem. Eng., October 2023).
Now, researchers at Rice University (Houston, Tex.; www.rice.edu) have developed a catalyst that allows the SMR reaction to be driven by light rather than heat, eliminating emissions from the reaction. When exposed to a specific wavelength of light, the copper-rhodium photocatalyst breaks down methane and water vapor into hydrogen and carbon monoxide, without external heating. Copper nanoparticles are used as the catalyst’s energy-harvesting “antennae.” Rhodium atoms and clusters were added to the catalyst system as reactor sites. The rhodium binds water and methane molecules to the plasmonic surface, tapping the energy to fuel the SMR reaction.
The research also shows that the technology can avoid catalyst deactivation due to oxidation and coking, and effectively regenerate the catalyst with light. The technology can be used for on-demand hydrogen generation, which would avoid the need to transport the hydrogen gas over long distances. Peter Nordlander and Naomi Halas are the authors of a study about the research that was published in Nature Catalysis. Halas stated that “This research showcases the potential for innovative photochemistry to reshape critical industrial processes, moving us closer to an environmentally sustainable energy future.”
Capturing Carbon from the Air
Capturing carbon dioxide from the air, known as direct air capture (DAC), is one of the promising tools in the arsenal of techniques for lowering atmospheric greenhouse-gas levels and slowing global warming. While some techniques for DAC work well for air that contains high concentrations of CO2, they may not be efficient in ambient air, where CO2 concentrations are low.
Chemists at the University of California, Berkeley (www.berkeley.edu) have developed a new type of absorbent that addresses this challenge. The porous absorbent is a covalent organic framework (COF) that they say captures CO2 from ambient air without degradation by water or other contaminants. COFs are held together by covalent carbon-carbon and carbon-nitrogen double bonds, as compared to metal organic frameworks (MOFs), which are held together by metal atoms. The research has been reported in the journal Nature in October, by authors Omar Yaghi, professor of chemistry at UC Berkeley, and graduate student Zihui Zhou.
Yaghi and Zhou, together with colleagues, developed COF-999, which is assembled from a backbone of olefin polymers with an amine group attached. The porous material is flushed with more amines that attach to NH2 and form short amine polymers inside the pores. Each amine can capture about one CO2 molecule. The COF can capture CO2 at room temperature. Heating the COF to a mild temperature of about 140°F releases the CO2, rendering the COF ready for reuse. The material reportedly holds up to 2 millimoles of CO2 per gram. Yaghi noted that it may be possible to enlarge the pores to capture even more CO 2. ❐