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Nanostructures made from gold concentrate light energy and boost molybdenums ability to pull apart the two nitrogen atoms in an N2 molecule illustration by the researchers

2% of world’s energy is used to manufacture synthetic fertilizer and similar chemical compounds. Princeton researchers potentially slash energy use by using sunlight instead.

Science Magazine estimates that making nitrogen-based synthetic fertilizers, ubiquitous around the globe, represents circa 2% of the world’s energy used every year. 

Now, a new method reported out of Princeton University, New Jersey (US), could significantly slash this excessive use of conventional energy by using sunlight instead. 

Currently, fertilizer, pharmaceuticals and other industrial chemicals are made by pulling nitrogen from the air and combining it with hydrogen. The problem is that atmospheric nitrogen is locked into pairs of atoms, N2, and the bond between these two atoms is the second strongest in nature. It thus takes a tremendous amount of energy to split up the N2 molecule and allow the nitrogen and hydrogen atoms to combine. 

Using solar energy instead of burning more fossil fuels

The century-old Haber-Bosch process exposes the N2 and hydrogen to an iron catalyst in a chamber heated to more than 400 degrees Celsius. “The current method for industrial ammonia synthesis, the Haber-Bosch, consumes energy to drive the reaction, which is otherwise spontaneous at room temperature,” explains Emily A Carter, Dean of Princeton’s School of Engineering and Applied Science and Gerhard R Andlinger Professor in Energy and the Environment. She emphasizes that her team’s new method “could potentially allow us to utilize solar energy as means to deliver this energy that would otherwise come from burning more fossil fuel.”

The team, which includes post-doctoral researcher and study co-author John Mark Martirez from Princeton’s Department of Mechanical and Aerospace Engineering, believed it would be possible to use plasmon resonances to boost a catalyst’s power to split apart nitrogen molecules, thus, using light instead of heat to break the N2 bond. “The new method proposes to concentrate light energy using plasmonic metal nanoparticles (e.g., gold) to activate nitrogen molecule dissociation,” Martinez explains. They envision to achieve reduced energy dependence of ammonia synthesis in two ways: a) using solar energy as primary source of energy to improve the kinetics of molecular activation instead of heat, and b) consequently, lower the operational pressure requirements needed to offset the negative effect of temperature on the fraction of ammonia in the equilibrium gas stream.

Promise for next-gen light-based technologies

Surface plasmon resonance already has a significant mark in the field of molecular detection through surface-enhanced Raman spectroscopy. “We envision, among many scientists in the field, to utilize this phenomenon to enhance catalytic production of industrially important chemicals, and perhaps even improve selectivity of these processes,” Carter says. “Other properties of plasmonic materials that could potentially be game changing are their larger light absorption efficiencies and photo-stability compared to most chromophoric organic molecules and semiconductors used in photovoltaics.”

The mechanism of light activation — a surprising discovered

“Perhaps the most surprising is that the mechanism of light activation we discovered is different from what is commonly proposed,” Carter says about the study. “When we think about plasmon-induced catalysis, many would assume it is because of the abundant energetic electrons created by light that catalyzes the reaction. We show instead that light-induced changes in the chemical property of the active site — where the reaction occurs — may in fact cause the catalysis.”

Moving forward with this research endeavor, the Princeton colleagues want to extend the plasmon resonance technique to other strong chemical bonds, for example the carbon-hydrogen bond in methane.

The article "Prediction of a low-temperature N2 dissociation catalyst exploiting near-IR–to–visible light nanoplasmonics,” published in Science Advances, covers this research. 

Written by Sandra Henderson, Research Editor, Novus Light Technologies Today

Labels: Surface Plasmon Resonance,Princeton University,Haber-Bosch,Emily A Carter,John Mark Martirez,low-temperature N2 dissociation,near-IR–to–visible light nanoplasmonics

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