Iron pyrite (Fool’s Gold) may prove an alternative lower cost catalytic material; Cambridge team focuses on NOx

13 February 2012

NO and NO2 disassociation on pyrite. Sacchi et al. Click to enlarge.

Developing new catalysts derived from inexpensive minerals, instead of increasingly costly (and rare) precious metals, is an important area of research that involves several groups around the world.

Researchers at the University of Cambridge have discovered that the sulfide material iron pyrite, commonly known as ‘Fool’s Gold’, may serve as a viable alternative to current—and increasingly expensive—catalytic materials. Their work, which focused on the removal of NO_x, were published in the RSC journal Physical Chemistry Chemical Physics.

In the past, sulfur was believed to be one of the most detrimental elements for surface chemical reactions, able to decrease dramatically the reactivity of a catalyst by occupying (poisoning) the active sites on the material, but more recently some sulfur materials (for example, molybdenum sulfides) have actually shown interesting catalytic properties of their own. (Earlier post.)

Using density functional theory (DFT), researchers led by Stephen Jenkins at the University’s Department of Chemistry, explored the explored the adsorption and dissociation of nitrogen monoxide (NO) and nitrogen dioxide (NO₂) on the surface of iron pyrite (FeS₂).

They found that both those NO_x species chemisorb on the surface Fe sites, while the S sites are basically unreactive for all the molecular species considered in the study and even prevent NO₂ adsorption onto one of the non-equivalent Fe–Fe bridge sites. From the calculated high barrier for NO and NO₂ direct dissociation on this surface, they concluded that both nitrogen oxides species are adsorbed molecularly on pyrite surfaces.

The next steps for the Cambridge researchers will be to investigate the activity of pyrite surfaces for strategically important industrial reactions, such as the manufacture of ammonia for fertilizers; the production of synthetic hydrocarbon fuels from renewable biomass; and the extraction of hydrogen for use in future fuel cell electric vehicles.

Recent European legislation has proposed increasingly strict legislative limits on the concentration of NO_x that can be emitted by vehicles; therefore the search for new and more efficient catalysts that can capture these molecules and transform them into innocuous gases such as nitrogen and water vapor, is urgently relevant.

The necessity of finding reliable alternatives to overexploited catalytic materials—such as platinum, rhodium and gold—will soon become unavoidable. Experimental work is currently underway in our group, and we hope that our work will ultimately allow us to test the potential for catalytic application of a wide range of sulfidic and carbidic materials. In future, we aim to develop fruitful scientific collaborations with chemical engineering groups and with industrial partners.

—Dr. Marco Sacchi, first author

Resources

• Marco Sacchi, Martin C. E. Galbraith and Stephen J. Jenkins (2012) The interaction of iron pyrite with oxygen, nitrogen and nitrogen oxides: a first-principles study. Phys. Chem. Chem. Phys. doi: 10.1039/C2CP23558G