Looking at Atoms to Make Cleaner Fuels from Petroleum

nc-AFM images enlarge

(Top) nc-AFM images can identify pollutant-causing atoms in aromatic hydrocarbon compounds found in crude oil. A partial periodic table illustrates discriminating atom properties. (Bottom) AFM images of dibenzothiophene, carbazole, and acridine, with corresponding chemical structure.

What is the scientific achievement?

CFN staff and users from ExxonMobil have developed a new approach to identifying heteroatoms, like nitrogen and sulfur, commonly found in aromatic hydrocarbon molecules. The team used non-contact atomic force microscopy (nc–AFM) measurements to determine the chemical structure of molecules that can be found in complex mixtures of crude oil.

Why does this achievement matter?

NOx and SOx are two major pollutants that result from the combustion of fossil fuels. Straightforward and robust methods for identifying nitrogen- and sulfur-containing hydrocarbon molecules can improve methods to produce cleaner fuels from crude oil.

What are the details?

Heteroatoms are essential to the functional groups in organic hydrocarbons molecules that provide chemical reactivity and other properties. It is challenging to quickly identify heteroatoms in small molecules, to resolve chemical structures in complex unknown mixtures. This study aimed to understand the effect of elemental types on the contrast of atomic force microscopy (AFM) images using a few selected model heterocycles, including dibenzothiophene, acridine, and carbazole. We identified several features that can be used to find sulfur and nitrogen heteroatoms and discriminate them from carbon atoms using only non-contact AFM. The mechanism of the atom and bond contrast was studied with image simulations and was found to be mostly correlated to van der Waals radii, but other factors such as bonding geometry, electron density, and substrate interaction, are considered. This work will allow for rapid AFM identification of these heteroatoms commonly found in petroleum.

CFN Capabilities

The CFN low-temperature nc–AFM, operated with the CFN-developed, open source GXSM software, was used to conduct experimental investigations and data analysis.

Publication Reference

Percy Zahl and Yunlong Zhang, Energy Fuels 33, 4775 (2019).


Journal Cover: https://pubs.acs.org/toc/enfuem/33/6

Imaging the Chemical Structure of Individual Molecules, Atom by Atom: https://www.bnl.gov/newsroom/news.php?a=216673

Acknowledgement of Support

This research used resources of the Center for Functional Nanomaterials, which is a U.S. DOE Office of Science Facility, at Brookhaven National Laboratory under Contract No. DE-SC0012704.

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