Researchers Image Atomic Structure of Fischer-Tropsch Catalysts

	These are the types of images collected by the NETL researchers. The larger image shows an array of iron catalyst particles having sizes of about 10 nanometers each collected with a specialized scanning tunneling microscope housed at NETL. The inset shows the atomic resolution possible when researchers zoom in on each of these individual particles. The white dots in the inset are individual oxygen atoms in the iron oxide lattice of these particles. Each oxygen atom is spaced approximately three angstroms from its neighbor.

Researchers in NETL’s Chemistry and Surface Science Division have characterized the atomic-scale structure of iron oxide catalysts similar to those used for converting gasified coal into liquids that can be used as hydrogen carriers or fuels.

They published a study that provides detailed images of the atomic structure in the highly-regarded, peer-reviewed publication, Journal of Physical Chemistry C.

The manuscript investigates the production of model iron and iron oxide catalyst particles on an inert gold growth substrate. Researchers characterized the atomic-scale structure of the particles using advanced surface analysis techniques, such as scanning tunneling microscopy (STM).

These particles serve as model catalysts reproducing the size, shape, defects, and other important structural features of real world iron-based catalysts used for the Fischer-Tropsch process.

The research shows that the production of different phases of iron-oxide can be controlled through the growth process by using different reactants for converting the iron into iron-oxide.

The STM studies of model iron oxide particles illustrate that catalyst particles in this size regime have oxygen-terminated surfaces and exposed edges which is an important finding for understanding the reactivity of Fischer-Trospsch catalysts and the mechanisms involved in activating the iron-oxides into iron-carbide phases.

Future work will focus on incorporating promoters, such as copper, into this system to better understand the mechanism involved in activating Fischer-Tropsch catalysts.

NETL Researchers Use Bees, Balloons, Pollen To Test Novel CO₂ Monitoring Approach

	Joe Shaw, a bee expert with Montana State University, examines control hives, distant from the carbon dioxide injection area in this NETL research project.

Bees and pollen are not just for honey anymore. NETL researchers are using them – along with helium-filled balloons – in field tests to verify the effectiveness of carbon dioxide (CO₂) storage sites.

Bees, balloons and pollen have roles in one of the innovative methods NETL is exploring to verify that no CO₂ leaks from sequestration sites.

They are part of a method to sample for the presence of chemical tracers that are co-injected at low levels with the CO₂. Bees collect pollen over wide areas, potentially offering an efficient method for assessing the levels of NETL-developed tracers that can fingerprint the stored CO₂, differentiating it from natural carbon dioxide.

NETL researchers used balloons to determine atmospheric variations in tracer content.

NETL conducted the studies at the Center for Zero Emissions Research and Technology (ZERT) research site on an agricultural field at Montana State University (MSU) in Bozeman.

NETL researchers in cooperation with bee experts at MSU placed hives about 150 meters upwind and downwind from a source of CO₂ marked with tracers to determine if pollen collected by bees would contain measurable quantities of tracer or if bees will bring back tracer from direct contact with foliage.

A third control hive was located some distance from the test plot. Along with the samples of the bee’s pollen, sorbent packets were placed near the hive entrances to monitor hive ventilation gas for tracer. A third monitor was placed about 25 meters from each hive in order to account for any background levels of tracer near the hive.

Levels of tracer in the atmosphere were also monitored throughout the test field using an extensive grid of monitors, and a light detection and ranging (LIDAR) system was employed by Montana State researchers to correlate field tracer levels with bee foraging locations.

To determine atmospheric variations in tracer content to assess boundary-layer mixing processes, NETL researchers contracted Apogee Scientific to use a large helium-filled balloon to elevate a carousel containing sealed sorbent tubes above the field for sequential exposures of sorbent tubes at known times and known elevations.

Researchers are conducting laboratory analysis of the tracer levels in the samples.

NETL Publishes Research Showing Feasibility of Emerging CLC Technology

	Ranjani Siriwardane, Thomas Simonyi and Hanjing Tian (from left) in the Thermogravimetric Analysis Laboratory where most of the CLC experiments were conducted.

NETL research indicates that it is feasible to develop chemical-looping combustion (CLC) with coal by metal oxides as oxygen carriers.

CLC is an emerging technology for clean energy production from fossil and renewable fuels. An oxygen carrier (typically a metal oxide) is first oxidized with air. The hot metal oxide is then reduced in contact with a fuel in a second reactor, thus combusting the fuel.

CLC produces sequestration-ready CO₂ streams without significant energy penalty.

A solid fuel such as coal is rarely used in CLC since the process with solid fuels faces many challenges.

A paper on NETL research into direct combustion of coal by CLC has been accepted for publication in the peer-reviewed Energy and Fuels Journal. The paper is “Chemical-Looping Combustion of Coal with Metal Oxide Oxygen Carriers.”

The paper reports results of the combustion and re-oxidation properties of CLC over oxides of copper, iron, nickel, cobalt and manganese.

Among various metal oxides evaluated, copper oxide showed the best reaction properties: copper oxide can initiate the reduction reaction as low as 500 °C and complete the full combustion at 700 °C.

In addition, the reduced copper can be fully re-oxidized by air at 700 °C.