LabNotes - June 2013
Utilizing and Storing Carbon Dioxide Emissions
Quantum Alloys Offer Unique Prospects for CO2 Management Technologies
Structure of a Quantum Alloy: The top illustrations depict how 13 Au atoms forming an icosohedron "core" bond with sulfur and gold atoms in a "shell" to form the Au2525 catalyst for CO2 remediation. The bottom illustration shows how 3 of the Au atoms in the shell can be replaced with Ag to form the Au2522Ag3 quantum alloy.
When common household metals, such as copper, gold, or silver, are reduced in size to clusters that consist of a few dozen atoms, the materials develop completely unexpected properties. One example occurs for gold, which is inert in its bulk form, but which develops the ability to efficiently catalyze chemical reactions when made as atomic-scale clusters that are over 1,000 times smaller than a human hair and invisible to the eye. These properties result from quantum confinement effects, a term scientists use to describe how small clusters and particles evolve with size. Quantum effects are the principal driving force behind the field of nanotechnology, where engineers manipulate the colors, electrical conductivity, and chemistry of matter simply by controlling and constraining size at the atomic scale.
Researchers at NETL have been using quantum effects to design radical new catalysts capable of converting CO2 emissions into fuels, chemicals, and plastics. Their unique discovery involves shrinking gold into a system consisting of just 25 atoms, commonly referred to as Au25. This material was recently demonstrated by NETL to be one of the most efficient catalysts ever reported for applications involving the use of carbon dioxide (CO2). In order to further improve catalytic activity and reduce production costs, NETL has been investigating ways to replace some of the Au (gold) atoms with Ag (silver), Cu (copper), and other metals. The mixing of metals to improve properties is commonly called alloying, but these small clusters behave very differently than bulk systems, and have been named quantum alloys to highlight their unique properties.
When researchers replace just 3 atoms in Au2525 with Ag or Cu, the catalysts take on exciting new properties. Laboratory experiments show that forming quantum alloys completely changes how the atoms in these clusters bond to each other, how they absorb light (e.g., their color), and more importantly, how they catalyze chemical reactions involving CO2.
Researchers have also used sophisticated computational modeling to probe the properties of these clusters. These calculations helped to predict where the Ag and Cu atoms prefer to reside in the alloy and how common gases, such as CO2 and oxygen, interact with the alloy.
Future work in this area will continue to address how to form these alloys and evaluate their ability to effectively convert CO2 into value-added products. These results were recently published in the highly regarded Journal of Physical Chemistry C (2013, 117, 7914-7923).
Contact: Christopher Matranga, Doug Kauffman
Estimating Carbon Dioxide Storage in Geologic Formations
|This map highlights potential regions of carbon dioxide storage for coal beds, oil and gas reservoirs, and saline formations that were assessed by the Regional Carbon Sequestration Partnerships and other sources and compiled by NATCARB.
Carbon, Capture, and Storage (CCS) is an option to reduce carbon dioxide (CO2) emissions. Carbon emissions are captured from stationary sources such as power plants and then injected in the form of supercritical CO2 into select deep geologic formations. Formations such as depleted oil and gas fields, deep saline formations, and unmineable coal seams have a competent seal and geologic trapping capability that will prevent CO2 from escaping back into the atmosphere. Estimates of CO2 storage capacity in geologic formations are required to assess the potential for CCS technologies to contribute towards reducing CO2 emissions globally. Governments and industries worldwide rely on these estimates for broad energy-related government policy and business decisions. Dependable CO2 storage estimates are necessary to ensure successful deployment of CCS technologies
Current estimates of CO2 storage in saline formations are subject to relatively large uncertainties. These assessments rely on simplifying assumptions due to lack of data from the subsurface associated with areas of potential storage in saline formations and the natural heterogeneity of geologic formations in general, resulting in undefined rock properties.
Initiatives for assessing CO2 geologic storage potential have been conducted since 1993. These initiatives vary from an overview description of assessment tools to a detailed, comprehensive method. While dependable prospective CO2 storage estimates provide essential information for policy and business decisions for CCS technologies, it is difficult to assess the uncertainty of these estimates without knowing how the methods targeted at CO2 storage estimates compare with one another.
Researchers at NETL compared a variety of CO2 storage methods for geologic storage in saline formations to determine if the method used for estimation of storage resource significantly impacts the results. Specifically, six prospective CO2 methods were applied to 13 saline formation data sets. Methods applied include those normally utilized by 1) international organizations; 2) U.S. Department of Energy and United States Geological Survey ); and 3) the peer-reviewed scientific community.
Despite the uncertainties arising from the simplifying assumptions inherent to each method, the assessments of CO2 storage potential were comparable. A statistical analysis revealed that the uncertainty in the underlying parameters of the general saline formation data sets has a much greater impact on overall prospective estimates of CO2 storage than the choice of method does, especially within subsets of methods defined by similar assumptions.
These results were recently published as a NETL Technical Report Series as NETL-TRS-1-2013, Comparison of Publicly Available Methods for Development of Geologic Storage Estimates for Carbon Dioxide in Saline Formations.
Contact: Angela Goodman