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Fall 2017

Science and Automobile Fuels from Natural Gas

Metal clusters decorate designer framework and upgrade shale-derived gas in one step

Jingyun Ye

A well-designed 3D porous material is anchored with copper clusters, shown as a chain composed of copper atoms (green spheres) and oxygen atoms (red spheres) that bridged the c pore (as shown in the circular inset). The material upgrades natural gas (methane) to liquid fuel (methanol); the c direction is the point in/out of the screen. Image courtesy of Jingyun Ye, ICDC EFRC

In 2015, the United States consumed approximately 19.4 million barrels of petroleum per day, with nearly half of the amount imported from other countries. As transportation accounts for almost three-fourths of the total U.S. petroleum consumption, reducing our dependence on petroleum-based fuels in this sector will support our economy and energy security. Natural gas is becoming the primary energy alternative to petroleum in the foreseeable future because of the abundant natural gas reserves in the United States.

Natural gas is an odorless, gaseous mixture of hydrocarbons, composed mainly of methane (CH4). It plays an essential role in daily life, generating electricity, heating buildings and cooking food. However, natural gas is not widely used as automotive fuel, mainly due to the difficulty in transportation and the lack of an efficient method to upgrade the gas to liquid hydrocarbons. Directly converting methane to methanol would allow it to be used as automobile fuel or a feedstock chemical in the production of more valuable chemicals. However, the carbon-hydrogen bond in methane is very stable, requiring a large amount of energy to break it to initiate the reaction. Development of cost-effective methods to convert natural gas to liquid fuels and chemicals would greatly enhance its value.

Researchers at the Inorganometallic Catalyst Design Center (ICDC), an Energy Frontier Research Center, have synthesized a copper catalyst on a metal-organic framework (NU-1000). The Cu-NU-1000 catalyst directly converts methane with a 45 percent to 60 percent selectivity to methanol and dimethyl ether. It works at a relatively low temperature (150 °C) compared with the thermal decomposition of methane at around 2,000 °C.

The structure of metal-organic frameworks. Metal-organic frameworks (MOFs) are composed of two types of building blocks: the metal ions/clusters (nodes) and organic molecules (linkers). The nodes and linkers are glued together through the chemical bond, forming highly ordered 3D networks. The networks resemble honeycomb. MOFs are porous materials and can be used for gas storage and separation, detection of chemicals and chemical reaction catalysis. The MOF studied in this work, NU-1000, has three types of pores. It has hexagonal pores, like the hexagonal prismatic wax cells of honeycomb. It also has smaller triangular pores that penetrate layers separated by still smaller pores, called c-pores.

Building with atomic layer deposition. In atomic layer deposition, the film grows on a substrate by exposing its surface to alternating gaseous species. It is similar to an oil painting in which artists paint the canvas in colorful layers, but chemists paint the material with atoms.

In this work, the copper atoms are anchored at the internal surface of a MOF through atomic layer deposition. With increasing deposition cycles, multiple copper atoms can form clusters distributed throughout the MOF. The structure of a Cu-NU-1000 catalyst is just like the honeycomb, with each hexagonal prismatic wax cell decorated with tiny sugar nonpareils. Each nonpareil is a catalytic active site (copper cluster) that makes gaseous methane react with gaseous oxygen to generate liquid fuels, such as methanol and dimethyl ether, which diffuse out of the hollow channels.

On the road to fuel. This study presents a promising first generation of MOF-based catalysts for selective methane oxidation, the “holy grail” reaction in a natural gas upgrade. It provides a promising way to produce automobile fuels to replace gasoline!

Acknowledgments

Sponsors: The Inorganometallic Catalyst Design Center, an Energy Frontier Research Center funded by the U.S. Department of Energy (DOE), Office of Science, Office of Basic Energy Sciences, funded this work. B.L.M. acknowledges support by Pacific Northwest National Laboratory’s (PNNL’s) Laboratory Directed Research and Development program. N.D.B. acknowledges support by PNNL’s Chemical Imaging Initiative.

Facilities: This research used resources of the Advanced Photon Source (APS), a DOE Office of Science, Office of Basic Energy Sciences user facility. Sector 20 operations at the APS are supported by DOE and the Canadian Light Source. The scanning transmission electron microscopy work was performed using the Environmental Molecular Sciences Laboratory (EMSL), a national scientific user facility sponsored by the DOE Office of Science, Office of Biological and Environmental Research, and located at Pacific Northwest National Laboratory, a multiprogram national laboratory operated by Battelle for DOE. The Minnesota Supercomputing Institute (MSI) at the University of Minnesota provided resources that contributed to the research results reported within this paper.

More Information

Ikuno T, J Zheng, A Vjunov, M Sanchez-Sanchez, MA Ortuño, DR Pahls, JL Fulton, DM Camaioni, Z Li, D Ray, BL Mehdi, ND Browning, OK Farha, JT Hupp, CJ Cramer, L Gagliardi, and JA Lercher. 2017. “Methane Oxidation to Methanol Catalyzed by Cu-Oxo Clusters Stabilized in NU-1000 Metal-Organic Framework.” Journal of the American Chemical Society 139(30):10294-10301. DOI: 10.1021/jacs.7b02936

About the author(s):

  • Jingyun Ye is a postdoctoral researcher in computational chemistry at the University of Minnesota. She is also a member of the Inorganometallic Catalyst Design Center (ICDC). Her research focuses on understanding reaction mechanisms from the atomic level to design new catalysts based on metal-organic frameworks.

Copper and the Keys to Automotive Fuel

New catalyst upgrades methane in natural gas to methanol, a liquid fuel

A copper catalyst on a metal-organic framework directly converts methane, with a 45 percent to 60 percent selectivity, to methanol. Image courtesy of Nathan Johnson, Pacific Northwest National Laboratory

Moving people and goods from one spot to another uses a significant amount of resources. In fact, transportation accounts for nearly 75 percent of U.S. petroleum use. What if we had other options? Researchers are looking at natural gas. Specifically, they are looking at methane, found in natural gas. A key challenge is creating a hardworking catalyst that can turn methane into the desired chemical building block in one step. Doing the reaction in a single step means no chemical middlemen. Scientists created such a catalyst: a molecular scaffolding laced with copper clusters. It traps the methane, converts it into a desirable hydrocarbon and releases it. The study shows that the scaffolding, a metal-organic framework, could hold the answers to creating industrially relevant catalysts. The researchers were from the Inorganometallic Catalyst Design Center (ICDC), led by the University of Minnesota.

More Information

Ikuno T, J Zheng, A Vjunov, M Sanchez-Sanchez, MA Ortuño, DR Pahls, JL Fulton, DM Camaioni, Z Li, D Ray, BL Mehdi, ND Browning, OK Farha, JT Hupp, CJ Cramer, L Gagliardi, and JA Lercher. 2017. “Methane Oxidation to Methanol Catalyzed by Cu-Oxo Clusters Stabilized in NU-1000 Metal-Organic Framework.” Journal of the American Chemical Society 139(30):10294-10301. DOI: 10.1021/jacs.7b02936

Disclaimer: The opinions in this newsletter are those of the individual authors and do not represent the views or position of the Department of Energy.