Materials For Energy

Catalytic Materials: Clean Fuels for the Future and Origins of Life

By Dr. Russell Chianelli, University of Texas at El Paso, Materials Research and Technology Institute

Catalytic materials have played a crucial role in providing fuels, commodities, and fine chemicals for more than 100 years. The role of these materials is going to become more important than ever in the future. Catalytic materials will provide fuels for environmentally friendly transportation vehicles, as well as materials for these vehicles, well into the future. Today, more than 60% of all chemical products and 90% of all chemical processes are catalytic processes. We define catalytic materials, such as the TMS (transition metal sulfide) catalysts (described below), as solid-state materials with the recognition that many catalysts are inorganic molecules or biological molecules. A full description of catalysts and catalytic materials and the breadth of the field can be found in the Encyclopedia of Catalysis, which includes an article by the author of this report.¹ Catalytic materials are the catalysts, solids in the case of heterogeneous catalytic processes, that are optimized for activity and selectivity in catalytic processes. The process of optimizing the activity and selectivity through synthetic techniques is called structure/function optimization. This process controls the surface chemistry of the catalytic material and has been used since the dawn of catalytic processes. Today, it is called optimization of nanomaterials.

An example of catalytic materials that will continue to be important in the future is the transition metal sulphides (TMSs). These catalysts have been mainstays of hydro-processing fuels (upgrading fuel quality and removing pollutants) and upgrading bitumen and coal for more than 100 years. Every refinery in the world uses them every day to remove sulphur and other pollutants from transportation liquid fuels. As environmental regulations increase the need for improved active and selective TMSs, refineries currently are using Co/Mo/Al₂O₃ or Ni/W/Al₂O₃ or combinations of both. The active materials are sulphides, such as WS₂, MoS₂, Ni₃S₂, and Co₉S₈, while Al₂O₃ is not part of the catalytic system. In addition, Co and Ni sulfides act as promoters of the M and W sulfides, increasing their activities by as much as a factor of 10. These are the so-called “synergic pairs.” These synergic pairs result from the interfacial coordination between the two solid-state phases, for example Co₉S₈ and MoS₂. A cluster of Co/Mo/S atoms exist at the interface, which through d-electron donation cause the Mo to mimic a noble metal catalytic material.

It is also crucial to remember that for a real understanding to develop, we must study the catalytically stabilized materials and not materials that are changing under catalytic conditions. In the case of the TMSs, this means that we must study catalytic materials such as MoS_2–xC_x and RuS_2–xC_x. It has been demonstrated that “surface carbides” are the catalytically stabilized state under hydro-treating conditions. This progress has been made by combining synthetic, experimental, and theoretical techniques, and thecombination of these techniques will be required to develop the catalytic materials of the future, which are crucial to transportation energy in the future.²

Finally, a few years ago, I was invited to speak at the Santa Fe Institute on the “Origins of Life.” Why? Because the molecules necessary for life are created on deep sea vents at the high pressures that occur at the deepest part of the oceans. Such a vent is shown below.

The black smoke, the Black Smoker, emerging from the vent is an iron sulfide catalytic material that is producing compounds necessary for life from indigenous gases (methane, CO). It is thought that similar reactions may occur on distant planets. Thus catalysis by the TMS is central to the search for life on other planets. When I presented at the “Origins of Life Conference,” I started by saying, “I don’t know anything about the “Origins of Life,” but I do know that my life began on the transition metal sulfides.

1. Encyclopedia of Catalysis, John Wiley and Sons Inc. (2010).
2. R.R. Chianelli, G. Berhault, B. Torres, "Unsupported Transition Metal Sulfide Catalysts: 100 years of Science and Application," Catalysis Today 147, 275 (2009).

No Resistance Needed!

By Manuel Ramos, UTEP and Allan J. Jacobson, TCSUH

In 1911, H.K. Onnes, a Dutch physicist, discovered superconductivity by cooling mercury metal to extremely low temperature and observing that the metal exhibited zero resistance to electric current. He received the Nobel Prize in 1913 “for his investigations on the properties of matter at low temperatures which led, inter alia, to the production of liquid helium.”¹

His discoveries opened up a new field to many physicists and materials scientists around the world who have worked subsequently in order to understand the phenomenon of superconductivity and to discover new materials; the field has continued to fascinate scientists and engineers for almost 100 years.

Before 1973, many metals and metal alloys were found to become superconducting at temperatures below 23.2 K. These became known as low temperature superconductor (LTS) materials. The LTS materials such as NbTi have been commercialized in superconducting magnets used in magnetic resonance imaging, nuclear magnetic resonance, high-energy physics accelerators, and plasma fusion reactors. The underlying mechanism of low-temperature superconductivity was shown experimentally and theoretically to depend on the coupling of electrons to the lattice vibrations. In 1957, based on this coupling mechanism, Bardeen, Cooper, and Schrieffer developed a theory of superconductivity (BCS theory) that gave a complete theoretical explanation of the phenomenon. ²

In 1986, Bednorz and Müller discovered oxide-based ceramic materials that demonstrated superconducting properties as high as 35 K.³ This was quickly followed in early 1997 by the announcement by C.W. Chu and colleagues of a copper oxide superconductor YBa₂Cu₃O₇ that became superconducting at 92 K, above the boiling point of liquid nitrogen 77 K. Further discoveries of copper oxides containing bismuth,⁴ thallium,⁵ or mercury,⁶ with even higher transition temperatures up to 138 K at ambient pressure in the mercurocuprate HgBa₂Ca₂Cu₃O_8+x, quickly followed. Today, the record stands at ~164 K for this phase under pressure.⁷ A superconducting material with a critical temperature above 23.2 K is known as a high-temperature superconductor (HTS), despite the need for cryogenic refrigeration.

After 20 years of research and development, HTSs, particularly YBCO, are poised for large-scale applications because of the development of the technology to produce long lengths of superconducting conductors in the form of thick films (~1 m) on a metallic substrate with high current carrying capability (~100 A cm width). Today, the only substantive commercial products incorporating HTS materials are electronic filters used in wireless base stations, which use HTS. However, much larger applications have either been successfully demonstrated or demonstrations are in progress.⁸ Examples include HTS transmission cables, fault current limiters and fault current limiting transformers, to aid our aging electric power grid, large electric motors for ship propulsion, and HTS generators to produce energy from wind power. High-field magnets that use HTS are also under development for magnetic resonance imaging and for use in high-energy physics projects. Several challenges remain to substantial commercial inroads of HTS technology into the new applications. Cost of HTS wire, refrigeration, demonstration of systems cost benefits, and long-term reliability are all issues that need to be addressed.

New superconductors continue to be discovered, for example MgB₂ (T_c= 39 K)⁹ and the iron arsenide family (with T_c up to 56 K),¹⁰ and while these materials have transition temperatures below the cuprates, they are still high-temperature superconductors under the definition given previously. Further, given that no complete theory exists at present as to how HTS materials work, many feel that it should be possible to raise the superconducting temperature to over 200 K in the next 10 years.¹¹ Consequently, in addition to pushing forward with the applications of the existing materials, particularly YBCO, a renewed interest in the search for new materials with higher transition temperatures has developed in the last few years.¹²

1. H.K. Onnes, Electrician 67, 657 (1911).
2. J. Bardeen, L.N. Cooper, J.R. Schrieffer, Phys. Rev. 106, 162 (1957).
3. M.K. Wu, J.R. Ashburn, C.J. Torng, P.H. Hor, R.L. Meng, L. Gao, Z.J. Huang, Y.Q. Wang, C.W. Chu, Phys. Rev. Lett. 58(9), 908 (1987).
4. H. Maeda, Y. Tanaka, M. Fukutomi, T. Asano, K. Togano, H. Kumakura, M. Uehara, S. Ikeda, K. Ogawa, Physica C: Superconductivity and Its Applications 153 (Pt. 1), 602 (1988).
5. Z.Z. Sheng, A.M. Hermann, Nature 332 (6160), 138 (1988).
6. S.N. Putilin, E.V. Antipov, O. Chmaissem, M. Marezio, Nature 362 (6417), 226 (1993).
7. J.H. Eggert, J.Z. Hu, H.K. Mao, L. Beauvais, R.L. Meng, C.W. Chu, Phys. Rev. B 49 (21), 15299 (1994
8. Coalition for the Commercial Application of Superconductors, http://www.ccas-web.org/
9. J. Nagamatsu, N. Nakagawa, T. Muranaka, Y. Zenitani, J. Akimitsu, Nature 410 (6824), 63 (2001).
10. Y. Kamihara, T. Watanabe, M. Hirano, H. Hosono, J. Am. Chem. Soc. 130 (11), 3296 (2008).
11. H. Wienstock, APS Division of Condensed Matter Physics Newsletter, Summer 2009, p. 5.
12. U.S. D.O.E. Office of Basic Energy Sciences, Basic Research Needs for Superconductivity: http://www.sc.doe.gov/bes/reports/list.html.