The coupling of one-carbon (C1) fragments to form carbon–carbon bonds has been studied on a Cu(110) surface. In these studies, methyl (CH3) and methylene (CH2) groups have been generated on Cu(110) by the dissociative adsorption of CH3I and CH2I2, respectively. Formation of CH3(a) below 200 K on this surface is inferred from the lack of molecular desorption as well as the lack of recombinative hydrogen desorption in temperature-programmed reaction (TPR) experiments. Similar low temperature C–I bond dissociation in CH2I2 to form CH2(a) is implicated based on the evolution of ethylene at 300 K in TPR studies. By studying the reactions of CD3(a) and CH2(a) coadsorbed and adsorbed separately on Cu(110), three C–C bond forming reactions have been identified: methyl coupling above 400 K to form ethane, methylene coupling at ∼300 K to form ethylene, and methyl/methylene coupling (methylene insertion) at 300–350 K to produce ethyl groups. To our knowledge, this is the first time that methylene insertion, a potentially important chain growth step in hydrocarbon syntheses, has been definitively established on metal surfaces.
Energy technologies affect virtually every aspect of life in modern societies—including transportation, utilities, agriculture, medicine, and the availability of a myriad of consumer products—and depend on human ability to accelerate and to guide chemical transformations. Controlling these transformations, which occur in the microscopic world of atoms and molecules, forms the basis of countless technologies such as production of fuels, fertilizers, plastics, pharmaceuticals and much more. At the very core of these chemical transformations are catalysts—specialized and often highly complex types of matter that allow chemical reactions to occur rapidly and produce specific products. Catalysts also have the remarkable ability to perform their tasks millions of times without themselves being consumed. The discovery of inexpensive and widely-deployable energy and chemical technologies, and their underpinning catalysis science, is critical to ensure the economic viability of U.S. energy and chemical industries. Over the past decade, remarkable new tools have been discovered that allow the observation of catalytic transformations in exquisite detail, and assembly of novel and elaborate catalytic architectures with atomic precision. Furthermore, increasingly sophisticated theoretical and computational tools allow understanding of the essential details of the catalytic processes, and this overall progress has led to the discovery of catalysts with superior performance and the associated economic benefit. In the next decade and beyond, science promises to revolutionize how catalysts and catalytic processes are designed, to enable the introduction of new energy resources, to provide routes to sustainable synthesis of chemicals and other valuable materials, and to create novel approaches to chemical energy storage. This report is the result of the Basic Energy Sciences Workshop on Basic Research Needs for Catalysis Science to Transform Energy Technologies that was held in May 2017, and was attended by more than 100 leading national and international scientific experts. The attendees were organized into four panels: 1. Diversified Energy Feedstocks and Carriers, 2. Novel Approaches to Energy Transformations, 3. Advanced Chemical Conversion Approaches, and 4. Crosscutting Capabilities and Challenges: Synthesis, Theory, and Characterization. The workshop identified five priority research directions (PRDs) that are aimed at harnessing complexity in catalysis to create next-generation energy technologies and realizing efficient catalytic processes to increase the diversity of resources for production of chemicals and energy.
The scientific discoveries that expand the frontiers of human understanding, and that lead to the innovations of our technological world, require scientific tools and instrumentation to enable observation and manipulation of the physical world. As science advances, so too must its tools; the quest for deeper scientific insights and the drive to control chemistry and materials at the atomic and molecular levels require increasingly powerful and sophisticated instruments. A secure energy future requires technologies that use existing resources more efficiently, harness renewable resources, and efficiently store energy. The urgent demand for new energy technologies has ushered in a new era in scientific pursuit to decipher the complexity found at the core of chemical and materials processes, as articulated by the basic energy science research community in its series of Basic Research Needs (BRN) workshops. Historically, novel experimental tools and methods have been foundational in both scientific and technological advances — ranging from high-resolution microscopes that “see” atomic structures, to lithography that has enabled advances in semiconductors and computing. Today, expanding the frontiers of basic research requires new generations of instrumentation to reveal the intricacies of complex materials and chemical systems; energy systems in realistic working environments; and systems that are dynamical, far from equilibrium, and extremely heterogeneous. A concerted effort to invent, design, and build scientific instrumentation will enable new scientific breakthroughs and transformative technologies to address the most pressing energy challenges of the 21st century. To identify the highest priorities for the instrumentation innovation and development needed to address grand challenges in energy sciences, the U.S. Department of Energy’s Office of Basic Energy Sciences sponsored a workshop entitled, “Basic Research Needs for Innovation and Discovery of Transformative Experimental Tools” on June 1–3, 2016 near Washington, D.C. The workshop was attended by approximately 100 leading national and international scientific experts representing areas of basic energy sciences in chemistry, materials, physics, and biology, and included a mix of experimentalists and theorists.
The thermal chemistry of iodomethane, iodoethane, 1-iodopropane, 1-iodobutane, and 2-iodohexane on copper (100), (110), and (111) single-crystal surfaces was characterized in this and previous studies by temperature-programmed desorption (TPD) spectroscopy. The main decomposition pathway available to the methyl surface moiety that results from C−I bond activation in adsorbed iodomethane is α-hydride elimination to methylene, a step that occurs around 460−470 K on all three surfaces. Some methylene dimerization to ethane is also seen at higher coverages, at a rate that depends significantly on surface structure; ethane desorption peaks at 400 K on Cu(110), but only above 440 K on Cu(100) and Cu(111). Ethyl groups produced by iodoethane decomposition react at much lower temperatures and mostly undergo β-hydride elimination to ethylene. The ethyl dehydrogenation reaction is structure sensitive as well, a fact illustrated by the different ethylene desorption peak maxima observed in the TPD experiments, at 225, 247, and 255 K on Cu(110), Cu(111), and Cu(100), respectively (at saturation). Perhaps the more telling observations are the difference in feasibility of H−D scrambling in the ethylene resulting from conversion of a 1:1 mixture of normal and perdeutero iodoethane, a reaction viable on Cu(100) but not on Cu(110), and the 10-fold difference in ethane yield between those two crystals. Additional studies with 1-iodopropane and 1-iodobutane provided some information on the effect of chain length on reactivity, and experiments with 2-iodohexane attested to the high selectivity for removal of internal hydrogen atoms during β-hydride elimination from alkyl species.
We have investigated the atomic structure of the twofold surface of the decagonal Al-Cu-Co quasicrystal using scanning tunneling microscopy and low-energy electron diffraction. We have found that most of the surface features can be interpreted using the bulk-structure model proposed by Deloudi and Steurer (S. Deloudi, Ph.D. thesis, ETH, Z\"urich, 2008). The surface consists of terraces separated by steps of various heights. Step heights and steps sequences match with the thickness and the stacking sequence of blocks of layers separated by gaps in the model. These blocks of layers define possible surface terminations consisting of periodic atomic rows which are aperiodically stacked. These surface terminations are dense $(\ensuremath{\sim}10\text{ }\text{at}\text{.}/{\text{nm}}^{2})$ and are of three types. The first two types are pure or almost pure Al while the third one contains $30--40\text{ }\text{at}\text{.}\text{ }%$ of transition-metal atoms. Experimentally, we observe three different types of fine structures on terraces, which can be interpreted using the three possible types of bulk terminations. Terraces containing transition metals exhibit a strong bias dependency and present a doubling of the basic 0.42 nm periodicity, in agreement with the 0.84 nm superstructure of the bulk. In addition, a high density of interlayer phason defects is observed on this surface that could contribute to the stabilization of this system through configurational entropy associated with phason disorder.
