Sessions Descriptions

Workshop on Neutron Scattering Techniques for Studies in Catalysis

Meeting Grand Challenges in Catalysis through Neutron Scattering Techniques
Moderators: Phil Britt and Ken Herwig; ORNL
Speakers: Bruce Gates, University of California, Davis
    Juergen Eckert, LANL and UC Santa Barbara

This session will discuss Grand challenges in catalysis as outlined in the BES Workshop report on BRN in Catalysis for Energy. The session would consist of two talks each of about 30 minutes. The goal of one lecture is to present selected grand challenge areas in catalysis and provide examples of current research approaches to meeting these challenges. Emphasis may be placed on those areas where the use of neutron based techniques might be expected to contribute to meeting the challenges. The goal of the second talk will be to discuss the current status and future directions of neutron scattering methods primarily with respect to their application for probing chemical catalysis and related materials problems and challenges in creating new environments for performing neutron methods on catalysts under reaction conditions.

Structural Characterization of Catalysts and Catalytic Materials
Moderators: Viviane Schwartz, ORNL
Takeshi Egami, University of Tennessee and ORNL
Speakers: J van Bokhoeven, ETH Zurich
    Thomas Proffen, Los Alamos National Laboratory

This session will focus on the use of neutron techniques to perform static or time dependent studies of structure of catalysts and catalytic materials and the opportunities for performing such measurements under in situ and operando conditions. Two lectures each of about 30 minutes will be followed by open discussion and questions. Of special interest is the possibility of probing novel materials and soft (low Z) materials that may be difficult to probe using x-rays or other techniques and where neutron methods may provide new or complementary information. Lectures and discussion may address may include studies 1) of catalytic materials (such as supported metals, oxides, nitrides, sulfides, phosphides, carbon and carbon derivatives (graphene, graphane, graphite oxide, CN, microporous and mesoporous materials) under catalytic or electrocatalytic reaction conditions; 2) of inorganic precursors materials (such as nitrates, phosphates, carbonates) under treatment or synthesis conditions; and 3) of surface species, especially molecular adsorbates, reactants, and products, under adsorption, electrocatalytic or reaction conditions. Elements of catalyst structure may include crystallographic phases, composition, morphology, disordered materials, clusters, functional groups, active sites, bulk structural transformations and defects on surfaces or bulk of catalysts. An important aspect is the ability to discover or monitor structural changes that occur as reaction conditions change or as a function of deactivation. Neutron scattering methods that may be discussed include nPDF, SANS, neutron powder diffraction and WANS and may be compared with x-ray based methods including xPDF, SAXS, XRD and EXAFS.

Probing Dynamics of Molecules in Catalysts Systems by Inelastic Neutron Scattering
Moderators: Dave Wesolowski and Steve Overbury; Oak Ridge National Laboratory
Speakers: Peter Stair, Northwestern University
    Eugene Mamontov, Oak Ridge National Lab
    Peter Albers, AQura

This session will focus on how inelastic neutron scattering, both coherent and incoherent, can be used to probe various dynamic processes involving molecules in catalyst systems. It will include four speakers followed by the moderated questions/answer and discussion. Speakers will provide examples from their own research or examples from the literature where dynamical information in catalyst systems was obtained or necessary for answering an important catalytic question. Speakers with specific neutron experience will discuss the capabilities of neutron inelastic scattering techniques and their demonstration in catalysis-related applications. Neutron scattering techniques will include inelastic neutron spectroscopy (INS), quasi-elastic neutron scattering (QENS) and neutron echo spectroscopy (NES). Subsequent questions and discussion will clarify and expand upon the presentations and bring out other attendee interests and challenges in understanding dynamics in catalytic systems.

Because the neutron scattering cross-section does not scale with the atomic number, it is often possible to probe the dynamics adsorbent molecules (e.g., water or hydrocarbons) in much heavier matrices (e.g., metals, oxides, or porous media), which would be impossible with x-rays. In particular, the incoherent neutron scattering cross-section of hydrogen is especially high compared to all other elements. This allows exploration of diffusion dynamics and transport properties of H-bearing species associated with both homogeneous and heterogeneous catalytic processes over wide ranges of time (subpicosecond to nanoseconds) and length (angstroms to tens of nanometers. Because the incoherent scattering cross-section of deuterium is much lower compared to that of hydrogen, selective deuteration can be used to isolate specific reactant and product species and even the dynamic properties of portions of more complex molecules Important application areas that could be discussed include: 1) probing proton and dihydrogen in the mixed phase environment of a fuel cell; 2) hydrogenation and dehydrogenation reactions at solid catalyst surfaces; 3) H2 sorption and bonding in materials for hydrogen storage and energy conversion; 4.) the dynamic properties of tethered and/or fluid-phase proton-donors involved in proton-coupled electron transfer reactions in photocatalyitic and electrocatalytic processes; 5.) tracking the in situ reactant/intermediate/product relationships in catalytic reactions. The high intensity neutron beam generated at the Spallation Neutron Source, and the unique BASIS, CNCS, NSE, ARCS, SEQUOIA, and VISION spectrometers, combined with the high penetration power of neutrons have made it possible to follow molecular dynamics, and explore in situ catalytic reaction under operando conditions.

Probing Biocatalysis by Neutron Scattering Methods
Moderator: Dean Myles, Oak Ridge National Laboratory
Speakers: speakers Robert Blankenship, Washington University of St. Louis
    Paul Langen, Los Alamos National Laboratory

This session will focus on current understanding of bio-catalysis, and highlight the future needs, challenges and opportunities for the development of efficient bio-inspired or biomimetic catalysts that use renewable feed stocks instead of fossil fuels.

Understanding how nature harvests energy from sunlight, converts and stores electrical and chemical energy, and uses this energy to power life offers great opportunities to engineer new functional materials and devices for capture and conversion of light, to improve efficiencies in conversion of biomass to biofuels, and to harness molecular designs in nano-machines. Many of these energy transduction processes are catalyzed by metalloproteins, which use simple metal ion-cofactors in complex organic frameworks to perform chemical reactions, providing exquisite substrate selectivity, region-selectivity, chemo-selectivity, enantio-selectivity and catalysis at ambient temperatures and pressures. Greater understanding of the physiochemical mechanisms involved in these transduction processes and of the protein structure-dynamics-function relationships that enable them could help guide the design of efficient bio-inspired catalysts, novel energy materials and aid in the design of new diagnostics and therapeutics of disease.

Many catalytic reactions depend on the transfer of protons, and a complete understanding of the catalytic power of an enzyme requires knowledge of the proton release and affinity capabilities of residues throughout the reaction pathway. Neutron diffraction is uniquely sensitive to hydrogen atoms and can aid in this process by providing more accurate and complete protein structures that show the positions and interactions of critical catalytic hydrogen atoms at the active site of enzymes. Once accurate hydrogen atom positions are determined from the neutron crystal structures, the entire reaction profile of an enzyme can be calculated by combining quantum mechanical and molecular mechanics methods. Such studies will provide more complete and detailed mechanistic understanding of electron and proton transport in enzymes, and aid in the design and synthesis of novel, bio-inspired catalysts for energy.

Modeling Neutron Scattering Data from Catalytic Systems
Moderators: Peter Cummings, Vanderbilt University and Oak Ridge National Lab
Speakers: David Sholl, Georgia Tech
    TBD

A major goal of this session is to discuss methods for modeling neutron experiments and for modeling the types of phenomena that can be obtained from neutron experiments. Modeling of neutron experiments could include how to interpret and extract quantitative information from QENS, INS and SANS. The reverse process of predicting quasi-eleastic and inelastic scattering response from first principles computations on catalytic systems, is also of interest. Speakers will ideally present examples and methodologies for modeling catalytic systems and tie these simulations to information obtainable from experiment. Phenomena and methodologies could include the use molecular dynamics methods to probe molecular motions, vibrations and reaction on catalyst surfaces with. One goal is to help catalyst practitioners understand the types of problems that can be addressed by neutron methods.