Research Program

The Catalysis Group has research efforts in the areas of:

  1. The development of instrumentation for the in-situ characterization of catalysts, with an emphasis on synchrotron based techniques.
  2. The role of mixed-metal oxides, metal/metal-oxide and metal/carbide interfaces in catalysis.
  3. The water gas shift reaction (WGS).
  4. Hydrodesulfurization (HDS).
  5. The synthesis and transformation of alcohols.

 A brief description of these efforts is summarized below.

Development of Techniques for In-situ Characterization of Powder Catalysts:

Time-resolved PDF, XAFS/XRD, XAFS/IR and XAFS/Raman (Hanson, Rodriguez, Senanayake, Stacchiola)

The development of techniques for characterizing the structural properties of catalysts under the high-pressure conditions of industrial processes is widely recognized as a top priority in the area of heterogeneous catalysis. In the last two years, the Catalysis Group at BNL has been very active in developing instrumentation for the characterization of catalysts with pair-distribution function (PDF) analysis and the integration of XAFS and XRD or XAFS and IR or Raman. The integration of IR and Raman with XAFS (Figure below)

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Schematic of the set-up for combined, operando XAFS/Raman experiments

allows a simultaneous determination of the reaction intermediates on the surface and the chemical state and structure of the catalyst. Raman spectroscopy adds sensitivity to crystallographic phase and long range order that both XANES and EXAFS are lacking. In-situ PDF has been used to study the structure of amorphous metal and metal oxide nanoparticles. Using a XAFS/IR combination, we have investigated reaction mechanisms and correlations between structure/reactivity for CO oxidation and ethanol steam reforming on Cu-ceria and Ni-ceria catalysts, and a combination of XAFS/Raman was used to study the oxidation of CO on a Cu/TiO+ catalysts. The NSLS-II is expected to come into operations in the second half of 2014. The Catalysis Group has been strongly involved in the design and planning of four new beamlines for XRD/(IR or Raman), PDF/(IR or Raman), XAFS/(IR or Raman),  ambient-pressure NEXAFS, and ambient-pressure XPS. These beamlines are expected to start operations in 2014 or 2015 giving the Catalysis Group a unique set of tools to study in-situ the structure of catalyst and reaction mechanisms.

 

Well-defined Surfaces of Mixed-Metal Oxides

(Liu, Rodriguez, Senanayake, Stacchiola)

Our group has synthesized atomically resolved mixed-metal oxides of the CeO2/CuOx , RuO2/TiO2 and others. Their catalytic properties have been tested  studying the oxidation of CO.  A Cu(111) surface displays a low activity for the oxidation of carbon monoxide (2CO + O2  2CO2).  Our results showed that the presence of ceria nanoparticles on Cu(111) improved considerably the activity with respect to the Cu(111) substrate alone (Figure below). 

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Arrhenius plots for CO oxidation on Cu(111), and CeO2-x/Cu(111) at CO (20Torr) + O2 (10Torr).

DFT calculations for these systems corroborated the importance of the role of the ceria nanoparticles. They identified that ceria nanoparticles in the oxide/metal configuration had special electronic properties clearly evident in the DOS of the system. In the case of RuOx/TiO2(110), STM showed the generation of nano-wires of RuOx on top of the titania substrate. The nanowires were very reactive toward CO being reduced to metallic Ru in their presence.

 

Activation of Noble Metals on Metal-Carbide Surfaces: Novel Catalysts for Desulfurization, CO Oxidation and Hydrogenation Reactions (Rodriguez, Liu)

In the continuous search for new catalysts, one may wonder whether metals deposited on supports other than metal oxides may provide alternative catalysts with increased activity or selectivity. Transition-metal carbides exhibit broad and amazing physical and chemical properties. High-resolution photoemission, scanning tunneling microscopy (STM) and first-principles periodic density-functional (DF) calculations have been used to study the interaction of metals of Groups 9, 10 and 11 with MC(001) (M= Ti, Zr, V, Mo) surfaces. DF calculations give adsorption energies that range from 2 eV (Cu, Ag, Au) to 6 eV (Co, Rh, Ir). STM images show that Au, Cu, Ni and Pt grow on the carbide substrates forming two-dimensional islands at very low coverage, and three-dimensional islands at medium and large coverage.


Left: Amount of S deposited on Au/MgO(100), Au/TiO2(110) and Au/TiC(001) after exposure to a fixed dose of SO2 at 300 K. Right: Calculated adsorption energies and geometries for SO2 on TiC(001) and different Au/TiC(001) systems.

In many systems, the results of DF calculations point to the preferential formation of admetal-C bonds with significant electronic perturbations in the admetal,r enhancing the chemical reactivity of the catalyst.

 

Synthesis and Reforming of Alcohols

A.   Methanol synthesis from CO2 Hydrogenation on Au/TiC(001) and Cu/TiC(001) (Liu, Rodriguez)

Among all greenhouse gases in the atmosphere, carbon dioxide plays a special role due to the magnitude of the emissions generated by human activities involving the combustion of carbonaceous fuels, principally wood, coal, oil and natural gas. The recovery of CO2 for its hydrogenation to alcohols or other hydrocarbon compounds is an important approach to recycle the released carbon dioxide.  This is a difficult task in C1 chemistry due to the challenges associated with the chemical activation of CO2. Can metals deposited on carbide supports be active enough for methanol synthesis?  Our studies indicate that small Cu and Au particles in contact with a TiC(001) surface undergo a charge polarization which makes them very active for CO2 activation and the catalytic synthesis of methanol.

 

http://dev.bnl.gov/chemistry/CRS/images/clip_image002.png
Arrhenius plot for methanol synthesis on Cu(111), ZnO(000ī) pre-covered with 0.2 ML of Cu, TiC(001) clean and pre-covered with 0.1 ML of Au or Cu. In a batch reactor, the catalysts were exposed to 0.049 MPa (0.5 atm) of CO2 and 0.441 MPa (4.5 atm) of H2. The reported values are for steady state rates measured at temperatures of 600, 575, 550, 525 and 500 K

 

B. Studies on Ethanol Steam Reforming on a Ni/CeO2 Catalyst (Liu, Rodriguez, Senanayake, Stacchiola)

In recent years, ethanol has received significant attention as a source of energy because it can be easily obtained from renewable energy sources.  One objective is the production of hydrogen from steam reforming (C2H5OH + 3H2O 2CO2 + 6H2). A major issue is the identification of non-expensive catalysts which can accomplish the cleavage of the C-C bond without subsequent deactivation by coke deposition. Our studies have shown that the NiO/CeO2 can accomplish this.  The steam reforming of ethanol on a Ni-based CeO2-supported catalyst, was studied using in-situ X-ray XRD, operando DRIFTS, and mass spectroscopy with a focus on the structural characterization of the catalysts, chemical identification of the reaction pathway, and understanding of the interaction between Ni and CeO2.

Fig1-XRD
In situ XRD data of Ni/CeO2 being reduced in pure EtOH vapor. Peaks from the CeO2 support, the NiO, the fcc-Ni, and the hexagonal intermediate phase (hex) are marked.

We observed that the Ni electronic structure is modified by its interaction with the ceria support, modifying its catalytic properties. In the future, we plan to use this phenomenon defined as Electronic Metal-Support Interactions (EMSI) to tune the activity of metal/oxide catalysts.

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Last Modified: October 25, 2013
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