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Controlled Active Metals

Problem

Many heterogeneous catalysts are inappropriate for conversion of biomass and hydrogen (H2) production in aqueous media, and the structural features of catalysts that facilitate desired reactions are still unclear. Researchers have not yet established a biomass catalyst screening reaction that facilitates catalyst testing.

Approach

In order to develop a roadmap for reaction mechanisms, researchers require a basic understanding of the factors that govern both reaction yield and selectivity on metal surfaces for key reactions of biomass-derived compounds. This understanding will enable them to develop catalysts that are highly selective, stable, and efficient.

Achieving catalyst activity and stability under aqueous reforming conditions is a significant challenge requiring expertise in the synthesis of advanced materials, catalytic performance and mechanistic studies, characterization of materials designed to understand their strengths and limitations, and computational prediction of improved catalytic systems and routes.

Using a wide range of tools and techniques, such as small-angle X-ray scattering (SAXS)/X-ray absorption spectroscopy (XAS), operando XAS, X-ray absorption fine structure (EXAFS)/X-ray absorption near-edge structure (XANES) measurement, and in-situ X-ray photoelectron spectroscopy (XPS), IACT researchers are investigating the chemical state of adsorbed atomic layer deposition precursors and the changes in oxidation state of the metal catalysts being evaluated. When used in tandem with a variety of approaches to model the observed thermochemistry, reaction pathways, catalyst structure, and performance, these tools are helping researchers identify potential catalysts with improved performance.

Graphic showing trends in thermochemistry for formic acid (HCOOH)

Trends in thermochemistry for formic acid (HCOOH) decomposition show which metals hold the most promise as catalytic surfaces.

Goals

IACT's overarching goals for the Controlled Active Metals effort are to:

  • Elucidate the reaction mechanisms for H2 production;
  • Control the selectivity for carbon-carbon (C-C), carbon-oxygen (C-O), and carbon-hydrogen (C-H) bond cleavage and formation to produce H2;
  • Understand the catalyst structure and reactivity under aqueous conditions; and
  • Develop advanced experimental and computational tools for investigating catalyst structure, reactive intermediates, and reaction dynamics in aqueous media.

Results

To date, the IACT Controlled Active Metals team has:

  1. Predicted that platinum (Pt), palladium (Pd) and copper (Cu) are promising catalytic surfaces;
  2. Determined that Pt/Mo is less prone to carbon monoxide (CO) poisoning, a common problem in catalysis;
  3. Achieved high selectivity to H2 using a platinum-cobalt/carbon (PtCo/C) catalyst; and
  4. Discovered a water-gas shift (WGS) reaction that correlates with a biomass reforming reaction.

Future Directions

Going forward, the IACT Controlled Active Metals team will extend earlier studies to the structural, energetic, electronic, and chemical reactivity properties of Pt, molybdenum (Mo), and Pt/Mo nanocatalysts on supports such as amorphous carbon and various oxides, to elucidate and characterize the effects of the supports on the catalytic functionality of the particles. They will model the structure and chemistry of bimetallic nanoparticles supported on zirconia, carbon nanotubes, and other materials. Other efforts will focus on extending IACT's studies of hydrogen production from glycerol and ethylene glycol to alcohols and higher polyols, and explore the feasibility of performing such studies for glucose and related ring compounds. By identifying bimetallic catalysts with superior performance for formic acid (HCOOH) decomposition, the researchers expect to identify bimetallic alloys with superior performance for HCOOH decomposition. They can then theoretically synthesize the most-promising alloys using atomic layer deposition.

 

November 2012


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