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Title: From First Principles Design to Realization of Bimetallic Catalysts for Ultrahigh Selectivity - Final Project Report

Abstract

(A) Synthesis, Characterization, and Fundamental Properties of Bimetallic DENs. AuAg alloy and core/shell bimetallic DENs were synthesized and characterized. Selective extraction was used as a structural characterization tool for these bimetallic nanoparticles. This is significant because there are few easily accessible methods for structure elucidation of bimetallic nanoparticles in this size regime. As a first step towards the synthesis of catalytically active, bimetallic heterogeneous materials we reported the incorporation of Au and Pd monometallic DENs and AuPd bimetallic DENs into amorphous titania networks. The compositional fidelity of the original DENs, and to some extent their size, is retained following dendrimer removal. Gas-phase catalytic activity for CO oxidation is higher for the bimetallic catalysts than for the corresponding Pd-only and Au-only monometallics. (B) Electrocatalysts based on dendrimer-encapsulated nanoparticles. Platinum dendrimer-encapsulated nanoparticles (DENs) were prepared within fourth-generation, hydroxyl-terminated, poly(amidoamine) dendrimers and immobilized on glassy carbon electrodes using an electrochemical immobilization strategy. X-ray photoelectron spectroscopy, electron microscopy, and electrochemical experiments confirm that the Pt DENs are about 1.4 nm in diameter and that they remain within the dendrimer following surface immobilization. The resulting Pt DEN films were electrocatalytically active for the oxygen reduction reaction (ORR). The films are also robust, surviving up tomore » 50 consecutive cyclic voltammograms and sonication. Monometallic Pd DENs were also prepared and found to have little catalytic activity for the ORR. However, PtPd bimetallic DENs had catalytic activity nearly identical to that found for Pt-only DENs. This indicates an overall catalytic enhancement for the bimetallic electrocatalysts.« less

Authors:
Publication Date:
Research Org.:
University of Texas at Austin, Austin, TX
Sponsoring Org.:
USDOE Office of Science (SC)
OSTI Identifier:
901980
Report Number(s):
DOE/ER/15683
TRN: US200722%%98
DOE Contract Number:
FG02-05ER15683
Resource Type:
Technical Report
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; ALLOYS; CARBON; CATALYSTS; DESIGN; ELECTROCATALYSTS; ELECTRODES; ELECTRON MICROSCOPY; OXIDATION; OXYGEN; PLATINUM; REMOVAL; SYNTHESIS; X-RAY PHOTOELECTRON SPECTROSCOPY; dendrimer encapsulated bimetallic catalysts

Citation Formats

Richard M. Crooks. From First Principles Design to Realization of Bimetallic Catalysts for Ultrahigh Selectivity - Final Project Report. United States: N. p., 2007. Web. doi:10.2172/901980.
Richard M. Crooks. From First Principles Design to Realization of Bimetallic Catalysts for Ultrahigh Selectivity - Final Project Report. United States. doi:10.2172/901980.
Richard M. Crooks. Wed . "From First Principles Design to Realization of Bimetallic Catalysts for Ultrahigh Selectivity - Final Project Report". United States. doi:10.2172/901980. https://www.osti.gov/servlets/purl/901980.
@article{osti_901980,
title = {From First Principles Design to Realization of Bimetallic Catalysts for Ultrahigh Selectivity - Final Project Report},
author = {Richard M. Crooks},
abstractNote = {(A) Synthesis, Characterization, and Fundamental Properties of Bimetallic DENs. AuAg alloy and core/shell bimetallic DENs were synthesized and characterized. Selective extraction was used as a structural characterization tool for these bimetallic nanoparticles. This is significant because there are few easily accessible methods for structure elucidation of bimetallic nanoparticles in this size regime. As a first step towards the synthesis of catalytically active, bimetallic heterogeneous materials we reported the incorporation of Au and Pd monometallic DENs and AuPd bimetallic DENs into amorphous titania networks. The compositional fidelity of the original DENs, and to some extent their size, is retained following dendrimer removal. Gas-phase catalytic activity for CO oxidation is higher for the bimetallic catalysts than for the corresponding Pd-only and Au-only monometallics. (B) Electrocatalysts based on dendrimer-encapsulated nanoparticles. Platinum dendrimer-encapsulated nanoparticles (DENs) were prepared within fourth-generation, hydroxyl-terminated, poly(amidoamine) dendrimers and immobilized on glassy carbon electrodes using an electrochemical immobilization strategy. X-ray photoelectron spectroscopy, electron microscopy, and electrochemical experiments confirm that the Pt DENs are about 1.4 nm in diameter and that they remain within the dendrimer following surface immobilization. The resulting Pt DEN films were electrocatalytically active for the oxygen reduction reaction (ORR). The films are also robust, surviving up to 50 consecutive cyclic voltammograms and sonication. Monometallic Pd DENs were also prepared and found to have little catalytic activity for the ORR. However, PtPd bimetallic DENs had catalytic activity nearly identical to that found for Pt-only DENs. This indicates an overall catalytic enhancement for the bimetallic electrocatalysts.},
doi = {10.2172/901980},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Wed Apr 11 00:00:00 EDT 2007},
month = {Wed Apr 11 00:00:00 EDT 2007}
}

Technical Report:

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  • In this project, we have integrated state-of-the-art Density Functional Theory (DFT) models of heterogeneous catalytic processes with high-throughput screening of bimetallic catalytic candidates for important industrial problems. We have studied a new class of alloys characterized by a surface composition different from the bulk composition, and investigated their stability and activity for the water-gas shift reaction and the oxygen reduction reaction. The former reaction is an essential part of hydrogen production; the latter is the rate-limiting step in low temperature H2 fuel cells. We have identified alloys that have remarkable stability and activity, while having a much lower material costmore » for both of these reactions. Using this knowledge of bimetallic interactions, we have also made progress in the industrially relevant areas of carbohydrate reforming and conversion of biomass to liquid alkanes. One aspect of this work is the conversion of glycerol (a byproduct of biodiesel production) to synthesis gas. We have developed a bifunctional supported Pt catalyst that can cleave the carbon-carbon bond while also performing the water-gas shift reaction, which allows us to better control the H2:CO ratio. Knowledge gained from the theoretical metal-metal interactions was used to develop bimetallic catalysts that perform this reaction at low temperature, allowing for an efficient coupling of this endothermic reaction with other reactions, such as Fischer-Tropsch or methanol synthesis. In our work on liquid alkane production from biomass, we have studied deactivation and selectivity in these areas as a function of metal-support interactions and reaction conditions, with an emphasis on the bifunctionality of the catalysts studied. We have identified a stable, active catalyst for this process, where the selectivity and yield can be controlled by the reaction conditions. While complete rational design of catalysts is still elusive, this work demonstrates the power of combining the insights gained from theoretical models and the work of experiments to develop new catalysts for current and future industrial challenges.« less
  • “Catalysis by design” has been a dream for decades. To specify the composition and structure of matter to effect a desired catalytic transformation with desired and predicted rate and selectivity remains a monumental challenge, especially in heterogeneous catalysis. Our research thrusts have been chosen not only for their practical and scientific relevance, e.g. for more efficient and sustainable chemicals and fuels production, but also because they provide a foundation for developing and exploring broadly applicable principles and strategies for catalyst design.
  • The nature of metal-oxide interaction as exemplified by Rh/TiO/sub 2/ and characterized by entended X-ray absorption fine structure (EXAFS) and X-ray absorption near edge structure (XANES) analyses is reviewed. The catalytic consequences of this interaction between a group VIII metal and a reducible support are reviewed by reference to the differences between different group VIII metals (Rh and Pt) supported on TiO/sub 2/ and the same metal (Rh) supported on different reducible supports (TiO/sub 2/ and V/sub 2/O/sub 3/). The effect of different silica supports on the metal-metal interaction (Ru-Cu cluster morphology) and on chemisorption and catalytic activity is brieflymore » outlined. Oxide-oxide interaction (MoO/sub 3/ and SiO/sub 2/ interaction with Al/sub 2/O/sub 3/ support) investigated by NMR is also addressed. 67 refs., 2 figs.« less
  • Bimetallic surfaces with tunable chemical properties have attracted broad attention in recent years due to their ample potential for heterogeneous catalysis applications. The local chemical properties of constituents are strongly altered from their parent metals by 'ligand effect', a term encompassing the influences of charge transfer, orbital rehybridization and lattice strain. In comparison to the aforementioned, the 'ensemble effect' associated with particular arrangements of the active constituents have received much less attention, despite their notable importance towards the determination of reactivity and selectivity of bimetallic catalysts. We performed theoretical studies for understanding the ensemble effects on bimetallic catalysis: (i) simulationsmore » for the formation of different ensembles on PdAu and PtAu nanoclusters; (ii) studies of the size, shape, and substrate dependence of their electronic properties; and (iii) simulations for model reactions such as CO oxidation, methanol, ethylene and water dehydrogenation on PdAu and PtAu nanoclusters. In close collaboration with leading experimental groups, our theoretical research elucidated the fundamentals of Au based bimetallic nanocatalysts.« less
  • Progress on supported bimetallic catalysts and the development of techniques for the characterization of supported catalysts is reported. Three bimetallic systems were studied: Rh-Pt, Ru-Cu and Rh-Ag. Goal has been the determination of the effect of the support on the kind and degree of metal-metal interaction. Small particles of Rh-Pt are found to be enriched in Rh on all supports, the degree of enrichment increasing in the order SiO/sub 2/