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Title: Characterization of the metal-support interface in supported metal and supported metal complex catalysts. [Final report]

Abstract

Re and Ir carbonyls, and other compounds, were chosen as precursors. MgO, La{sub 2}O{sub 3}, zeolite NaX and KL, among others, were chosen as supports. EXAFS was used to study the metal-support interactions. Structures formed on almost fully dehydroxylated MgO by HRe(CO){sub 5}, and on MgO by Ir{sub 4}(CO){sub 12}, were studied. A metal-oxygen distance of 2.15 {angstrom} holds in for the metal-support interface in oxide-supported metal clusters following reduction in H{sub 2} above 450 C; for reduction below 350 C, the distance is 2.5--2.7 {angstrom}.

Authors:
Publication Date:
Research Org.:
Delaware Univ., Newark, DE (United States). Center for Catalytic Science and Technology
Sponsoring Org.:
USDOE, Washington, DC (United States)
OSTI Identifier:
10191456
Report Number(s):
DOE/ER/13790-5
ON: DE94001798; BR: KC0302010
DOE Contract Number:
FG02-87ER13790
Resource Type:
Technical Report
Resource Relation:
Other Information: PBD: [1992]
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; CATALYSTS; CATALYST SUPPORTS; INTERFACES; PROGRESS REPORT; RHENIUM COMPLEXES; IRIDIUM COMPLEXES; CARBONYLS; POWDERS; MAGNESIUM OXIDES; 400201; CHEMICAL AND PHYSICOCHEMICAL PROPERTIES

Citation Formats

Gates, B.C.. Characterization of the metal-support interface in supported metal and supported metal complex catalysts. [Final report]. United States: N. p., 1992. Web. doi:10.2172/10191456.
Gates, B.C.. Characterization of the metal-support interface in supported metal and supported metal complex catalysts. [Final report]. United States. doi:10.2172/10191456.
Gates, B.C.. Thu . "Characterization of the metal-support interface in supported metal and supported metal complex catalysts. [Final report]". United States. doi:10.2172/10191456. https://www.osti.gov/servlets/purl/10191456.
@article{osti_10191456,
title = {Characterization of the metal-support interface in supported metal and supported metal complex catalysts. [Final report]},
author = {Gates, B.C.},
abstractNote = {Re and Ir carbonyls, and other compounds, were chosen as precursors. MgO, La{sub 2}O{sub 3}, zeolite NaX and KL, among others, were chosen as supports. EXAFS was used to study the metal-support interactions. Structures formed on almost fully dehydroxylated MgO by HRe(CO){sub 5}, and on MgO by Ir{sub 4}(CO){sub 12}, were studied. A metal-oxygen distance of 2.15 {angstrom} holds in for the metal-support interface in oxide-supported metal clusters following reduction in H{sub 2} above 450 C; for reduction below 350 C, the distance is 2.5--2.7 {angstrom}.},
doi = {10.2172/10191456},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Thu Dec 31 00:00:00 EST 1992},
month = {Thu Dec 31 00:00:00 EST 1992}
}

Technical Report:

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  • This report discusses work on the characterization by extended x-ray absorption fine structure spectroscopy, structures formed on the surface of partially dehydroxylated magnesium oxides by adsorption of (HRe(CO){sub 5}).
  • The research is an investigation of the synthesis, structure, and bonding of a family of oxide-supported metal complexes: W, Re, Os, Ir, and Pt on /gamma/-Al/sub 2/O/sub 3/, MgO, and SiO/sub 2/. The surface species are being prepared from mononuclear organometallic precursors and characterized by TPD, IR, NMR, EXAFS, and other spectroscopies. The emphasis is on the structure of the metal-support interface. The surface-bound complexes are to be reduced gently in H/sub 2/ and the structural changes followed as ultradispersed supported metals are formed. The first results have been obtained for the precursors W(CO)/sub 6/, HRe(CO)/sub 5/, and H/sub 2/Os(CO)/submore » 4/ combined with /gamma/-Al/sub 2/O/sub 3/ and with MgO. 1 tab.« less
  • Support-metal interactions have been studied by incorporating silica, alumina, titania, and niobia into the surface of a clean Pt foil. Auger electron spectroscopy (AES) and temperature-programmed desorption (TPD) of CO and H/sub 2/ were used for surface characterization. Reaction kinetics for methanation were also measured at 400 torr H/sub 2/ and 100 torr CO. While no new desorption states of CO or H/sub 2/ were ever observed for any of the oxides, our results show that we can reproduce all of the unusual support effects normally observed on titania-supported Pt. We have found that a suboxide of titania can dissolvemore » into bulk Pt at high temperatures but segregate back to the surface at room temperature. Titania tends to form a thin oxide layer which can prevent the adsorption of CO and H/sub 2/ but actually enhances methanation on Pt. X-ray photoelectron results indicate that this titania is TiO and appears to be chemically bound to Pt. Results for niobia show that it is almost identical to titania in its effect on Pt. For silica and alumina, however, much larger quantities of oxide were necessary to prevent the adsorption of CO and H/sub 2/. This indicates that these oxides form clusters or are subsurface on Pt. There is no evidence that they interact chemically with Pt. To compare the effect of supports on different metals, we investigated titania deposition on Rh. Although there are significant differences between Pt and Rh, we observed many similarities in the character of titania on these two metals, indicating that similar phenomena are responsible for support effects in both metals. 52 refs., 21 figs.« less
  • The principal objectives of our research were: ''to gain a better understanding of the chemistry and physics which produce these metal-support effects and, as a consequence, to use this information to quide us in the development of new and improved catalyst systems for particular reactions.'' We chose to do this by investigating Pt and Pd dispersed on selected supports using a multifaceted approach involving DSC, TGA, NMR, adsorption, and kinetic studies of selected probe reactions. This approach has led us to the preparation of: 1) the most active Pd catalysts to date for benzene hydrogenation; 2) the most active Ptmore » catalysts to date (by more than an order of magnitude) for acetone hydrogenation to isopropanol; and 3) the only Pt catalysts capable of significant selectivity to crotyl alcohol during crotonaldehyde hydrogenation. Calorimetric studies using DSC have shown that the principal reason for decreased chemisorption capacity on TiO/sub 2/-supported Pt and Pd is the physical blockage of metal surface by TiO/sub x/ species rather than by a large decrease in the heats of adsorption, Q/sub ad/. Also, with Pd a large crystallite size effect was found which increased Q/sub ad/ values on particles smaller than 3 nm. Each of these aspects will be addressed. 15 refs., 4 figs.« less
  • Objectives of our current grant were: ''to gain a better understanding of the chemistry and physics which produce these metal-support effects and, as a consequence, to use this information to guide us in the development of new and improved catalyst systems for particular reactions.'' We investigated Pt and Pd dispersed on selected supports using a multifaceted approach involving DSC, TGA, NMR, adsorption, and kinetic studies of selected probe selected probe reactions. This approach has led us to the preparation of: (1) the most active Pd catalysts to date for benzene hydrogenation; (2) the most active Pt catalysts to date (bymore » more than an order of magnitude) for acetone hydrogenation to isopropanol; and (3) the only Pt catalysts capable of significant selectivity to crotyl alcohol during crotonaldehyde hydrogenation. Calorimetric studies using DSC have shown that the principal reason for decreased chemisorption capacity on TiO/sub 2/-supported Pt and Pd is the physical blockage of metal surface by TiO/sub x/ species rather than by a large decrease in the heats of adsorption, Q/sub ad/. Also, with Pd a large crystallite size effect was found which increased Q/sub ad/ values on particles smaller than 3 nm. 4 figs.« less