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Title: Zeolite-supported bimetallic catalyst: controlling selectivity of rhodium complexes by nearby iridium complexes

Authors:
; ; ; ;  [1];  [2]
  1. (UCD)
  2. (
Publication Date:
Research Org.:
Argonne National Lab. (ANL), Argonne, IL (United States). Advanced Photon Source (APS)
Sponsoring Org.:
UNIVERSITYDOE - BASIC ENERGY SCIENCES
OSTI Identifier:
1123963
Resource Type:
Journal Article
Resource Relation:
Journal Name: Catal. Sci. Technol.; Journal Volume: 3; Journal Issue: (8) ; 2013
Country of Publication:
United States
Language:
ENGLISH

Citation Formats

Lu, Jing, Martinez-Macias, Claudia, Aydin, Ceren, Browning, Nigel D., Gates, Bruce C., and PNNL). Zeolite-supported bimetallic catalyst: controlling selectivity of rhodium complexes by nearby iridium complexes. United States: N. p., 2014. Web. doi:10.1039/C3CY00113J.
Lu, Jing, Martinez-Macias, Claudia, Aydin, Ceren, Browning, Nigel D., Gates, Bruce C., & PNNL). Zeolite-supported bimetallic catalyst: controlling selectivity of rhodium complexes by nearby iridium complexes. United States. doi:10.1039/C3CY00113J.
Lu, Jing, Martinez-Macias, Claudia, Aydin, Ceren, Browning, Nigel D., Gates, Bruce C., and PNNL). Mon . "Zeolite-supported bimetallic catalyst: controlling selectivity of rhodium complexes by nearby iridium complexes". United States. doi:10.1039/C3CY00113J.
@article{osti_1123963,
title = {Zeolite-supported bimetallic catalyst: controlling selectivity of rhodium complexes by nearby iridium complexes},
author = {Lu, Jing and Martinez-Macias, Claudia and Aydin, Ceren and Browning, Nigel D. and Gates, Bruce C. and PNNL)},
abstractNote = {},
doi = {10.1039/C3CY00113J},
journal = {Catal. Sci. Technol.},
number = (8) ; 2013,
volume = 3,
place = {United States},
year = {Mon Jul 21 00:00:00 EDT 2014},
month = {Mon Jul 21 00:00:00 EDT 2014}
}
  • Special information on bimetallic complexes of rhodium(I), iridium(I), platinum(II), and gold(I) is reported. We report spectra, polarization characteristics of the principal bands splittings of the triplet manifolds, and the response of the phosphorescence lifetimes to an external magnetic field. Our intent is to arrive at descriptions of the low-lying excited states that not only harmonize all the facts but also expose the reasons for the remarkable spectral similarities among species containing different metals and possessing diverse geometries. 26 refs., 6 figs., 5 tabs.
  • Clusters of rhodium and of iridium were synthesized in the cages of the sodium form of the faujasite zeolite Y by decarbonylation of zeolite-supported [Rh{sub 6}(CO){sub 16}] or [Ir{sub 4}(CO){sub 12}] in H{sub 2} at 200 or 300 C, respectively. Larger clusters (aggregates) of rhodium or iridium consisting of 10 to 20 atoms each on average were formed by treatment of zeolite-supported [Rh{sub 6}(CO){sub 16}] or [Ir{sub 6}(CO){sub 16}] in H{sub 2} at 250 or 300 C. The samples were characterized by extended X-ray absorption fine structure (EXAFS) spectroscopy under vacuum and in (a) H{sub 2}, (b) propene, and (c)more » H{sub 2}/propene mixtures (with catalytic hydrogenation taking place). The EXAFS data indicate that the clusters or aggregates were intact, with the metal frames changed undetectably in the presence of any of the gases, even during catalysis and at temperatures up to 140 C. In the presence of propene only, rhodium clusters showed changes in their X-ray absorption near-edge spectra, but the iridium clusters did not. When propene was present with H{sub 2} during catalysis, the near-edge spectra were essentially the same as those characterizing the metal clusters (or aggregates) in H{sub 2} only. The data are consistent with the inference that the metal clusters, approximated as predominantly Ir{sub 4} or Rh{sub 6} (the latter not fully decarbonylated) are catalytically active themselves, as are larger aggregates of those metals.« less
  • The reaction of the triniobium-substituted polyoxometalate [(n-C{sub 4}H{sub 9}){sub 4}N]{sub 9}P{sub 2}W{sub 15}Nb{sub 3}O{sub 62} with an equimolar amount of [Ir(1,5-COD)(CH{sub 3}CN){sub 2}]BF{sub 4} or [Rh(1,5-COD)(CH{sub 3}CN){sub 2}]BF{sub 4} (1,5-COD = 1,5-cyclooctadiene) leads to the formation of the air-sensitive polyoxometalate-supported organometallic complexes [(1,5-COD)Ir{center_dot}Pr{sub 2}W{sub 15}Nb{sub 3}O{sub 62}]{sup 8{minus}}, 1, and [(1,5-COD)Rh{center_dot}P{sub 2}W{sub 15}Nb{sub 3}O{sub 62}]{sup 8{minus}}, 2. These complexes were isolated as their mixed 5[(n-C{sub 4}H{sub 9}){sub 4}N]{sup +}/3Na{sup +} salts and have been characterized by {sup 1}H, {sup 13}C, {sup 31}P, and {sup 183}W NMR spectroscopy as well as IR spectroscopy, sedimentation-equilibrium molecular-weight measurements, and complete elemental analyses. Additionalmore » studies of 1 by {sup 17}O NMR demonstrate that the iridium binds in overall average C{sub 3v}(pseudo) symmetry to the {open_quotes}Nb{sub 3}O{sub 9}{sup 3{minus}}{close_quotes} minisurface (pseudo due to the 2-fold axis in 1,5-COD and thus the local C{sub s} symmetry at iridium). For 2, the results of the {sup 17}O NMR studies are definitive in showing that 2 can also be successfully {sup 17}O-enriched in the niobium-oxygen sites. However, the {sup 17}O NMR data subsequently acquired for 2 require the formulation of two or more (possibly rapidly interconverting) support-site isomers in solution. These {sup 17}O NMR results provide direct evidence for the M-ONb{sub 2} bonding between [(1,5-COD)M]{sup +} (M = Ir, Rh) and P{sub 2}W{sub 15}Nb{sub 3}O{sub 62}{sup 9{minus}} in solution, where catalysis beginning with 1 and 2 as a precatalyst has been demonstrated.« less
  • Mechanisms of partial oxidation of methane were studied using a pulsed reaction technique and temperature jump measurement. Catalyst bed temperatures were directly measured by introducing a pulse of a mixture of methane and oxygen (2/1). With Ir/TiO{sub 2} catalyst, a sudden temperature increase at the front edge of the catalyst bed was observed upon introduction of the pulse, but the temperature of the rear end of the catalyst bed increased only slightly. The synthesis gas production basically proceeded via a two-step path consisting of highly exothermic methane complete oxidation to give H{sub 2}O and CO{sub 2}, followed by the endothermicmore » reforming of methane with H{sub 2}O and CO{sub 2} over Ir/TiO{sub 2} catalyst. However, with Rh/TiO{sub 2} and Rh/Al{sub 2}O{sub 3} catalysts, the temperature at the front edge of the catalyst bed decreased upon introduction of the CH{sub 4}/O{sub 2} (2/1) pulse, and a small increase in the temperature at the rear end was observed. At first, endothermic decomposition of CH{sub 4} to H{sub 2} and deposited carbon or CH{sub x} probably took place at the front edge of the catalyst bed and then deposited carbon or generated CH{sub x} species would be oxidized into CO{sub x}. However, on Rh/SiO{sub 2}, synthesis gas was produced via a two-step path similar to the case of Ir/TiO{sub 2} catalyst. The reaction pathway of partial oxidation of methane with Rh-loaded catalysts depended strongly on the support materials.« less