Site distribution studies of Rh supported on Al2O3—An infrared study of chemisorbed CO

Cavanagh, Richard R.; Yates, John T.

doi:10.1063/1.441544

Cited by 187 publications

(93 citation statements)

References 35 publications

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“…3D). Similar qualitative behavior has been observed on supported catalyst (5,6,8) and surface science studies (4, 34) of supported Rh particles, which have demonstrated that larger catalyst loadings (likely associated with larger particles sizes) exhibit resistance to dispersion. Thus, the nature of Rh particle dispersion and CO surface adsorbates under elevated pressures, depend on both initial Rh particle size and CO pressure at a given temperature.…”

Section: Discussionsupporting

confidence: 58%

“…For example, elevated pressure CO ambients have been shown to oxidatively disrupt and disperse Rh nanoparticles, creating highly dispersed gem-dicarbonyl species RhðCOÞ 2 on oxide supports (1)(2)(3)(5)(6)(7)(8). Under elevated pressure (CO∕H 2 ) and (CO 2 ∕H 2 ) hydrogenation reaction conditions, Rh(CO)H carbonyl hydride species can also be formed (3,(9)(10)(11)(12).…”

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confidence: 99%

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Planar oxide supported rhodium nanoparticles as model catalysts

McClure

Lundwall²,

Goodman³

2010

Proc. Natl. Acad. Sci. U.S.A.

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C 2 H 4 ∕CO∕H 2 reaction is investigated on Rh∕SiO 2 model catalyst surfaces. Kinetic reactivity and infrared spectroscopic measurements are investigated as a function of Rh particle size under near atmospheric reaction conditions. Results show that propionaldehyde turnover frequency (TOF) (CO insertion pathway) exhibits a maximum activity near hd p i ¼ 2.5 nm. Polarization modulation infrared reflection absorption spectroscopy under CO and reaction (C 2 H 4 ∕CO∕H 2 ) conditions indicate the presence of Rh carbonyl species (RhðCOÞ 2 , Rh(CO)H) on small Rh particles, whereas larger particles appear resistant to dispersion and carbonyl formation. Combined these observations suggest the observed particle size dependence for propionaldehyde production via CO insertion is driven by two factors: (i) an increase in propionaldehyde formation on undercoordinated Rh sites and (ii) creation of carbonyl hydride species (Rh(CO)H)) on smaller Rh particles, whose presence correlates with the lower activity for propionaldehyde formation for hd p i < 2.5 nm.Ethylene hydroformylation | CO insertion | polarization modulation infrared reflection absorption spectroscopy | Rh/SiO2 A complicating effect of understanding the structure-activity relationships of heterogeneous catalytic reactions at ambient pressures (near 1 atm or above) is the known ability of reactant gas environments to alter the morphology, particle dispersion, and even the types of adsorbates present on certain supported nanoparticle (NP) systems (1-4). For example, elevated pressure CO ambients have been shown to oxidatively disrupt and disperse Rh nanoparticles, creating highly dispersed gem-dicarbonyl species RhðCOÞ 2 on oxide supports (1-3, 5-8). Under elevated pressure (CO∕H 2 ) and (CO 2 ∕H 2 ) hydrogenation reaction conditions, Rh(CO)H carbonyl hydride species can also be formed (3, 9-12). The creation and stability of such carbonyl species (RhðCOÞ 2 , Rh(CO)H) can depend on particle size, gas pressure, and surface temperature. The cumulative effect of such factors could potentially have an important effect on the overall catalytic properties of the supported Rh NP surface, especially for catalytic reactions involving surface bound CO. Developing an understanding of how such factors can affect the catalytic properties of supported Rh NPs is important from a fundamental surface chemistry perspective. Unraveling these details will require the ability to conduct spectroscopic and kinetic investigations of an informative probe reaction (i) under near atmospheric reaction conditions and (ii) on supported Rh nanoparticles surfaces with well defined initial particle size distributions.CO insertion into adsorbed alkyl groups (R-C x H y ) to form oxygenates (e.g., alcohols, aldehydes) is an important reaction step in many heterogeneous catalytic reactions. For example, C 2 H 4 hydroformylation (C 2 H 4 þ CO þ H 2 ) is a well known reaction for the synthesis of aldehydes via the CO insertion reaction (13). Insightful studies by Chuang and coworkers (14-17) and others (...

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Section: Discussionsupporting

confidence: 58%

mentioning

confidence: 99%

Planar oxide supported rhodium nanoparticles as model catalysts

McClure

Lundwall²,

Goodman³

2010

Proc. Natl. Acad. Sci. U.S.A.

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“…This trend was the same as that observed for Rh _ P/SiO2. TiO2 is well k n ow n t o b e m o r e r e d u c i b l e t h a n o t h e r m e t a l oxides 37), 38) . Thus, the large peak observed at 540 would be attributed to the reduction of phosphate and TiO2 support.…”

Section: (Iv) (B)mentioning

confidence: 99%

“…Assuming that CO molecules are linearly adsorbed onto Rh atom, Rh dispersion in Rh/Al2O3 catalyst reduced at 400 was about 1.3. After CO was adsorbed on Rh/ Al2O3 catalyst with high dispersion, the Rh(CO)2 species was identified by infrared spectroscopy 38) . Thus, the remarkable CO uptake of Rh/Al2O3 could be explained by the formation of Rh(CO)2 species.…”

Section: Co Adsorption On Rh/mox and Rh-p/moxmentioning

confidence: 99%

Effects of Support on Formation of Active Sites and Hydrodesulfurization Activity of Rhodium Phosphide Catalyst

Kanda

Nakata

Temma

et al. 2012

J. Jpn. Petrol. Inst.

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The effects of the support on active site formation and hydrodesulfurization (HDS) activity of Rh2P catalyst were examined, using metal oxides (MOx), such as SiO2, TiO2, Al2O3, MgO and ZrO2, as the support. Rh2P was formed on MOx support after reduction of supported rhodium and phosphorus (Rh _ P) catalysts. However, differences in the formation temperatures of Rh2P were observed by changing the MOx support. Furthermore, the HDS activities of the supported Rh _ P catalysts strongly changed with higher reduction temperature. The order of HDS activities of Rh _ P/MOx catalysts reduced at optimal temperatures was SiO2 ~ TiO2 ~ Al2O3 MgO ZrO2. The TOF of Rh _ P/MOx catalysts was enhanced by increasing the reduction temperature to form Rh2P. The order of TOF of supported Rh2P catalysts was TiO2 ZrO2 Al2O3 SiO2 MgO, and this order disagreed with that of thiophene conversion. The high TOF of Rh _ P/TiO2 catalyst may be explained by formation of partially sulfided TiO2 in the HDS reaction. The low TOF of Rh _ P/MgO catalyst was attributed to the basicity of the support with low sulfur tolerance.

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“…The peaks observed after calcination can similarly be attributed to linearly bound CO to Rh of oxidation state 0 (~2070 cm -1 ) or 1 (~2100 cm -1 ) and after reduction only linear bound CO on zero valent Rh is present. [47][48][49][50][51][52][53] This change in available binding sites in schematically represented in Figure 8(A).…”

Section: Diffuse Reflectance Infrared Spectroscopymentioning

confidence: 99%

Colloidally Synthesized Monodisperse Rh Nanoparticles Supported on SBA-15 for Size- and Pretreatment-Dependent Studies of CO Oxidation

Graß¹,

Zhang²,

Somorjai³

2009

J. Phys. Chem. C

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1A particle size dependence for CO oxidation over rhodium nanoparticles of 1.9 -11.3 nm has been investigated and determined to be modified by the existence of the capping agent, poly(vinylpyrrolidone) (PVP). The particles were prepared using a polyol reduction procedure with PVP as the capping agent. The Rh nanoparticles were subsequently supported on SBA-15 during hydrothermal synthesis to produce Rh/SBA-15 supported catalysts for size-dependent catalytic studies.CO oxidation by O 2 at 40 Torr CO and 100 Torr O 2 was investigated over two series of Rh/SBA-15 catalysts: as-synthesized Rh/SBA-15 covering the full range of Rh sizes and the same set of catalysts after high temperature calcination and reduction. The turnover frequency at 443 K increases from 0.4 to 1.7 s -1 as the particle size decreases from 11.3 to 1.9 nm for the as-synthesized catalysts. For the catalyst series after calcination and reduction, the turnover frequency is between 0.1 and 0.4 s -1 with no particle size dependence. The apparent activation energy for all catalysts is ~ 30 kcal mol -1 and is independent of particle size and thermal treatment. Infrared spectroscopy of CO on the Rh nanoparticles indicates that the heat treatments used influence the mode of CO adsorption. As a result, the particle size dependence for CO oxidation is altered after calcination and reduction of the catalysts.CO adsorbs at two distinct bridge sites on as-synthesized Rh/SBA-15, attributable to metallic Rh(0) and oxidized Rh(I) bridge sites. After calcination and reduction, however, CO adsorbs only at Rh(0) atop sites. The change in adsorption geometry and oxidation activity may be attributable to the interaction between PVP and the Rh surface. This capping agent affect may open new possibilities for the tailoring of metal catalysts using solution nanoparticle synthesis methods.

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Site distribution studies of Rh supported on Al2O3—An infrared study of chemisorbed CO

Cited by 187 publications

References 35 publications

Planar oxide supported rhodium nanoparticles as model catalysts

Planar oxide supported rhodium nanoparticles as model catalysts

Effects of Support on Formation of Active Sites and Hydrodesulfurization Activity of Rhodium Phosphide Catalyst

Colloidally Synthesized Monodisperse Rh Nanoparticles Supported on SBA-15 for Size- and Pretreatment-Dependent Studies of CO Oxidation

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