Zeolite-Supported Transition Metal Catalysts

Sachtler, Wolfgang M.H.; Zhang, Zongchao

doi:10.1016/s0360-0564(08)60578-7

Cited by 278 publications

(190 citation statements)

References 295 publications

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“…The original threeband carbonylic spectrum becomes more resolved and is transformed into a two-band spectrum, with main components at 1890 and 1765 cm -complexes (corresponding computed IR spectra are reported in Figure S1 of the Supporting Information), while the ∆V CO calculated for the cationic [CpCr(CO) 3 ] + species is one order of magnitude lower with respect to the experimental values. We can therefore infer that quantum mechanical calculations support the experimental results, and our previous assignment in terms of the copresence of anionic [CpCr(CO) ).…”

Section: Structural and Vibrational Properties Of Hosted Cp 2 Cr: Examentioning

confidence: 97%

“…Minor features are the appearance of a weak component at ∼1980 cm -1 (green squares) and of complex absorptions in the 1450-1350 cm -1 (left inset, Figure 4a) and 950-800 cm -1 (right inset, Figure 4a) regions that will be further discussed. The evolution of the FTIR spectra in the ν(CO) region suggests that the main phenomenon occurring with time is the transformation of the monocarbonyl Cp 2 Cr(CO) precursor (blue curve, Figure 4) into a tricarbonyl species of type CpCr(CO) 3 + species are not compatible with the observed Ṽ(CO). 68 The previous assignment implies a fast release of a Cp ligand from the Cp 2 Cr(CO) precursor to the NaY system, as is discussed in section 4.…”

Section: Electronic Properties Of Hosted Cp 2 Cr: Uv-vis and Xanes Rementioning

confidence: 99%

“…69 Note that no conclusions can be drawn for the concentration of the cationic species from the intensity of the band at ∼1980 cm -1 , because of the lower extinction coefficient expected for carbonyls giving absorption in this frequency range. 70 The previous assignments of the FTIR spectra, in terms of the copresence of the anionic [CpCr(CO) 3 ]…”

Section: Structural and Vibrational Properties Of Hosted Cp 2 Cr: Examentioning

confidence: 99%

“…Features A and C are better resolved than those of the Cp 2 Cr/NaY system, suggesting a better molecular definition of the Cr species formed upon CO contact. In this regard, it is worth noticing that having no inversion center the [CpCr(CO) 3 ] -and [Cp 2 Cr(CO)] + product species hypothesized from the IR study (section 3.2.1) could justify the important increase in intensity of the dipole-forbidden feature A of the XANES spectrum. Conversely, the position of the edge is almost unaltered with respect to the Cp 2 Cr/NaY system.…”

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confidence: 99%

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Structure and Enhanced Reactivity of Chromocene Carbonyl Confined inside Cavities of NaY Zeolite

et al. 2009

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Chromocene (Cp 2 Cr) hosted inside the supercage cavities of a NaY zeolite undergoes a structural distortion induced by the strong local electric fields generated by charge-balancing counterions. This effect, clearly observed by an in situ Cr K-edge extended X-ray absorption fine structure (EXAFS) study, is the key factor in enhancing the reactivity of Cp 2 Cr toward CO. The Cp 2 Cr(CO) adducts initially formed are not as stable as when hosted in nonpolar environments such as toluene solution or polystyrene. The presence of strong anionic/ cationic pairs (Y -/Na + ) favors, in a CO atmosphere, the loss of a Cp ring driven by an electron transfer mechanism (accompanied by ligand rearrangement) that results in the formation of the charged [CpCr(CO) 3 ] - and [Cp 2 Cr(CO)]+ carbonyl species that are stabilized by Na + and Y -pairs. Shape selectivity of the supercage cavity of the Y zeolite is necessary for this reaction, as it can host the two Cp 2 Cr molecules needed for disproportionation. Fast Fourier transform infrared (FTIR) spectroscopy, working in operando conditions, allows us to follow the time evolution of the IR stretching modes peculiar of reactants and products and thus to infer a reaction mechanism. The combination of quantum mechanical calculation with an in situ EXAFS study supports the hypothesis made on the basis of IR results. The work is further demonstration that zeolitic voids act as "nanoscale reaction chambers", where the reactivity of guest organometallic complexes can provide molecular insights into the elementary steps of heterogeneous catalysis. In this context, the investigation of metallocene reactivity inside a polar matrix can be extremely useful to understanding their properties in polymerization conditions, where they are usually found as part of an ion pair, together with the anionic form of the activator (e.g., MAO).

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Section: Structural and Vibrational Properties Of Hosted Cp 2 Cr: Examentioning

confidence: 97%

Section: Electronic Properties Of Hosted Cp 2 Cr: Uv-vis and Xanes Rementioning

confidence: 99%

Section: Structural and Vibrational Properties Of Hosted Cp 2 Cr: Examentioning

confidence: 99%

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confidence: 99%

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Structure and Enhanced Reactivity of Chromocene Carbonyl Confined inside Cavities of NaY Zeolite

et al. 2009

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“…A highly dispersed Pt/zeolite catalyst using O 2 calcination and H 2 reduction process was reported by Sachtler and Gallezot [5]. Pt was found favourable to locate in supercages at 300 o C with a particle size of 6 -13 Å.…”

Section: Introductionmentioning

confidence: 82%

Proton Modified Pt Zeolite Fuel Cell Electrocatalysts

Yao

Mirzaii³

2015

Renewable Energy in the Service of Mankind Vol I

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NaY Zeolite has been selected as a suitable material to host 1.5 wt% Platinum (Pt) loading on zeolite using ion exchange methods of Pt(NH 3 ) 4 (NO 3 ) 2 without excess NH 4 NO 3 nitrate and Pt(NH 3 ) 4 (NO 3 ) 2 with excess NH 4 NO 3 nitrate. The structure/reactivity relationship of Pt nanoparticle was experimentally studied via Nafion @ bound electrodes to investigate the interaction nature of Pt with zeolite and electron transfer. By using extended X-ray adsorption fine structure technique, Pt particle size was predicted as 0.7 -1.5 nm. It was found Pt oxides can be electrochemically reduced via a hydrogen 'spillover' phenomenon. A highly dispersed small Pt particle distribution can be achieved with excessive H + ions on zeolite acidic sites.

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X-ray photoelectron spectroscopy analysis of platinum- and/or cobalt-loaded zeolites relevant for selective catalytic reduction of NOx

Boix

Fierro

1999

Surf. Interface Anal.

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Zeolite-Supported Transition Metal Catalysts

Cited by 278 publications

References 295 publications

Structure and Enhanced Reactivity of Chromocene Carbonyl Confined inside Cavities of NaY Zeolite

Structure and Enhanced Reactivity of Chromocene Carbonyl Confined inside Cavities of NaY Zeolite

Proton Modified Pt Zeolite Fuel Cell Electrocatalysts

X-ray photoelectron spectroscopy analysis of platinum- and/or cobalt-loaded zeolites relevant for selective catalytic reduction of NOx

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