Studies of the interaction of palladium(3+) and palladium(1+) with organic adsorbates, water, and molecular oxygen in palladium-Ca-X zeolite by electron spin resonance and electron spin-echo modulation spectroscopy

Michalik, J.; Narayna, M.; Kevan, Larry

doi:10.1021/j100267a028

Cited by 49 publications

(30 citation statements)

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“…Kasai et al suggested that the reduction of Cu(II) ions in Cu-exchanged mordenite observed when heating in a vacuum is due to reduction by residual water. Michalik et al also showed that retained water in PdCa−X zeolite plays a significant role in the reduction of Pd upon heating in a vacuum. However, in our case, dehydration generates a framework defect and a much stronger Ni(I) signal in the ion-exchanged sample, whereas in the synthesized sample, the Ni(I) signal is weaker and is produced along with a free radical.…”

Section: Discussionmentioning

confidence: 99%

Electron Spin Resonance and Electron Spin−Echo Modulation Studies of Synthesized NiAPSO-34 Molecular Sieve and Comparison with Ion-Exchanged NiH−SAPO-34 Molecular Sieve

1999

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The formation of monovalent nickel in where nickel is believed to be incorporated into the framework of SAPO-34, and its interaction with several adsorbates are compared to Ni(I) species formed in NiH-SAPO-34, where Ni(II) is incorporated by solid-state ion exchange into known extraframework sites using electron spin resonance (ESR) and electron spin-echo modulation (ESEM) spectroscopies. Dehydration at temperatures above 573 K and hydrogen treatment at 573 K as well as γ-irradiation at 77 K produce one nickel species assigned by ESR as isolated Ni(I) in the two samples. Even though the ESR parameters of isolated Ni(I) species are similar after reduction, NiAPSO-34 and NiH-SAPO-34 show noticeable differences in their ESR characteristics after adsorption of various adsorbates, suggesting that Ni(I) in these two materials is in different sites. As a supplement to this, ESEM studies of 31 P and 27 Al, used to ascertain the location of the incorporated paramagnetic transition metal ion, also show significant differences in the modulation patterns. Simulation of the 31 P modulation observed for NiH-SAPO-34 shows two nearest-neighbor phosphorus atoms at 3.9 Å and three next-nearest-neighbor phosphorus atoms at 6.5 Å, indicating that Ni(I) is at site II′ in the chabazite cage near a six ring window after reduction. The 31 P simulation for NiAPSO-34 shows three nearestneighbor phosphorus atoms at a distance of 4 Å and two next-nearest-neighbor phosphorus atoms at 5.3 Å. This is consistent with Ni(I) ions substituting into a framework phosphorus site. In as-synthesized NiAPSO-34, the nickel ion is possibly also coordinated to additional waters to give distorted octahedral coordination. On dehydration, tetrahedrally coordinated nickel in a framework site of SAPO-34 is formed.

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Section: Discussionmentioning

confidence: 99%

Electron Spin Resonance and Electron Spin−Echo Modulation Studies of Synthesized NiAPSO-34 Molecular Sieve and Comparison with Ion-Exchanged NiH−SAPO-34 Molecular Sieve

1999

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“…Kasai et al suggested that the reduction of Cu(II) ions in Cu(II)-exchanged modenite zeolite that occurs upon heating in a vacuum is due to reduction by residual water . Michalik et al suggested that water in PdCa-X zeolite plays a role in the reduction of Pd(II) upon heating in a vacuum …”

Section: Discussionmentioning

confidence: 99%

Electron Spin Resonance of Ni(I) in Ni−Containing MCM-41 Molecular Sieves

1999

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Nickel-containing MCM-41 molecular sieves have been synthesized hydrothermally using cetyltrimethylammonium chloride as a template. The stabilization of Ni(I) in NiMCM-41 is minimal. The various Ni(I) species formed by reduction and adsorbate interactions in NiAlMCM-41 in which Ni(II) is incorporated into a framework position by addition of Ni(II) into the synthesis mixture and in Ni-AlMCM-41 where Ni(II) is incorporated into extraframework positions by liquid state ion exchange were studied by electron spin resonance (ESR) and electron spin-echo modulation. Dehydration at elevated temperature or thermal reduction by hydrogen produces Ni(I) species in Ni-AlMCM-41 which are detectable by ESR. By contrast, in NiAlMCM-41 neither dehydration at high temperature nor hydrogen reduction is effective in producing Ni(I). Ni(I) is obtained in NiAlMCM-41 by γ-irradiation at 77 K. Both NiAlMCM-41 and Ni-AlMCM-41 show differences in their ESR characteristics after reduction and adsorption of D 2 O, CO, and ethylene. D 2 O adsorption forms Ni(I)-(O 2 ) n indicating water decomposition in both materials. CO adsorption onto Ni-AlMCM-41 and NiAlMCM-41 produces Ni(I)-(CO) 3 and Ni(I)-(CO) 2 , respectively. The interaction between Ni(I) and ethylene seems weaker in NiAlMCM-41 than in Ni-AlMCM-41. The contrasting characteristics of Ni(I) in NiAlMCM-41 and Ni-AlMCM-41 suggest that Ni(I) is in a framework site in NiAlMCM-41. The differentiation between extraframework and framework sites is confirmed by the effect of sodium ethylenediaminetetraacetate on removing nickel ions from ion-exchanged Ni-AlMCM-41 but not from synthesized NiAlMCM-41.

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“…For both modes of alumina incorporation into Pd/SZ, the sample spectra collected at 300 K in Figure a,b show the presence of Pd + species indicated by the g ∥ factor of 2.3 and the g ⊥ factor of 2.13, as well as the g ∥ factors at 2.85 and 2.68. These species are likely formed as a result of the partial transformation of Pd 2+ species through an interaction with Pd 0 . , Zr 3+ species were also observed in the samples based on the g ⊥ factor at 1.975 and the g ∥ factor at 1.96 …”

Section: Results and Discussionmentioning

confidence: 72%

Investigation of the Effect of Alumina Binder Addition to Pd/SO₄^2––ZrO₂ Catalysts during Sol–Gel Synthesis

Majumdar

Çelik

Ozkan

2016

Ind. Eng. Chem. Res.

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We have incorporated alumina into palladium catalysts supported on sulfated zirconia (Pd/SZ) during sol–gel synthesis for application in a washcoat for NO x emissions control in natural gas-fired lean-burn engines. In situ incorporation of the adhesivity-enhancing “binder”, alumina, during the sol–gel synthesis of the Pd/SZ catalyst demonstrated significantly improved NO x reduction activity of the previously reported dual-catalyst bed when compared to the conventional ex situ mode of binder addition in a slurry. The effects of alumina addition during sol–gel synthesis of Pd/SZ on the structural, textural, and chemical properties of the resulting catalyst were examined in this study. The evolution of the crystal phase of zirconia during calcination of the Pd/SZ catalyst with the binder incorporated during the sol–gel process was studied using in situ XRD during calcination under air. Comparison of the crystal phase composition of the binder-free and binder-incorporated samples calcined at 700 and 900 °C demonstrated a stabilizing effect on the tetragonal zirconia in the presence of alumina or boehmite dopants. N2 adsorption experiments at 77 K indicated the presence of slit-shaped multimodal hierarchical pores as a result of sol–gel alumina addition. EPR spectra indicated that sol–gel alumina incorporation affected the nature of the Pd species on the resulting catalyst. 27Al MAS NMR spectroscopy revealed a strong interaction of the alumina binder with the zirconia support. The possible formation of a zirconia–alumina solid solution was suggested and was further examined using laser Raman spectroscopy. The influence of the alumina dopant in the zirconia matrix on the chemical states of Zr, S, O, and Al was investigated using XPS. Ar+-ion-gun sputtering provided valuable insights into the nature of the alumina–support interaction due to in situ alumina incorporation during the sol–gel synthesis of Pd/SZ catalysts.

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Studies of the interaction of palladium(3+) and palladium(1+) with organic adsorbates, water, and molecular oxygen in palladium-Ca-X zeolite by electron spin resonance and electron spin-echo modulation spectroscopy

Cited by 49 publications

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Electron Spin Resonance and Electron Spin−Echo Modulation Studies of Synthesized NiAPSO-34 Molecular Sieve and Comparison with Ion-Exchanged NiH−SAPO-34 Molecular Sieve

Electron Spin Resonance and Electron Spin−Echo Modulation Studies of Synthesized NiAPSO-34 Molecular Sieve and Comparison with Ion-Exchanged NiH−SAPO-34 Molecular Sieve

Electron Spin Resonance of Ni(I) in Ni−Containing MCM-41 Molecular Sieves

Investigation of the Effect of Alumina Binder Addition to Pd/SO₄^2––ZrO₂ Catalysts during Sol–Gel Synthesis

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Studies of the interaction of palladium(3+) and palladium(1+) with organic adsorbates, water, and molecular oxygen in palladium-Ca-X zeolite by electron spin resonance and electron spin-echo modulation spectroscopy

Cited by 49 publications

References 0 publications

Electron Spin Resonance and Electron Spin−Echo Modulation Studies of Synthesized NiAPSO-34 Molecular Sieve and Comparison with Ion-Exchanged NiH−SAPO-34 Molecular Sieve

Electron Spin Resonance and Electron Spin−Echo Modulation Studies of Synthesized NiAPSO-34 Molecular Sieve and Comparison with Ion-Exchanged NiH−SAPO-34 Molecular Sieve

Electron Spin Resonance of Ni(I) in Ni−Containing MCM-41 Molecular Sieves

Investigation of the Effect of Alumina Binder Addition to Pd/SO42––ZrO2 Catalysts during Sol–Gel Synthesis

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Investigation of the Effect of Alumina Binder Addition to Pd/SO₄^2––ZrO₂ Catalysts during Sol–Gel Synthesis