Catalytically important metal ion intermediates on zeolites and silica surfaces

Kevan, Larry

doi:10.1007/bf03155660

Cited by 33 publications

(18 citation statements)

References 44 publications

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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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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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“…5,6,[8][9][10] On the basis of the absence of deuterium modulation from D 2 O and a weak interaction between Cu 2+ and adsorbed ethylene (C 2 D 4 ) in the ESEEM studies, 5, 23 Kevan's group suggested that Cu 2+ was located at site II′ displaced 0.12 nm from the six-ring plane into the cage and coordinated to three O(3) atoms. 11,23 On the other hand, Schoonheydt located Cu 2+ in the dehydrated species at site II on the basis of the diffuse reflectance spectrum. 8 When Cu 2+ is in a trigonal plane, the plane of maximum probability amplitude of the singly occupied 3d orbital coincides with the trigonal plane and the g z direction invariably is perpendicular to this plane.…”

Section: Discussionmentioning

confidence: 99%

Observation of Single-Crystal-Type EPR Spectra from Monolayers of Copper-Exchanged Zeolite Na-A Crystals Assembled on Glass Plates

Lee

et al. 2003

J. Phys. Chem. B

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Single-crystal-type EPR spectra were observed for microcrystals of copper(II)-exchanged zeolite Na-A assembled on glass plates when the magnetic field was perpendicular to the glass surface. Two copper species (H and D) were identified both in the powder sample and in the assembled crystals. The g z direction of species H is parallel to [001] of the cubic crystal, while that of species D is tilted 9°away from [001]. Previously, other authors assumed the g z directions of the two corresponding species to be parallel to [111]. On the basis of the g z directions, we suggest that Cu 2+ in species H is displaced 0.149 nm along [111] from the six-ring plane into the cage and octahedrally coordinated to three zeolite oxygen atoms in the six-ring plane and three water molecules. The g z direction of Cu 2+ in species D is not compatible with site II in the six-ring plane. Species D is probably a trigonal complex with Cu 2+ displaced into the cage and coordinated to three zeolite oxygen atoms.

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“…1, faujasite) the g 8 and A 8 (Cu) values have usually been interpreted based on the well established distinct cation sites within the faujasite structure. 69,70 However, based on earlier suggestion derived from 27 Al electronspin echo envelope modulation (ESEEM) spectroscopy, 71 an extensive theoretical analysis of the g-tensor and the optical spectra of Cu 21 in dehydrated zeolites A, ZK-4 and Y challenged this traditional assignment proposing that the EPR parameters are instead related to the number of Al atoms in the six-membered ring. 72 This study has also shown that in the dehydrated zeolites Cu 21 adapts a tetragonal coordination sphere by coordinating four zeolite oxygens and not three as previously believed.…”

Section: Exchanged Transition Metal Ionsmentioning

confidence: 99%

High field ENDOR as a characterization tool for functional sites in microporous materials

Goldfarb

2006

Phys. Chem. Chem. Phys.

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The determination of the details of the spatial and electronic structure of functional sites (centers) in any system, be it in materials chemistry or in biology, is the first step towards understanding their function. When such sites happen to be paramagnetic in any point of their activity cycle, the tool box offered by a variety of high resolution electron paramagnetic resonance (EPR) spectroscopic techniques becomes very attractive for their characterization. This tool box has been considerably expanded by the developments in high field (HF) EPR in general, and HF electron nuclear double resonance (ENDOR), in particular. These have led to numerous new applications in the fields of biology, physics, chemistry and materials sciences. This overview focuses specifically on recent applications of pulsed HF ENDOR spectroscopy to microporous materials, such as zeotype materials, presenting the new opportunities it offers. First, a brief description of the theoretical basis required for the analysis of the HF ENDOR spectrum is given, followed by a description of the pulsed techniques used to record spectra and assign the signals, along with a brief presentation of the required instrumentation. Next, specific applications are given, including transition metal ions and complexes exchanged into zeolite cages, transition metal substitution into frameworks of zeolites, aluminophosphate molecular sieves, and silicious mesoporous materials, the interaction of NO with Lewis sites in zeolite cages and trapped S. We end with a discussion of the advantages and the shortcomings of the method and conclude with a future outlook.

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Catalytically important metal ion intermediates on zeolites and silica surfaces

Cited by 33 publications

References 44 publications

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

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

Observation of Single-Crystal-Type EPR Spectra from Monolayers of Copper-Exchanged Zeolite Na-A Crystals Assembled on Glass Plates

High field ENDOR as a characterization tool for functional sites in microporous materials

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Catalytically important metal ion intermediates on zeolites and silica surfaces

Cited by 33 publications

References 44 publications

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

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

Observation of Single-Crystal-Type EPR Spectra from Monolayers of Copper-Exchanged Zeolite Na-A Crystals Assembled on Glass Plates

High field ENDOR as a characterization tool for functional sites in microporous materials

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

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