The Selective Catalytic Reduction of NOxwith NH3over Titania Supported Rhenium Oxide Catalysts

Wachs, Israel E.; Deo, Goutam; Andreini, A.; Vuurman, Michael A.; Boer, Michiel de

doi:10.1006/jcat.1996.0152

Cited by 31 publications

(11 citation statements)

References 20 publications

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“…Accordingly, formation of surface sulfates is likely to occur initially at or near the vanadyl sites. This causes an increase in the de-NO x activity, possibly due (i) to the strengthening of the Lewis acidity of the vanadyl sites caused by the nearby sulfate species, as proposed by Ramis et al (1993), or (ii) to the formation of new acid sulfate sites (either Lewis or Brønsted) close-by to the vanadyl sites, which has been suggested to favor the SCR reaction in view of the dual site (Wachs et al, 1996) or dual-function (Topsøe et al, 1995) requirements of the reaction. Once the vanadyl sites and/or the surface near vanadium is saturated, formation of sulfates still proceeds at the fraction of exposed titania and tungsta.…”

Section: Discussionmentioning

confidence: 98%

Dynamic Investigation of the Role of the Surface Sulfates in NO_x Reduction and SO₂ Oxidation over V₂O₅−WO₃/TiO₂ Catalysts

Orsenigo

Lietti

Tronconi

et al. 1998

Ind. Eng. Chem. Res.

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Transient experiments performed over synthesized and commercial V2O5−WO3/TiO2 catalysts during catalyst conditioning and during step changes of the operating variables (SO2 inlet concentration and temperature) show that conditioning of the catalyst is required to attain significant and reproducible steady-state data in both the reduction of NO x and the oxidation of SO2 . The response time of conditioning for NO x reduction is of a few hours and that for SO2 oxidation is of several hours. Fourier transform infrared spectroscopy temperature programmed decomposition, and thermogravimetric measurements showed that catalyst conditioning is associated with a slow process of buildup of sulfates: the different characteristic conditioning times observed in the reduction of NO x and in the oxidation of SO2 suggest that the buildup of sulfates occurs first at the vanadyl sites and later on at the exposed titania surface. Formation of sulfates at or near the vanadyl sites increases the reactivity in the de-NO x reaction, possibly due to the increase in the Brønsted and Lewis acidity of the catalyst, whereas the titania surface acts as SO3 acceptor and affects the outlet SO3 concentration during catalyst conditioning for the SO2 oxidation reaction. The response time to step changes in SO2 concentration and temperature is of a few hours in the case of SO2 oxidation and much shorter in the case of NO x reduction. The different time responses associated with conditioning and with step changes in the settings of the operating variables have been rationalized in terms of the different extent of perturbation of the sulfate coverage experienced by the catalyst.

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Section: Discussionmentioning

confidence: 98%

Dynamic Investigation of the Role of the Surface Sulfates in NO_x Reduction and SO₂ Oxidation over V₂O₅−WO₃/TiO₂ Catalysts

Orsenigo

Lietti

Tronconi

et al. 1998

Ind. Eng. Chem. Res.

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“…17 The catalysis of supported rhenia was reported to be mainly derived from the acidity and redox properties of the rhenium species in these catalysts. 2 For example, reduction of Re 7+ was reported to be essential to form metal-carbene complexes, reported to be the active sites for olefin metathesis.…”

Section: Introductionmentioning

confidence: 99%

Highly Dispersed and Active ReO_x on Alumina-Modified SBA-15 Silica for 2-Butanol Dehydration

She

Kwak

et al. 2012

ACS Catal.

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SBA-15 silica supported rhenium catalysts were synthesized using solution-based atomic layer deposition method, and their activity and stability were studied in the acid-catalyzed 2-butanol dehydration. We find that ReO x /SBA-15 exhibited an extremely high initial activity but a fast deactivation for 2-butanol dehydration at 90−105°C. Fast deactivation was likely due to the sintering, sublimation, and reduction of rhenia as confirmed by TEM, elemental analysis, and in situ UV−vis (DRS) measurements. To overcome these issues, ReO x /AlO x / SBA-15 catalysts with significantly improved stability were prepared by first modifying the surface identity of SBA-15 with alumina followed by dispersion of rhenia using atomic layer deposition. The AlO x phase stabilizes the dispersion of small and uniform rhenia clusters (<2 nm) as as confirmed by TEM, STEM, and UV−vis (DRS) characterizations. Additional 27 Al MAS NMR characterization revealed that modification of the SBA-15 surface with alumina introduces a strong interaction between rhenia and alumina, which consequently improves the stability of supported rhenia catalysts by suppressing the sintering, sublimation, and reduction of rhenia albeit at a moderately reduced initial catalytic dehydration activity.

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“…Adsorption of these strongly interacting atoms is important for understanding the primary processes of many important reactions on Re such as ammonia synthesis, selective oxidation of methanol, thiophene, and hydrodesulfurization. [16][17][18][19][20][21] In the present work, we study the ES of Re particles in contact either with O 2 or N 2 . By combining DFT and thermodynamic considerations we obtain the surface energies of O-and N-covered Re surfaces, which are then used to determine the ES by means of a Wulff construction.…”

Section: Introductionmentioning

confidence: 99%

Structure-activity relation of Re nanoparticles

Kaghazchi¹,

Jacob²

2012

Phys. Rev. B

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By combining density functional theory and thermodynamic considerations we determined the equilibrium shape of Re particles in contact with O 2 and N 2 environments. At low and intermediate coverages oxygen adsorption has a minor influence on the particle shape, while nitrogen adsorption leads to the stabilization of spherically shaped polyhedra with a large contribution from atomically rough faces. At very high coverages of O and N particles are perfect prisms consisting of low-index faces. By comparing these results with the experimental data for the activity of different Re surfaces we propose that the experimentally measured high initial activity of polycrystalline Re for ammonia synthesis might be due to the N-induced formation of high-index faces with a high density of low-coordinated atoms (roughening). Moreover, the measured decrease in the activity of polycrystalline Re at saturation coverage might be because of the N-induced formation of close-packed faces (smoothing). Our calculations suggest that adsorbate-induced roughening or smoothing of catalytic particles on the atomic scale is capable of controlling the activity of the catalysts.

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The Selective Catalytic Reduction of NOxwith NH3over Titania Supported Rhenium Oxide Catalysts

Cited by 31 publications

References 20 publications

Dynamic Investigation of the Role of the Surface Sulfates in NO_x Reduction and SO₂ Oxidation over V₂O₅−WO₃/TiO₂ Catalysts

Dynamic Investigation of the Role of the Surface Sulfates in NO_x Reduction and SO₂ Oxidation over V₂O₅−WO₃/TiO₂ Catalysts

Highly Dispersed and Active ReO_x on Alumina-Modified SBA-15 Silica for 2-Butanol Dehydration

Structure-activity relation of Re nanoparticles

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The Selective Catalytic Reduction of NOxwith NH3over Titania Supported Rhenium Oxide Catalysts

Cited by 31 publications

References 20 publications

Dynamic Investigation of the Role of the Surface Sulfates in NOx Reduction and SO2 Oxidation over V2O5−WO3/TiO2 Catalysts

Dynamic Investigation of the Role of the Surface Sulfates in NOx Reduction and SO2 Oxidation over V2O5−WO3/TiO2 Catalysts

Highly Dispersed and Active ReOx on Alumina-Modified SBA-15 Silica for 2-Butanol Dehydration

Structure-activity relation of Re nanoparticles

Contact Info

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Dynamic Investigation of the Role of the Surface Sulfates in NO_x Reduction and SO₂ Oxidation over V₂O₅−WO₃/TiO₂ Catalysts

Dynamic Investigation of the Role of the Surface Sulfates in NO_x Reduction and SO₂ Oxidation over V₂O₅−WO₃/TiO₂ Catalysts

Highly Dispersed and Active ReO_x on Alumina-Modified SBA-15 Silica for 2-Butanol Dehydration