Determination of Surface Coverage of Catalysts: Temperature Programmed Experiments on Platinum and Iridium Sponge Catalysts after Low Temperature Ammonia Oxidation

Broek, van den Acm Noud; Grondelle, van J Joop; Santen, van Ra Rutger

doi:10.1006/jcat.1999.2506

Cited by 62 publications

(20 citation statements)

References 33 publications

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“…[19] In addition, further knowledge is necessary to increase the activity of AMOX catalysts to full NH 3 conversion below 250°C. [20] Despite many data about NH 3 oxidation to NO x over single-and polycrystalline platinum surfaces, Pt gauzes or sponges as well as supported platinum catalysts, [3,[20][21][22][23][24][25] the structure-activity relationships for Pt-based systems for selective NH 3 oxidation to N 2 are still under discussion and require further systematic fundamental studies. [10] However, using Pt-based catalysts requires increasing N 2 selectivity by minimizing the formation of undesired N 2 O.…”

Section: Introductionmentioning

confidence: 99%

Insight into the Nature of Active Species of Pt/Al₂O₃ Catalysts for low Temperature NH₃ Oxidation

et al. 2019

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Two series of Pt/γ-Al 2 O 3 catalysts for low temperature NH 3 oxidation were prepared using Pt(NO 3 ) 4 and H 2 PtCl 6 precursors. Using both precursors results in the formation of small Pt particles (d < 1.5 nm), however, Cl-containing Pt precursors give a higher fraction of highly dispersed Pt species. Such species show high stability against thermal or H 2 treatment probably due to the presence of a substantial amount of chlorine on the surface. Treatment of the samples prepared from Pt(NO 3 ) 4 with H 2 leads to the formation of metallic Pt nanoparticles accompanied by the improvement of catalytic activity in NH 3 oxidation at T < 200°C. The main products of ammonia oxidation at temperatures below 250°C were molecular nitrogen and nitrous oxide with the N 2 selectivity reaching 80 %. Operando XANES/ EXAFS revealed that even after H 2 pretreatment at least 40 % of Pt surface remains in oxidized state under reaction conditions resulting in the appearance of N 2 O as a by-product.

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Section: Introductionmentioning

confidence: 99%

Insight into the Nature of Active Species of Pt/Al₂O₃ Catalysts for low Temperature NH₃ Oxidation

et al. 2019

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“…These marked differences in the product selectivity of NH 3 oxidation were similar to those reported for supported nanoparticle catalysts of Pt and Ir. 16 , 24 , 31 , 32 A higher selectivity for N 2 relative to N 2 O is a notably superior characteristic of the Ir overlayer as compared with a Pt overlayer. Besides their different product selectivity, notably, both catalysts showed irregular NH 3 conversion behavior at higher temperatures.…”

Section: Results and Discussionmentioning

confidence: 99%

“…As an alternative to supported Pt catalysts, supported Ir catalysts are less selective for N 2 O and thus more selective for N 2 . 16 , 24 , 31 , 32 These studies explained the lower N 2 O production on Ir relative to that on Pt by the higher activity of Ir to dissociate NO, which is a byproduct of NH 3 oxidation, with the reduced NO lifetime on the surface negatively affecting N 2 O formation. In our previous study, 30 we obtained a preliminary result showing a low light-off temperature of NH 3 oxidation over the Ir overlayer comparable with that over the Pt overlayer.…”

Section: Introductionmentioning

confidence: 98%

Nanometric Iridium Overlayer Catalysts for High-Turnover NH₃ Oxidation with Suppressed N₂O Formation

et al. 2020

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In the present study, we prepared a 12 nm thick Ir overlayer via pulsed cathodic arc plasma deposition on a 50 μm thick Fe–Cr–Al metal (SUS) foil. Using this thin-film catalyst made NH 3 –O 2 reactions more environmentally benign due to a much lower selectivity for undesirable N 2 O (<5%) than that of a Pt overlayer (∼70%) at 225 °C. Despite its small surface area, Ir/SUS exhibited promising activity as an ammonia slip catalyst according to a turnover frequency (TOF) >70-fold greater than that observed with conventional Ir nanoparticle catalysts supported on γ-Al 2 O 3 . We found that the high-TOF NH 3 oxidation was associated with the stability of the metallic Ir surface against oxidation by excess O 2 present in simulated diesel exhaust. Additionally, we found that the Ir overlayer structure was thermally unstable at reaction temperatures ≥400 °C and at which point the Ir surface coverage dropped significantly; however, thermal deterioration was substantially mitigated by inserting a 250 nm thick Zr buffer layer between the Ir overlayer and the SUS foil substrate (Ir/Zr/SUS). Although N 2 O formation was suppressed by NH 3 oxidation over Ir/Zr/SUS, other undesired byproducts (i.e., NO and NO 2 ) were readily converted to N 2 by coupling with a V 2 O 5 –WO 3 /TiO 2 catalyst in a second reactor for selective catalytic reduction by NH 3 . These results demonstrated that this tandem reactor configuration converted NH 3 to N 2 with nearly complete selectivity at a range of 200–600 °C in the presence of excess O 2 (8%) and H 2 O (10%).

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“…To achieve such goal, various catalysts (e.g., noble metal catalysts, transition metal catalysts) for oxidizing NH3 have been developed. The noble metals (e.g., Pt, Pd, Rh, Ag) are active for ammonia oxidation reaction, [4][5][6][7][8][9] but the selectivity of N2 is low. The transition metal catalysts such as V2O5, Fe2O3, CuO, MnO2, TiO2 are also employed for the ammonia oxidation reaction.…”

Section: Introductionmentioning

confidence: 99%

Selective Catalytic Oxidation of Ammonia to Nitrogen over Iron and Copper Bimetallic Catalysts

Sun¹,

Yi²,

Lan³

et al. 2014

Acta Physico-Chimica Sinica

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Iron and copper bimetallic catalysts with fixed total contents of copper and iron were prepared by a co-impregnation method, and then used for selective catalytic oxidation of ammonia to nitrogen. The properties of the catalysts were characterized by N2 adsorption-desorption, H2 temperature-programmed reduction (H2-TPR), NH3 temperature-programmed desorption (NH3-TPD), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). The iron and copper bimetallic catalysts exhibited good activity and high selectivity of N2 at the gas hourly space velocity (GHSV) of 100000 h-1. The activity and N2 selectivity in the low temperature range increased with increasing Cu loading, whereas in the high temperature range (above 400°C) the selectivity of N2 was directly related to the content of iron. The highest NH3 conversion was achieved at about 350°C for Fe0.25Cu0.75/ZSM-5, and the N2 selectivity was up to 97% at 300°C. On the other hand, the extremely high N2 selectivity about 98% was obtained over Fe0.75Cu0.25/ZSM-5 at 500°C. In addition, N2O as the by-product and greenhouse gas was obtained in very low amounts for all the catalysts. The characterization results showed that the activity was influenced by the acid content and the amounts of copper species. Moreover, the highly reducing capacity could improve the N2 selectivity.

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Determination of Surface Coverage of Catalysts: Temperature Programmed Experiments on Platinum and Iridium Sponge Catalysts after Low Temperature Ammonia Oxidation

Cited by 62 publications

References 33 publications

Insight into the Nature of Active Species of Pt/Al₂O₃ Catalysts for low Temperature NH₃ Oxidation

Insight into the Nature of Active Species of Pt/Al₂O₃ Catalysts for low Temperature NH₃ Oxidation

Nanometric Iridium Overlayer Catalysts for High-Turnover NH₃ Oxidation with Suppressed N₂O Formation

Selective Catalytic Oxidation of Ammonia to Nitrogen over Iron and Copper Bimetallic Catalysts

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Determination of Surface Coverage of Catalysts: Temperature Programmed Experiments on Platinum and Iridium Sponge Catalysts after Low Temperature Ammonia Oxidation

Cited by 62 publications

References 33 publications

Insight into the Nature of Active Species of Pt/Al2O3 Catalysts for low Temperature NH3 Oxidation

Insight into the Nature of Active Species of Pt/Al2O3 Catalysts for low Temperature NH3 Oxidation

Nanometric Iridium Overlayer Catalysts for High-Turnover NH3 Oxidation with Suppressed N2O Formation

Selective Catalytic Oxidation of Ammonia to Nitrogen over Iron and Copper Bimetallic Catalysts

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Insight into the Nature of Active Species of Pt/Al₂O₃ Catalysts for low Temperature NH₃ Oxidation

Insight into the Nature of Active Species of Pt/Al₂O₃ Catalysts for low Temperature NH₃ Oxidation

Nanometric Iridium Overlayer Catalysts for High-Turnover NH₃ Oxidation with Suppressed N₂O Formation