The catalytic reduction of nitric oxide over supported ruthenium catalysts

Taylor, Kathleen C.

doi:10.1016/0021-9517(73)90166-8

Cited by 80 publications

(8 citation statements)

References 4 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…This is connected with the second-order maximum in Figure B, which is now shifted to higher temperatures in the absence of O ads , indicating that the lateral interactions between O ads and N ads are repulsive. The absence of NH 3 production shows that either reaction 4 is favored over reaction 5 under our conditions or the production of N 2 proceeds through the formation of NH x , as has been suggested for supported Ru catalysts, , although other studies conclude that this is not the major pathway for the N 2 formation. , The high selectivity for N 2 was explained by the high N ads surface coverage . Moreover, Nishida et al did not observe an NH x species with UPS or XPS during the NO−H 2 reaction over Ru(0001) (although it is questionable whether these techniques are sensitive enough to discriminate between N ads and NH x ,ads ) and Thiel et al did not mention species other than NO ads , N ads , and O ads after studying the coadsorption of NO and H 2 over a Ru(0001) single-crystal surface with EELS.…”

Section: Discussionmentioning

confidence: 50%

“…It has long been recognized that ruthenium would be a far more selective catalyst for the reduction of nitrogen oxides to dinitrogen with a minimum of NH 3 production. − Unfortunately, volatile and toxic ruthenium oxides are formed under the conditions present in the automotive catalysis, which make ruthenium-based catalysts unpractical for this application …”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Hysteresis Phenomena in the NO−H₂ Reaction over Ru(0001)

2000

View full text Add to dashboard Cite

The NO−H2 reaction was studied at NO pressures between 7.7 × 10-8 and 7.7 × 10-7 mbar and for H2/NO ratios varying from 6 to 127. Hysteresis phenomena were observed during a heat and cool cycle dependent on the H2/NO ratio, with the heating branch exhibiting less activity than the cooling branch. Apart from the H2/NO ratio, the shape of the hysteresis also depends on the heating rate and the NO pressure. An almost 100% selectivity toward N2 is observed with only small amounts of NH3 formation at higher H2/NO ratios. From the AES and TDS experiments it was concluded that an O layer that is inactive to reaction with hydrogen is responsible for the low reaction rate on the heating branch. Once the O layer is removed, the total reaction rate is determined by the removal of Nads. The lateral interaction between Oads and Nads turns out to be repulsive.

show abstract

Section: Discussionmentioning

confidence: 50%

Section: Introductionmentioning

confidence: 99%

Hysteresis Phenomena in the NO−H₂ Reaction over Ru(0001)

2000

View full text Add to dashboard Cite

show abstract

“…In a lean period, the conversions of C 3 H 6 and CO were more than 90% owing to the presence of excess O 2 , whereas NO conversion was much lower (<50%). This is because the excess O 2 leads to not only the complete oxidation of reducing gases (C 3 H 6 and CO) but also the oxidation of active Rh 0 to the less-active Rh 3+ . − ,− Conversely, the conversions of C 3 H 6 and CO are lower in a rich period where NO conversion is complete because of the presence of excess reducing agents. Figure also clearly shows the effect of the support materials.…”

Section: Resultsmentioning

confidence: 99%

“…Rhodium is well-known as an active metal component for NO reduction in three-way catalysis (TWC), and the activity of Rh changes depending on the oxidation state. − In TWC, the catalyst is exposed to a dynamic oxidation–reduction perturbation atmosphere, which is expressed in terms of an air-to-fuel ratio (A/F) on a weight basis. A reducing (fuel-rich) condition occurs below the stoichiometric ratio (A/F < 14.6), whereas an oxidizing (fuel-lean) condition occurs at A/F > 14.6.…”

Section: Introductionmentioning

confidence: 99%

Redox Dynamics of Rh Supported on ZrP₂O₇ and ZrO₂ Analyzed by Time-Resolved In Situ Optical Spectroscopy

et al. 2017

View full text Add to dashboard Cite

In situ time-resolved diffuse reflectance spectroscopy was first applied to supported Rh catalysts (0.4 wt % Rh/ZrO 2 and Rh/ZrP 2 O 7 ) under dynamic three-way catalysis conditions fluctuating between fuel-lean and fuel-rich gas atmospheres. The optical absorption at 650 nm was found to decrease upon lean-to-rich switching of the gas feed, which led to the reduction of Rh oxide (Rh 3+ ) to metallic Rh (Rh 0 ), followed by a reversible increase upon back switching rich-to-lean. The kinetic analysis suggested that the reduction of Rh 3+ to Rh 0 was faster than the reoxidation over Rh/ ZrP 2 O 7 , whereas the reduction was comparable with or slower than the reoxidation over Rh/ZrO 2 . The activation energy of Rh/ZrP 2 O 7 for the reduction, 13.6 kJ mol −1 , was smaller than that for the oxidation, 48.7 kJ mol −1 , which contrasted with those of Rh/ZrO 2 (21.4 and 34.1 kJ mol −1 , respectively). These results were closely associated with the higher NO reduction activity of Rh/ZrP 2 O 7 than Rh/ZrO 2 under a lean-gas atmosphere because Rh was more active in the metallic state than in the oxide state. Applying fast lean−rich perturbation of the gas feed with 1 s intervals led to an immediate and significant drop of the optical absorption intensity, suggesting that the reduction of Rh substantially penetrated to deeper layers under the surface. This study provided the first in situ evidence for the formation of active metallic Rh species under high-frequency lean−rich oscillations.

show abstract

“…Unlike many other industrial catalytic processes, however, the TWC is characterized by unsteady-state operation, where the reaction atmosphere and/or temperature fluctuate rapidly. An example of this is the perturbation between fuel-rich and fuel-lean conditions, which is expressed in terms of the air-to-fuel ratio ( A / F ) on a weight basis below and above 14.6, respectively. ,, Precious metals are in their metallic state under rich conditions ( A / F < 14.6), while their oxides tend to form under lean conditions ( A / F > 14.6). ,,− The resulting redox behavior is closely related to the catalytic activity. Another significant feature is the so-called light-off characteristic, which can be assessed by increasing/decreasing the feed temperature, while monitoring the reactor outlet concentration or the fractional conversion efficiency of each gas.…”

Section: Introductionmentioning

confidence: 99%

Change in the Pd Oxidation State during Light-Off of Three-Way Catalysis Analyzed by in situ Diffuse Reflectance Spectroscopy

et al. 2020

View full text Add to dashboard Cite

The changes in the oxidation state of supported Pd catalysts during light-off of NO−CO−C 3 H 6 −O 2 reactions were evaluated during temperature ramp up and down cycles (10 °C min −1 ) under fuel-rich (air-to-fuel ratio, A/F = 14.1) and fuel-lean (A/F = 15.0) conditions. Real-time analysis of the Pd oxidation state was carried out by acquiring a diffuse reflectance at a wavelength of 450 nm every second. The correlation between the Kubelka−Munk function and the Pd oxidation state was confirmed by Pd 3d X-ray photoelectron spectroscopy. At the onset of the catalytic reaction, the oxidized Pd species (PdO) supported on Al 2 O 3 was converted to metallic Pd to a varying extent, depending on whether the provided gas feed was rich or lean. Under the rich conditions, >70% of Pd was reduced during light-off, which remained unchanged following the completion of the reaction and the subsequent temperature ramp down. Even under lean conditions, >40% of Pd on the surface was temporally reduced to the metallic state at 300 °C, although the thermodynamic estimation revealed that Pd should be stable in the oxide form. The obtained outcomes suggest that the real catalyst surface at the onset of light-off should be in a more reductive environment than that estimated from the equilibrium O 2 concentration in the gas phase. This is because the Pd surface site was predominantly occupied by the adsorbed CO and/or C 3 H 6 . Nevertheless, following the completion of light-off at ≥400 °C, the Pd surface was immediately reoxidized, as the surface concentration of CO/C 3 H 6 became negligible. The Pd reduction during light-off under lean conditions was determined to be considerably less pronounced when using the oxygen storage CeO 2 − ZrO 2 support. Because of its oxygen storage and release abilities, the reductive atmosphere of the Pd surface was mitigated, and the three-phase boundary formed at the interface with CeO 2 −ZrO 2 provided suitable active sites for the CO/C 3 H 6 light-off at the lowest possible temperatures.

show abstract

The catalytic reduction of nitric oxide over supported ruthenium catalysts

Cited by 80 publications

References 4 publications

Hysteresis Phenomena in the NO−H₂ Reaction over Ru(0001)

Hysteresis Phenomena in the NO−H₂ Reaction over Ru(0001)

Redox Dynamics of Rh Supported on ZrP₂O₇ and ZrO₂ Analyzed by Time-Resolved In Situ Optical Spectroscopy

Change in the Pd Oxidation State during Light-Off of Three-Way Catalysis Analyzed by in situ Diffuse Reflectance Spectroscopy

Contact Info

Product

Resources

About

The catalytic reduction of nitric oxide over supported ruthenium catalysts

Cited by 80 publications

References 4 publications

Hysteresis Phenomena in the NO−H2 Reaction over Ru(0001)

Hysteresis Phenomena in the NO−H2 Reaction over Ru(0001)

Redox Dynamics of Rh Supported on ZrP2O7 and ZrO2 Analyzed by Time-Resolved In Situ Optical Spectroscopy

Change in the Pd Oxidation State during Light-Off of Three-Way Catalysis Analyzed by in situ Diffuse Reflectance Spectroscopy

Contact Info

Product

Resources

About

Hysteresis Phenomena in the NO−H₂ Reaction over Ru(0001)

Hysteresis Phenomena in the NO−H₂ Reaction over Ru(0001)

Redox Dynamics of Rh Supported on ZrP₂O₇ and ZrO₂ Analyzed by Time-Resolved In Situ Optical Spectroscopy