NO Reduction by H<sub>2</sub> on the Rh(111) and Rh(221) Surfaces: A Mechanistic and Kinetic Study

Huai, Liyuan; Su, Tan; Wen, Hao; Jin, Xin; Liu, Jing-Yao

doi:10.1021/acs.jpcc.5b10740

Cited by 29 publications

(38 citation statements)

References 40 publications

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“…Previous density functional theory (DFT) studies on bare Rh(111) and (221) surfaces suggest that direct dissociation of NO is the most favorable route . This is consistent with the observation of dissociative adsorption of NO at low coverages NO* .…”

Section: Introductionsupporting

confidence: 85%

Mechanism and Effects of Coverage and Particle Morphology on Rh-Catalyzed NO–H₂ Reactions

2020

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Three-way catalysts, which typically include Rh, are used to treat automotive exhaust and reduce nitric oxide (NO) with a combination of CO and H2, although few kinetic and theoretical investigations have studied NO–H2 reactions on Rh. Here, we examine NO activation, which is believed to control the rate of NO reduction, through direct, NO-assisted, and H2-assisted dissociation pathways on NO*-covered Rh(111) surfaces and Rh nanoparticle models using density functional theory (DFT) and contrast these results with previously reported data on Pt(111) surfaces. Saturation coveragesdetermined by incrementally adsorbing NO*were determined to be 5/9 ML NO* on Pt(111), 6/9 ML on Rh(111), and 1.38 ML on a 201-atom Rh nanoparticle (∼2 nm). Free energies of activation and reaction were calculated by DFT for the pathways at these coverages and interpreted through maximum rate analyses over a wide range of NO and H2 pressures to predict NO activation mechanisms and kinetics. Rates are inhibited by NO at all relevant NO pressures and to similar extents on all catalyst models. On Pt(111) surfaces, NO is activated through NOH* formation and dissociation (to N* and OH*) at low H2 pressures (<0.5 bar) and through HNOH* (to HN* and OH*) at high H2 pressures (>0.5 bar), resulting in a shift in the H2 dependency from half order to first order. NO is activated through NOH* formation and dissociation on Rh(111) at all relevant H2 pressures, with all other pathways being >1000 times slower. NO activation occurs with similar rates through either NOH* or HNO* on Rh particles at 1.38 ML NO*, indicating that these high coverages can shift mechanistic preferences. Predicted NO consumption rates are half order in H2 on Rh particles and surfaces and are similar in magnitude to one another, despite shifts in the mechanism; these rates on Rh are 106 times slower than Pt, consistent with the prior reports that demonstrate that equal turnover rates for Pt at 60 °C occur for Rh at 200 °C. This work demonstrates that strong NO bonds activate through bimolecular (assisted) pathways and that particle models of catalysts enable high coverages of strongly bound species, which can then influence relative rates and mechanistic predictions.

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Section: Introductionsupporting

confidence: 85%

Mechanism and Effects of Coverage and Particle Morphology on Rh-Catalyzed NO–H₂ Reactions

2020

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“…Most of the current ab initio research in surfacek inetics focuses on establishing accurate activation energies over ideal surfaces by static density functional theory (DFT) methods, [8,[11][12][13][14][15][16] with transition states (TSs) generally estimatedusing the nudged elastic band (NEB) method. [17] The structure sensitivity of CO pathways on Rh surfacesw as first investigated for the Rh(111)a nd Rh(211) slabs using the RPBE functional by Mavrikakise tal.…”

Section: Introductionmentioning

confidence: 99%

Constrained Chemical Dynamics of CO Dissociation/Hydrogenation on Rh Surfaces

Kraus

Frank

2018

Chemistry A European J

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Among noble metal catalysts, rhodium (Rh) is unique in its ability to perform a one-step synthesis of ethanol from syngas. The first steps following the adsorption of syngas on Rh surfaces are assumed to be responsible for the conversion of CO and the selectivity effects between C , C , and oxygenated species. In the current work, constrained ab initio molecular dynamics are applied to investigate the kinetics of CO dissociation and hydrogenation over flat and stepped Rh surfaces. The obtained barriers for the Rh(111) surface are in good agreement with the literature data. On the stepped Rh(211) surface, a large site-dependent variation in barrier height is shown, with the upper terrace exhibiting behavior comparable to the Rh(111) surface, whereas the barriers over the lower terrace site are generally significantly lower. The rate constants are calculated using transition state theory for both surfaces, and are applied successfully in a microkinetic model, confirming the predicted impact on CO conversion and CH /C -oxygenate/C H selectivity. In addition to the high-accuracy energetics and rate constants reported for CO dissociation/hydrogenation and the presentation of an updated microkinetic mechanism for Rh catalysts, the applicability of constrained molecular dynamics for reaction barrier calculation is confirmed, and sensitive pathways affecting the selectivity between formaldehyde/methanol over Rh catalysts are highlighted.

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“…The calculated dissociation energy barrier of NO is ca. 1.5–1.6 eV on Rh(111) (1.50 eV obtained by Huai et al and 1.63 eV obtained by Tan et al). With this value as a reference, we selected the Fe-, Co-, and Ni-doped Pt(111) surfaces in the following study.…”

Section: Resultsmentioning

confidence: 87%

Catalytic Activity of the Transition-Metal Atom Doped Platinum Surface for NO Reduction by CO

et al. 2021

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The formation of bimetallic surface alloy catalysts is one of the most promising methods to improve the NO reduction activity of three-way catalysts. Here, the reduction of NO by CO on (100) and (111) surfaces of a series of transition metal (TM)-Pt alloy catalysts (TM = Fe, Co, Ni, Ru, Rh, Pd, Os, and Ir) was systematically studied by a density functional theory calculation and a microkinetics simulation. Under the actual reaction conditions, the surface alloy systems are stable, and TM doping enhances the adsorption strength of NO. On the basis of the dissociation energy barrier of NO, five TM-Pt(100) (Fe, Co, Ni, Rh, Ir) and three TM-Pt(111) (Fe, Co, Ni) were selected to study the overall reaction mechanism of NO+CO. Possible elementary steps for three N-containing products (N2, N2O, and NO2) and CO2 were considered. Microkinetic calculations further demonstrate that the conversion rates [turnover frequency] of products and product selectivity toward N2 are improved in varying degrees on TM-Pt alloy catalysts. This work indicates that Fe–Pt(100), Co–Pt(100), and Ni–Pt(111) can be the optimal catalysts for NO reduction by CO, with a high N2 conversion rate and nearly 100% N2 selectivity in the whole temperature range of 300–1000 K.

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NO Reduction by H₂ on the Rh(111) and Rh(221) Surfaces: A Mechanistic and Kinetic Study

Cited by 29 publications

References 40 publications

Mechanism and Effects of Coverage and Particle Morphology on Rh-Catalyzed NO–H₂ Reactions

Mechanism and Effects of Coverage and Particle Morphology on Rh-Catalyzed NO–H₂ Reactions

Constrained Chemical Dynamics of CO Dissociation/Hydrogenation on Rh Surfaces

Catalytic Activity of the Transition-Metal Atom Doped Platinum Surface for NO Reduction by CO

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NO Reduction by H2 on the Rh(111) and Rh(221) Surfaces: A Mechanistic and Kinetic Study

Cited by 29 publications

References 40 publications

Mechanism and Effects of Coverage and Particle Morphology on Rh-Catalyzed NO–H2 Reactions

Mechanism and Effects of Coverage and Particle Morphology on Rh-Catalyzed NO–H2 Reactions

Constrained Chemical Dynamics of CO Dissociation/Hydrogenation on Rh Surfaces

Catalytic Activity of the Transition-Metal Atom Doped Platinum Surface for NO Reduction by CO

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Product

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NO Reduction by H₂ on the Rh(111) and Rh(221) Surfaces: A Mechanistic and Kinetic Study

Mechanism and Effects of Coverage and Particle Morphology on Rh-Catalyzed NO–H₂ Reactions

Mechanism and Effects of Coverage and Particle Morphology on Rh-Catalyzed NO–H₂ Reactions