Chemistry of Supported Palladium Nanoparticles during Methane Oxidation

Nilsson, Jan-Olof; Carlsson, Per-Anders; Fouladvand, Sheedeh; Martin, Natalia; Gustafson, Johan; Newton, Mark A.; Lundgren, Edvin; Grönbeck, Henrik; Skoglundh, Magnus

doi:10.1021/cs502036d

Cited by 106 publications

(77 citation statements)

References 42 publications

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“…Using a quantum/classical approach they demonstrated that Pd(IV) oxide would be stabilized on ceria due to its interaction with the support, yielding low methane activation barriers. The enhancement in oxide formation of Pd clusters due to the effect of CeO 2 is in agreement with the work of Farrauto et al 53 and Nilsson et al 54 Although sophisticated sampling and advanced optimization methods may correctly identify the global minimum structure of the cluster catalyst, it is not the ultimate, complete representation of the active site. First of all, unlike extended surfaces, catalytic clusters do not stay put in their starting global minimum during the reaction.…”

Section: The Global Minimum Structure Of the Cluster Catalyst: Not supporting

confidence: 89%

Surface‐supported cluster catalysis: Ensembles of metastable states run the show

Zandkarimi

Alexandrova

2019

WIREs Comput Mol Sci

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It has recently been shown that the dynamic behavior of surface‐supported nanocluster catalysts in realistic reaction conditions defies conventional models used in catalysis. This opens new doors in catalysis by giving more leverage in catalyst design, but also requires a major revision of the understanding of how dynamic heterogeneous catalytic interfaces operate, as well as of the computational approaches of catalyst modeling, and experimental methods of catalyst characterization. Major aspects of the new paradigm include the collective action of many catalyst states that form a statistical ensemble in reaction conditions, the catalytic activity and selectivity being driven by rare and metastable catalyst states, reaction thermodynamics and kinetics being controlled by different states of the catalyst, broken scaling relationships, non‐Arrhenius behaviors, and catalyst dynamic restructuring being an essential part of the reaction mechanism. For computation, this complexity means the departure from the standard density functional theory calculations of reaction mechanisms on a single catalyst structure. For experiment, it calls for the development of operando characterization tools with the per‐site resolution and the ability to find the minority sites that govern the catalytic activity. For catalyst design, the goal becomes the creation of the catalyst state (geometric and electronic) that might not be present in the as‐prepared catalyst, but would develop in the reaction conditions and would have the desired activity then. While cluster catalysts are the most dramatic in their dynamic fluxionality, other amorphous interfaces also exhibit some of it, and thus are also subject to similar paradigm revision. This article is categorized under: Structure and Mechanism > Reaction Mechanisms and Catalysis

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Section: The Global Minimum Structure Of the Cluster Catalyst: Not supporting

confidence: 89%

Surface‐supported cluster catalysis: Ensembles of metastable states run the show

Zandkarimi

Alexandrova

2019

WIREs Comput Mol Sci

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“…Palladium is ak nown efficient catalyst for CH 4 oxidation and has been studied extensively.V arying hypotheses of the active phase have been reported, from aP dO-like phase to Pd 0 . [1] Unfortunately,o fa ll the catalysts currently reported, none are sufficiently active under coldstart conditions,w ith most catalysts requiring light-off temperatures of around 400 8 8C. [2] Such high temperatures are required because of the high activation barriers to CH 4 dehydrogenation;particularly formation of surface adsorbed CH 3 *a nd H*, which is thought to be the rate-determining step.F or example,J ørgensen and Grçnbeck predicted that the extraction of the first Hfrom CH 4 had activation barriers of 0.99 and 0.79 eV over Pd(111) and Pd(100), respectively.…”

mentioning

confidence: 99%

Probing the Role of a Non‐Thermal Plasma (NTP) in the Hybrid NTP Catalytic Oxidation of Methane

et al. 2017

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Three recurring hypotheses are often used to explain the effect of non‐thermal plasmas (NTPs) on NTP catalytic hybrid reactions; namely, modification or heating of the catalyst or creation of new reaction pathways by plasma‐produced species. NTP‐assisted methane (CH4) oxidation over Pd/Al2O3 was investigated by direct monitoring of the X‐ray absorption fine structure of the catalyst, coupled with end‐of‐pipe mass spectrometry. This in situ study revealed that the catalyst did not undergo any significant structural changes under NTP conditions. However, the NTP did lead to an increase in the temperature of the Pd nanoparticles; although this temperature rise was insufficient to activate the thermal CH4 oxidation reaction. The contribution of a lower activation barrier alternative reaction pathway involving the formation of CH3(g) from electron impact reactions is proposed.

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“…[28][29][30][31] In fact, the XANES signals are mostly sensitive to the oxidation state of an element, and less sensitive to its local coordination and structure. 32 Hence, from the spectroscopic point of view, PdO and Pd(OH) 4 2− cannot be easily discriminated, whereas the redox change from Pd to Pd(II) can be easily monitored, even using a single fixed energy of 24370 eV (Fig.…”

Section: Discussionmentioning

confidence: 99%

Computational Speciation Models: A Tool for the Interpretation of Spectroelectrochemistry for Catalytic Layers under Operative Conditions

Montegrossi

Giaccherini

Berretti

et al. 2017

J. Electrochem. Soc.

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In this study, the first coupled FEXRAV and chemical speciation modelling study of the Pd deactivation is presented. Due to the high brilliance of synchrotron light, FEXRAV can investigate deeply buried surfaces. More specifically, we directly analyzed the evolution of the Pd/C catalytic layer during a voltammetric cycle, through a specifically designed electrochemical cell. Still, we observed a complex interfacial chemistry of Pd, which impairs a straightforward interpretation of FEXRAV data. Exploiting thermodynamic chemical speciation modelling we were able to overcome this issue. The study leads to three main results: 1) the confirmation of the relationship between the change of the Pd/Pd(II) ratio and the change of the Fluorescence intensity 2) the investigation of the deactivation mechanism 3) the identification of the relevant species leading to the electrodissolution of Pd under operative conditions. This study opens new perspectives for the application of the chemical speciation modelling to the study of the deactivation mechanism of Pd in Pd/C catalytic layers under operative conditions in different electrolytes. In recent times, Palladium-based electrocatalysts proved to be able to promisingly substitute Pt in several electrocatalytic applications due to their lower cost and higher availability.1 Moreover, Pd catalysts resulted very effective in direct alcohol fuel cell (DAFC). One of the benefits consists in the bypass of the deactivation process occurring in Pt catalysts due to reaction with CO.2,3 Nowadays, the main issue still preventing full exploitation of such electrodic materials is their anodic deactivation, which is not fully understood and manageable. In fact, although the origin of the deactivation has been related to the formation of an oxide layer on the Pd surface, its formation mechanism is still an open question. 4 Moreover, other studies suggested that Pd electrodes are also subjected to electrodissolution under operative condition. 5 In principle, the latter process is competitive with the formation of the oxide layer and it is not observable by means of ex-situ techniques. In this context, a natural follow-up of the conventional ex-situ experiments are in situ/operando spectroelectrochemical measurements, performed to investigate the competition between these two processes under operative conditions. For operative conditions, we refer to the strongly anodic and basic conditions usually applied to the catalytic layer for the electrooxidation of alcohols. In the same context, the catalytic layer is usually intended as the place where the interaction between the electrolyte, the catalysts and the support occurs.6 Several in-situ/operando techniques applied to catalysts are reported in literature, most of them are carried out on model systems with specific surface preparation or they require concentrated materials (i.e. on Pd electrodes).7-10 As shown by Minguzzi et al., the Fixed Energy X-ray Absorption Voltammetry 11 enables the direct study of the oxidation state for chemical specie...

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Chemistry of Supported Palladium Nanoparticles during Methane Oxidation

Cited by 106 publications

References 42 publications

Surface‐supported cluster catalysis: Ensembles of metastable states run the show

Surface‐supported cluster catalysis: Ensembles of metastable states run the show

Probing the Role of a Non‐Thermal Plasma (NTP) in the Hybrid NTP Catalytic Oxidation of Methane

Computational Speciation Models: A Tool for the Interpretation of Spectroelectrochemistry for Catalytic Layers under Operative Conditions

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