Dual pulsed-beam controlled mole fraction studies of the catalytic oxidation of CO on supported Pd nanocatalysts

Harding, Christopher John; Kunz, Sebastian; Habibpour, Vahideh; Teslenko, V. V.; Arenz, Matthias; Heiz, Ulrich

doi:10.1016/j.jcat.2008.02.008

Cited by 30 publications

(31 citation statements)

References 2 publications

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“…The pulsed molecular beam (PMB) technique used in our lab has been described previously [40,45,46] and a brief overview will be given here. A piezo pulser, which allows for highly reproducible gas pulses, was filled with a 2 Torr background pressure of ethylene.…”

Section: Methodsmentioning

confidence: 99%

Assessing the concept of structure sensitivity or insensitivity for sub-nanometer catalyst materials

et al. 2016

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The nature of the nano-catalyzed hydrogenation of ethylene, yielding benchmark information pertaining to the concept of structure sensitivity/insensitivity and its applicability at the bottom of the catalyst particle size-range, is explored with experiments on size-selected Ptn (n=7-40) clusters softlanded on MgO, in conjunction with first-principles simulations. As in the case of larger particles both the direct ethylene hydrogenation channel and the parallel hydrogenation-dehydrogenation ethylidyne-producing route must be considered, with the fundamental uncovering that at the <1 nm size-scale the reaction exhibits characteristics consistent with structure sensitivity, in contrast to the structure insensitivity found for larger particles. In this size-regime, the chemical properties can be modulated and tuned by a single atom, reflected by the onset of low temperature hydrogenation at T >150 K catalyzed by Pt n (n≥10) clusters, with maximum room temperature reactivity observed for Pt 13 using a pulsed molecular beam technique. Structure insensitive behavior, inherent for specific cluster sizes at ambient temperatures, can be induced in the more active sizes, e.g. Pt 13 , by a temperature increase, up to 400 K, which opens dehydrogenation channels leading to ethylidyne formation. This reaction channel was, however found to be attenuated on Pt 20 , as catalyst activity remained elevated after the 400 K step. Pt 30 displayed behavior which can be understood from extrapolating bulk properties to this size range; in particular the calculated d-band center. In the non-scalable subnanometer size regime, however, precise control of particle size may be used for atom-by-atom tuning and manipulation of catalyzed hydrogenation activity and selectivity.

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Section: Methodsmentioning

confidence: 99%

Assessing the concept of structure sensitivity or insensitivity for sub-nanometer catalyst materials

et al. 2016

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“…Figure 2 shows an average of 20 pulses for the palladium samples. Between a time of 40 ms and 80 ms we define a 'quasi steady state' regime and use this value for the calculation of turnover frequencies (TOF) [26]. The TOF was determined by calibrating the QMS with a monolayer CO TPD from Pt(111) in the same chamber, and determining the sensitivity factor with respect to ethane (m/z = 30).…”

Section: Methodsmentioning

confidence: 99%

Ethylene hydrogenation on supported Ni, Pd and Pt nanoparticles: Catalyst activity, deactivation and the d-band model

Crampton

Rötzer

Schweinberger

et al. 2016

Journal of Catalysis

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Ethylene hydrogenation catalyzed at 300 K by 1-1.5 nm nanoparticles of Ni, Pd and Pt supported on MgO(100) with a narrow size-distribution, as well as the deactivation under reaction conditions at 400 K, were investigated with pulsed molecular beam experiments. Ni nanoparticles deactivate readily at 300 K, whereas Pd particles deactivate only after pulsing at 400 K, and Pt particles were found to retain hydrogenation activity even after the 400 K heating step. The hydrogenation turnover frequency normalized to the number of particles exhibited the trend, Pt>Pd>Ni. The activity/deactivation was found to scale with the location of the particles' d-band centroid, ε c , with respect to the Fermi energy of the respective metals calculated with density-functional theory. An ε c closer to the Fermi level is indicative of a facile deactivation/low activity and an ε c farther from the Fermi level is characteristic of higher activity/impeded deactivation. CO adsorption, probed with infrared reflection absorption spectroscopy was used to investigate the clusters before and after the reaction, and the spectral features correlated with the observed catalytic behavior.

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“…[2][3][4][5][6][7][14][15][16][17][18][19][20] This reaction therefore, is a good test system for probing changes in the physical and chemical properties of metal particles as their size is reduced into the range (<50 atoms) where a number of size-selected deposition studies have shown behavior quite different from what could be predicted by scaling bulk properties. 4,6,7,14,15,[21][22][23][24][25][26][27][28][29] Recently, we reported a study of CO oxidation over Pd n / TiO 2 (110) (n ≤ 25) where both CO adsorption and CO 2 production varied non-monotonically with size, and where activity was shown to correlate strongly with shifts in the electronic properties of the Pd clusters, as probed by X-ray photoelectron spectroscopy (XPS) of the Pd 3d core level. 7 We recently showed that under the conditions studied, much of the size dependence reflected differences in the ability of the clusters to activate O 2 , however, competition for binding sites between O ads and CO is also an important factor.…”

Section: Introductionmentioning

confidence: 99%

CO adsorption and desorption on size-selected Pdn/TiO2(110) model catalysts: Size dependence of binding sites and energies, and support-mediated adsorption

Kaden

Kunkel

Roberts

et al. 2012

The Journal of Chemical Physics

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The nature of CO adsorption on Pd(n)/TiO(2)(110) (n = 1, 2, 7, 20) has been examined using temperature-programmed desorption (TPD), temperature-dependent helium ion scattering (TD-ISS), and X-ray photoelectron spectroscopy (XPS). All samples contain the same number of Pd atoms (0.10 ML-equivalent) deposited as different size clusters. The TPD and TD-ISS show that CO binds in two types of sites associated with the Pd clusters. The most stable sites are on top of the Pd clusters ("on-top" sites), however, there are also less stable sites, in which CO is bound in association with, but not on top of the Pd ("peripheral" sites). For saturation CO coverage over a fixed atomic concentration of Pd (present in the form of Pd(n) clusters of varying size), the population of CO in peripheral sites decreases with increasing cluster size, while the on-top site population is size-independent. This is consistent with what geometric considerations would predict for the density of the two types of sites, provided the clusters adsorb predominantly as 2D islands, which ISS results suggest to be the case. The XPS analysis indicates that CO-Pd binding is dominated by π-backbonding to the Pd(n) clusters. The results also show evidence for efficient support-mediated adsorption (reverse-spillover) of CO initially impinging on TiO(2) to binding sites associated with the Pd clusters.

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Dual pulsed-beam controlled mole fraction studies of the catalytic oxidation of CO on supported Pd nanocatalysts

Cited by 30 publications

References 2 publications

Assessing the concept of structure sensitivity or insensitivity for sub-nanometer catalyst materials

Assessing the concept of structure sensitivity or insensitivity for sub-nanometer catalyst materials

Ethylene hydrogenation on supported Ni, Pd and Pt nanoparticles: Catalyst activity, deactivation and the d-band model

CO adsorption and desorption on size-selected Pdn/TiO2(110) model catalysts: Size dependence of binding sites and energies, and support-mediated adsorption

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