Effect of Zn addition on the water–gas shift reaction over supported palladium catalysts

Bollmann, Luis; Ratts, Joshua L.; Joshi, Ajay M.; Williams, W. J.; Pazmiño, Jorge H.; Joshi, Yogesh V.; Miller, Jeffrey T.; Kropf, A. Jeremy; Delgass, W. Nicholas; Ribeiro, Fabio H.

doi:10.1016/j.jcat.2008.04.005

Cited by 93 publications

(87 citation statements)

References 45 publications

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“…Pd has a lower surface tension, a larger atomic radius and much less loading than Mg. As a result, there is a trend that Pd is expelled out of the MgO matrix. This agrees with the previous reports where similar Pd-containing alloy compounds are excluded in supported Pd-Ni, Pd-Cu and Pd-Zn catalysts [19,33,34].…”

Section: Xrdsupporting

confidence: 93%

Role of MgO over γ-Al2O3-supported Pd catalysts for carbon dioxide reforming of methane

Shi

Zhang

2015

Applied Catalysis B: Environmental

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a b s t r a c tA series of Pd/Al 2 O 3 catalysts with varying Mg loading (1, 3, 7 and 10 wt%) were investigated for carbon dioxide reforming of methane. It was observed that the initial catalytic activities and long-term stabilities in terms of both CO 2 and CH 4 conversions increased with increasing Mg content when its loading was below 7 wt%. When Mg content was up to 10 wt%, the initial activity and stability decreased. Moreover, Pd7Mg/Al 2 O 3 displayed the highest H 2 and CO yields. Characterization results conducted on catalysts before and after reaction test demonstrated that MgO mainly presented in amorphous form for catalysts with additive content below 7 wt%; while a fraction of MgO transformed into crystalline form when more additive was introduced to the catalyst. The amorphous MgO significantly enhanced surface metal dispersion, decreased average Pd crystallite size and thus improved resistances against both metal sintering and carbon deposition, which contributed to the enhanced initial activities and long-term stabilities. On the contrary, the crystalline MgO decreased exposed Pd active sites, caused metal sintering and thus led to increased amount of carbon deposition owing to both its negative decoration effect on surface metal and deterioration effect on textural characteristics of support. These factors were responsible for the worse catalytic performance of Pd10Mg/Al 2 O 3 as compared to that of Pd7Mg/Al 2 O 3 .

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Section: Xrdsupporting

confidence: 93%

Role of MgO over γ-Al2O3-supported Pd catalysts for carbon dioxide reforming of methane

Shi

Zhang

2015

Applied Catalysis B: Environmental

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“…All the DRIFT results showed the coordination bands of CO in two regions. CO The bands with a wavenumber higher than 2150 cm −1 can be assigned to CO in gas phase [52]. As it can be seen from this study, the type of ZnO substrate affects the vibrational frequency of adsorbed CO.…”

Section: Drift Study Of Co Adsorption On Pdzn/zno Catalystsmentioning

confidence: 52%

“…12 D). Moreover, higher concentration of CO linearly bonded to Pd was found on the samples with higher concentration of Zn on the surface [52]. Taking shift of wavenumber to lower values can be ascribed to the electronic interaction between Pd and ZnO support.…”

Section: Drift Study Of Co Adsorption On Pdzn/zno Catalystsmentioning

confidence: 84%

Ultraselective low temperature steam reforming of methanol over PdZn/ZnO catalysts—Influence of induced support defects on catalytic performance

Eblagon

Concepción

Silva

et al. 2014

Applied Catalysis B: Environmental

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The influence of the calcination atmosphere of ZnO precursor (Zn4(CO)3(OH)6·H2O) on the catalytic performance of a series of PdZn/ZnO catalysts was studied for production of H2 via low temperature (180 • C) direct methanol steam reforming (low temperature-MSR). The catalytic activity and selectivity of PdZn/ZnO were found to be strongly influenced by the calcination atmosphere of ZnO precursor and increased from oxidizing to reducing atmosphere, following the order (O2 < air < N2 < H2). As a result, a very active catalyst was obtained by simply supporting Pd on ZnO calcined in H2. Further evidence from XPS and TPR analysis indicated that calcination in reducing atmosphere gave rise to a significant increase in the concentration of oxygen vacancies on the surface of ZnO support. Thus, the superb performance of the best catalyst was attributed to the defect chemistry of ZnO support; mainly to the amount of oxygen vacancies present in the interface region, which act as additional active sites for water adsorption and subsequent activation. In addition, the formation of CO was drastically suppressed by replenishment of oxygen vacancies on ZnO support. Thus, it is clear that the abundance of specific active sites on PdZn/ZnO catalyst is strongly influenced by the preparation route of the ZnO support. Additionally, the PdZn alloy was discovered to be unstable under prolonged exposure to CO atmosphere and the stability test under methanol steam reforming conditions showed a 24% drop in conversion over 48 h testing period. This phenomena can have detrimental effect on the performance of this type of catalytic systems in continuous prolonged duty cycle time on-stream.

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“…The mechanism by which Zn alters the reactivity of the Pd, however, is only starting to be understood [7][8][9][10][11][12]. Since the observed CO 2 selectivity during the steam reforming of methanol on Pd/ZnO exceeds the equilibrium selectivity obtainable by the water gas shift (WGS) reaction, a pathway involving the dehydrogenation of methoxide to CO followed by WGS to produce CO 2 can be ruled out [1,13].…”

Section: Introductionmentioning

confidence: 99%

Reaction of Formic Acid on Zn-Modified Pd(111)

Jeroro

Vohs

2009

Catal Lett

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The decomposition of formic acid on Zn/Pd(111) was studied using Temperature Programmed Desorption and High Resolution Electron Energy Loss Spectroscopy. On Pd(111), HCOOH decomposes via both dehydration and dehydrogenation pathways to produce CO, CO 2 , H 2 and H 2 O. Small amounts of Zn (\0.1 mL) incorporated the Pd(111) surface were found to increase the stability of formate species and alter their decomposition selectivity to favor dehydrogenation, resulting in an increase in CO 2 production. This difference in reactivity appears to be caused by relatively long range electronic interactions between surface Pd and Zn atoms and may be important in Pd/ZnO methanol steam reforming catalysts which exhibit high selectivities to CO 2 and H 2 .

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Effect of Zn addition on the water–gas shift reaction over supported palladium catalysts

Cited by 93 publications

References 45 publications

Role of MgO over γ-Al2O3-supported Pd catalysts for carbon dioxide reforming of methane

Role of MgO over γ-Al2O3-supported Pd catalysts for carbon dioxide reforming of methane

Ultraselective low temperature steam reforming of methanol over PdZn/ZnO catalysts—Influence of induced support defects on catalytic performance

Reaction of Formic Acid on Zn-Modified Pd(111)

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