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Iwasa, Nobuhiro; Takezawa, Nobutsune

doi:10.1023/a:1023571819211

Cited by 265 publications

(239 citation statements)

References 40 publications

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“…On the other hand, Pd supported on easily reducible oxides such as ZnO, Ga2O3 or In2O3 becomes active and selective in MSR. Unusual behavior of these Pd based catalysts was attributed to a formation 4 of alloys PdMe (Me = Zn, Ga, In) upon proper reductive pretreatment, leading to a bifunctional synergism between intermetallic and oxide species which is necessary for a good catalytic performance in MSR [19,20]. In addition, the in situ partial oxidation of PdZn nanoparticles was observed recently to result in the formation of a large interface between the intermetallic PdZn and small ZnO patches, which improved the selectivity to CO2 in MSR [20].…”

Section: Introductionmentioning

confidence: 99%

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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Section: Introductionmentioning

confidence: 99%

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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“…Most of the literature data devoted to this preparation technique is focused on EDTAAl 2 O 3 [2][3][4][5], EDTA-AlPO 4 [6] and EDTA-MgO/Al 2 O 3 systems [7]. Contrary to SiO 2 or Al 2 O 3 , zinc oxide is a partially reducible support [8][9][10] and therefore reduced Zn may form alloys with main metallic phase. In some cases such binary catalyst performs better than a singlephase one: Iwasa [11] reported that in the reaction of CO 2 hydrogenation on Pd-Zn/ZnO catalysts showed higher activities and selectivities towards methanol than pure palladium based ones.…”

Section: Introductionmentioning

confidence: 99%

FT-IR/PAS Study of Surface EDTA-ZnO Interactions

Kuśmierz¹,

Pasieczna-Patkowska²

2014

Annales UMCS, Chemia

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“…Recently, novel Pd/ZnO systems 3-15 (as well as Pd/Ga 2 O 3 and Pd/In 2 O 3 18,19 ) have attracted more attention because of their enhanced long-term and thermal stability 20,21 . As unsupported pure Pd exhibits only a poor selectivity 22 , the observed high activity and selectivity for CO 2 formation was ascribed to the formation of distinct PdZn, PdIn and PdGa alloys upon reductive activation at elevated temperatures 18 . Best characterized is the Pd/ZnO system, where alloy formation has been studied and confirmed by X-ray diffraction (XRD) 18,23 , temperature-programmed reduction (TPR) 18,23 and X-ray and ultraviolet photoelectron spectroscopy (XPS and UPS) [24][25][26] .…”

mentioning

confidence: 98%

“…As unsupported pure Pd exhibits only a poor selectivity 22 , the observed high activity and selectivity for CO 2 formation was ascribed to the formation of distinct PdZn, PdIn and PdGa alloys upon reductive activation at elevated temperatures 18 . Best characterized is the Pd/ZnO system, where alloy formation has been studied and confirmed by X-ray diffraction (XRD) 18,23 , temperature-programmed reduction (TPR) 18,23 and X-ray and ultraviolet photoelectron spectroscopy (XPS and UPS) [24][25][26] . Iwasa et al 23 observed PdZn alloy formation upon reduction at very low T (≥ 473 K).…”

mentioning

confidence: 99%

Growth and structural stability of well-ordered PdZn alloy nanoparticles

Penner

Jenewein

Gabasch

et al. 2006

Journal of Catalysis

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Despite many recent attempts to unravel the structure of novel PdZn alloys, promising catalysts in methanol steam reforming, a detailed study on the formation of Pd-Zn alloy particles and of their structural and thermal stability is still missing. We take advantage of the unique properties of epitaxially grown Pd particles embedded in layers of amorphous ZnO and mechanically stabilized by SiO 2 , and present an electron microscopy study of the preparation of well-ordered PdZn alloy nanoparticles at surprisingly low reduction temperatures. They are formed by topotactic growth on the surface of the Pd nanoparticles and are structurally and thermally stable in a broad temperature regime (473 -873 K). At and above 873K, partial decomposition of PdZn and beginning interaction with the SiO 2 support has been observed. Keywords:Thin film model catalyst, hydrogen reduction, alloy formation, electron microscopy, selected area electron diffraction ManuscriptMuch recent effort has been invested in the development of suitable catalysts for methanol steam reforming 1-15 as this is one of the most promising processes for hydrogen production with a high hydrogen-to-carbon ratio 16 . Cu/ZnO catalysts have been commercially used to produce hydrogen with high selectivity and activity 2-6 , but they suffer from deactivation at reaction temperatures above 573 K 17 . Recently, novel Pd/ZnO systems 3-15 (as well as Pd/Ga 2 O 3 and Pd/In 2 O 3 18,19 ) have attracted more attention because of their enhanced long-term and thermal stability 20,21 . As unsupported pure Pd exhibits only a poor selectivity 22 , the observed high activity and selectivity for CO 2 formation was ascribed to the formation of distinct PdZn, PdIn and PdGa alloys upon reductive activation at elevated temperatures 18 . Best characterized is the Pd/ZnO system, where alloy formation has been studied and confirmed by X-ray diffraction (XRD) 18,23 , temperature-programmed reduction (TPR) 18,23 and X-ray and ultraviolet photoelectron spectroscopy (XPS and UPS) [24][25][26] . Iwasa et al. 23 observed PdZn alloy formation upon reduction at very low T (≥ 473 K). Density functional studies revealed the close relationship between the electronic structure of PdZn and Cu-based catalysts giving rise to a similar catalytic performance in methanol steam reforming 27,28 . Comparatively few studies have been carried out on the structural characterization of the PdZn alloys by electron microscopy, and these were limited to overview imaging of powder catalysts in the as-prepared state and after hydrogen reduction, thereby mainly supporting XRD measurements 29,30 . The Pd-Zn system is known to form several stable bulk alloy phases 31 . The most important and thermally most stable is the PdZn (β1) phase, which crystallizes in a tetragonal (AuCu-type) L1 0 structure 32 . A key point for understanding the catalytic pecularities of the above-mentioned Pd-Zn alloy particles is also to determine their surface composition. Recent experiments in our laboratory 33 show that a well-orde...

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Cited by 265 publications

References 40 publications

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

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

FT-IR/PAS Study of Surface EDTA-ZnO Interactions

Growth and structural stability of well-ordered PdZn alloy nanoparticles

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