Effect of Zn addition to supported Pd catalysts in the steam reforming of methanol

Iwasa, Nobuhiro; Mayanagi, Tomoyuki; Nomura, Wataru; Arai, Masahiko; Takezawa, Nobutsune

doi:10.1016/s0926-860x(03)00184-4

Cited by 185 publications

(126 citation statements)

References 14 publications

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“…In line with previous studies on PdZn formation 8,[12][13][14] , the present electron microscopy study unambiguously reveals the onset of the formation of a tetragonal PdZn phase upon reduction at T ≥ 473 K. The formation of the alloy phase proceeds most likely via topotactic formation of PdZn on top of the Pd particles. This growth mechanism is probably favoured by the relatively small mismatch of the lattice constants of fcc Pd (0.388 nm) and tetragonal PdZn (0.410 nm).…”

supporting

confidence: 91%

“…The strong particle stabilization effect (SPSE) is of importance for catalytic processes such as methanol steam reforming and methanol synthesis on Pd/ZnO catalysts. In particular, the striking differences between the Pd/SiO 2 and Pd/ZnO/SiO 2 systems demonstrated in this work may lead to a better understanding of the drastic activity and selectivity differences between Pd/SiO 2 and Pd/ZnO reported in the literature 13,23 . According to recent single crystal experiments 33,38 and theory studies 38,39 it seems that this very stable PdZn alloy phase of stoichiometric surface composition is stable over a wide range of temperatures.…”

mentioning

confidence: 60%

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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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supporting

confidence: 91%

mentioning

confidence: 60%

Growth and structural stability of well-ordered PdZn alloy nanoparticles

Penner

Jenewein

Gabasch

et al. 2006

Journal of Catalysis

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“…Znmodified Pd catalysts supported on CeO2 also show high selectivity for methanol steam reforming. XRD results indicate the formation of the Pd-Zn alloy, as well as the complete disappearance of the metallic Pd after reduction [57]. Methanol steam reforming performances over Pd/ZnO and Pd/CeO2 catalysts were compared.…”

Section: Palladium Based Catalystsmentioning

confidence: 99%

Review on Copper and Palladium Based Catalysts for Methanol Steam Reforming to Produce Hydrogen

Shuai

2017

Catalysts

101

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Abstract:Methanol steam reforming is a promising technology for producing hydrogen for onboard fuel cell applications. The methanol conversion rate and the contents of hydrogen, carbon monoxide and carbon dioxide in the reformate, significantly depend on the reforming catalyst. Copper-based catalysts and palladium-based catalysts can effectively convert methanol into hydrogen and carbon dioxide. Copper and palladium-based catalysts with different formulations and compositions have been thoroughly investigated in the literature. This work summarized the development of the two groups of catalysts for methanol steam reforming. Interactions between the activity components and the supports as well as the effects of different promoters were discussed. Compositional and morphological characteristics, along with the methanol steam reforming performances of different Cu/ZnO and Pd/ZnO catalysts promoted by Al 2 O 3 , CeO 2 , ZrO 2 or other metal oxides, were reviewed and compared. Moreover, the reaction mechanism of methanol steam reforming over the copper based and palladium based catalysts were discussed.

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“…High selectivity to CO 2 and H 2 production is crucial due to the poisoning effect of CO on fuel cell anodes in polymer electrolyte membrane fuel cells (PEMFC), requiring <20 ppm CO in the H 2 fuel [10]. Pd supported on ZnO has attracted much attention due to its superior stability compared with Cu/ZnO [3,11,12]. In contrast to Pd on inert supports such as SiO 2 or active carbon, which catalyzes methanol decomposition to CO and H 2 [13], Pd on ZnO, Ga 2 O 3 , and In 2 O 3 can show high activity and selectivity for steam reforming to CO 2 and H 2 [14,15].…”

Section: Introductionmentioning

confidence: 99%

In situ study of the formation and stability of supported Pd2Ga methanol steam reforming catalysts

Haghöfer

Föttinger

Girgsdies

et al. 2012

Journal of Catalysis

105

138

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Pd/Ga2O3 methanol steam reforming (MSR) catalysts were characterized in detail by utilizing a range of in situ techniques of varying surface sensitivity. Correlating the nature of the intermetallic Pd-Ga compound (IMC; formed upon reduction) with the corresponding activity/selectivity revealed pronounced differences. Generally, a dynamic response of the catalyst surface to the surrounding gas environment was observed. Special attention was paid to the bulk and surface stability of the Pd-Ga IMCs. Whereas the bulk was stable in O2, decomposition of the surface occurred resulting in a partial coverage by GaxOy islands. In addition, we focused on the formation mechanism of undesired CO and were able to identify the reasons limiting the selectivity to MSR. We observed a detrimental effect of CO on the selective Pd-Ga intermetallic compound, causing partial decomposition of the IMC to metallic Pd at the surface. Consequently, patches of Pd metal are present under reaction conditions, catalyzing the unwanted parallel methanol decomposition reaction.

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Effect of Zn addition to supported Pd catalysts in the steam reforming of methanol

Cited by 185 publications

References 14 publications

Growth and structural stability of well-ordered PdZn alloy nanoparticles

Growth and structural stability of well-ordered PdZn alloy nanoparticles

Review on Copper and Palladium Based Catalysts for Methanol Steam Reforming to Produce Hydrogen

In situ study of the formation and stability of supported Pd2Ga methanol steam reforming catalysts

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