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Shido, Takafumi; Yamaguchi, Aritomo; Inada, Yuji; Asakura, Kiyotaka; Nomura, Masaharu; Iwasawa, Yasuhiro

doi:10.1023/a:1013830216879

Cited by 37 publications

(53 citation statements)

References 19 publications

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“…Bunluesin et al have recently proposed a mechanism that involves a ceriamediated redox process, whereby CO adsorbed on the precious metal is oxidized by ceria that in turn is oxidized by water [30]. Shido and co-workers [50,51] investigated the catalytic WGS on Rh-doped CeO 2 by using TPD and infrared spectroscopy and found that the intermediate for the reaction is a bidentate formate which is produced by the reaction of CO with terminal surface hydroxyl groups on Ce ions. The rate-determining step is the decomposition of the bidentate formate to H 2 and a unidentate carbonate.…”

Section: Ceo 2 and Pd/ceomentioning

confidence: 99%

Pd/CeO2?TiO2 catalyst for CO oxidation at low temperature: a TPR study with H2 and CO as reducing agents

Zhu

2004

Journal of Catalysis

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The catalysts Pd/TiO 2 , Pd/CeO 2 , and Pd/CeO 2 -TiO 2 for CO oxidation at low temperature together with their corresponding supports TiO 2 , CeO 2 , and CeO 2 -TiO 2 prepared by sol-gel precipitation followed by supercritical fluid drying were characterized by means of N 2 adsorption, XRD, diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) of CO adsorption and temperature-programmed reduction (TPR) with H 2 and CO as reducing agents. The results showed that PdO is finely dispersed on the supports with high surface area. DRIFTS of CO adsorption further indicated that both Pd 2+ and Pd 0 species coexist in Pd/CeO 2 , while only Pd 0 is detected in Pd/TiO 2 and Pd/CeO 2 -TiO 2 . H 2 -TPR showed that no bulk CeO 2 exists in CeO 2 -TiO 2 and the reduction of CeO 2 -TiO 2 is more difficult than that of the surface oxygen in the individual CeO 2 probably due to the formation of CeO 2 -TiO 2 solid solution. PdO in Pd/TiO 2 can be fully reduced by H 2 at ambient temperature, whereas PdO in Pd/CeO 2 and Pd/CeO 2 -TiO 2 is reduced respectively at 162 and 80 • C, accompanied by the reduction of surface CeO 2 . CO-TPR showed that the reduction of PdO in PdO/TiO 2 is limited within the outermost layer at ambient temperature and the core PdO can only be reduced with a further increase of temperature. PdO/CeO 2 is also reduced both at ambient temperature and with the increase of temperature during the CO-TPR process, and the reduction temperature of CeO 2 decreased significantly in the presence of PdO, which may be due to the different degrees of interaction between PdO and CeO 2 . In contrast, a complete reduction of PdO in Pd/CeO 2 -TiO 2 by CO is observed at ambient temperature, accompanied by the partial reduction of CeO 2 , which may indicate that the special Pd-Ce-Ti interaction in Pd/CeO 2 -TiO 2 is favorable for the reduction of PdO and interfacial CeO 2 species. The water-gas shift (WGS) between CO and the hydroxyl groups in the catalysts is detected at a temperature higher than 210 • C on all of the Pd-supported catalysts as well as the individual CeO 2 and TiO 2 supports.  2004 Elsevier Inc. All rights reserved.

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Section: Ceo 2 and Pd/ceomentioning

confidence: 99%

Pd/CeO2?TiO2 catalyst for CO oxidation at low temperature: a TPR study with H2 and CO as reducing agents

Zhu

2004

Journal of Catalysis

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“…Compounds such as hydrocarbons, formates, and carboxylates are reported to be present as reaction intermediates at the catalyst surface. Surface formates have been demonstrated to be the intermediates of WGSR on MgO and ZnO catalysts (7).…”

Section: Charged Aumentioning

confidence: 99%

Spectroscopic Identification of Adsorbed Intermediates Derived from the CO+H2O Reaction on Zeolite-Encapsulated Gold Catalysts

Mohamed

Salama

Ichikawa

2000

Journal of Colloid and Interface Science

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“…This carbonate restrains the formation of the formate species, which is known to be an intermediate in the shift reaction mechanism. 19 Furthermore, naphthalene gasification not only occurs by way of the shift reaction but also through naphthalene pyrolysis and later gasification of the carbonaceous matter deposited on the catalysts, carbonaceous matter being recognized as compounds with C-(C, H) and/or C-O-C species. Therefore, the influence of the different carbonate species formed and their relative stability should be analysed in this regard.…”

Section: Reactive Atmosphere Simulationmentioning

confidence: 99%

“…The more stable bidentate carbonate, formed on the surface of pure CaO, would deactivate their sites and then inhibit steam dissociative adsorption over them, which is a necessary step for the occurrence of both deposited carbon gasification as well as the shift reaction involved in the gasification mechanism. 6,19 This would not be the case when pure MgO or the mixture are used as catalysts, where exposure of the free cation to steam favours its adsorption and subsequent formation of hydroxyl groups in sufficient amounts to proceed with gasification. Then, cooperation in the 10% CaO C 90% MgO mixture is evidenced by the fact that MgO allows the more basic sites of CaO to be cleared and freed from carbonates and deposited carbon.…”

Section: Interpretation Of the Synergistic Effectmentioning

confidence: 99%

Catalytic cooperation at the interface of physical mixtures of CaO and MgO catalysts during steam gasification of naphthalene

Alarcón

Garcı́a

Centeno

et al. 2001

Surface & Interface Analysis

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Oxides CaO, MgO and a physical mixture of 10% CaO + 90% MgO were used as catalysts for the steam gasification of naphthalene. A synergistic effect in the conversion was observed with the mixture. Catalysts were characterized by diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and XPS techniques. Basicity was significant for CaO as compared to MgO and the mixture, but did not correlate with catalytic activity. Bidentate carbonate-type formation, which remained even in the presence of steam at high temperature (1033 K), was observed on CaO. Carbonates on MgO and on the mixture are unidentate and disappeared when steam was present. Formates, carboxylic and aldehydic groups also were formed, at 723 K on MgO and at 423 K on the mixture and on CaO. These species disappeared at 873 and 1033 K for the mixture and CaO, respectively, thus indicating their greater stability on CaO than on the mixture and on the MgO. Deposition of carbonaceous matter on solids was observed. The order of the deposited content is mixture < MgO < CaO. No indication of mutual contamination by the metal composing the oxides was observed. A higher carbonate removal and less carbonaceous matter deposition were observed in CaO when in the mixture, as compared with CaO alone, suggesting a beneficial effect of MgO in the mixture. The synergistic effect observed using the 10% CaO + 90% MgO mixture was related to the inhibition of carbonaceous matter and carbonate formation on the catalysts. This inhibition is due to a catalytic cooperation between both oxides, as two separate phases. The presence of MgO is assumed to avoid the formation of stable bidentate carbonates on CaO, promoting instead unidentate species formation; this facilitates the gasification of naphthalene by steam.

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Untitled

Cited by 37 publications

References 19 publications

Pd/CeO2?TiO2 catalyst for CO oxidation at low temperature: a TPR study with H2 and CO as reducing agents

Pd/CeO2?TiO2 catalyst for CO oxidation at low temperature: a TPR study with H2 and CO as reducing agents

Spectroscopic Identification of Adsorbed Intermediates Derived from the CO+H2O Reaction on Zeolite-Encapsulated Gold Catalysts

Catalytic cooperation at the interface of physical mixtures of CaO and MgO catalysts during steam gasification of naphthalene

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