Defect formation and the water–gas shift reaction on β-Ga2O3

Jochum, Wilfrid; Penner, Simon; Kramer, R.; Föttinger, Karin; Rupprechter, Günther; Klötzer, Bernhard

doi:10.1016/j.jcat.2008.03.018

Cited by 40 publications

(56 citation statements)

References 23 publications

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“…For MgGa and PdMgGa, the presence of Pd leads to an increase in the total HTR hydrogen consumption and to a decrease in temperature from 736 to 695 K. In both samples, CO was detected by MS. Thus, at sufficiently high temperature CO 2 from decarboxylation of the interlayer carbonate anions undergoes rWGS on the reducible oxides [16]. In case of PdMgGa the hydrogen uptake due to rWGS and support reduction overlaps with IMC formation (Fig.…”

Section: Tpr and Ms Measurementsmentioning

confidence: 93%

Comparative study of hydrotalcite-derived supported Pd2Ga and PdZn intermetallic nanoparticles as methanol synthesis and methanol steam reforming catalysts

Ota

Kunkes

Kasatkin

et al. 2012

Journal of Catalysis

137

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a b s t r a c tAn effective and versatile synthetic approach to produce well-dispersed supported intermetallic nanoparticles is presented that allows a comparative study of the catalytic properties of different intermetallic phases while minimizing the influence of differences in preparation history. Supported PdZn, Pd 2 Ga, and Pd catalysts were synthesized by reductive decomposition of ternary Hydrotalcite-like compounds obtained by co-precipitation from aqueous solutions. The precursors and resulting catalysts were characterized by HRTEM, XRD, XAS, and CO-IR spectroscopy. The Pd 2+ cations were found to be at least partially incorporated into the cationic slabs of the precursor. Full incorporation was confirmed for the PdZnAlHydrotalcite-like precursor. After reduction of Ga-and Zn-containing precursors, the intermetallic compounds Pd 2 Ga and PdZn were present in the form of nanoparticles with an average diameter of 6 nm or less. Tests of catalytic performance in methanol steam reforming and methanol synthesis from CO 2 have shown that the presence of Zn and Ga improves the selectivity to CO 2 and methanol, respectively. The catalysts containing intermetallic compounds were 100 and 200 times, respectively, more active for methanol synthesis than the monometallic Pd catalyst. The beneficial effect of Ga in the active phase was found to be more pronounced in methanol synthesis compared with steam reforming of methanol, which is likely related to insufficient stability of the reduced Ga species in the more oxidizing feed of the latter reaction. Although the intermetallic catalysts were in general less active than a Cu-/ZnO-based material prepared by a similar procedure, the marked changes in Pd reactivity upon formation of intermetallic compounds and to study the tunability of Pd-based catalysts for different reactions.

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Section: Tpr and Ms Measurementsmentioning

confidence: 93%

Comparative study of hydrotalcite-derived supported Pd2Ga and PdZn intermetallic nanoparticles as methanol synthesis and methanol steam reforming catalysts

Ota

Kunkes

Kasatkin

et al. 2012

Journal of Catalysis

137

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“…Recently, the influence and role of oxygen defects on β-Ga 2 O 3 samples was investigated for the (reverse) water-gas shift reaction [29,30] by systematically studying the interaction with H 2 , CO 2 , CO, and H 2 O after different pretreatments. In another work, Ga 2 O 3 supported on TiO 2 showed remarkable activity for steam reformingmof dimethylether [31].…”

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

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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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“…Pure In 2 O 3 is highly CO 2 -selective, both ZnO and Ga 2 O 3 are not [11,13]. Partly this is also due to their activity in the reverse water-gas shift reaction [14,15] , which renders an extension of the studies to the fourth main group of the periodic system useful. Contrary to SnO 2 , structural information on GeO 2 thin films is scarce and mainly limited to the preparation of GeO 2 nanomaterials [16][17][18].…”

Section: Introductionmentioning

confidence: 99%

Preparation and structural characterization of SnO2 and GeO2 methanol steam reforming thin film model catalysts by (HR)TEM

Lorenz

Zhao

Turner

et al. 2010

Materials Chemistry and Physics

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Structure, morphology and composition of different tin oxide and germanium oxide thin film catalysts for the methanol steam reforming (MSR) reaction have been studied by a combination of (High-resolution) Transmission Electron Microscopy, Selected Area Electron Diffraction, Darkfield imaging and Electron Energy-Loss Spectroscopy. Deposition of the thin films on NaCl(001) cleavage faces has been carried out by thermal evaporation of the respective SnO2 and GeO2 powders in varying oxygen partial pressures and at different substrate temperatures. Preparation of tin oxide films in high oxygen pressures (10 -3 mbar) exclusively resulted in SnO phases, at and above 473 K substrate temperature epitaxial growth of SnO on NaCl(001) leads to well-ordered films. For lower oxygen partial pressures (10 -4 -10 -5 mbar), mixtures of SnO and β-Sn are obtained. Well-ordered SnO2 films, as verified by electron diffraction patterns and energy loss spectra, are only obtained after post-oxidation of SnO films at temperatures T ≥ 673 K in 1 bar O2. Preparation of GeOx films inevitably results in amorphous films with a composition close to GeO2, which cannot be crystallized by annealing treatments in oxygen or hydrogen at temperatures comparable to SnO/SnO2. Similarities and differences to neighbouring oxides relevant for selective MSR in the third group of the periodic system (In2O3 and Ga2O3) are also discussed with the aim of cross-correlation in formation of nanomaterials, and ultimately, also catalytic properties.

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Defect formation and the water–gas shift reaction on β-Ga2O3

Cited by 40 publications

References 23 publications

Comparative study of hydrotalcite-derived supported Pd2Ga and PdZn intermetallic nanoparticles as methanol synthesis and methanol steam reforming catalysts

Comparative study of hydrotalcite-derived supported Pd2Ga and PdZn intermetallic nanoparticles as methanol synthesis and methanol steam reforming catalysts

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

Preparation and structural characterization of SnO2 and GeO2 methanol steam reforming thin film model catalysts by (HR)TEM

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