Hydrogen on polycrystalline β-Ga2O3: Surface chemisorption, defect formation, and reactivity

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

doi:10.1016/j.jcat.2008.03.019

Cited by 64 publications

(91 citation statements)

References 16 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…For clean Ga 2 O 3 this includes H 2 O and CH 3 OH (MSR reactants), CO, H 2 , CO 2 and HCOOH (MSR products). Typically, formate species, H ads and OH ads are the most important surfacebound species on Ga 2 O 3 [17]. We do not consider species limited to the surface such as methoxy or formyl.…”

Section: Discussionmentioning

confidence: 99%

“…We do not consider species limited to the surface such as methoxy or formyl. At 500-550 K, decomposition of the Ga 2 O 3 -adsorbed formate species is feasible via either decarbonylation (to CO and OH ads ) or decarboxylation (to CO 2 and H ads ) as outlined in detail in ref [17]. Some of the formate species may react with H ads to form HCOOH which desorbs.…”

Section: Discussionmentioning

confidence: 99%

See 1 more Smart Citation

Pd/Ga2O3 methanol steam reforming catalysts: Part II. Catalytic selectivity

Lorenz

Penner

Jochum

et al. 2009

Applied Catalysis A: General

View full text Add to dashboard Cite

Structure, morphology and composition of two Pd/Ga2O3 methanol steam reforming catalysts were correlated with the associated activity and selectivity changes in the methanol steam reforming reaction and linked to studies on pure Ga2O3 supports. For both systems, that are, a Pd/Ga2O3 thin film model catalyst and a powder-supported Pd catalyst, we identified a temperature range in which the reduction with hydrogen yields a single Pd-Ga bimetallic on a reduced oxide support, which in turn suppresses methanol dehydrogenation and results in a high CO2-selectivity in methanol steam reforming. For the thin film catalyst, this included the Pd5Ga2 bimetallic present after reduction in the temperature range 523-600 K, for the powder-supported catalyst, Pd2Ga, formed after reduction between 523 and 773 K, was found to account for the high CO2-selectivity. In contrast to studies on the corresponding Pd/ZnO catalysts, sintering and metal decoration by reduced GaOx species will additionally have to be considered for discussions about structure-activity correlations in Pd/Ga2O3 thin film model catalysts. Reduction at 673 K causes catalyst deactivation and loss of CO2-selectivity due to encapsulation of catalytically active bimetallic particles by mobile GaOx species and hampers oxidative catalyst regeneration. No such behavior has been observed for the powder-supported catalyst. This difference in catalytic activity and selectivity between the two catalysts is interpreted in terms of their different (bi-) metallic -oxide contact area. Formic acid formation has been observed on pure Ga2O3 supports, which yields additional CO by formic acid decarbonylation. For the CO2-selective methanol steam reforming reaction over a Pd-Ga bimetallic particle, formic acid is not a gas phase species, which indicates a preferential decarboxylation pathway of adsorbed formate species at low temperatures.

show abstract

Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Pd/Ga2O3 methanol steam reforming catalysts: Part II. Catalytic selectivity

Lorenz

Penner

Jochum

et al. 2009

Applied Catalysis A: General

View full text Add to dashboard Cite

show abstract

“…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

105

138

View full text Add to dashboard Cite

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.

show abstract

“…Because of it's higher band gap than that of ZnO, it is possible for ZnGa 2 O 4 to function above 300 C. Therefore, ZnGa 2 O 4 might be useful in the low temperature fuel cell electrolyte (LTFCE) materials similar to SDC (samarium doped ceria) [17]. There are also some examples for wide band gap gallete based semiconductors used in LTFCE; i.e., the study on b-Ga 2 O 3 has shown that defect formation dependent conductivity begins at around 700 K due to surface/lattice oxygen reduction in H 2 [18]. For b-Ga 2 O 3, thermal activation for charge carriers requires $1 eV under H 2 and increase up to $2.2 eV without H 2 [18].…”

Section: Introductionmentioning

confidence: 99%

“…There are also some examples for wide band gap gallete based semiconductors used in LTFCE; i.e., the study on b-Ga 2 O 3 has shown that defect formation dependent conductivity begins at around 700 K due to surface/lattice oxygen reduction in H 2 [18]. For b-Ga 2 O 3, thermal activation for charge carriers requires $1 eV under H 2 and increase up to $2.2 eV without H 2 [18]. Furthermore, the other gallate based structure, CuZnGaO x, showed a high concentration of point defects due to Cu clusters in the structure [19].…”

Section: Introductionmentioning

confidence: 99%