Catalytic Methanol Oxidation over Copper: Observation of Reaction-Induced Nanoscale Restructuring by Means of In Situ Time-Resolved X-ray Absorption Spectroscopy

Böttger, Ingolf; Schedel‐Niedrig, Th.; Timpe, Olaf; Gottschall, Rainer; Hävecker, Michael; Ressler, Thorsten; Schlögl, Robert

doi:10.1002/(sici)1521-3765(20000515)6:10<1870::aid-chem1870>3.0.co;2-0

Cited by 42 publications

(18 citation statements)

References 11 publications

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“…In this view the observation that a very small average lattice expansion of Cu correlates well with the catalytic activity indicates the importance of lattice defects as "exchange sites" for the surface-to-subsurface migration of oxygen species. Since this lattice expansion is below 0.2% [58] it would also explain why we do not observe a shift of the Cu d-band center in our experiments.…”

Section: Resultsmentioning

confidence: 99%

Methanol Oxidation on a Copper Catalyst Investigated Using in Situ X-ray Photoelectron Spectroscopy

Bluhm¹,

Hävecker²,

et al. 2004

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The surface and near-surface region of an active catalyst and the adjacent gas-phase reactants were investigated simultaneously under reaction conditions using in situ X-ray photoelectron spectroscopy (XPS). This investigation of methanol oxidation on a copper catalyst showed that there was a linear correlation between the catalytic activity of the sample and the presence of a sub-surface oxygen species that can only be observed in situ. The concentration profile of the sub-surface oxygen species within the first few nanometers below the surface was determined using photon energy-dependent depth-profiling. The chemical composition of the surface and the near-surface region varied strongly with the oxygen-tomethanol ratio in the reactant stream. The experiments show that the pure metal is not an active catalyst for the methanol oxidation reaction, but that a certain amount of oxygen has to be present in the sub-surface region to activate the catalytic reaction. Oxide formation was found to be detrimental to formaldehyde production. Our results demonstrate also that for an understanding of heterogeneous catalysts a characterization of the surface alone may not be sufficient, and that sub-surface characterization is essential.

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Section: Resultsmentioning

confidence: 99%

Methanol Oxidation on a Copper Catalyst Investigated Using in Situ X-ray Photoelectron Spectroscopy

Bluhm¹,

Hävecker²,

et al. 2004

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“…[7][8][9][10][11][12][13][14][15][16] Different in situ techniques were applied in order to identify the active surface phases on polycrystalline Cu at higher pressure (mbar range). [17][18][19][20][21][22][23][24][25][26] Cu(110) surfaces were investigated with temperatureprogrammed desorption (TPD), molecular beam techniques, low energy electron diffraction (LEED), x-ray photoelectron spectroscopy (XPS) and scanning tunnelling microscopy (STM). 7,8,[10][11][12]15,[27][28][29][30] These techniques were typically applied under non-stationary conditions using sequential dosing and temperature-programmed experiments.…”

Section: Introductionmentioning

confidence: 91%

Adsorbate coverages and surface reactivity in methanol oxidation over Cu(110): An in situ photoelectron spectroscopy study

Günther

Zhou

Hävecker

et al. 2006

The Journal of Chemical Physics

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The adsorbate species present during partial oxidation of methanol on a Cu(110) surface have been investigated in the 10 -5 mbar range with in situ x-ray photoelectron spectroscopy (XPS) and rate measurements. Two reaction intermediates were identified, methoxy with a C 1s binding energy (BE) of 285.4 eV and formate with a C 1s BE of 287.7 eV. The c(2x2) overlayer formed under reaction conditions is assigned to formate. Two states of adsorbed oxygen were found characterized by O 1s BE's of 529.6 and 528.9 eV, respectively. On the inactive surface present at low T around 300 -350 K formate dominates while methoxy is almost absent. Ignition of the reaction correlates with a decreasing formate coverage. A large hysteresis of ≈ 200 K width occurs in T-cycling experiments whose correlation with adsorbate species was studied with varying oxygen and methanol partial pressures. The two branches of the hysteresis differ mainly in the amount of adsorbed oxygen, the methoxy species and a carbonaceous species. Methoxy covers only a minor part of the catalytic surface reaching at most 20%. Above 650 K the surface is largely adsorbate free.

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“…5a). The existence of subsurface oxygen at the Cu-O-Zn interface which also has been ascribed to cause disorder in the Cu particles can not ruled out for the Cu/ZnO/Al 2 O 3 catalysts investigated [41]. The catalyst CZA-1 exhibited the lowest reduction temperature and a rather narrow and symmetrical TPR peak compared to the other samples.…”

Section: Microstructure Of Cu In Cu/zno/al 2 O 3 Catalystsmentioning

confidence: 99%

Microstructural characterization of Cu/ZnO/Al2O3 catalysts for methanol steam reforming—A comparative study

Kurr

Kasatkin

Girgsdies

et al. 2008

Applied Catalysis A: General

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Microstructural characteristics of various real Cu/ZnO/Al 2 O 3 catalysts for methanol steam reforming (MSR) were investigated by in situ X-ray diffraction (XRD), in situ X-ray absorption spectroscopy (XAS), temperature programmed reduction (TPR) and electron microscopy (TEM). Structure-activity correlations of binary Cu/ZnO model catalysts were compared to microstructural properties of the ternary catalysts obtained from in situ experiments under MSR conditions. Similar to the binary system, in addition to a high specific copper surface area the catalytic activity of Cu/ZnO/Al 2 O 3 catalysts is determined by defects in the bulk structure. The presence of lattice strain in the copper particles as the result of an advanced Cu-ZnO interface was detected only for the most active Cu/ZnO/Al 2 O 3 catalyst in this study. Complementarily, a highly defect rich nature of both Cu and ZnO has been found in the short-range order structure (XAS). Conventional TPR and TEM investigations confirm a homogeneous microstructure of Cu and ZnO particles with a narrow particle size distribution. Conversely, a heterogeneous microstructure with large copper particles and a pronounced bimodal particle size distribution was identified for the less active catalysts. Apparently, lattice strain in the copper nanoparticles is an indicator for a homogeneous microstructure of superior Cu/ZnO/Al 2 O 3 catalyst for methanol chemistry.

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Catalytic Methanol Oxidation over Copper: Observation of Reaction-Induced Nanoscale Restructuring by Means of In Situ Time-Resolved X-ray Absorption Spectroscopy

Cited by 42 publications

References 11 publications

Methanol Oxidation on a Copper Catalyst Investigated Using in Situ X-ray Photoelectron Spectroscopy

Methanol Oxidation on a Copper Catalyst Investigated Using in Situ X-ray Photoelectron Spectroscopy

Adsorbate coverages and surface reactivity in methanol oxidation over Cu(110): An in situ photoelectron spectroscopy study

Microstructural characterization of Cu/ZnO/Al2O3 catalysts for methanol steam reforming—A comparative study

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