STM studies of methanol oxidation to formate on Cu(110) surfaces: I. sequential dosing experiments

Silva, S.L.; Lemor, Robert; Leibsle, F.M.

doi:10.1016/s0039-6028(98)00844-9

Cited by 36 publications

(15 citation statements)

References 19 publications

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“…Because all of these formates cannot be accommodated on gold and gold is necessary to selectively produce carbon dioxide, we suggest that the support acts as a reservoir of formates, which, in the presence of oxygen, decompose into carbon dioxide after diffusion to gold [25,48,49]. In the absence of gold, most of these formates remain as inert spectators, whereas a minor fraction (the monodentate formates) slowly decompose to form carbon monoxide ( Figure 9).…”

Section: Oxygen and Oxygen-water Synergy: Nature And Reactivity Of Sumentioning

confidence: 99%

Water-assisted oxygen activation during gold-catalyzed formic acid decomposition under SCR-relevant conditions

Sridhar

Ferri

Bokhoven

et al. 2017

Journal of Catalysis

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Owing to the problems associated with the usage of urea as the ammonia precursor compound in the selective catalytic reduction (SCR) process in automobiles, alternative compounds such as ammonium formate, methanamide and guanidinium formate have been suggested as more efficient and cleaner candidates. For the application of such formate-based ammonia precursors, a fundamental understanding of catalytic formic acid decomposition in the presence of the diesel exhaust components water and oxygen is required. Oxygen activation is a reaction step common to many catalytic processes. We observed that oxygen activation over titania and base-modified titania-supported gold catalysts is greatly enhanced in the presence of water, resulting in a significant increase in carbon dioxide production from the decomposition of formic acid. Unlike the supports, gold catalyzed the selective production of carbon dioxide. Monodentate and bidentate formates are the kinetically relevant surface species for carbon monoxide and carbon dioxide production, respectively. The support acts as a reservoir, storing bidentate formates that do not react in the steady state when formic acid and oxygen (and water) are co-fed. However, during transient experiments, when the feed is switched from formic acid to oxygen (and water), they are reactivated upon reverse spillover to the active site associated with gold, where they decompose to carbon dioxide. In the presence of oxygen and water, carbon monoxide oxidation and the water gas shift reaction do not produce carbon dioxide. Instead, a direct oxidative-dehydrogenationtype (ODH) pathway proceeds, which strongly differs from stoichiometric formic acid decomposition. A kinetically consistent mechanism is proposed in which the hydroperoxy species facilitate the C-H bond cleavage of formates to release carbon dioxide and water in the rate-determining step.

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Section: Oxygen and Oxygen-water Synergy: Nature And Reactivity Of Sumentioning

confidence: 99%

Water-assisted oxygen activation during gold-catalyzed formic acid decomposition under SCR-relevant conditions

Sridhar

Ferri

Bokhoven

et al. 2017

Journal of Catalysis

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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).…”

Section: Introductionmentioning

confidence: 99%

“…[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. Despite the characterization of ordered adlayers of reactive intermediates , the (5x2)-methoxy and a c(2x2) with STM and LEED, it remained unclear to what extent these structures really determine the reactivity of the Cu(110) surface.…”

Section: Introductionmentioning

confidence: 99%

“…Despite the characterization of ordered adlayers of reactive intermediates , the (5x2)-methoxy and a c(2x2) with STM and LEED, it remained unclear to what extent these structures really determine the reactivity of the Cu(110) surface. [10][11][12][27][28][29] Furthermore, the assignment of the c(2x2) to an adsorbate, i. e. the question whether it is a methoxy or a formate structure has been discussed controversially in the literature. 12,27,[30][31][32][33] In a recent study of the stationary reaction kinetics on Cu(110) we showed that below 10 -5 mbar range a pronounced low temperature reaction peak occurs between 400 and 500 K. A second about equally high reactivity maximum occurs at T > 800 K. In the whole temperature regime the CO 2 formation rate is very low, about 100 times smaller than the formaldehyde production rate.…”

Section: Introductionmentioning

confidence: 99%

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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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“…As such, the (5 Â 2) phase may be viewed as a kinetically-limited metastable phase. We note that in several of the published STM images [8,9,19], particularly in regions close to surface steps that provide a convenient sink for excess adatoms, a cð2 Â 2Þ ordering is seen. Indeed in some images (n Â 2) regions, with n > 5, are seen, the bright zig-zag rows we attribute to adatombridging methoxy species being separated by narrow regions of cð2 Â 2Þ regions.…”

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confidence: 75%

Methoxy Species on Cu(110): Understanding the Local Structure of a Key Catalytic Reaction Intermediate

et al. 2010

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Partial oxidation of methanol to formaldehyde over Cu(110) is one of the most studied catalytic reactions in surface science, yet the local site of the reaction intermediate, methoxy, remains unknown. Using a combination of experimental scanned-energy mode photoelectron diffraction, and density functional theory, a consistent structural solution is presented in which all methoxy species occupy twofold coordinated ''short-bridge'' adsorption sites. The results are consistent with previously-published scanning tunnelling microscopy images and theoretical calculations of the reaction mechanism.

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STM studies of methanol oxidation to formate on Cu(110) surfaces: I. sequential dosing experiments

Cited by 36 publications

References 19 publications

Water-assisted oxygen activation during gold-catalyzed formic acid decomposition under SCR-relevant conditions

Water-assisted oxygen activation during gold-catalyzed formic acid decomposition under SCR-relevant conditions

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

Methoxy Species on Cu(110): Understanding the Local Structure of a Key Catalytic Reaction Intermediate

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