In Situ X-ray Photoelectron Spectroscopy Detects Multiple Active Sites Involved in the Selective Anaerobic Oxidation of Methane in Copper-Exchanged Zeolites

Abstract. Despite a large body of literature on microbial anaerobic oxidation of methane (AOM) in marine sediments and saline waters and its importance to the global methane (CH4) cycle, until recently little work has addressed the potential occurrence and importance of AOM in non-marine systems. This is particularly true for peatlands, which represent both a massive sink for atmospheric CO2 and a significant source of atmospheric CH4. Our knowledge of this process in peatlands is inherently limited by the methods used to study CH4 dynamics in soil and sediment and the assumption that there are no anaerobic sinks for CH4 in these systems. Studies suggest that AOM is CH4-limited and difficult to detect in potential CH4 production assays against a background of CH4 production. In situ rates also might be elusive due to background rates of aerobic CH4 oxidation and the difficulty in separating net and gross process rates. Conclusive evidence for the electron acceptor in this process has not been presented. Nitrate and sulfate are both plausible and favorable electron acceptors, as seen in other systems, but there exist theoretical issues related to the availability of these ions in peatlands and only circumstantial evidence suggests that these pathways are important. Iron cycling is important in many wetland systems, but recent evidence does not support the notion of CH4 oxidation via dissimilatory Fe(III) reduction or a CH4 oxidizing archaea in consortium with an Fe(III) reducer. Calculations based on published rates demonstrate that AOM might be a significant and underappreciated constraint on the global CH4 cycle, although much about the process in unknown, in vitro rates may not relate well to in situ rates, and projections based on those rates are fraught with uncertainty. We suggest electron transfer mechanisms, C flow and pathways, and quantifying in situ peatland AOM rates as the highest priority topics for future research.

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Role Of Surface Defects In Metal-Ceramic Bonding

MRS Proceedings ◽

10.1557/proc-238-787 ◽

1991 ◽

Vol 238 ◽

Cited By ~ 1

Author(s):

S. M. Mukhopadhyay ◽

C. S. Chen

Keyword(s):

Photoelectron Spectroscopy ◽

Active Sites ◽

Surface Defects ◽

Second Phase ◽

Interfacial Chemistry ◽

X Ray ◽

Thin Oxide Film ◽

Metal Ceramic

ABSTRACTThe interfacial chemistry between Ni and Al2O3 has been studied during the initial stages of bonding. We have evaporated thin films of Ni on different alumina substrates (thin oxide film on metallic Al, polished and scratched sapphire crystals, surface with second phase precipitates) and have analyzed how the interface grows, in situ, using X-ray Photoelectron Spectroscopy. It was found that a certain fraction of the first monolayer of Ni which forms on the alumina surface undergoes charge transfer to form NiO. This is due to oxygen-active sites such as unattached oxygen bonds on the surface. A measure of the concentration of such sites can therefore be obtained from the submonolayer fraction of Ni that gets oxidized. It was found that a rough surface offered less oxidation sites for Ni than a smooth one whereas a surface with second phase MgAI2O4 (spinel) precipitates offered more oxidation sites. Also, there is much less oxidation on a thin film of amorphous alumina grown on metallic Al than on a polished bulk sapphire surface. The implications of these studies to further understanding of the metal-ceramic interface have been discussed.

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Removal of trace mercury (II) from aqueous solution by in situ MnOx combined with poly-aluminum chloride

Journal of Water and Health ◽

10.2166/wh.2014.156 ◽

2014 ◽

Vol 13 (2) ◽

pp. 383-393 ◽

Cited By ~ 2

Author(s):

Xixin Lu ◽

Xiaoliu Huangfu ◽

Xiang Zhang ◽

Yaan Wang ◽

Jun Ma

Keyword(s):

Water Quality ◽

Aqueous Solution ◽

Mercury Concentration ◽

Aluminum Chloride ◽

Photoelectron Spectroscopy ◽

Active Sites ◽

Mercury Removal ◽

Experimental Conditions ◽

X Ray

Removal of trace mercury from aqueous solution by Mn (hydr)oxides formed in situ during coagulation with poly-aluminum chloride (PAC) (in situ MnOx combined with PAC) was investigated. The efficiency of trace mercury removal was evaluated under the experimental conditions of reaction time, Mn dosage, pH, and temperature. In addition, the ionic strength and the initial mercury concentration were examined to evaluate trace mercury removal for different water qualities. The results clearly demonstrated that in situ MnOx combined with PAC was effective for trace mercury removal from aqueous solution. A mercury removal ratio of 9.7 μg Hg/mg Mn was obtained at pH 3. Furthermore, at an initial mercury concentration of 30 μg/L and pH levels of both 3 and 5, a Mn dosage of 4 mg/L was able to lower the mercury concentration to meet the standards for drinking water quality at less than 1 μg/L. Analysis by Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy suggests that the hydroxyls on the surface of Mn (hydr)oxides are the active sites for adsorption of trace mercury from aqueous solution.

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The effect of precursors salts on surface state of Pd/Al2O3 and Pd/CeO2/Al2O3 catalysts

Anais da Academia Brasileira de Ciências ◽

10.1590/s0001-37652004000400014 ◽

2004 ◽

Vol 76 (4) ◽

pp. 825-832 ◽

Cited By ~ 10

Author(s):

André L. Guimarães ◽

Lídia C. Dieguez ◽

Martin Schmal

Keyword(s):

Photoelectron Spectroscopy ◽

Active Sites ◽

Diffuse Reflectance ◽

Diffuse Reflectance Spectroscopy ◽

Oxygen Storage ◽

Promoting Effect ◽

X Ray ◽

Surface Active ◽

Al2o3 Catalyst

The influence of the precursors on the promoting effect of ceria on Pd/Al2O3 catalyst, when ceria is coated over alumina was studied. The reaction of propane oxidation proceeded under different feed conditions and the surface active sites were characterized by X-ray photoelectron spectroscopy (XPS) and in situ diffuse reflectance spectroscopy (DRS). XPS and DRS results show that PdO/Pd0 interface are the active sites independent of the precursor, while the catalysts containing CeO2 showed formation of palladium species in the highest oxidation state, probably PdO2 (338 eV) after the oxidation of propane. Besides, the O/Al and O/Ce ratios evidenced the increase of oxygen storage in the presence of CeO2. In addition, the precursor acetylacetonate favors the oxygen storage in the lattice.

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The Partial Oxidation of Methane Over Pd/Al2O3 Catalyst Nanoparticles Studied In-Situ by Near Ambient-Pressure X-ray Photoelectron Spectroscopy

Topics in Catalysis ◽

10.1007/s11244-015-0520-8 ◽

2016 ◽

Vol 59 (5-7) ◽

pp. 516-525 ◽

Cited By ~ 13

Author(s):

Rachel Price ◽

Tuǧçe Eralp-Erden ◽

Ethan Crumlin ◽

Sana Rani ◽

Sonia Garcia ◽

...

Keyword(s):

Partial Oxidation ◽

Photoelectron Spectroscopy ◽

Ambient Pressure ◽

Partial Oxidation Of Methane ◽

Catalyst Nanoparticles ◽

X Ray ◽

Oxidation Of Methane ◽

Al2o3 Catalyst

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Anaerobic oxidation of methane: an underappreciated aspect of methane cycling in peatland ecosystems?

Biogeosciences ◽

10.5194/bg-8-779-2011 ◽

2011 ◽

Vol 8 (3) ◽

pp. 779-793 ◽

Cited By ~ 107

Author(s):

K. A. Smemo ◽

J. B. Yavitt

Keyword(s):

Large Body ◽

Conclusive Evidence ◽

Future Research ◽

Anaerobic Oxidation Of Methane ◽

Anaerobic Oxidation ◽

Ch4 Oxidation ◽

Oxidation Of Methane ◽

Ch4 Production

Abstract. Despite a large body of literature on microbial anaerobic oxidation of methane (AOM) in marine sediments and saline waters and its importance to the global methane (CH4) cycle, until recently little work has addressed the potential occurrence and importance of AOM in non-marine systems. This is particularly true for peatlands, which represent both a massive sink for atmospheric CO2 and a significant source of atmospheric CH4. Our knowledge of this process in peatlands is inherently limited by the methods used to study CH4 dynamics in soil and sediment and the assumption that there are no anaerobic sinks for CH4 in these systems. Studies suggest that AOM is CH4-limited and difficult to detect in potential CH4 production assays against a background of CH4 production. In situ rates also might be elusive due to background rates of aerobic CH4 oxidation and the difficulty in separating net and gross process rates. Conclusive evidence for the electron acceptor in this process has not been presented. Nitrate and sulfate are both plausible and favorable electron acceptors, as seen in other systems, but there exist theoretical issues related to the availability of these ions in peatlands and only circumstantial evidence suggests that these pathways are important. Iron cycling is important in many wetland systems, but recent evidence does not support the notion of CH4 oxidation via dissimilatory Fe(III) reduction or a CH4 oxidizing archaea in consortium with an Fe(III) reducer. Calculations based on published rates demonstrate that AOM might be a significant and underappreciated constraint on the global CH4 cycle, although much about the process is unknown, in vitro rates may not relate well to in situ rates, and projections based on those rates are fraught with uncertainty. We suggest electron transfer mechanisms, C flow and pathways, and quantifying in situ peatland AOM rates as the highest priority topics for future research.

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