Asymmetric structure analysis of active surface-sites by in situ polarized total-reflection fluorescence EXAFS

1993 ◽  
Vol 20 (1-2) ◽  
pp. 117-124 ◽  
Author(s):  
K. Asakura ◽  
M. Shirai ◽  
Y. Iwasawa
Keyword(s):  
Structure Analysis ◽  
Active Surface ◽  
Total Reflection ◽  
Asymmetric Structure ◽  
Surface Sites ◽  
Active Surface Sites

Mechanistic Insights into the Spontaneous Reaction Between CO2 and La2-xSrxCuO4

2021 ◽  
Author(s):  
Alexander William Henry Whittingham ◽  
Jordan Lau ◽  
Rodney David Lucien Smith
Keyword(s):  
Electrochemical Impedance ◽  
Co2 Reduction ◽  
Active Surface ◽  
Structural Instability ◽  
Redox Couple ◽  
Surface Sites ◽  
Carbonate Ions ◽  
Redox Active ◽  
Spontaneous Reaction

Layered perovskites such as La2-xSrxCuO4 are active electrocatalysts for CO2 reduction, but they suffer from structural instability under catalytic conditions. This structural instability is found to arise from the reaction of CO2 with surface sites. Variable scan rate voltammetry shows the growth of a Cu-based redox couple when potentials cathodic of 0.6 V vs. RHE are applied in the presence of CO2. Electrochemical impedance spectroscopy identifies a redox active surface state at this voltage, whose concentration is increased by electrochemical reduction in the presence of CO2. In-situ spectroelectrochemical FTIR identifies surface bound carbonates as being involved formation of these surface sites. The orthorhombic lattice for La2-xSrxCuO4 is found to uniquely enable monodentate binding of (bi)carbonate ions from solution as well as bidentate carbonate ions through reaction with CO2. The incorporation of Sr(II) induces a transition to a tetragonal lattice, for which only monodentate carbonate ions are observed. It is proposed that the binding of carbonate ions in a bidentate fashion generates sufficient strain at the surface to result in amorphization at the surface, yielding the observed Cu(II)/Cu(I) redox couple.

Etching-Assisted Route to Heterophase Au Nanowires with Multiple Types of Active Surface Sites for Silane Oxidation

Nano Letters ◽  
2019 ◽  
Vol 19 (9) ◽  
pp. 6363-6369 ◽  
Author(s):  
Chaoqi Wang ◽  
Xiang Li ◽  
Lei Jin ◽  
Peng-Han Lu ◽  
Catherine Dejoie ◽  
...  
Keyword(s):  
Active Surface ◽  
Surface Sites ◽  
Active Surface Sites ◽  
Au Nanowires

scholarly journals Unveiling the Active Surface Sites in Heterogeneous Titanium-Based Silicalite Epoxidation Catalysts: Input of Silanol-Functionalized Polyoxotungstates as Soluble Analogues

ACS Catalysis ◽  
2018 ◽  
Vol 8 (3) ◽  
pp. 2330-2342 ◽  
Author(s):  
Teng Zhang ◽  
Louis Mazaud ◽  
Lise-Marie Chamoreau ◽  
Céline Paris ◽  
Anna Proust ◽  
...  
Keyword(s):  
Active Surface ◽  
Surface Sites ◽  
Active Surface Sites

scholarly journals Irreversible loss of ice nucleation active sites in mineral dust particles caused by sulphuric acid condensation

2010 ◽  
Vol 10 (23) ◽  
pp. 11471-11487 ◽  
Author(s):  
R. C. Sullivan ◽  
M. D. Petters ◽  
P. J. DeMott ◽  
S. M. Kreidenweis ◽  
H. Wex ◽  
...  
Keyword(s):  
Sulphuric Acid ◽  
Active Sites ◽  
Mineral Dust ◽  
Active Surface ◽  
Ice Nucleation ◽  
Dust Particles ◽  
Ammonia Gas ◽  
Surface Sites ◽  
Active Surface Sites ◽  
Acid Coating

Abstract. During the FROST-2 (FReezing Of duST) measurement campaign conducted at the Leipzig Aerosol Cloud Interaction Simulator (LACIS), we investigated changes in the ice nucleation properties of 300 nm Arizona Test Dust mineral particles following thermochemical processing by varying amounts and combinations of exposure to sulphuric acid vapour, ammonia gas, water vapour, and heat. The processed particles' heterogeneous ice nucleation properties were determined in both the water subsaturated and supersaturated humidity regimes at −30 °C and −25 °C using Colorado State University's continuous flow diffusion chamber. The amount of sulphuric acid coating material was estimated by an aerosol mass spectrometer and from CCN-derived hygroscopicity measurements. The condensation of sulphuric acid decreased the dust particles' ice nucleation ability in proportion to the amount of sulphuric acid added. Heating the coated particles in a thermodenuder at 250 °C – intended to evaporate the sulphuric acid coating – reduced their freezing ability even further. We attribute this behaviour to accelerated acid digestion of ice active surface sites by heat. Exposing sulphuric acid coated dust to ammonia gas produced particles with similarly poor freezing potential; however a portion of their ice nucleation ability could be restored after heating in the thermodenuder. In no case did any combination of thermochemical treatments increase the ice nucleation ability of the coated mineral dust particles compared to unprocessed dust. These first measurements of the effect of identical chemical processing of dust particles on their ice nucleation ability under both water subsaturated and mixed-phase supersaturated cloud conditions revealed that ice nucleation was more sensitive to all coating treatments in the water subsaturated regime. The results clearly indicate irreversible impairment of ice nucleation activity in both regimes after condensation of concentrated sulphuric acid. This implies that the sulphuric acid coating caused permanent chemical and/or physical modification of the ice active surface sites; the possible dissolution of the coating during droplet activation did not restore all immersion/condensation-freezing ability.

scholarly journals Bioethanol Transformations Over Active Surface Sites Generated on Carbon Nanotubes or Carbon Nanofibers Materials

2014 ◽  
Vol 7 (1) ◽  
pp. 1-7 ◽  
Author(s):  
M. Almohalla ◽  
M.V. Morales ◽  
E. Asedegbega-Nieto ◽  
A. Maroto-Valiente ◽  
B. Bachiller-Baeza ◽  
...  
Keyword(s):  
Carbon Nanotubes ◽  
Carbon Nanofibers ◽  
Active Surface ◽  
Surface Sites ◽  
Active Surface Sites
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