Synthesis, Spectroscopy, and Catalytic Properties of Cationic Organozirconium Adsorbates on “Super Acidic” Sulfated Alumina. “Single-Site” Heterogeneous Catalysts with Virtually 100 Active Sites

2003 ◽  
Vol 125 (14) ◽  
pp. 4325-4331 ◽  
Author(s):  
Christopher P. Nicholas ◽  
Hongsang Ahn ◽  
Tobin J. Marks
Keyword(s):  
Active Sites ◽  
Heterogeneous Catalysts ◽  
Catalytic Properties ◽  
Single Site ◽  
Sulfated Alumina

scholarly journals Hollow PdAg-CeO2 heterodimer nanocrystals as highly structured heterogeneous catalysts

2019 ◽  
Vol 9 (1) ◽  
Author(s):  
Javier Patarroyo ◽  
Jorge A. Delgado ◽  
Florind Merkoçi ◽  
Aziz Genç ◽  
Guillaume Sauthier ◽  
...  
Keyword(s):  
Beneficial Effect ◽  
Selective Hydrogenation ◽  
Active Sites ◽  
Heterogeneous Catalysts ◽  
Catalytic Properties ◽  
Reaction Times ◽  
Catalytic Performance ◽  
Internal Alkynes ◽  
First Time ◽  
Full Conversion

AbstractIn the present work, hollow PdAg-CeO2 heterodimer nanocrystals (NCs) were prepared and tested as catalysts for the selective hydrogenation of alkynes. These nanostructures combine for the first time the beneficial effect of alloying Pd with Ag in a single NC hollow domain with the formation of active sites at the interface with the CeO2 counterpart in an additive manner. The PdAg-CeO2 NCs display excellent alkene selectivity for aliphatic alkynes. For the specific case of hydrogenation of internal alkynes such as 4-octyne, very low over-hydrogenation and isomerization products were observed over a full conversion regime, even after prolonged reaction times. These catalytic properties were remarkably superior in comparison to standard catalysts. The promotion of Ag on the moderation of the reactivity of the Pd phase, in combination with the creation of interfacial sites with the CeO2 moiety in the same nanostructure, is pointed as the responsible of such a remarkable catalytic performance.

Active Sites of Iron Catalysts for Oxidation Reactions - H2O Oxidation and H2O2 Decomposition

1996 ◽  
Vol 454 ◽  
Author(s):  
V. L. Kuznetsov ◽  
G. L. Elizarova ◽  
A. N. Usoltseva ◽  
L. G. Matvienko ◽  
O. I. Shchegolikhina
Keyword(s):  
Active Site ◽  
Active Sites ◽  
Heterogeneous Catalysts ◽  
Catalytic Properties ◽  
Iron Catalysts ◽  
Structural Factors ◽  
Oxidation Reactions ◽  
H2o2 Decomposition ◽  
The Comparative Study ◽  
Selective Oxidation Catalysts

ABSTRACTSystems containing metal ions stabilized in Si-O matrix are perspective for the development of new selective oxidation catalysts. The comparative study of the following catalysts were performed to elucidate the influence of structural factors on the catalytic properties of iron systems in the reactions H2O oxidation, H2O2 decomposition, N2O decomposition and 16O2 ⇔ O18O2 exchange. The following catalysts were used: A) carbon-supported polyhedral silsesquioxanes (PhSiO1.5)12(MO)nL ((MO)n = (FeO)6, Fe2Ni4O6, (NiO)6; L=ROH, H2O); B) Fe-containing zeolites ZSM-5 (0.1−3.5 wt.% Fe); C) hydroxocomplexes Fe4(OH)10SO4 and NaFe3(OH)6(SO4)2). Fe silsesquoxanes in contrast to Fe-ZSM5 do not activate N2O decomposition and isotopie oxygen exchange. However, they are active in H2O oxidation and H2O2 decomposition. It was found that both reactions proceed via nonradical mechanism in the presence of Fe heterogeneous catalysts. For H2O oxidation active site contains at least two Fe atoms situated at appropriate distance from each other. H2O2 decomposition can proceed with participation either one and two metal active sites.

scholarly journals Hybrid organic–inorganic structured materials as single-site heterogeneous catalysts

2012 ◽  
Vol 468 (2143) ◽  
pp. 1927-1954 ◽  
Author(s):  
Urbano Díaz ◽  
Mercedes Boronat ◽  
Avelino Corma
Keyword(s):  
Active Sites ◽  
Heterogeneous Catalysts ◽  
Structural Characteristics ◽  
Inorganic Materials ◽  
Single Site ◽  
Structured Materials ◽  
Solid Catalysts ◽  
Highly Active ◽  
Molecular Catalysts ◽  
Inorganic Structure

Catalyst selectivity is associated with well-defined homogeneous active sites. Transition metal complexes and organocatalysts are highly active and selective in the homogeneous phase, and their heterogenization by incorporating them into inorganic solid materials allows combining their excellent catalytic activity with improved separation, recovering and recycling properties. In this article, we present the structural characteristics and catalytic properties of hybrid organic–inorganic materials in which the molecular catalysts are part of the inorganic structure, emphasizing the possibilities of periodic mesoporous hybrid materials and coordination polymers as single-site solid catalysts.

What catalysis needs from the electron microscopist

1988 ◽  
Vol 46 ◽  
pp. 694-695
Author(s):  
Alexis T. Bell
Keyword(s):  
Active Sites ◽  
Heterogeneous Catalysts ◽  
Catalyst Deactivation ◽  
Surface Composition ◽  
Internal Surface ◽  
Active Phase ◽  
Atomic Scale ◽  
Metal Catalyst ◽  
Internal Surface Area ◽  
Porous Support

Heterogeneous catalysts, used in industry for the production of fuels and chemicals, are microporous solids characterized by a high internal surface area. The catalyticly active sites may occur at the surface of the bulk solid or of small crystallites deposited on a porous support. An example of the former case would be a zeolite, and of the latter, a supported metal catalyst. Since the activity and selectivity of a catalyst are known to be a function of surface composition and structure, it is highly desirable to characterize catalyst surfaces with atomic scale resolution. Where the active phase is dispersed on a support, it is also important to know the dispersion of the deposited phase, as well as its structural and compositional uniformity, the latter characteristics being particularly important in the case of multicomponent catalysts. Knowledge of the pore size and shape is also important, since these can influence the transport of reactants and products through a catalyst and the dynamics of catalyst deactivation.

A Pyridinic Fe-N4 Macrocycle Effectively Models the Active Sites in Fe/N-Doped Carbon Electrocatalysts

2020 ◽  
Author(s):  
Travis Marshall-Roth ◽  
Nicole J. Libretto ◽  
Alexandra T. Wrobel ◽  
Kevin Anderton ◽  
Nathan D. Ricke ◽  
...  
Keyword(s):  
Oxygen Reduction ◽  
Active Sites ◽  
Catalytic Properties ◽  
Reduction Reaction ◽  
Iron Phthalocyanine ◽  
Electrochemical Studies ◽  
Onset Potential ◽  
Nitrogen Doped Carbon ◽  
Iron Active Sites

Iron- and nitrogen-doped carbon (Fe-N-C) materials are leading candidates to replace platinum in fuel cells, but their active site structures are poorly understood. A leading postulate is that iron active sites in this class of materials exist in an Fe-N<sub>4</sub> pyridinic ligation environment. Yet, molecular Fe-based catalysts for the oxygen reduction reaction (ORR) generally feature pyrrolic coordination and pyridinic Fe-N<sub>4</sub> catalysts are, to the best of our knowledge, non-existent. We report the synthesis and characterization of a molecular pyridinic hexaazacyclophane macrocycle, (phen<sub>2</sub>N<sub>2</sub>)Fe, and compare its spectroscopic, electrochemical, and catalytic properties for oxygen reduction to a prototypical Fe-N-C material, as well as iron phthalocyanine, (Pc)Fe, and iron octaethylporphyrin, (OEP)Fe, prototypical pyrrolic iron macrocycles. N 1s XPS signatures for coordinated N atoms in (phen<sub>2</sub>N<sub>2</sub>)Fe are positively shifted relative to (Pc)Fe and (OEP)Fe, and overlay with those of Fe-N-C. Likewise, spectroscopic XAS signatures of (phen<sub>2</sub>N<sub>2</sub>)Fe are distinct from those of both (Pc)Fe and (OEP)Fe, and are remarkably similar to those of Fe-N-C with compressed Fe–N bond lengths of 1.97 Å in (phen<sub>2</sub>N<sub>2</sub>)Fe that are close to the average 1.94 Å length in Fe-N-C. Electrochemical studies establish that both (Pc)Fe and (phen<sub>2</sub>N<sub>2</sub>)Fe have relatively high Fe(III/II) potentials at ~0.6 V, ~300 mV positive of (OEP)Fe. The ORR onset potential is found to directly correlate with the Fe(III/II) potential leading to a ~300 mV positive shift in the onset of ORR for (Pc)Fe and (phen<sub>2</sub>N<sub>2</sub>)Fe relative to (OEP)Fe. Consequently, the ORR onset for (phen<sub>2</sub>N<sub>2</sub>)Fe and (Pc)Fe is within 150 mV of Fe-N-C. Unlike (OEP)Fe and (Pc)Fe, (phen<sub>2</sub>N<sub>2</sub>)Fe displays excellent selectivity for 4-electron ORR with <4% maximum H<sub>2</sub>O<sub>2</sub> production, comparable to Fe-N-C materials. The aggregate spectroscopic and electrochemical data establish (phen<sub>2</sub>N<sub>2</sub>)Fe as a pyridinic iron macrocycle that effectively models Fe-N-C active sites, thereby providing a rich molecular platform for understanding this important class of catalytic materials.<p><b></b></p>

Physicochemical and Catalytic Properties of Spinels Formed by Solid-Solid Interaction Between Fe2O3and V2O5

1996 ◽  
Vol 61 (8) ◽  
pp. 1131-1140 ◽  
Author(s):  
Abd El-Aziz Ahmed Said
Keyword(s):  
Vanadium Oxide ◽  
Active Sites ◽  
Catalyst Surface ◽  
Catalytic Properties ◽  
Flow System ◽  
Oxide Catalysts ◽  
X Ray Diffraction ◽  
Selective Catalyst ◽  
X Ray ◽  
Solid Catalysts

Vanadium oxide catalysts doped or mixed with 1-50 mole % Fe3+ ions were prepared. The structure of the original samples and those calcined from 200 up to 500 °C were characterized by TG, DTA, IR and X-ray diffraction. The SBET values and texture of the solid catalysts were investigated. The catalytic dehydration-dehydrogenation of isopropanol was carried out at 200 °C using a flow system. The results obtained showed an observable decrease in the activity of V2O5 on the addition of Fe3+ ions. Moreover, Fe2V4O13 is the more active and selective catalyst than FeVO4 spinels. The results were correlated with the active sites created on the catalyst surface.

Single-Site Heterogeneous Catalysts for Olefin Polymerization Enabled by Cation Exchange in a Metal-Organic Framework

2016 ◽  
Vol 138 (32) ◽  
pp. 10232-10237 ◽  
Author(s):  
Robert J. Comito ◽  
Keith J. Fritzsching ◽  
Benjamin J. Sundell ◽  
Klaus Schmidt-Rohr ◽  
Mircea Dincă
Keyword(s):  
Cation Exchange ◽  
Heterogeneous Catalysts ◽  
Olefin Polymerization ◽  
Metal Organic Framework ◽  
Single Site ◽  
Metal Organic ◽  
Organic Framework

The fairweather fault ten years after the southeast Alaska earthquake of 1958

1969 ◽  
Vol 59 (5) ◽  
pp. 1927-1936 ◽  
Author(s):  
Robert Page
Keyword(s):  
Fault Zone ◽  
Active Sites ◽  
Single Site ◽  
Field Observations ◽  
Southeast Alaska ◽  
San Andreas ◽  
Lake Region ◽  
Alaska Earthquake

abstract Field observations made ten years after the southeast Alaska earthquake (M = 7.9) of 10 July 1958 reveal environmental and geomorphic changes in the Fairweather fault zone. Faulting associated with the earthquake killed many trees in the Crillon Lake region. Trees were tilted and later fell, and possibly were drowned because of changes in drainage conditions. A nearly vertical, 2-meter scarp in soil has been eroded to a slope of 35° to 40° in the decade since 1958. Microearthquake activity sampled at a single site on the fault is at least equal to or possibly greater than that reported from active sites on the San Andreas and Denali faults. The distribution of S-P times is consistent with a uniform planar distribution of shocks on a segment of the fault that slipped in 1958. The expected seismicity from aftershocks of the 1958 earthquake is less, but not significantly less, than the observed seismicity.

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