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.

Investigation of the active sites for NO oxidation reactions over MnOx–CeO2 catalysts

2017 ◽  
Vol 41 (8) ◽  
pp. 3106-3111 ◽  
Author(s):  
Zhihui Sun ◽  
Jun Wang ◽  
Jinxin Zhu ◽  
Chen Wang ◽  
Jianqiang Wang ◽  
...  
Keyword(s):  
Active Site ◽  
Active Sites ◽  
No Oxidation ◽  
Oxidation Reactions

Mn4+/Mn3+ is the active site for NO oxidation reactions, according to the TOF calculated with respect to the initial reducibility measured by H2-TPR quantification.

Investigation of the Catalytic Properties of the Dysthrombin, Thrombin Quick

1979 ◽  
Author(s):  
R.A. Henriksen ◽  
W.G. Owen ◽  
M.E. Nesheim ◽  
K.G. Mann
Keyword(s):  
Active Site ◽  
Mayo Clinic ◽  
Active Sites ◽  
Fluorescence Enhancement ◽  
Catalytic Mechanism ◽  
Antithrombin Iii ◽  
Catalytic Properties ◽  
Inhibitor Binding ◽  
Equivalent Number ◽  
Aggregation Of Platelets

Thrombin Quick (TQ) may be isolated following treatment of Prothrombin Quick [Owen, et al, Mayo Clinic Proceedings, 53: 29-33, (1978)] with Taipan venom, phospholipid and Ca2+. The clotting activity of TQ with fibrinogen is 1/200 that of normal thrombin (T) The activation of Factors V and VIII, and the aggregation of platelets by TQ occurs with an effectiveness of about 1/50 that of thrombin. When incubated with antithrombin III, both T and TQ form inhibitor complexes as determined by dodecylsulfate gel electropheresis. Titration of T and TQ with the fluorescent inhibitor dansylarginine-4-ethylpiperidine amide indicates an equivalent number of active sites based on protein absorption at 280 nm. However, the two enzymes may be distinguished by the decreased fluorescence enhancement observed with TQ relative to T, indicating an increased polarity in the inhibitor binding site of TQ. With the substrate benzoylarginine ethylester, TQ has a Km = 4.5 x 10-5M and kcat - 6.93 compared to Km = 4.0 × 10-5M and kcat = 17.7 for T. This indicates that the defect in TQ esterase activity is in the catalytic mechanism itself and not in substrate binding. The rate of inhibition of TQ by diisopropylphosphofluoridate is decreased. Decreased acylation and deacylation rates for TQ relative to T are observed for tydrolysis of the active site titrant 4-methyumbel1 i feryl-p-guanidlnobenzoate.

Investigation of the Catalytic Properties of the Dysthrombin, Thrombin Quick

1979 ◽  
Author(s):  
R Henriksen ◽  
W Owen ◽  
M Nesheim ◽  
K Mann
Keyword(s):  
Active Site ◽  
Active Sites ◽  
Fluorescence Enhancement ◽  
Catalytic Mechanism ◽  
Antithrombin Iii ◽  
Catalytic Properties ◽  
Inhibitor Binding ◽  
Equivalent Number ◽  
Hydrolysis Of ◽  
Aggregation Of Platelets

Thrombin Quick (TQ) may be isolated following treatment of Prothrombin Quick [Owen, et al, Mayo Clinic Proceedings, 53: 29-33, (1978)] with Taipan venom, phospholipid and ca2+. The clotting activity of TQ with fibrinogen is 1/200 that of nornar thrombin (T). The activation of Factors V and VIII, and the aggregation of platelets by TQ occurs with an effectiveness of about 1/50 that of thrombin. when incubated with antithrombin III, both T ad TQ fom inhibitor complexes as determined by dodecylsulfate gel electropheresis. Titration of T and TQ with the fluorescent inhibitor dansylarginine-4-ethylpiperidine amide indicates an equivalent number of active sites based on protein absorption at 280 nm. However, the two enzymes may be distinquished by the decreased fluorescence enhancement observed with TQ relative to T, indicating an increased polarity in the inhibitor binding site of TQ. With the substrate benzoylarginine ethylester, TQ has a Km = 4.5 × 10-5M and kcat= 6.93 compared to Km = 4.0 × 10-5M and kcat= 17.7 for T. This indicates that the defect in TQ esterase activity is in the catalytic mechanism itself and not in substrate binding. The rate of inhibition of TQ by diisopropylphosphofluoridate is decreased. Decreased acylation and deacylation rates for TQ relative to T are observed for hydrolysis of the active site titrant 4-methykl-umbelliferyl-p-guanidinobenzoate

Dynamic Interconversion of Metal Active Site Ensembles in Zeolite Catalysis

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Siddarth H. Krishna ◽  
Casey B. Jones ◽  
Rajamani Gounder
Keyword(s):  
Active Site ◽  
Active Sites ◽  
Heterogeneous Catalysts ◽  
Mean Field ◽  
Future Research ◽  
Annual Review ◽  
Publication Date ◽  
Turnover Rates ◽  
Practical Applications ◽  
Structure And Motion

Catalysis science is founded on understanding the structure, number, and reactivity of active sites. Kinetic models that consider active sites to be static and noninteracting entities are routinely successful in describing the behavior of heterogeneous catalysts. Yet, active site ensembles often restructure in response to their external environment and even during steady-state catalytic turnover, sometimes requiring non-mean-field kinetic treatments to describe distance-dependent interactions among sites. Such behavior is being recognized more frequently in modern catalysis research, with the advent of experimental methods to quantify turnover rates with increasing precision, an expanding arsenal of operando characterization tools, and computational descriptions of atomic structure and motion at chemical potentials and timescales increasingly relevant to reaction conditions. This review focuses on dynamic changes to metal active site ensembles on zeolite supports, which are silica-based crystalline materials substituted with Al that generate binding sites for isolated and low-nuclearity metal site ensembles. Metal sites can become solvated and mobilized during reaction, facilitating interactions among sites that change their nuclearity and function. Such intersite communication can be regulated by the zeolite support, resulting in non-single-site and potentially non-mean-field kinetic behavior arising from mechanisms of catalytic action that combine elements of those canonically associated with homogeneous and heterogeneous catalysis. We discuss recent literature examples that document dynamic active site behavior in metal-zeolites and outline methodologies to identify and interpret such behavior. We conclude with our outlook on future research directions to develop this evolving branch of catalysis science and harness it for practical applications. Expected final online publication date for the Annual Review of Chemical and Biomolecular Engineering, Volume 12 is June 2021. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

scholarly journals Titanium Dioxide as a Catalyst Support in Heterogeneous Catalysis

2014 ◽  
Vol 2014 ◽  
pp. 1-21 ◽  
Author(s):  
Samira Bagheri ◽  
Nurhidayatullaili Muhd Julkapli ◽  
Sharifah Bee Abd Hamid
Keyword(s):  
Active Sites ◽  
Heterogeneous Catalysts ◽  
High Surface ◽  
Catalyst Support ◽  
High Surface Area ◽  
Supported Metal Catalysts ◽  
Support Material ◽  
Oxidation Reactions ◽  
Base Property ◽  
Metal Support Interaction

The lack of stability is a challenge for most heterogeneous catalysts. During operations, the agglomeration of particles may block the active sites of the catalyst, which is believed to contribute to its instability. Recently, titanium oxide (TiO2) was introduced as an alternative support material for heterogeneous catalyst due to the effect of its high surface area stabilizing the catalysts in its mesoporous structure. TiO2supported metal catalysts have attracted interest due to TiO2nanoparticles high activity for various reduction and oxidation reactions at low pressures and temperatures. Furthermore, TiO2was found to be a good metal oxide catalyst support due to the strong metal support interaction, chemical stability, and acid-base property. The aforementioned properties make heterogeneous TiO2supported catalysts show a high potential in photocatalyst-related applications, electrodes for wet solar cells, synthesis of fine chemicals, and others. This review focuses on TiO2as a support material for heterogeneous catalysts and its potential applications.

scholarly journals Stoichiometric active site modification observed by alkali ion titrations of Sn-Beta

2019 ◽  
Vol 9 (16) ◽  
pp. 4339-4346 ◽  
Author(s):  
Samuel G. Elliot ◽  
Irene Tosi ◽  
Sebastian Meier ◽  
Juan S. Martinez-Espin ◽  
Søren Tolborg ◽  
...  
Keyword(s):  
Active Site ◽  
Active Sites ◽  
Catalytic Properties ◽  
Alkali Ions ◽  
Functional Assays ◽  
Insight Into ◽  
Alkali Ion

Titrations and functional assays are combined to gain insight into the stoichiometric correlations for alkali ions and the tin active sites in Sn-Beta, and show that three different states with distinct catalytic properties exist.

scholarly journals Directing reaction pathways via in situ control of active site geometries in PdAu single-atom alloy catalysts

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Mengyao Ouyang ◽  
Konstantinos G. Papanikolaou ◽  
Alexey Boubnov ◽  
Adam S. Hoffman ◽  
Georgios Giannakakis ◽  
...  
Keyword(s):  
Active Site ◽  
Active Sites ◽  
Heterogeneous Catalysts ◽  
Bimetallic Catalyst ◽  
Theoretical Calculations ◽  
Atomic Scale ◽  
Single Atom ◽  
In Situ Control ◽  
Single Atom Alloy

AbstractThe atomic scale structure of the active sites in heterogeneous catalysts is central to their reactivity and selectivity. Therefore, understanding active site stability and evolution under different reaction conditions is key to the design of efficient and robust catalysts. Herein we describe theoretical calculations which predict that carbon monoxide can be used to stabilize different active site geometries in bimetallic alloys and then demonstrate experimentally that the same PdAu bimetallic catalyst can be transitioned between a single-atom alloy and a Pd cluster phase. Each state of the catalyst exhibits distinct selectivity for the dehydrogenation of ethanol reaction with the single-atom alloy phase exhibiting high selectivity to acetaldehyde and hydrogen versus a range of products from Pd clusters. First-principles based Monte Carlo calculations explain the origin of this active site ensemble size tuning effect, and this work serves as a demonstration of what should be a general phenomenon that enables in situ control over catalyst selectivity.

scholarly journals A pyridinic Fe-N4 macrocycle models the active sites in Fe/N-doped carbon electrocatalysts

2020 ◽  
Vol 11 (1) ◽  
Author(s):  
Travis Marshall-Roth ◽  
Nicole J. Libretto ◽  
Alexandra T. Wrobel ◽  
Kevin J. Anderton ◽  
Michael L. Pegis ◽  
...  
Keyword(s):  
Active Site ◽  
Active Sites ◽  
Catalytic Properties ◽  
Molecular Model ◽  
Reduction Reaction ◽  
Electrochemical Studies ◽  
Onset Potential ◽  
Nitrogen Doped ◽  
Nitrogen Doped Carbon ◽  
Excellent Selectivity

Abstract Iron- and nitrogen-doped carbon (Fe-N-C) materials are leading candidates to replace platinum catalysts for the oxygen reduction reaction (ORR) in fuel cells; however, their active site structures remain poorly understood. A leading postulate is that the iron-containing active sites exist primarily in a pyridinic Fe-N4 ligation environment, yet, molecular model catalysts generally feature pyrrolic coordination. Herein, we report a molecular pyridinic hexaazacyclophane macrocycle, (phen2N2)Fe, and compare its spectroscopic, electrochemical, and catalytic properties for ORR to a typical Fe-N-C material and prototypical pyrrolic iron macrocycles. N 1s XPS and XAS signatures for (phen2N2)Fe are remarkably similar to those of Fe-N-C. Electrochemical studies reveal that (phen2N2)Fe has a relatively high Fe(III/II) potential with a correlated ORR onset potential within 150 mV of Fe-N-C. Unlike the pyrrolic macrocycles, (phen2N2)Fe displays excellent selectivity for four-electron ORR, comparable to Fe-N-C materials. The aggregate spectroscopic and electrochemical data demonstrate that (phen2N2)Fe is a more effective model of Fe-N-C active sites relative to the pyrrolic iron macrocycles, thereby establishing a new molecular platform that can aid understanding of this important class of catalytic materials.

scholarly journals X-ray spectroscopy for chemical and energy sciences: the case of heterogeneous catalysis

2014 ◽  
Vol 21 (5) ◽  
pp. 1084-1089 ◽  
Author(s):  
Anatoly I. Frenkel ◽  
Jeroen A. van Bokhoven
Keyword(s):  
Heterogeneous Catalysis ◽  
Active Site ◽  
Time Scale ◽  
Active Sites ◽  
Heterogeneous Catalysts ◽  
Time Range ◽  
Bond Breaking ◽  
Single Shot ◽  
X Rays ◽  
X Ray

Heterogeneous catalysis is the enabling technology for much of the current and future processes relevant for energy conversion and chemicals synthesis. The development of new materials and processes is greatly helped by the understanding of the catalytic process at the molecular level on the macro/micro-kinetic time scale and on that of the actual bond breaking and bond making. The performance of heterogeneous catalysts is inherently the average over the ensemble of active sites. Much development aims at unravelling the structure of the active site; however, in general, these methods yield the ensemble-average structure. A benefit of X-ray-based methods is the large penetration depth of the X-rays, enablingin situandoperandomeasurements. The potential of X-ray absorption and emission spectroscopy methods (XANES, EXAFS, HERFD, RIXS and HEROS) to directly measure the structure of the catalytically active site at the single nanoparticle level using nanometer beams at diffraction-limited storage ring sources is highlighted. The use of pump–probe schemes coupled with single-shot experiments will extend the time range from the micro/macro-kinetic time domain to the time scale of bond breaking and making.

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