Catalytic Activity and the Nature of Active Centers in Zeolites

A complex of modern physicochemical methods (X-ray phase analysis, low-temperature adsorption of nitrogen, scanning electron microscopy, element analysis)was used to studythe phase and texture properties of the phosphomolybdenum heteropoly acid–titanium oxide catalytic system. It was found that the optimal content of phosphomolybdenum heteropoly acid, which leads to an increase in the catalytic activity of titanium dioxide, is 7% wt.: the diisopropyl ether yield is higher,it reaches maximum values in a shorter period of time, and the samples are characterized by greater stability. It is shown that the textural characteristics of the specific surface area and dispersion are not the key factors responsible for the catalytic activity.It has been suggested that the activity of phosphomolybdenum heteropoly acid-containing samples is associated with the emergence of a new type of active centers that exhibit increased electron-donorproperties(terminal oxygen atoms of the outer frag-ments of octahedra М = О heteropolyacids). A drop in the catalytic activity of samples with a phosphomolyb-denum heteropoly acid content of more than 7% wt. associated with the formation of surface metaphosphoric acid and entails a decrease in active centers.

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Effects of Promoters on Properties of Cu-Zn-Al Catalyst for Selective Hydrogenation of Cinnamaldehyde to Cinnamyl Alcohol

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.393-395.1185 ◽

2011 ◽

Vol 393-395 ◽

pp. 1185-1188

Author(s):

Chang You Li ◽

Xiao Yan Li ◽

Yi Fei Guo

Keyword(s):

Catalytic Activity ◽

Reaction Time ◽

Catalytic Hydrogenation ◽

Selective Hydrogenation ◽

Reaction Rate ◽

Steric Effect ◽

Cinnamyl Alcohol ◽

Active Centers ◽

Hydrogenation Activity

Cu-Zn-Al catalyst was modified by the additives such as Ni and Mn, and the prepared catalyst was employed in the selective catalytic hydrogenation of cinnamaldehyde. The results showed that the addition of Ni could improve catalytic activity significantly, moreover, the improving effect was highest when Zn was replaced by Ni, simultaneously leading to excessive hydrogenation. The Cu-(5%)Mn-Zn-Al catalyst exhibited a higher selectivity of 93.6% for C = O bond to cinnamyl alcohol and hydrogenation activity of 33.0% conversion at 130°C under 1.0 MPa of H2 pressure with the reaction time of 1 h. TPR and XRD characterization showed that Mn promoter was favorable for the growth of Cu0 fine grains on the surface of catalyst, which not only led to steric effect which improved the selectivity for cinnamyl alcohol, but also reduced the numbers of active centers, consequently decreased the reaction rate.

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A Simulation Study for Trimetallic Nanosized Alloy (Ni, Cu, and Ag) in Hydrogenation of Organic Compounds: A Case Study of “Nitrophenols”

Journal of Nanomaterials ◽

10.1155/2017/9464209 ◽

2017 ◽

Vol 2017 ◽

pp. 1-8 ◽

Cited By ~ 1

Author(s):

Salem M. Bawaked ◽

Islam Hamdy Abd El Maksod ◽

Abdulmohsen Alshehri

Keyword(s):

Catalytic Activity ◽

Three Dimensional ◽

High Accuracy ◽

Metallic Surface ◽

Active Centers ◽

Bimetallic Systems ◽

Complex Calculation ◽

Bimetallic System

Trimetallic system (Ni, Cu, and Ag) supported on alumina was utilized for hydrogenation of nitrophenols. The catalytic active centers for hydrogenation were attributed only to the presence of Ni. However, the presence of bi- or trimetallic systems improves the catalytic activity via extra synergism. The catalytic activity was measured as the time for reaching 100% conversion. The function of synergism was fitted for both bimetallic systems (Ni:Ag; Ni:Cu) individually. Subsequently, three-dimensional function was fitted for trimetallic system (Ni:Cu:Ag) based on the linear combination of data for individual bimetallic system. After a complex calculation areal function was evaluated. An Excel program was written to simply evaluate the catalytic activity of trimetallic system with high accuracy. Characterization of catalysts was performed using EPR and pulsed chemisorption by hydrogen. These characterizations of samples enable us to evaluate particle size, metallic surface area, and degree of dispersion. These values were successfully correlated with the synergism function. The program written then could be capable of predicting these values for any trimetallic system.

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Synthesis and Evaluation of Structural and Functional Biomimetic Models of Oxidase-Type Metalloenzymes Based on Polynuclear Compounds with Copper (II) and Manganese (II) Ions

10.20944/preprints202103.0534.v1 ◽

2021 ◽

Author(s):

Yenny Ávila - Torres ◽

Didier Gómez ◽

Jorge Acosta ◽

Efraim Serna- Galvis ◽

Ricardo A. Torres-Palma ◽

...

Keyword(s):

Catalytic Activity ◽

Dehydroascorbic Acid ◽

Ascorbate Oxidase ◽

Water Molecules ◽

Active Centers ◽

Metal Centers ◽

Biomimetic Models ◽

Natural Enzyme ◽

Pure Compounds ◽

The Relationship

Biomimetic compounds are an alternative for to the limited action and fragile nature of enzymes. This work deals with the synthesis, characterization and evaluation of catalytic activity of two new biomimetic models for the active centers of ascorbate oxidase and catalase. [Cu3(S,S(+)cpse)3(H2O)3][Cu3(R,R(-)cpse)3(H2O)3]·17H2O (model for ascorbate oxidase, 1), and [Mn2(S,S(+)Hcpse)4(NaClO4)2(NaOH)(CH4O)]n·[(C2H6O)2]n·[(CH4O)2]n (model for catalase, 2) were prepared through the synchronic method (yields > 78%). The compound 1 has electronic and optical characteristics for racemic compound. The magnetic properties and electrochemical behavior evidence electronic transfer between metal centers. Meanwhile, the compound 2 showed polymeric properties in solid state and dimeric behavior in solution. Compound 1 was able to effectively catalyze the oxidation of ascorbic acid to dehydroascorbic acid (65.6% and 78.24% for racemic and enantiomeric pure compounds) showing structural and functional similarity to the natural enzyme. Besides, Compound 2 catalyzed the decomposition of hydrogen peroxide toward oxygen and water molecules (45%), evidencing that the prepared complex mimics the action of catalases. These two biomimetic models are relationship between them for the structural ligands, the coordination form to metal center and the catalytic activity as oxidase. This research shows the relationship with the design, evaluation, and comprehension of fundamentals aspects for the biomimetic models of active center of metalloenzymes that have importance for biological and industrial processes.

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Tailoring the catalytic activity of nickel sites in NiFe2O4 by cobalt substitution for highly enhanced oxygen evolution reaction

Sustainable Energy & Fuels ◽

10.1039/d1se00318f ◽

2021 ◽

Author(s):

Zhe Zhang ◽

Xiaodong Yan ◽

Jiangyong Liu ◽

Bing Liu ◽

Zhi-Guo Gu

Keyword(s):

Density Functional Theory ◽

Catalytic Activity ◽

Dft Calculations ◽

Oxygen Evolution ◽

Oxygen Evolution Reaction ◽

Density Functional ◽

Active Centers ◽

Functional Theory ◽

Cobalt Substitution ◽

Fe Sites

Density functional theory (DFT) calculations predict that Fe sites are the preferred active centers for OER, while Ni centers are activated at higher potentials. Tuning the local electronic environment of...

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New Method for Removal of Organic Dyes Using Supported Iron Oxide as a Catalyst

Journal of Chemistry ◽

10.1155/2016/1873175 ◽

2016 ◽

Vol 2016 ◽

pp. 1-9 ◽

Cited By ~ 1

Author(s):

Samia A. Kosa ◽

Naha M. Al-sebaii ◽

Islam H. Abd El Maksod ◽

Eman Z. Hegazy

Keyword(s):

Thermal Analysis ◽

Titanium Dioxide ◽

Catalytic Activity ◽

Organic Dyes ◽

Catalytic Decomposition ◽

Organic Dye ◽

Active Centers ◽

Dissolved Iron ◽

Surface Iron

In this study, we perform a catalytic decomposition of organic dye over Fe2O3-CeO2-TiO2-γ-Al2O3catalyst in the presence of molecular oxygen and chlorate ions. The results showed that organic dye acts as a sensitizer during this process. The mechanism of the allover process is hypothesized. Several techniques were employed for the characterization of the catalyst, including XRD, SEM, EDAX, and thermal analysis and catalytic activity. The analysis showed that iron is the main active centers, and we have two types of active centers in this process: surface iron and dissolved iron in titanium dioxide. The dissolved iron was found to be the most active center; however, after Fe/Ti = 2.76, a synergism was observed to be occurring between the two active centers.

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Catalytic conversion of ethanol on H-Y zeolite

Hemijska industrija ◽

10.2298/hemind0510267c ◽

2005 ◽

Vol 59 (9-10) ◽

pp. 267-269

Author(s):

Nedeljko Cegar ◽

Jelena Penavin-Skundric ◽

Branko Skundric ◽

Rada Petrovic

Keyword(s):

Catalytic Activity ◽

Diethyl Ether ◽

Ethanol Conversion ◽

Static System ◽

Nay Zeolite ◽

Y Zeolite ◽

Active Centers ◽

Zeolite Nay ◽

Catalytically Active ◽

Lower Temperature

The catalytic activity of the H-form of synthetic zeolite NaY was examined in this study. The catalytic activity was determined according to the rate of ethanol conversion in a gas phase in the static system. In the conversion of ethanol on synthetic NaY zeolite at 585, 595, and 610 K, on which the reaction develops at an optimal rate, ethene and diethyl ether are evolved in approximately the same quantity. After transforming the NaY zeolite into the H-form, its catalytic activity was extremely increases so, the reaction develops at a significantly lower temperature with a very large increase in the reaction rate. The distribution of the products also changes, so that at lower temperatures diethyl ether is elvolved in most cases, and the development of ethene is favored at higher ones, and after a certain period of time there is almost complete conversion of ethanol into ethene. The increase in catalytic activity, as well as the change of selectivity of conversion of ethanol on the H-form of zeolite, is the result of removing Na+ cations in the NaY zeolite, so that more acidic catalyst is obtained which contains a number of acidic catalytically active centers, as well as a more powerful one compared to the original NaY zeolite.

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Facile One-Step Flame Synthesis of La1−xSrxMnO3 Nanoparticles for CO Catalytic Oxidation

Journal of Chemistry ◽

10.1155/2021/9472008 ◽

2021 ◽

Vol 2021 ◽

pp. 1-11

Author(s):

Hao Zhou ◽

Qiwei Wu ◽

Boyang Qi

Keyword(s):

Catalytic Activity ◽

Active Oxygen Species ◽

Synthesis Method ◽

Flame Synthesis ◽

High Concentration ◽

Active Centers ◽

Oxidation Activity ◽

Co Conversion ◽

One Step ◽

Perovskite Catalysts

A large amount of CO as hazardous emission in the iron ore sintering process has caused severe harm to the environment and human health. To control the emission of CO more effectively, the preparation of highly efficient catalysts has attracted much attention. In this study, the La1-xSrxMnO3 (0 ≤ x < 1) perovskite catalysts with different Sr2+ contents were prepared by the one-step flame synthesis method to treat CO pollutants in the iron and steel industry. The influence of Sr2+ doping on the structure and activity of catalytic were characterized and analyzed. La1-xSrxMnO3 perovskite catalysts exhibit good perovskite phases and loose spherical structures. The specific surface areas are between 4.1 and 12.0 m2 g−1. Combined with the results of H2-TPR and O2-TPD, the improvement of catalytic activity of La1-xSrxMnO3 perovskite can be attributed to the high concentration of active centers and oxygen vacancies. Significantly, the La0.4Sr0.6MnO3 catalyst presented the best reducibility and high content of absorbed active oxygen species, leading to a superior CO oxidation catalytic activity and reaches 50% CO conversion at 134.9°C and 90% at 163.2°C, respectively. The effects of water vapor and CO2 on the oxidation activity of La1-xSrxMnO3 perovskite was investigated. The flame-produced catalysts exhibit favorable catalytic stability and antisintering ability, achieving 100% CO conversion after fifth consecutive oxidation cycles.

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Effect of polymer support functionalization on enzyme immobilization and catalytic activity

Pure and Applied Chemistry ◽

10.1515/pac-2014-0715 ◽

2014 ◽

Vol 86 (11) ◽

pp. 1793-1803 ◽

Cited By ~ 1

Author(s):

Viorica Parvulescu ◽

Adriana Popa ◽

Gabriela Paun ◽

Ramona Ene ◽

Corneliu-Mircea Davidescu ◽

...

Keyword(s):

Catalytic Activity ◽

Catalytic Properties ◽

Quaternary Ammonium Salts ◽

Ammonium Salts ◽

Polymer Support ◽

Phosphonium Salts ◽

Active Centers ◽

Styrene Divinylbenzene ◽

Activity Of Enzymes ◽

Sufficient Concentration

Abstract Two enzymes, laccase and peroxidase, were immobilized on chloromethylated styrene-divinylbenzene copolymers supports functionalized with phosphonates ((RO)2PO) or mixed ammonium and phosphonium groups (N+R3Cl–, P+Ph3Cl–). Phosphonates groups and quaternary ammonium salts were grafted on the “gel-type” copolymer by Michaelis–Becker polymer analogue reaction. Mixed polymer-supported ammonium and phosphonium salts were obtained by transquaternization of the ammonium groups to phosphonium group. The degrees of functionalization for obtained polymers were relatively high ensuring a sufficient concentration of active centers per unit mass of the copolymer. The obtained materials were characterized by thermal analysis, FTIR spectroscopy and SEM microscopy. The effects of OR1 and R2 radicals from phosphonate and respectively ammonium groups, as well as those of glutaraldehyde utilization on the immobilization yield and the catalytic properties of the supported enzymes were indicated. The activity of enzymes increased after immobilization and high immobilization yield was obtained for all the samples. The higher interaction of enzymes with support was indicated for mixed ammonium and phosphonium functions. A higher catalytic activity was obtained for peroxidase in oxidation of phenol and laccase in oxidation of anisole. The low effect of glutaraldehyde on enzyme activity reveals the strong interaction of enzyme with the polymer support, respectively with the functional groups.

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