Kinetic heterogeneity of the active sites of titanium-containing catalytic systems in the stereospecific polymerization of isoprene

2007 ◽  
Vol 48 (4) ◽  
pp. 556-561 ◽  
Author(s):  
N. N. Sigaeva ◽  
F. F. Saitova ◽  
E. A. Glukhov ◽  
A. R. Gareev ◽  
E. R. Maksyutova ◽  
...  
Keyword(s):  
Active Sites ◽  
Catalytic Systems ◽  
Stereospecific Polymerization ◽  
Kinetic Heterogeneity

scholarly journals Methanol conversion on borocarbonitride catalysts: Identification and quantification of active sites

2020 ◽  
Vol 6 (26) ◽  
pp. eaba5778 ◽  
Author(s):  
Xuefei Zhang ◽  
Pengqiang Yan ◽  
Junkang Xu ◽  
Fan Li ◽  
Felix Herold ◽  
...  
Keyword(s):  
Active Sites ◽  
Density Functional ◽  
Catalytic Mechanism ◽  
Reaction Pathway ◽  
Methanol Conversion ◽  
Kinetic Measurements ◽  
Catalytic Systems ◽  
X Ray Absorption ◽  
Further Development

Borocarbonitrides (BCNs) have emerged as highly selective catalysts for the oxidative dehydrogenation (ODH) reaction. However, there is a lack of in-depth understanding of the catalytic mechanism over BCN catalysts due to the complexity of the surface oxygen functional groups. Here, BCN nanotubes with multiple active sites are synthesized for oxygen-assisted methanol conversion reaction. The catalyst shows a notable activity improvement for methanol conversion (29%) with excellent selectivity to formaldehyde (54%). Kinetic measurements indicate that carboxylic acid groups on BCN are responsible for the formation of dimethyl ether, while the redox catalysis to formaldehyde occurs on both ketonic carbonyl and boron hydroxyl (B─OH) sites. The ODH reaction pathway on the B─OH site is further revealed by in situ infrared, x-ray absorption spectra, and density functional theory. The present work provides physical-chemical insights into the functional mechanism of BCN catalysts, paving the way for further development of the underexplored nonmetallic catalytic systems.

scholarly journals Development of In2O3-based Catalysts for CO2-based Methanol Production

2020 ◽  
Vol 74 (4) ◽  
pp. 257-262 ◽  
Author(s):  
Matthias S. Frei ◽  
Cecilia Mondelli ◽  
Javier Pérez-Ramírez
Keyword(s):  
Life Cycle Analysis ◽  
Active Sites ◽  
Large Scale ◽  
Atomic Level ◽  
Minimal Amount ◽  
Monoclinic Zirconia ◽  
Planetary Boundaries ◽  
Hydrogen Activation ◽  
Catalytic Systems ◽  
Methanol Production

CO2 valorization into chemicals and fuels is a key area in current academic and industrial research, with thermocatalytic hydrogenation to methanol comprising one of the most advanced routes. Life-cycle analysis coupled to the framework of planetary boundaries has recently confirmed the sustainability of this process in absolute terms, emphasizing the need for cheaper CO2 and renewable H2 and for a catalytic system embracing high activity, selectivity, and durability to meet economic requirements. Herein, our research efforts aimed to gather atomic-level understanding of electronic and geometric properties of active sites in breakthrough In2O3-based catalytic systems guiding their development are reviewed. In-depth mechanistic elucidations identified limited hydrogen activation ability as well as water-driven sintering as limitations of pure In2O3. The former aspect was successfully addressed by adding through coprecipitation a minimal amount of palladium, forming tiny clusters strongly anchored to the oxide lattice leading to an unprecedented sustained methanol productivity. The use of monoclinic zirconia as a carrier, enabling high In2O3 dispersion in two-dimensional nanostructures, inducing the formation of additional active sites on In2O3, and contributing to CO2 activation, offered an efficient way to further boost activity and tackle In2O3 sintering. Overall, our findings set solid grounds to rationally design a supported and promoted In2O3 catalyst holding bright prospects for use at a large scale.

Relationship of the microheterogeneity of isoprene-butadiene copolymers with the kinetic heterogeneity of active sites

2010 ◽  
Vol 435 (1) ◽  
pp. 286-288 ◽  
Author(s):  
V. Z. Mingaleev ◽  
V. P. Zakharov ◽  
P. A. Taibulatov ◽  
Yu. B. Monakov
Keyword(s):  
Active Sites ◽  
Relationship Of ◽  
Kinetic Heterogeneity

scholarly journals New Supports for Carbon-Metal Catalytic Systems Based on Shungite and Carbonizates of Plant Raw Materials

2015 ◽  
Vol 17 (3) ◽  
pp. 223 ◽  
Author(s):  
R.R. Tokpayev ◽  
A.A. Atchabarova ◽  
S.A. Abdullayeva ◽  
S.V. Nechipurenko ◽  
S.A. Yefremov ◽  
...  
Keyword(s):  
Active Sites ◽  
Raw Materials ◽  
Base Catalysis ◽  
Metal Catalyst ◽  
Active Centers ◽  
Catalytic Systems ◽  
Homogeneous Surface ◽  
Plant Raw Materials ◽  
Bet Method ◽  
Catalyst Systems

<p>In this paper, new carbon containing materials based on products of shungite ore enrichment and carbonizates of plant raw materials were studied. The phase transformations occurring during the carbonization process were studied. Scanning electron microscopy (SEM) was used to visualize the surface topography. It was established that supports based on plant raw materials have more developed and homogeneous surface. Specific surface area and porosity was studied by BET (Method of Brunauer-Emmet Taylor). It was found that supports based on plant raw materials have developed microporous surface (383–480 m<sup>2</sup>/g), with predominant micropores on the surface with dimensions of 1.8–2.5 nm. The mechanical strength of the obtained supports is higher than their industrial analogs and it equals 53–91%. Conversion of methylbutynol on active centers of supports was studied. Supports based on plant raw materials have basic active sites whereby they can be used in base catalysis. Supports based on carbon-mineral raw materials possess acid and basic active sites and they can be used to prepare bidirectional type action of catalysts. Conducted research have shown the possibility of using these materials as supports for creating carbon-metal catalyst systems.</p>

On the nature of active sites and catalytic activity for OCM reaction of alkaline-earth oxides-neodymia catalytic systems

2010 ◽  
Vol 375 (1) ◽  
pp. 172-178 ◽  
Author(s):  
Florica Papa ◽  
Dana Gingasu ◽  
Luminita Patron ◽  
Akane Miyazaki ◽  
Ioan Balint
Keyword(s):  
Catalytic Activity ◽  
Active Sites ◽  
Alkaline Earth ◽  
Catalytic Systems

scholarly journals KINETIC HETEROGENEITY OF POLYMER PRODUCTS OBTAINED IN THE PRESENCE OF MICROHETEROGENIC CATALYTIC SYSTEMS BASED ON GEL CHROMATOGRAMS

2021 ◽  
Vol 18 (38) ◽  
pp. 27-37
Author(s):  
Eldar N. MIFTAKHOV ◽  
Svetlana A. MUSTAFINA ◽  
Ildus Sh NASYROV ◽  
Azat Kh DAMINOV
Keyword(s):  
Molecular Weight ◽  
Average Molecular Weight ◽  
Polymerization Process ◽  
Fredholm Integral Equations ◽  
Molecular Characteristics ◽  
Active Centers ◽  
Catalytic Systems ◽  
Polymer Product ◽  
Software Algorithms ◽  
Kinetic Heterogeneity

Background: the polymer product obtained in the presence of microheterogeneous catalytic systems is characterized by fairly molecular weight distribution (MWD), resulted from kinetically nonequivalent active centers (ACs) in the system that initiate the polymerization process. The nature and composition of ACs are determined by setting and solving an inverse problem on the formation of MWD. This problem is acute because revealing the nature of the kinetic heterogeneity explains changes in the molecular and consumer parameters of the product for different catalyst compositions and propagation modes in polymerizations. Aim: This study aimed to develop methods and algorithms for interpreting gel chromatograms to analyze the kinetic heterogeneity of a polymer product obtained industrially in microheterogeneous catalytic systems. Methods: the solution method is based on the assumption that the formed MWD is a superposition of distributions inherent in each type of ACs. Since the problem in the final formulation refers to the Fredholm integral equations of the first kind, the regularization method of A. N. Tikhonov is used for its numerical solution, with the original problem being preliminary discretized. This methodology and the developed software algorithms were used to determine the kinetic heterogeneity of titanium- and neodymium-containing catalytic systems. Results and discussion: The MWD analysis revealed two types of ACs with an average molecular weight of ATi-lnM = 11.3 and BTi-lnM = 13.2 in the titanium catalyst and three types of ACs ANd-lnM = 11.1, BNd-lnM = 12.7 and CNd-lnM = 14 for the neodymium catalyst, respectively. Conclusions: repeated computational experiments under different polymerization conditions and requirements for the preparation of a catalytic system make it possible to reveal a relationship with the resulting heterogeneity of ACs. It allows us to set and solve problems of controlling the molecular characteristics of the resulting polymer product.

scholarly journals Direct Evidence of Cobalt Oxyhydroxide Formation on a La0.2Sr0.8CoO3 Perovskite Water Splitting Catalyst

2021 ◽  
Author(s):  
Anthony Boucly ◽  
Luca Artiglia ◽  
Emiliana Fabbri ◽  
Dennis Palagin ◽  
Dino Aergerter ◽  
...  
Keyword(s):  
Photoelectron Spectroscopy ◽  
Active Sites ◽  
Direct Evidence ◽  
Ambient Pressure ◽  
Spectral Feature ◽  
Ex Situ ◽  
Oxide Surface ◽  
Catalytic Systems ◽  
Cobalt Oxyhydroxide

Abstract Understanding the mechanism of oxygen evolution reaction (OER) on perovskite materials is of great interest to tailor the synthesis of better catalyst materials. Despite the huge amount of literature reports, the complexity of catalytic systems and scarce in situ and operando surface sensitive spectroscopic tools render the detection of active sites and the understanding of the reaction mechanisms challenging. Here, we carried out and compared in situ and ex situ ambient pressure X-ray photoelectron spectroscopy experimental procedures on a La0.2Sr0.8CoO3 perovskite OER catalyst. Experimental results show that segregated surface strontium, which is present in the as prepared sample, is leached into the electrolyte after immersion, leading to surface cobalt active sites enrichment. Such cobalt-enriched oxide surface evolves into a new phase, whose spectral feature is detected in situ, during/after OER. With the help of theoretical simulations, such species is assigned to cobalt oxyhydroxide, providing a direct evidence of its crucial role in the reaction.

scholarly journals Sustainable Catalytic Processes Driven by Graphene-Based Materials

Processes ◽  
2020 ◽  
Vol 8 (6) ◽  
pp. 672 ◽  
Author(s):  
Sergio Navalón ◽  
Wee-Jun Ong ◽  
Xiaoguang Duan
Keyword(s):  
Environmental Remediation ◽  
Active Sites ◽  
Structural Defects ◽  
Future Research ◽  
Honeycomb Lattice ◽  
Catalytic Systems ◽  
Mechanistic Investigation ◽  
Future Research Directions ◽  
Catalytic Processes ◽  
Green Catalysis

In the recent two decades, graphene-based materials have achieved great successes in catalytic processes towards sustainable production of chemicals, fuels and protection of the environment. In graphene, the carbon atoms are packed into a well-defined sp2-hybridized honeycomb lattice, and can be further constructed into other dimensional allotropes such as fullerene, carbon nanotubes, and aerogels. Graphene-based materials possess appealing optical, thermal, and electronic properties, and the graphitic structure is resistant to extreme conditions. Therefore, the green nature and robust framework make the graphene-based materials highly favourable for chemical reactions. More importantly, the open structure of graphene affords a platform to host a diversity of functional groups, dopants, and structural defects, which have been demonstrated to play crucial roles in catalytic processes. In this perspective, we introduced the potential active sites of graphene in green catalysis and showcased the marriage of metal-free carbon materials in chemical synthesis, catalytic oxidation, and environmental remediation. Future research directions are also highlighted in mechanistic investigation and applications of graphene-based materials in other promising catalytic systems.

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