Role of polyaniline morphology in Pd particles dispersion. Hydrogenation of alkynes in the presence of Pd-polyaniline catalysts

AbstractTwo polyaniline (PANI) samples of various molecular masses were used for the preparation of palladium catalysts (with 2 mass % of Pd). The physicochemical features of starting polyanilines were found to substantially affect the size and extent of palladium nanoparticles aggregation. Strongly aggregated large palladium particles appeared in the PANI sample of more compact morphology (PANI-H), higher crystallinity and lower specific surface area. Pd nanoparticles of a definitively smaller size were formed in the more amorphous PANI sample of looser morphology (PANI-L) and the extent of particles aggregation was markedly lower. The catalytic properties of Pd/PANI samples were studied in a liquid phase hydrogenation of unsaturated triple bond (C≡C) in alkynes reactants, phenylacetylene, and cyclohexylacetylene. The 2 mass % Pd/PANI-L catalyst prepared using polymer of less compact texture exhibited much higher activity in both reactions. In the presence of the 2 mass % Pd/PANI-L catalyst, alkene products were formed with a high selectivity (approximately 90 %) attained at the almost complete conversion of alkynes. This highly selective hydrogenation of the C≡C to the C=C bond was related to the presence of an electroactive polymer, PANI, in close proximity with Pd active sites. Polyaniline could have a role in a steric effect as well as in a modification of adsorptive properties of Pd centres.

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The promotion effect of π-π interactions in Pd NPs catalysed selective hydrogenation

10.21203/rs.3.rs-871287/v1 ◽

2021 ◽

Author(s):

Miao Guo ◽

Sanjeevi Jayakumar ◽

Xiangtao Kong ◽

Chunzhi Li ◽

He Li ◽

...

Keyword(s):

Active Sites ◽

Weak Interactions ◽

Activation Barrier ◽

Pd Nanoparticles ◽

Catalytic Performance ◽

Supported Metal Catalysts ◽

Rate Determining Step ◽

Non Covalent Interactions ◽

Supported Metal

Abstract The utilization of weak interactions to improve the catalytic performance of supported metal catalysts is an important strategy for catalysts design, but still remains a big challenge. Herein, the weak interactions nearby the Pd nanoparticles (NPs) were finely tuned by using a series of imine-linked covalent organic frameworks (COFs) with different conjugation skeletons. The Pd NPs embedded in pyrene-COF were ca. 3 to 10-fold more active than those in COFs without pyrene in the hydrogenation of aromatic ketones/aldehydes, quinolines and nitrobenzene, though Pd have similar size and surface structure. With acetophenone (AP) hydrogenation as a model reaction, systematic studies imply that the π-π interaction of AP and pyrene rings in the vicinity of Pd NPs could significantly reduce the activation barrier in the rate-determining step. This work highlights the important role of non-covalent interactions beyond the active sites in modulating the catalytic performance of supported metal NPs.

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Liquid-phase Hydrogenation of Phenol to Cyclohexanone over Supported Palladium Catalysts

BULLETIN OF CHEMICAL REACTION ENGINEERING AND CATALYSIS ◽

10.9767/bcrec.11.3.575.354-362 ◽

2016 ◽

Vol 11 (3) ◽

pp. 354 ◽

Cited By ~ 4

Author(s):

Lihui Fan ◽

Luyang Zhang ◽

Yanming Shen ◽

Dongbin Liu ◽

Nasarul Wahab ◽

...

Keyword(s):

Liquid Phase ◽

Palladium Catalysts ◽

Pd Nanoparticles ◽

Moderate Amount ◽

Supported Palladium Catalysts ◽

Phenol Hydrogenation ◽

Liquid Phase Hydrogenation ◽

Supported Palladium ◽

Phenol Conversion ◽

Supported Pd

The ZSM-5, g-Al2O3, SiO2 and MgO supported Pd-catalysts were prepared for the phenol hydrogenation to cyclohexanone in liquid-phase. The natures of these catalysts were characterized by XRD, N2 adsorption-desorption analysis, H2-TPR, CO2-TPD and NH3-TPD. The catalytic performance of the supported Pd-catalyst for phenol hydrogenation to cyclohexanone is closely related to nature of the support and the size of Pd nanoparticles. The Pd/MgO catalyst which possesses higher basicity shows higher cyclohexanone selectivity, but lower phenol conversion owing to the lower specific surface area. The Pd/SiO2 catalyst prepared by precipitation gives higher cyclohexanone selectivity and phenol conversion, due to the moderate amount of Lewis acidic sites, and the smaller size and higher dispersion of Pd nanoparticles on the surface. Under the reaction temperature of 135 oC and H2 pressure of 1 MPa, after reacting for 3.5 h, the phenol conversion of 71.62% and the cyclohexanone selectivity of 90.77% can be obtained over 0.5 wt% Pd/SiO2 catalyst. Copyright © 2016 BCREC GROUP. All rights reservedReceived: 7th March 2016; Revised: 13rd May 2016; Accepted: 7th June 2016How to Cite: Fan, L., Zhang, L., Shen, Y., Liu, D., Wahab, N., Hasan, M.M. (2016). Liquid-phase Hydrogenation of Phenol to Cyclohexanone over Supported Palladium Catalysts. Bulletin of Chemical Reaction Engineering & Catalysis, 11 (3): 354-362 (doi: 10.9767/bcrec.11.3.575.354-362)Permalink/DOI: <a href="http://doi.org/10.9767/bcrec.11.3.575.354-362">http://doi.org/10.9767/bcrec.11.3.575.354-362</a>

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Model reactions for the study of hydrogenation and acidic activity of palladium catalysts

Collection of Czechoslovak Chemical Communications ◽

10.1135/cccc19872019 ◽

1987 ◽

Vol 52 (8) ◽

pp. 2019-2027 ◽

Cited By ~ 1

Author(s):

Libor Červený ◽

Nguyen Thi Du ◽

Ivo Paseka

Keyword(s):

Palladium Catalysts ◽

Styrene Oxide ◽

Side Reactions ◽

Pd Catalysts ◽

Variable Parameters ◽

Acid Properties ◽

Liquid Phase Hydrogenation ◽

Acid Catalysed Reactions ◽

Different Content ◽

Model Reactions

Palladium catalysts have been used to study the hydrogenation of 1-phenyl-2-butene-1-ol which is accompanied by several side reactions considered to be acid-catalysed. Another model reaction studied was dehydration and subsequent hydrogenation or hydrogenolysis of 1-phenyl-1,3-propanediol to 3-phenyl-1-propanol, accompanied by formation of propylbenzene. The dehydration and propylbenzene formation can be again classified as acid-catalysed reactions. Another one is methanolysis of styrene oxide taking place under conditions of liquid phase hydrogenation due to the acid properties of Pd-H systems. Hydrogenation activity of Pd catalysts was tested by hydrogenation of cyclohexene. Sixteen Pd catalysts on different supports and with different content of active component were used, their activity and selectivity was determined and the effect of variable parameters in the synthesis of these catalysts on the activity and selectivity is discussed.

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Role of the Structure and Electronic Properties of Fe2O3-MoO3 Catalyst on the Dehydration of Isopropyl Alcohol

Collection of Czechoslovak Chemical Communications ◽

10.1135/cccc19931591 ◽

1993 ◽

Vol 58 (7) ◽

pp. 1591-1599 ◽

Cited By ~ 3

Author(s):

Abd El-Aziz A. Said

Keyword(s):

Active Sites ◽

Isopropyl Alcohol ◽

Oxide Catalyst ◽

Flow System ◽

Charge Carriers ◽

X Ray Diffraction ◽

X Ray ◽

Catalyst Composition ◽

Surface Active

Molybdenum oxide catalyst doped or mixed with (1 - 50) mole % Fe3+ ions were prepared. The structure of the original samples and the samples calcined at 400 °C were characterized using DTA, X-ray diffraction and IR spectra. Measurements of the electrical conductivity of calcined samples with and without isopropyl alcohol revealed that the conductance increases on increasing the content of Fe3+ ions up to 50 mole %. The activation energies of charge carriers were determined in presence and absence of the alcohol. The catalytic dehydration of isopropyl alcohol was carried out at 250 °C using a flow system. The results obtained showed that the doped or mixed catalysts are active and selective towards propene formation. However, the catalyst containing 40 mole % Fe3+ ions exhibited the highest activity and selectivity. Correlations were attempted to the catalyst composition with their electronic and catalytic properties. Probable mechanism for the dehydration process is proposed in terms of surface active sites.

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Geometric Factor in Skeletal Reactions of 2-Methylpentane on Stepped Surfaces of Platinum Catalyst

Collection of Czechoslovak Chemical Communications ◽

10.1135/cccc19922012 ◽

1992 ◽

Vol 57 (10) ◽

pp. 2012-2020

Author(s):

Vladimír Hejtmánek

Keyword(s):

Active Sites ◽

Platinum Catalyst ◽

Point Of View ◽

Geometric Factor ◽

Published Data ◽

Stepped Surfaces ◽

Geometric Conditions ◽

Surface Intermediates ◽

Isomerization Mechanism

The role of geometric factor in the course of skeletal reactions (isomerization, hydrogenolysis) of 2-methylpentane on stepped (119), (557) and reconstructed R(557) surfaces of single crystals of platinum was evaluated with computer designed models. These calculations were compared with reported experimental data. It was found by analysis of geometric conditions that there are accessible active ensembles on double step of the reconstructed R(557) surface. In addition, these active sites are unsaturated in their coordination sphere and thus catalytically effective. This finding is consistent with published data, confirming higher catalytic activity of this surface. The various pathways of Bond Shift isomerization mechanism of 2-methylpentane from the point of view of steric demands of surface intermediates on differently located ensembles are discussed, too.

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The RelA hydrolase domain acts as a molecular switch for (p)ppGpp synthesis

Communications Biology ◽

10.1038/s42003-021-01963-z ◽

2021 ◽

Vol 4 (1) ◽

Author(s):

Anurag Kumar Sinha ◽

Kristoffer Skovbo Winther

Keyword(s):

Active Sites ◽

Molecular Switch ◽

Cell Physiology ◽

Synthetase Activity ◽

Wild Type ◽

Functional Studies ◽

Loop Region ◽

A Site ◽

Trna Binding

AbstractBacteria synthesize guanosine tetra- and penta phosphate (commonly referred to as (p)ppGpp) in response to environmental stresses. (p)ppGpp reprograms cell physiology and is essential for stress survival, virulence and antibiotic tolerance. Proteins of the RSH superfamily (RelA/SpoT Homologues) are ubiquitously distributed and hydrolyze or synthesize (p)ppGpp. Structural studies have suggested that the shift between hydrolysis and synthesis is governed by conformational antagonism between the two active sites in RSHs. RelA proteins of γ-proteobacteria exclusively synthesize (p)ppGpp and encode an inactive pseudo-hydrolase domain. Escherichia coli RelA synthesizes (p)ppGpp in response to amino acid starvation with cognate uncharged tRNA at the ribosomal A-site, however, mechanistic details to the regulation of the enzymatic activity remain elusive. Here, we show a role of the enzymatically inactive hydrolase domain in modulating the activity of the synthetase domain of RelA. Using mutagenesis screening and functional studies, we identify a loop region (residues 114–130) in the hydrolase domain, which controls the synthetase activity. We show that a synthetase-inactive loop mutant of RelA is not affected for tRNA binding, but binds the ribosome less efficiently than wild type RelA. Our data support the model that the hydrolase domain acts as a molecular switch to regulate the synthetase activity.

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Green Nanocoatings Based on the Deposition of Zirconium Oxide: The Role of the Substrate

Materials ◽

10.3390/ma14041043 ◽

2021 ◽

Vol 14 (4) ◽

pp. 1043

Author(s):

Vitor Bonamigo Moreira ◽

Anna Puiggalí-Jou ◽

Emilio Jiménez-Piqué ◽

Carlos Alemán ◽

Alvaro Meneguzzi ◽

...

Keyword(s):

Zirconium Oxide ◽

Active Sites ◽

Modified Electrodes ◽

Chemical Conversion ◽

Ceramic Materials ◽

Point Of View ◽

Oxide Coatings ◽

Alloying Element ◽

Substrate Nature

Herein, the influence of the substrate in the formation of zirconium oxide monolayer, from an aqueous hexafluorozirconic acid solution, by chemical conversion and by electro-assisted deposition, has been approached. The nanoscale dimensions of the ZrO2 film is affected by the substrate nature and roughness. This study evidenced that the mechanism of Zr-EAD is dependent on the potential applied and on the substrate composition, whereas conversion coating is uniquely dependent on the adsorption reaction time. The zirconium oxide based nanofilms were more homogenous in AA2024 substrates if compared to pure Al grade (AA1100). It was justified by the high content of Cu alloying element present in the grain boundaries of the latter. Such intermetallic active sites favor the obtaining of ZrO2 films, as demonstrated by XPS and AFM results. From a mechanistic point of view, the electrochemical reactions take place simultaneously with the conventional chemical conversion process driven by ions diffusion. Such findings will bring new perspectives for the generation of controlled oxide coatings in modified electrodes used, as for example, in the construction of battery cells; in automotive and in aerospace industries, to replace micrometric layers of zinc phosphate by light-weight zirconium oxide nanometric ones. This study is particularly addressed for the reduction of industrial waste by applying green bath solutions without the need of auxiliary compounds and using lightweight ceramic materials.

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On the Role of Protonic Acid Sites in Cu Loaded FAU31 Zeolite as a Catalyst for the Catalytic Transformation of Furfural to Furan

Molecules ◽

10.3390/molecules26072015 ◽

2021 ◽

Vol 26 (7) ◽

pp. 2015

Author(s):

Łukasz Kuterasiński ◽

Małgorzata Smoliło-Utrata ◽

Joanna Kaim ◽

Wojciech Rojek ◽

Jerzy Podobiński ◽

...

Keyword(s):

Active Sites ◽

Acid Sites ◽

Bronsted Acid ◽

Brønsted Acid ◽

Brønsted Acid Sites ◽

Protonic Acid ◽

Brönsted Acid ◽

Brönsted Acid Sites ◽

Bronsted Acid Sites

The aim of the present paper is to study the speciation and the role of different active site types (copper species and Brønsted acid sites) in the direct synthesis of furan from furfural catalyzed by copper-exchanged FAU31 zeolite. Four series of samples were prepared by using different conditions of post-synthesis treatment, which exhibit none, one or two types of active sites. The catalysts were characterized by XRD, low-temperature sorption of nitrogen, SEM, H2-TPR, NMR and by means of IR spectroscopy with ammonia and CO sorption as probe molecules to assess the types of active sites. All catalyst underwent catalytic tests. The performed experiments allowed to propose the relation between the kind of active centers (Cu or Brønsted acid sites) and the type of detected products (2-metylfuran and furan) obtained in the studied reaction. It was found that the production of 2-methylfuran (in trace amounts) is determined by the presence of the redox-type centers, while the protonic acid sites are mainly responsible for the furan production and catalytic activity in the whole temperature range. All studied catalysts revealed very high susceptibility to coking due to polymerization of furfural.

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Machine learning differentiates enzymatic and non-enzymatic metals in proteins

Nature Communications ◽

10.1038/s41467-021-24070-3 ◽

2021 ◽

Vol 12 (1) ◽

Author(s):

Ryan Feehan ◽

Meghan W. Franklin ◽

Joanna S. G. Slusky

Keyword(s):

Machine Learning ◽

Metal Binding ◽

Binding Sites ◽

Active Sites ◽

De Novo ◽

Enzyme Design ◽

Metal Binding Sites ◽

Ensemble Machine Learning ◽

Machine Learning Model ◽

Physicochemical Features

AbstractMetalloenzymes are 40% of all enzymes and can perform all seven classes of enzyme reactions. Because of the physicochemical similarities between the active sites of metalloenzymes and inactive metal binding sites, it is challenging to differentiate between them. Yet distinguishing these two classes is critical for the identification of both native and designed enzymes. Because of similarities between catalytic and non-catalytic metal binding sites, finding physicochemical features that distinguish these two types of metal sites can indicate aspects that are critical to enzyme function. In this work, we develop the largest structural dataset of enzymatic and non-enzymatic metalloprotein sites to date. We then use a decision-tree ensemble machine learning model to classify metals bound to proteins as enzymatic or non-enzymatic with 92.2% precision and 90.1% recall. Our model scores electrostatic and pocket lining features as more important than pocket volume, despite the fact that volume is the most quantitatively different feature between enzyme and non-enzymatic sites. Finally, we find our model has overall better performance in a side-to-side comparison against other methods that differentiate enzymatic from non-enzymatic sequences. We anticipate that our model’s ability to correctly identify which metal sites are responsible for enzymatic activity could enable identification of new enzymatic mechanisms and de novo enzyme design.

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Particle size effects in the selective hydrogenation of cinnamaldehyde over supported palladium catalysts

RSC Advances ◽

10.1039/c6ra17000e ◽

2016 ◽

Vol 6 (79) ◽

pp. 75541-75551 ◽

Cited By ~ 37

Author(s):

Feng Jiang ◽

Jian Cai ◽

Bing Liu ◽

Yuebing Xu ◽

Xiaohao Liu

Keyword(s):

Particle Size ◽

Size Effect ◽

Selective Hydrogenation ◽

Size Effects ◽

Palladium Catalysts ◽

Particle Size Effect ◽

Particle Size Effects ◽

Supported Palladium Catalysts ◽

Supported Palladium ◽

Palladium Particles

Palladium particles of different sizes obtained directly and indirectly by various methods were studied to clarify the particle size effect in the selective hydrogenation of cinnamaldehyde (CAL).

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