scholarly journals Synthesis of Chalcone Using LDH/Graphene Nanocatalysts of Different Compositions

2019 ◽  
Vol 3 (1) ◽  
pp. 29 ◽  
Author(s):  
Mayra Álvarez ◽  
Dana Crivoi ◽  
Francesc Medina ◽  
Didier Tichit
Keyword(s):  
Active Sites ◽  
Mixed Oxides ◽  
Catalytic Properties ◽  
Condensation Reaction ◽  
Nanocomposite Materials ◽  
Acid Base ◽  
Basic Sites ◽  
Base Catalysts ◽  
Reduced Graphene ◽  
Double Hydroxides

Layered double hydroxides (LDH) or their derived mixed oxides present marked acid-base properties useful in catalysis, but they are generally agglomerated, inducing weak accessibility to the active sites. In the search for improving dispersion and accessibility of the active sites and for controlling the hydrophilic/hydrophobic balance in the catalysts, nanocomposite materials appear among the most attractive. In this study, a series of nanocomposites composed of LDH and reduced graphene oxide (rGO), were successfully obtained by direct coprecipitation and investigated as base catalysts for the Claisen–Schmidt condensation reaction between acetophenone and benzaldehyde. After activation, the LDH-rGO nanocomposites exhibited improved catalytic properties compared to bare LDH. Moreover, they reveal great versatility to tune the selectivity through their composition and the nature or the absence of solvent. This is due to the enhanced basicity of the nanocomposites as the LDH content increases which is assigned to the higher dispersion of the nanoplatelets in comparison to bulk LDH. Lewis-type basic sites of higher strength and accessibility are thus created. The nature of the solvent mainly acts through its acidity able to poison the basic sites of the nanocatalysts.

Electron Donating, Acid-Base and Catalytic Properties of Perovskite-Type Mixed Oxides of Rare Earths

1995 ◽  
Vol 60 (6) ◽  
pp. 977-982
Author(s):  
S. Sugunan ◽  
V. Meera
Keyword(s):  
Catalytic Activity ◽  
Electron Donor ◽  
Rare Earths ◽  
Electron Affinity ◽  
Mixed Oxides ◽  
Catalytic Properties ◽  
Surface Acidity ◽  
Electron Acceptors ◽  
Acid Base ◽  
Perovskite Type

The electron donor properties of perovskite-type mixed oxides (LaFeO3, PrFeO3, SmFeO3, LaCoO3, PrCoO3, SmCoO3, LaNiO3, PrNiO3 and SmNiO3) were studied based on the adsorption of electron acceptors exhibiting different electron affinity viz. 7,7,8,8-tetracyanoquinodimethane, 2,3,5,6-tetrachloro-1,4-benzoquinone, p-dinitrobenzene, and m-dinitrobenzene. The surface acidity/basicity of the oxides was determined using a set of Hammett indicators. The data were correlated with the catalytic activity of the oxides for the reduction of cyclohexanone with 2-propanol.

scholarly journals Hf-based metal–organic frameworks as acid–base catalysts for the transformation of biomass-derived furanic compounds into chemicals

2018 ◽  
Vol 20 (13) ◽  
pp. 3081-3091 ◽  
Author(s):  
Sergio Rojas-Buzo ◽  
Pilar García-García ◽  
Avelino Corma
Keyword(s):  
Aldol Condensation ◽  
Condensation Reaction ◽  
Metal Organic Frameworks ◽  
Acid Base ◽  
Base Catalysts ◽  
Metal Organic ◽  
Furanic Compounds

Hafnium-based metal–organic frameworks are promising catalysts for upgrading biomass derivatives via an aldol condensation reaction.

Mixed oxides obtained from Co and Mn containing layered double hydroxides: Preparation, characterization, and catalytic properties

2006 ◽  
Vol 179 (3) ◽  
pp. 812-823 ◽  
Author(s):  
František Kovanda ◽  
Tomáš Rojka ◽  
Jana Dobešová ◽  
Vladimír Machovič ◽  
Petr Bezdička ◽  
...  
Keyword(s):  
Layered Double Hydroxides ◽  
Mixed Oxides ◽  
Catalytic Properties ◽  
Double Hydroxides

scholarly journals The Influence of the Preparation Method on the Physico-Chemical Properties and Catalytic Activities of Ce-Modified LDH Structures Used as Catalysts in Condensation Reactions

Molecules ◽  
2021 ◽  
Vol 26 (20) ◽  
pp. 6191
Author(s):  
Alexandra-Elisabeta Stamate ◽  
Rodica Zăvoianu ◽  
Octavian Dumitru Pavel ◽  
Ruxandra Birjega ◽  
Andreea Matei ◽  
...  
Keyword(s):  
Preparation Method ◽  
Mixed Oxides ◽  
Condensation Reaction ◽  
Chemical Properties ◽  
Precipitation Method ◽  
Synthesis Methods ◽  
Molar Ratios ◽  
Base Catalysts ◽  
Physico Chemical ◽  
Co Precipitation

Mechanical activation and mechanochemical reactions are the subjects of mechanochemistry, a special branch of chemistry studied intensively since the 19th century. Herein, we comparably describe two synthesis methods used to obtain the following layered double hydroxide doped with cerium, Mg3Al0.75Ce0.25(OH)8(CO3)0.5·2H2O: the mechanochemical route and the co-precipitation method, respectively. The influence of the preparation method on the physico-chemical properties as determined by multiple techniques such as XRD, SEM, EDS, XPS, DRIFT, RAMAN, DR-UV-VIS, basicity, acidity, real/bulk densities, and BET measurements was also analyzed. The obtained samples, abbreviated HTCe-PP (prepared by co-precipitation) and HTCe-MC (prepared by mechanochemical method), and their corresponding mixed oxides, Ce-PP (resulting from HTCe-PP) and Ce-MC (resulting from HTCe-MC), were used as base catalysts in the self-condensation reaction of cyclohexanone and two Claisen–Schmidt condensations, which involve the reaction between an aromatic aldehyde and a ketone, at different molar ratios to synthesize compounds with significant biologic activity from the flavonoid family, namely chalcone (1,3-diphenyl-2-propen-1-one) and flavone (2-phenyl-4H-1benzoxiran-4-one). The mechanochemical route was shown to have indisputable advantages over the co-precipitation method for both the catalytic activity of the solids and the costs.

scholarly journals Mg-Fe-mixed oxides derived from layered double hydroxides: A study of the surface properties

2011 ◽  
Vol 76 (12) ◽  
pp. 1661-1671 ◽  
Author(s):  
Milica Hadnadjev-Kostic ◽  
Tatjana Vulic ◽  
Radmila Marinkovic-Neducin ◽  
Aleksandar Nikolic ◽  
Branislav Jovic
Keyword(s):  
Surface Properties ◽  
Layered Double Hydroxides ◽  
Active Sites ◽  
Mixed Oxides ◽  
Lower Surface ◽  
Multiphase System ◽  
Fischer Tropsch ◽  
Acid And Base ◽  
Phase Range ◽  
Double Hydroxides

The influence of surface properties on the selectivity of the synthesized catalysts was studied, considering that their selectivity towards particular hydrocarbons is crucial for their overall activity in the chosen Fischer- -Tropsch reaction. Magnesium- and iron-containing layered double hydroxides (LDH), with the general formula: [Mg1-xFex(OH)2](CO3)x/2?mH2O, x = = n(Fe)/(n(Mg)+n(Fe)), synthesized with different Mg/Fe ratio and their thermally derived mixed oxides were investigated. Magnesium was chosen because of its basic properties, whereas iron was selected due to its well-known high Fischer-Tropsch activity, redox properties and the ability to form specific active sites in the layered LDH structure required for catalytic application. The thermally less stable multiphase system (synthesized outside the optimal single LDH phase range with additional Fe-phase), having a lower content of surface acid and base active sites, a lower surface area and smaller fraction of smaller mesopores, showed higher selectivity in the Fischer-Tropsch reaction. The results of this study imply that the metastability of derived multiphase oxides structure has a greater influence on the formation of specific catalyst surface sites than other investigated surface properties.

scholarly journals Ethynylation of Formaldehyde over Binary Cu-Based Catalysts: Study on Synergistic Effect between Cu+ Species and Acid/Base Sites

Nanomaterials ◽  
2019 ◽  
Vol 9 (7) ◽  
pp. 1038 ◽  
Author(s):  
Zhipeng Wang ◽  
Lijun Ban ◽  
Pingfan Meng ◽  
Haitao Li ◽  
Yongxiang Zhao
Keyword(s):  
Catalytic Activity ◽  
Synergistic Effect ◽  
Active Sites ◽  
Electronic Configuration ◽  
Acid Base ◽  
Basic Sites ◽  
Surface Basicity ◽  
Acidic Sites ◽  
Reaction Cycles

Most studies on the Cu-based catalysts in the ethynylation of formaldehyde are merely focused on the tuning of electronic configuration and dispersion of the Cu+ species. So far, little attention has been paid to the synergy between Cu species and promoters. Herein, binary nano-CuO-MOx catalysts (M = Si, Al, and Mg) were synthesized and the effects of the promoter on the surface basicity/acidity were systematically studied as well as the ethynylation performance of the nano-CuO-based catalysts. The results show that the introduction of MgO provided a large number of basic sites, which could coordinate with the active Cu+ species and facilitate the dissociation of acetylene as HC ≡ Cδ− and Hδ+. The strongly nucleophilic acetylenic carbon (HC≡Cδ−) is favorable to the attack at the electropositive carbonyl Cδ+ of formaldehyde. The MgO-promoted CuO catalyst showed the highest yield of BD (94%) and the highest stability (the BD yield decreased only from 94% to 82% after eight reaction cycles). SiO2 effectively dispersed Cu species, which improved catalytic activity and stability. However, the introduction of Al2O3 resulted in a large number of acidic sites on the catalyst’s surface. This led to the polymerization of acetylene, which covered the active sites and decreased the catalyst’s activity.

scholarly journals Tracing The Acid-Base Catalytic Properties Of MON2O Mixed Oxides (M=Be, Mg, Ca; N=Li, Na, K) By Theoretical Calculations

2021 ◽  
Author(s):  
Dawid Faron ◽  
Piotr Skurski ◽  
Iwona Anusiewicz
Keyword(s):  
Alkali Metal ◽  
Gas Phase ◽  
Mixed Oxides ◽  
Catalytic Properties ◽  
Theoretical Calculations ◽  
Lewis Acidity ◽  
Free Energies ◽  
Acid Base ◽  
The Stability ◽  
Fragmentation Processes

Abstract The stability and acid-base properties of MON2O mixed oxides (where M = Be, Mg, Ca; N = Li, Na, K) are studied by using ab initio methods. It is demonstrated that (i) the basicity of such designed systems evaluated by estimation of electronic proton affinity and gas-phase basicity (defined as the electronic and Gibbs free energies of deprotonation processes for [MON2O]H+) were found significant (in the ranges of 272–333 kcal/mol and 260–322 kcal/mol, respectively); (ii) in each series of MOLi2O/MONa2O/MOK2O the basicity increases with an increase of the atomic number of alkali metal involved; (ii) the Lewis-acidity of the corresponding [MON2O]H+ determined with respect to hydride anion (assessed as the electronic and Gibbs free energies of H− detachment processes for [MON2O]H2) decreases as the basicity of the corresponding oxide increases. The thermodynamic stability of all [MON2O]H2 systems is confirmed by estimating the Gibbs free energies for the fragmentation processes yielding either H2 or H2O.

Acid–base properties of the active sites responsible for C2+ and CO2 formation over MO–Sm2O3 (M=Zn, Mg, Ca and Sr) mixed oxides in OCM reaction

2011 ◽  
Vol 346 (1-2) ◽  
pp. 46-54 ◽  
Author(s):  
Florica Papa ◽  
Patron Luminita ◽  
Petre Osiceanu ◽  
Ruxandra Birjega ◽  
Miyazaki Akane ◽  
...  
Keyword(s):  
Active Sites ◽  
Mixed Oxides ◽  
Acid Base ◽  
Base Properties

scholarly journals Biodiesel: Modified Mixed Oxides as Catalyst for Transesterification of Rapeseed Oil

Catalysts ◽  
2020 ◽  
Vol 10 (12) ◽  
pp. 1397
Author(s):  
Vávra Aleš ◽  
Tišler Zdeněk ◽  
Kocík Jaroslav ◽  
Smutek Jakub
Keyword(s):  
Active Sites ◽  
Heterogeneous Catalysts ◽  
Fossil Fuels ◽  
Mixed Oxides ◽  
Catalyst Activity ◽  
Textural Properties ◽  
Carbon Fibres ◽  
Key Factor ◽  
Double Hydroxides

Biodiesel, as one of the alternative biofuels replacing the common fossil fuels, is prepared by transesterification of oils and fats. Commonly, the reaction is catalysed by either acidic or basic catalysts. The availability of the active sites to large triglyceride molecules is the key factor of the heterogeneous catalysts. The use of carbon fibres during the synthesis of Mg/Fe layered double hydroxides results in the formation of macropores during the calcination. The amount of carbon fibres showed an important effect on the textural properties of the resulting mixed oxides. The texture was determined by N2-adsorption and Hg-porosity. The catalyst activity in the studied reaction was examined by determination of ester amount by gas chromatography and the activity was compared with unmodified mixed oxides. The highest ester yield (40 wt.%) was achieved by adding 1 wt.% of carbon fibres to the catalyst with the largest size of macropores.

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