scholarly journals Hybrid organic–inorganic structured materials as single-site heterogeneous catalysts

2012 ◽  
Vol 468 (2143) ◽  
pp. 1927-1954 ◽  
Author(s):  
Urbano Díaz ◽  
Mercedes Boronat ◽  
Avelino Corma
Keyword(s):  
Active Sites ◽  
Heterogeneous Catalysts ◽  
Structural Characteristics ◽  
Inorganic Materials ◽  
Single Site ◽  
Structured Materials ◽  
Solid Catalysts ◽  
Highly Active ◽  
Molecular Catalysts ◽  
Inorganic Structure

Catalyst selectivity is associated with well-defined homogeneous active sites. Transition metal complexes and organocatalysts are highly active and selective in the homogeneous phase, and their heterogenization by incorporating them into inorganic solid materials allows combining their excellent catalytic activity with improved separation, recovering and recycling properties. In this article, we present the structural characteristics and catalytic properties of hybrid organic–inorganic materials in which the molecular catalysts are part of the inorganic structure, emphasizing the possibilities of periodic mesoporous hybrid materials and coordination polymers as single-site solid catalysts.

ChemInform Abstract: Hybrid Organic-Inorganic Structured Materials as Single-Site Heterogeneous Catalysts

ChemInform ◽  
2012 ◽  
Vol 43 (48) ◽  
pp. no-no
Author(s):  
Urbano Diaz ◽  
Mercedes Boronat ◽  
Avelino Corma
Keyword(s):  
Heterogeneous Catalysts ◽  
Single Site ◽  
Structured Materials

Biodiesel Production Using Mixed Solid Catalysts

2013 ◽  
Vol 824 ◽  
pp. 451-458
Author(s):  
A.K. Temu
Keyword(s):  
Active Sites ◽  
Heterogeneous Catalysts ◽  
Biodiesel Production ◽  
Environmentally Benign ◽  
Catalyst Loading ◽  
Yield Data ◽  
Continuous Processes ◽  
Solid Catalysts ◽  
Base Catalysts ◽  
Astm D6751

One of the disadvantages of homogeneous base catalysts in biodiesel production is that they cannot be reused or regenerated because they are consumed in the reaction. Besides, homogeneous catalysed process is not environmentally friendly because a lot of waste water is produced in the separation step. Unlike homogeneous, heterogeneous catalysts are environmentally benign, can be reused and regenerated, and could be operated in continuous processes, thus providing a promising option for biodiesel production. This paper presents catalytic activity of single and mixed solid catalysts in production of biodiesel from palm oil using methanol as well as ethanol at atmospheric pressure. The catalysts used are CaO, K2CO3, Al2O3, and CaO/K2CO3, CaO/Al2O3, K2CO3/Al2O3 mixtures. Results show that methanol is a better reactant with biodiesel yield ranging from 48 to 96.5% while ethanol gives yields ranging from 20 to 95.2%. The yield data for single catalysts range from 20 to 89.2% while that for mixed catalysts range from 52 to 96.5% indicating improvement in the activity by mixing the catalysts. The study also shows that biodiesel yield increases with catalyst loading which emphasizes the need for sufficient number of active sites. The properties of biodiesel produced compares well with ASTM D6751 and EN 14124 biodiesel standards.

scholarly journals Reflections on the value of electron microscopy in the study of heterogeneous catalysts

2017 ◽  
Vol 473 (2197) ◽  
pp. 20160714 ◽  
Author(s):  
John Meurig Thomas
Keyword(s):  
Electron Microscopy ◽  
High Resolution ◽  
Active Sites ◽  
Heterogeneous Catalysts ◽  
Three Dimensions ◽  
Single Atom ◽  
Catalyst Characterization ◽  
Solid Catalysts ◽  
Valence States ◽  
Ac Transmission

Electron microscopy (EM) is arguably the single most powerful method of characterizing heterogeneous catalysts. Irrespective of whether they are bulk and multiphasic, or monophasic and monocrystalline, or nanocluster and even single-atom and on a support, their structures in atomic detail can be visualized in two or three dimensions, thanks to high-resolution instruments, with sub-Ångstrom spatial resolutions. Their topography, tomography, phase-purity, composition, as well as the bonding, and valence-states of their constituent atoms and ions and, in favourable circumstances, the short-range and long-range atomic order and dynamics of the catalytically active sites, can all be retrieved by the panoply of variants of modern EM. The latter embrace electron crystallography, rotation and precession electron diffraction, X-ray emission and high-resolution electron energy-loss spectra (EELS). Aberration-corrected (AC) transmission (TEM) and scanning transmission electron microscopy (STEM) have led to a revolution in structure determination. Environmental EM is already playing an increasing role in catalyst characterization, and new advances, involving special cells for the study of solid catalysts in contact with liquid reactants, have recently been deployed.

scholarly journals Metal-Organic Frameworks as Versatile Heterogeneous Solid Catalysts for Henry Reactions

Molecules ◽  
2021 ◽  
Vol 26 (5) ◽  
pp. 1445
Author(s):  
Francisco G. Cirujano ◽  
Rafael Luque ◽  
Amarajothi Dhakshinamoorthy
Keyword(s):  
Active Sites ◽  
Heterogeneous Catalysts ◽  
Final Section ◽  
Metal Organic Frameworks ◽  
Henry Reaction ◽  
Solid Catalysts ◽  
Wide Range ◽  
Metal Organic ◽  
Materials Used ◽  
Heterogeneous Solid

Metal–organic frameworks (MOFs) have become one of the versatile solid materials used for a wide range of applications, such as gas storage, gas separation, proton conductivity, sensors and catalysis. Among these fields, one of the more well-studied areas is the use of MOFs as heterogeneous catalysts for a broad range of organic reactions. In the present review, the employment of MOFs as solid catalysts for the Henry reaction is discussed, and the available literature data from the last decade are grouped. The review is organized with a brief introduction of the importance of Henry reactions and structural properties of MOFs that are suitable for catalysis. The second part of the review discusses the use of MOFs as solid catalysts for the Henry reaction involving metal nodes as active sites, while the third section provides data utilizing basic sites (primary amine, secondary amine, amides and urea-donating sites). While commenting on the catalytic results in these two sections, the advantage of MOFs over other solid catalysts is compared in terms of activity by providing turnover number (TON) values and the structural stability of MOFs during the course of the reaction. The final section provides our views on further directions in this field.

scholarly journals A Review on Metal-Organic Frameworks as Congenial Heterogeneous Catalysts for Potential Organic Transformations

2021 ◽  
Vol 9 ◽  
Author(s):  
Kranthi Kumar Gangu ◽  
Sreekantha B. Jonnalagadda
Keyword(s):  
Active Sites ◽  
Heterogeneous Catalysts ◽  
Metal Organic Frameworks ◽  
Value Added ◽  
Biological Molecules ◽  
Full Potential ◽  
Organic Transformations ◽  
Solid Catalysts ◽  
Metal Organic ◽  
Catalytic Active Sites

Metal-organic frameworks (MOFs) have emerged as versatile candidates of interest in heterogeneous catalysis. Recent research and developments with MOFs positively endorse their role as catalysts in generating invaluable organic compounds. To harness the full potential of MOFs in value-added organic transformation, a comprehensive look at how these materials are likely to involve in the catalytic processes is essential. Mainstays of MOFs such as metal nodes, linkers, encapsulation materials, and enveloped structures tend to produce capable catalytic active sites that offer solutions to reduce human efforts in developing new organic reactions. The main advantages of choosing MOFs as reusable catalysts are the flexible and robust skeleton, regular porosity, high pore volume, and accessible synthesis accompanied with cost-effectiveness. As hosts for active metals, sole MOFs, modified MOFs, and MOFs have made remarkable advances as solid catalysts. The extensive exploration of the MOFs possibly led to their fast adoption in fabricating new biological molecules such as pyridines, quinolines, quinazolinones, imines, and their derivatives. This review covers the varied MOFs and their catalytic properties in facilitating the selective formation of the product organic moieties and interprets MOF’s property responsible for their elegant performance.

scholarly journals Application of scanning electron microscopy in catalysis

2004 ◽  
pp. 67-77 ◽  
Author(s):  
Gizela Lomic ◽  
Erne Kis ◽  
Goran Boskovic ◽  
Radmila Marinkovic-Neducin
Keyword(s):  
Electron Microscopy ◽  
Scanning Electron Microscopy ◽  
Heterogeneous Catalysis ◽  
Active Sites ◽  
Heterogeneous Catalysts ◽  
Sem Analysis ◽  
Catalyst Preparation ◽  
Chemical Processes ◽  
Structured Materials ◽  
Scanning Electron

A short survey of various information obtained by scanning electron microscopy (SEM) in the investigation of heterogeneous catalysts and nano-structured materials have been presented. The capabilities of SEM analysis and its application in testing catalysts in different fields of heterogeneous catalysis are illustrated. The results encompass the proper way of catalyst preparation, the mechanism of catalyst active sites formation catalysts changes and catalyst degradation during their application in different chemical processes. Presented SEM pictures have been taken on a SEM JOEL ISM 35 over 25 years of studies in the field of heterogeneous catalysis.

scholarly journals Fly Ash-Based Geopolymers as Sustainable Bifunctional Heterogeneous Catalysts and Their Reactivity in Friedel-Crafts Acylation Reactions

Catalysts ◽  
2019 ◽  
Vol 9 (4) ◽  
pp. 372 ◽  
Author(s):  
Mohammad I. M. Al-Zeer ◽  
Kenneth J. D. MacKenzie
Keyword(s):  
Fly Ash ◽  
Active Sites ◽  
Heterogeneous Catalysts ◽  
Coal Fly Ash ◽  
Solid Catalysts ◽  
Redox Sites ◽  
Redox Active ◽  
Porous Architecture ◽  
Acidic Sites ◽  
Catalytic Reactivity

This study presents the synthesis, characteristics and catalytic reactivity of sustainable bifunctional heterogeneous catalysts derived from coal fly ash-based geopolymer, particularly those with a high Ca content (C-class) fly ash. The developed catalysts were synthesized at room temperature and pressure in a simple ecologically-benign procedure and their reactivity was evaluated in the Friedel-Crafts acylation of various arenes. These catalysts can be produced with multilevel porous architecture, and a combination of acidic and redox active sites allowing their use as bifunctional catalysts. The acidic sites (Lewis and Brønsted acidic sites) were generated within the catalyst framework by ion-exchange followed by thermal treatment, and redox sites that originated from the catalytically reactive fly ash components. The developed catalysts demonstrated higher reactivity than other commonly used solid catalysts such as Metal-zeolite and Metal-mesoporous silicate, heteropolyacids and zeolite imidazole frameworks (ZIF).

scholarly journals Highly Active Fenton-Like Catalyst Derived from Solid Waste-Iron Ore Tailings Using Wheat Straw Pyrolysis

2021 ◽  
Author(s):  
Lihui Gao ◽  
Lizhang Wang ◽  
Shulei Li ◽  
Yijun Cao
Keyword(s):  
Wheat Straw ◽  
Active Sites ◽  
Iron Ore ◽  
Heterogeneous Catalysts ◽  
Redox Cycles ◽  
Highly Active ◽  
Iron Ore Tailings ◽  
Catalytic Stability ◽  
Iron Active Sites

Abstract The pollutants degradation rate of iron ore tailings-based heterogeneous catalysts is the main factor limiting its application. Herein, an iron ore tailings-based Fenton-like catalyst(I/W(3:1)-900-60) with relative fast catalysis rate was constructed by co-pyrolysis(900 ℃, 60min holding time) of iron ore tailings and wheat straw with mass ratio of 3:1. With wheat straw blending, the generated I/W(3:1)-900-60 presented a larger surface area(24.3 m2/g), smaller pore size(3.707 nm), reduced iron species (Fe2+ from magnetic) and a higher catalytic activity(0.0229 min-1) than I-900-60 (1.196 m2/g, 12.935 nm, 0.012 min-1) pyrolyzed using a single iron ore tailings under the same pyrolysis conditions. In addition, biochar and iron ore tailings in I/W(3:1)-900-60 were tightly combined through chemical bonding. The optimal catalyst remains active after three cycles, indicating its catalytic stability and recyclability. The good Fenton-like MB degradation efficiency of I/W(3:1)-900-60 was ascribed to the sacrificial role of biochar, as well as the electron transfer between biochar and iron active sites or the redox cycles of ≡Fe3+/Fe2+. This finding provides a facile construction strategy for a highly active iron ore tailings-based Fenton-like catalyst, and thereby had a great potential application in wastewater treatment.

scholarly journals Biodiesel production from alternative raw materials using a heterogeneous Low Ordered Biosilicified Enzyme as biocatalyst

2020 ◽  
Author(s):  
Gabriel Orlando Ferrero ◽  
Edgar Maximiliano Sánchez Faba ◽  
Griselda Alejandra Eimer
Keyword(s):  
Active Sites ◽  
Heterogeneous Catalysts ◽  
Raw Materials ◽  
Biomass Conversion ◽  
High Water ◽  
Raw Material ◽  
Biodiesel Production ◽  
Waste Frying Oil ◽  
Solid Catalysts ◽  
Pork Fat

Abstract Background: Nowadays, as an alternative to the production of fuels and chemicals from the fossil platform, renewable feedstocks are widely investigated. For biomass conversion, a new generation of catalysts with specific characteristics such as high activity and selectivity, easy recovery and reusability is necessary. The design of highly efficient and stable heterogeneous catalysts represents a challenge in this field, mainly to overcome current energy and environmental issues. The combination of enzymatic and heterogeneous inorganic catalysis generates an unprecedented platform that combines the advantages of both. Among the techniques for producing solid catalysts, enzymatic mineralization with an organic silicic precursor to obtain hybrid biocatalysts (biosilicification) is highlighted. This technique can provide exceptional stability to the biocatalyst in drastic conditions of use.Results: Then, under these criteria, this work presents the one-step synthesis of a solid enzymatic catalyst, denominated Low Ordered Biosilicified Enzyme (LOBE) due to their structural properties. Pseudomonas Fluorescens lipase forms aggregates that are contained in the heart of a silicon-covered micelle, providing active sites with the ability to process different raw materials (commercial sunflower and soybean oil, Jatropha excisa oil, waste frying oil, residual soybeans, and pork fat) to produce first and second generation biodiesel. Obtaining yields between 81 and 93% by weight depending on the used raw material.Conclusions: Therefore, refined, non-edible and residual oils (with high water and free fatty acid contents) can be transformed into biodiesel through LOBE catalysts with commercial ethanol as co-substrate.

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