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).

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.

Bamboo-Shaped Carbon Nanotubes on Coal Fly Ash Cenospheres for Pb(II) Adsorption

2020 ◽  
Vol 20 (8) ◽  
pp. 5089-5095
Author(s):  
Xiaomin Zhang ◽  
Jin Li ◽  
Bo He ◽  
Heng Li ◽  
Chao Qi ◽  
...  
Keyword(s):  
Carbon Nanotubes ◽  
Fly Ash ◽  
Adsorption Capacity ◽  
Active Sites ◽  
Coal Fly Ash ◽  
Chemical Vapor ◽  
Structural Defects ◽  
3D Network ◽  
Supporting Material ◽  
High Level

The structural defects of bamboo-shaped carbon nanotubes (B-CNTs) provide abundant active sites for ion adsorption during wastewater treatment. However, a suitable supporting material for the growth of B-CNTs growth is less reported. In this paper, the catalytic growth of B-CNTs on the cenospheres (CSs) of coal fly ash was studied. The results showed that all CSs were covered by a layer of B-CNTs during the chemical vapor deposition (CVD) process, regardless of the fluctuation of the iron distribution from 0.52 to 2.09 wt%. B-CNTs with a diameter of 30–40 nm shared a similar morphology of compartment structures, which were uniformly scattered on the surfaces of the CSs and formed a 3D network structure. A high level of structural defects was present on the B-CNTs, which was denoted by an ID/IG value of 1.77 via Raman spectrum analysis. Adsorption experiments of the as-prepared CSs@B-CNTs revealed an excellent adsorption capacity for lead ions of 37.32 mg/g (pH 7, initial concentration of 70 mg/L). By excluding the function of CSs, the adsorption capacity of the pure B-CNTs was estimated to be as high as 275.19 mg/g, which has not been previously reported.

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.

Coal Fly Ash as a Dual Site Material for Cr(VI) Adsorption: Comparation between Single Site and Dual Site Isotherm Models

2015 ◽  
Vol 1101 ◽  
pp. 149-152
Author(s):  
Widi Astuti ◽  
Triastuti Sulistyaningsih ◽  
Dewi Selvia Fardhyanti
Keyword(s):  
Fly Ash ◽  
Active Sites ◽  
Power Plants ◽  
Coal Fly Ash ◽  
Thermal Power ◽  
Single Site ◽  
Unburned Carbon ◽  
Isotherm Models ◽  
Equilibrium Data ◽  
Dual Site

The major problem in coal-based thermal power plants is related to solid waste called coal fly ash (CFA). CFA is mainly composed of some oxides including SiO2, Al2O3 having active site and unburned carbon as a mesopore that enables it to act as a dual site adsorbent for heavy metals including Cr (VI). To get different characters of dual site, CFA was treated by sulfuric acid (H2SO4) at different concentrations, temperatures and reaction time. Furthermore, treated CFA were used as an adsorbent to adsorb Cr (VI) in aqueous solutions. Equilibrium data were evaluated by single site and dual site isotherm models. It can be concluded, although unburned carbon contributes on the Cr (VI) adsorption, the existence of unburned carbon decreases the amount of Cr (VI) adsorbed because unburned carbon can plug active sites where dominant adsorption occurs. However, dual site isotherm model yielded excellent fit with equilibrium data.

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 Development of Heterogeneous Alkali Methoxide Catalyst from Fly Ash and Limestone

2020 ◽  
Vol 14 (4) ◽  
pp. 521-530
Author(s):  
W. Widayat ◽  
◽  
Marcelinus Christwardana ◽  
S. Syaiful ◽  
Hantoro Satriadi ◽  
...  
Keyword(s):  
Fly Ash ◽  
Palm Oil ◽  
Active Sites ◽  
Heterogeneous Catalysts ◽  
Raw Materials ◽  
Fatty Acid Content ◽  
Physicochemical Characteristics ◽  
Biodiesel Production ◽  
X Ray Diffraction ◽  
Initial Value

This study is aimed to use fly ash and limestone as raw materials for preparing alkali methoxide heterogeneous catalysts for transesterification of palm oil into biodiesel. The heterogeneous catalyst was synthesized from fly ash and limestone through wet and dry methods and calcined within 1073–1273 K. X-ray diffraction and scanning electron microscopy analyses indicated the well-dispersed presence of the Ca(OCH3)2 crystal over the fly ash and limestone framework, which was mixed using wet method and calcined at 1073 K (W-800). Results showed that W-800 exhibited larger surface area and more uniform active sites than the other catalysts. About 88.6 % of biodiesel was produced from commercial palm oil with W-800 as the catalyst. The product possesses physicochemical characteristics, such as density, kinematic viscosity and free fatty acid content, which satisfy the international biodiesel standard. The catalyst was used for biodiesel production for four cycles, and the biodiesel yield was maintained up to 91.87 % from the initial value.

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 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.

Chemo-catalytic Esterification and Transesterification over Organic Polymer-Based Catalysts for Biodiesel Synthesis

2019 ◽  
Vol 23 (20) ◽  
pp. 2190-2203 ◽  
Author(s):  
Heng Zhang ◽  
Chunbao (Charles) Xu ◽  
Kaichen Zhou ◽  
Song Yang
Keyword(s):  
Active Sites ◽  
Heterogeneous Catalysts ◽  
Organic Polymer ◽  
Catalytic Systems ◽  
Solid Catalysts ◽  
Catalytic Materials ◽  
Oil Resources ◽  
Biodiesel Synthesis ◽  
Esterification Reactions ◽  
Hydrophilicity And Hydrophobicity

The major sources of fuels in today's world predominantly come from traditional fossil resources such as coal, petroleum and natural gas, which are limited and nonrenewable. Meanwhile, their consumption releases large undesirable greenhouse gas and noxious gases. Therefore, the development of renewable and sustainable feedstocks to replace traditional fossil resources has attracted great interest. Biodiesel, mainly produced through esterification and transesterification reaction from renewable oil resources using acids and bases as catalysts, is deemed as a green and renewable biofuel that shows enormous potential to replace fossil diesel. Compared to homogeneous catalytic systems, the development of efficient and stable heterogeneous catalysts is vital to synthesizing biodiesel in an efficient and green manner. Among the developed solid catalysts, organic polymer- based catalytic materials are an extremely important topic, wherein distinct advantages of higher concentration of active sites and better stability of active groups are associated with each other. In this review, effective catalytic valorization of sustainable feedstocks into biodiesel via transesterification and esterification reactions mediated by functionalized organic polymer-based catalysts is discussed. Special emphasis has been given to the synthetic routes to the versatile organic polymers-based catalytic materials, and some other interesting catalytic roles derived from physicochemical property, like adjustable hydrophilicity and hydrophobicity along with swelling property in transesterification and esterification, are also illustrated.

Reductive Catalytic Fractionation of Lignocellulosic Biomass: A New Promising Method of its Integrated Processing

2021 ◽  
Vol 21 (6) ◽  
pp. 425-443
Author(s):  
A. V. Miroshnikova ◽  
A. S. Kazachenko ◽  
B. N. Kuznetsov ◽  
O. P. Taran
Keyword(s):  
Lignocellulosic Biomass ◽  
Active Sites ◽  
Heterogeneous Catalysts ◽  
Ruthenium Catalysts ◽  
Platinum Group Metals ◽  
Lignocellulosic Feedstock ◽  
Acidic Sites ◽  
Integrated Processing ◽  
Carbohydrate Components ◽  
Molecular Compounds

The review discusses the results of recent studies in the promising field of integrated processing of lignocellulosic biomass – the reductive catalytic fractionation (RCF). The effect of catalysts, cocatalysts, solvents, hydrogen sources and features of lignocellulosic feedstock on the selectivity of monomeric products formation from lignin is considered. RCF processes are performed mostly with the heterogeneous catalysts, which allow implementing the reductive depolymerization of lignin to obtain low-molecular compounds and preserve carbohydrate components of biomass. Among the studied catalysts based on platinum group metals and transition metals, the highest activity is observed for the catalysts containing Pd, Pt, Ru and Ni. Features of the metal also affect the composition of the resulting products. Thus, ruthenium catalysts make it possible to obtain 4-propylguaiacol as the main product, while Ni and Pd – 4-propanolguaiacol. Mo-containing catalysts, owing to their lower hydrogenating activity, can be used to obtain monolignols or their etherified derivatives with the preservation of carbohydrate components of lignocellulosic biomass. However, most efficient in RCF processes are the bifunctional catalysts, which have both the acidic and metallic active sites. Acidic sites promote the cleavage of the ether β-O-4 bonds, whereas metallic sites – the reduction of the formed intermediate compounds. An important aspect of choosing the appropriate catalysts for RCF process is the possibility of their repeated application. The use of a ferromagnetic catalyst or a catalyst basket allows separating the catalyst from the products.

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