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Solid-supported Catalyst in Heterogeneous Catalysis
Published in Varun Rawat, Anirban Das, Chandra Mohan Srivastava, Heterogeneous Catalysis in Organic Transformations, 2022
Garima Sachdeva, Dipti Vaya, Varun Rawat, Pooja Rawat
Solid materials, including metals, metal oxides, and metal sulfides, are classified as catalysts. In industries, few catalytic materials used are simple such as pure metals and binary oxides. Heterogeneous catalysts activity can be made better with the help of supports. Catalyst support plays a vital role in bringing out the catalytically active center, contributing to industrial processes. The majority of heterogeneous solid catalysts are base or basic oxides coated over a large surface area. Generally, solid-base catalysts are found to be more active than solid-acid catalysts. Various classifications of solid catalysts are unsupported catalysts (bulk), supported catalysts, coated catalysts, confined catalysts, polymerization catalysts, etc. but our primary focus will be on solid-supported catalysts. Solid catalysts can be separated easily from the reaction mixture and reused, making them ideal for catalysis.
Introduction to Catalysts
Published in Qingmin Ji, Harald Fuchs, Soft Matters for Catalysts, 2019
Heterogeneous catalysis refers to the phase of the catalyst differing from the reactants. In most of the cases, heterogeneous catalysts are solids and the reactants are gases or liquids. The solids are often expensive metals (e.g., Pt, Au, Ni, Pd). Therefore, to economically use the catalysts, nanometer-sized particles with well-dispersed state are preferred. The related studies about heterogeneous catalysis have won the Nobel Prizes several times. For example, in 1912 Paul Sabatier was awarded the Nobel Prize in chemistry for performing the first hydrogenation of ethylene using nickel (Ni) as a catalyst. In 1918, the award went to Fritz Haber, who developed the catalytic formation of ammonia from atmospheric nitrogen and hydrogen with the help of iron as a catalyst. Irving Langmuir (1932) and Sir Cyril Norman Hinshelwood (1956) were awarded for their research studies on the surface catalytic mechanism of chemical reactions. These achievements greatly promoted and expanded the industrial catalysts for a large range of chemicals.
Inorganic Nanoparticles for Catalysis
Published in Claudia Altavilla, Enrico Ciliberto, Inorganic Nanoparticles: Synthesis, Applications, and Perspectives, 2017
Catalysts can be classified into two categories according to the applied reaction phase, i.e., homogeneous catalysts and heterogeneous catalysts, which can be used in a homogeneous and a heterogeneous phase, respectively. For example, metal complex catalysts and biocatalysts are usually used in solution, into which catalysts and reactants can be dissolved. In contrast, metal catalysts are often used in heterogeneous phases such as gas/solid and liquid/solid phases. For this purpose, small metal particles are immobilized on the inorganic oxide supports such as alumina (Al2O3) and silica (SiO2). Solid supports have advantages not only in the separation of catalysts from reactants and products in a heterogeneous phase but also in the enhancement of catalytic functions, including life time by the dispersion and dilution of metal particles, tuning of the electronic state of catalytic sites by interactions between metal particles and supports, and so on.
Prospects of novel heterogeneous base catalysts and nanocatalysts in achieving sustainable biodiesel production
Published in International Journal of Green Energy, 2023
Dhnyaneshwar Raising Rathod, Sandesh Suresh Karkal, Akil Salim Jamadar, Aliaa M.A. Hashem, P. V Suresh, S.S Mamatha, Tanaji G. Kudre
Heterogeneous catalysts differ from homogeneous catalysts based on the aspect that these catalysts are in a different state than the reactants. The heterogeneous catalysts form active sites with their reactants. The active site, nature, porosity, structural morphology, and thermal stability mainly determine the catalytic activity of the heterogeneous catalysts. The reaction rate of heterogeneous catalysts is slower than homogeneous catalysts, but the reaction rate can be increased by increasing methanol concentration and temperature (Avhad and Marchetti 2015). Further, heterogeneous base catalysts have added advantages over homogeneous base catalysts since they can be easily recovered and reused, lowers the cost of purification, and helps in the easy recovery of the by-product (glycerol) (Atadashi et al. 2013). Compared to homogeneous base catalysts, heterogeneous base catalysts are eco-friendly (can be prepared from bio-waste), benign, don’t produce toxic wastewater, and might aid in sustainable biodiesel production owing to their reusability. Similar to homogeneous base catalysts, heterogeneous catalysts are also categorized as heterogeneous acid and heterogeneous base catalysts.
Oxidative desulfurization utilizing activated carbon supported phosphotungstic acid in the frame of ultrasonication
Published in Chemical Engineering Communications, 2023
Gerje Ronelle H. Barilla, Charles Adrian W. Chen, Martin Zechariah M. Valencia, Nathaniel P. Dugos, Angelo Earvin Sy Choi
The utilization of a catalyst is vital in the UAOD. One type of catalyst that is used in the desulfurization process is the heterogeneous catalyst. A heterogeneous catalyst is a catalyst that appears in different phases in chemical reactions. An advantage of this type of catalyst is its ease to separate from the resulting product. A heterogeneous catalyst widely used in UAOD is called heteropoly acid (HPA) that is known for incorporating polyoxometalate anions (Wan et al. 2012). Specifically, the phosphotungstic acid (HPW) is a highly effective HPA for oxidation reactions (Afzalinia et al. 2017). Furthermore, the catalyst performance can be further improved when supported by carbon materials. Carbon based substances help in the desulfurization of aromatic sulfur compounds (Timko et al. 2016). The carbon substance acts as both catalyst and adsorbent in the process that makes it more efficient. However, the aforementioned catalyst is still effective in terms of selectivity but are more efficient when impregnated with activated carbon (AC) (Liu et al. 2014b).
Irreversibility analysis of Reiner-Rivlin nanofluid squeezing flow amidst two rotating disks with heterogeneous catalysis
Published in Waves in Random and Complex Media, 2022
Muhammad Ramzan, Saima Riasat, Hassan Ali S. Ghazwani
The speed of some chemical reactions may be very slow or sometimes the reaction may not proceed after a specific instant without the contribution of a catalyst. In some industrial processes, it might not be economical to proceed without a catalyst. Researchers have been attracted by the topic of fluid flows with chemical reactions (homogeneous and heterogeneous) because of its role in diverse processes including food processing, atmospheric fluxes, air pollution, etc. It is appropriate to point out that although heterogeneous reactions only occur in a confined area, homogeneous reactions occur across the entire phase. An examination of the literature reveals that there are many research articles available discussing fluid flows in the presence of a homogeneous-heterogenous reaction in various scenarios. Chaudhary and Merkin [48-50] pitched the idea of isothermal homogeneous-heterogenous reactions. Hayat et al. [51] examined the rotating fluid flow considering chemical reactions of both types using the Homotopy Analysis technique. Heterogeneous catalysis is one where the phase of catalysts varies from that of the products or reactants. Reactions between a liquid and a gas, or between a metal and an acid are examples of heterogeneous reactions. Some recent studies highlighting the heterogenous reactions in rotating disks can be approached in [52-54].