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Role of Metal-heterogeneous Catalysts in Organic Synthesis
Published in Varun Rawat, Anirban Das, Chandra Mohan Srivastava, Heterogeneous Catalysis in Organic Transformations, 2022
The use of homogeneous catalysts in organic synthesis is well established. However, there are a few disadvantages associated with the usage of homogeneous catalysts in synthetic chemistry. The prominent ones are the formation of soluble complex, especially at a large scale, the problem of separation from the reaction mixture and lack of reusability and toxicity issues that pose health risks. On the other hand, heterogeneous catalysts provide a great advantage over homogeneous catalysts. They are easy to use, cheap and reusable and, their handling and separation from the reaction mixture are very simple. Moreover, they are less toxic, and more stable than homogeneous catalysts. Heterogeneous catalysts come in different forms like pure metals (especially transition metals, metal powders, etc.), metals combined with some other components such as metal sulfides, metal nitrides, metal carbides, metal alloys, molecular sieves, etc., or they can be supported on other surfaces. Supported catalysts are popular in industrial applications because they are considered to be chemically, mechanically and thermally stable to a great extent. The supports can be organic such as polymers (e.g., polystyrene), copolymers (e.g., styrene-divinylbenzene) as well as inorganic such as zeolites, alumina, activated carbon, titanium dioxide, silica and graphene [1].
Computational Investigations on Metal Oxide Clusters and Graphene-Based Nanomaterials for Heterogeneous Catalysis
Published in Nazmul Islam, Satya Bir Singh, Prabhat Ranjan, A. K. Haghi, Mathematics Applied to Engineering in Action, 2021
Neetu Goel, Navjot Kaur, Mohd Riyaz, Sarita Yadav
Traditionally, catalysts have been classified as homogeneous and heterogeneous. In homogeneous catalyst, molecules are in same phase as reactant while the phase of molecules in heterogeneous catalyst is different from that of reactant. Though homogeneous catalyst demonstrates exceptional catalytic behavior along with high selectivity and efficiency at milder temperature and pressure, however, its separation from reaction mixture is intricate. Advent of novel materials with potential catalytic properties and ease of their removal has generated lot of interest in heterogeneous catalysis. Design and development of new catalysts to boost the production of essential commodities is highly desirable to cater to the demands of modern society. In order to achieve this, it is necessary to replace present technologies with new, energy-efficient, environment-friendly catalytic processes of high selectivity. This quest has triggered a renewed interest in metal oxide and carbon-based nanomaterials owing to their large surface area, chemical stability, and remarkable catalytic properties.
Characterization of Zeolite Catalysts
Published in Subhash Bhatia, Zeolite Catalysis: Principles and Applications, 2020
The activity of heterogeneous catalysts is known to be mainly a surface property. It is therefore often possible to reduce the amount of active component without affecting the overall activity by increasing its surface-to-volume ratio. This surface-to-volume ratio of the active component is usually referred to as its dispersion. Dispersion measurements6,7 are of prime importance for studying reaction mechanisms. The most common technique for measuring dispersion is the selective chemisorption of a suitable gas onto the surface of the active component. In addition, chemisorption techniques are generally of little use for nonmetallic catalysts. The other major methods for dispersion measurements are based on X-ray diffraction, photoelectron spectroscopy, and electron spectroscopy. Figure 8.5 shows the various techniques which can be used to obtain dispersion and particle size of active phase.
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].