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Surface Catalysis on Metals
Published in Arthur T. Hubbard, The Handbook of Surface Imaging and Visualization, 2022
Fabio H. Ribeiro, Gabor A. Somorjai
A catalyst is a substance that can accelerate the rate by which a chemical reaction reaches equilibrium without being consumed in the process. An example of a heterogeneous catalytic reaction is the synthesis of NH3 from N2 and H2 with iron as the catalyst. The reaction between N2 and H2 does not proceed to equilibrium in the gas phase possibly because the high activation energy required for the homogeneous gas phase steps makes the rates too slow. However, when a catalyst is introduced (e.g., iron), N2 and H2 can dissociate on the surface and then recombine in a sequence of low activation energy steps and consequently high rates (Fig. 56.1).14
Methods of Thin Film Deposition
Published in Fredrick Madaraka Mwema, Tien-Chien Jen, Lin Zhu, Thin Film Coatings, 2022
Fredrick Madaraka Mwema, Tien-Chien Jen, Lin Zhu
Catalysis is a process for increasing the rate of a chemical reaction. ALD is used to design and synthesise catalytic materials. ALD is useful in making a constantly distributed catalyst on a large surface area [123]. The catalytic application of ALD has found applications in several fields such as the pharmaceutical industry, chemicals and food processing field, healthcare, energy, and agriculture [124].
Introduction to Heterogeneous Catalysis in Organic Transformation
Published in Varun Rawat, Anirban Das, Chandra Mohan Srivastava, Heterogeneous Catalysis in Organic Transformations, 2022
Garima Sachdeva, Gyandshwar Kumar Rao, Varun Rawat, Ved Prakash Verma, Kaur Navjeet
A homogeneous catalyst has the same phase in the reaction mixture as that of reactants. The high homogeneity of the same phase of reactants and catalyst results in their high interactions, leading to high reactivity and selectivity under mild reaction conditions. Some important instances of homogeneous catalysts include Brønsted and Lewis acids, transition metal complexes, organometallic complexes, and organocatalysts. Some notable examples of chemical reactions that use homogeneous catalysts are carbonylation, oxidation, hydrocyanation, metathesis, hydrogenation, and C–H and C–C activation/functionalization [6].
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.
Utilization of zinc doped biochar catalyst for biodiesel production from waste cooking oil: process optimization and characterization
Published in Biofuels, 2023
Kasinathan Cholapandian, Rajendran Naveenkumar, Gurunathan Baskar
The production of biodiesel from any feedstock needs a suitable catalyst. There are many types of catalysts: homogeneous (acid/base), heterogeneous (acid/base), enzymatic, biomass-based, and bifunctional catalysts [14]. The disadvantages of using base homogeneous catalysts are the high cost and their tendency to produce a soap with the free fatty acids (FFAs) present during the process. Acid catalysts are corrosive and difficult to store, making them unsuitable for industrial use [15]. Heterogeneous catalysts form visible physical phases with reactants that can be easily separated, unlike homogeneous catalyst that results in a uniform undifferentiated mixture [16]. However, the reaction rate with a heterogeneous catalyst is much lower compared to using a homogeneous catalyst. Heterogeneous catalysts are reusable, non-corrosive, and less susceptible to the saponification process [6,17]. Despite being advantageous, heterogeneous catalysts can cause environmental damage. Enzyme catalysts can be used only around 35 to 40 °C and have disadvantages such as deactivation, high cost and slower reaction rates, making them unsuitable for the large-scale production of biodiesel [18].
Combustion and emission characteristics of light duty diesel engine fueled with transesterified algae biodiesel by K2CO3/ZnO heterogeneous base catalyst
Published in Energy Sources, Part A: Recovery, Utilization, and Environmental Effects, 2020
Jayashri Narayanan Nair, Yeditha Veera Venkata SatyanarayanaMurthy, Syed Javed
Transesterification method and type of catalyst used influence oil characteristics and its yield. Transesterification of oil can be carried out with homogeneous and heterogeneous catalysts. Homogeneous catalyst function in same phase as reactants whereas heterogeneous catalyst function in different phases from reaction mixture. Though homogeneous catalyst gives high yield at low cost, it is not suitable for large production of biodiesel. Water formation during esterification increases its production cost as washing is involved. Homogeneous catalyst needs to be removed with glycerol but cannot be easily separated and reused again. Some homogeneous catalysts tend to loose their properties if stored for a long duration. Biocatalyst enzymes can be used for transesterification but are too costly from large production point of view. Heterogeneous catalyst has less number of unit operation and simple product separation and purification process. For the present research algae biodiesel was produced using a novel base heterogeneous catalyst K2CO3/ZnO and the blends were tested on low-powered diesel engine with mechanical injection.