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Enzymatic Reaction Kinetics
Published in Debabrata Das, Debayan Das, Biochemical Engineering, 2019
The protein structure of an enzyme is responsible for the catalytic ability. One must understand the significance of active sites as they are important in explaining the science behind enzyme kinetics. An active site refers to a small portion on the surface of an enzyme where a specific chemical reaction is catalyzed.
Fundamental Principles
Published in Martyn V. Twigg, Catalyst Handbook, 2018
Impurities (in feed or catalyst) can affect catalyst performance when their interaction with the catalyst is stronger than that of the feed.68, 77, 80–82 The active site of the catalytic reaction or, less often, the pore structure giving access to the active site, is modified in some way so that catalyst performance is altered—for the worse, as is implied by the use of the word “poison”. Overall catalyst activity may be decreased without affecting selectivity when some of the sites are totally deactivated while others are unaffected. If, however, some active sites are modified without losing all activity, then the relative rates of different reactions may change to give a different catalyst selectivity.
Ceria-Based Nanocrystalline Oxide Catalysts: Synthesis, Characterization, and Applications
Published in Nandakumar Kalarikkal, Sabu Thomas, Obey Koshy, Nanomaterials, 2018
Anushka Gupta, v. Sai Phani Kumar, Manjusha Padole, Mallika Saharia, K. B. Sravan Kumar, Parag A. Deshpande
In the Eley-Rideal mechanism, CO adsorbs on the metal ion (M) and steam (H2O) reacts with the adsorbed CO. Upon completion of the reaction, the reactants get desorbed thus regenerating the active site of the catalyst. On the other hand, in the Langmuir-Hinshelwood mechanism, all the reacting species (CO and H2O) get adsorbed on the metal ion site. As no significant conversion was observed over unsubstituted ceria, adsorption over the oxide ion vacancies was neglected. However, due to evidence of the dependence of the support in WGS, a mechanism based on the utilization of dual sites, was also proposed. Reduced ceria has oxide ion vacancies and the presence of more anionic vacancies due to substitution of ionic metals could provide for an oxidizing environment. Therefore, the following mechanism was proposed.1, 14Novel dual site mechanism:
Thermal damages in spray drying: Particle size-dependent protein denaturation using phycocyanin as model substrate
Published in Drying Technology, 2023
Nora Alina Ruprecht, Reinhard Kohlus
In a food matrix, proteins serve functional properties such as foaming, gelling, and emulsifying which influence the product texture, appearance, and stability. The functional properties are determined by the protein conformation. For instance, the surface activity, and thus, their ability to stabilize interphases, is defined by the exposed amino acids of a protein.[27] Some proteins also serve biological functions, which are determined by their structure. Enzymes catalyze reactions, if the shape of their active site is compatible with the shape of the substrate.[28] Protein denaturation causes an unfolding of the three-dimensional structure, which changes their functionality and in consequence alters the product.[29]
Flow line of density functional theory in heterogeneous persulfate-based advanced oxidation processes for pollutant degradation: A review
Published in Critical Reviews in Environmental Science and Technology, 2023
Binghua Jing, Juan Li, Chunyang Nie, Junhui Zhou, Didi Li, Zhimin Ao
Tables 1 and S1 listed the lO−O, Eads, and Q of PMS and PDS in different catalytic systems and compared the reaction carriers and parameters for several P-AOPs based on DFT calculations. The corresponding phenomena are explained in Text S2. It can be found that lO−O, Eads, and Q change under the influence of dimension, doping, oxygen functional groups, defect, pore, active surfaces, and active sites on catalysts, implying the feasibility to adjust the activation performance by controlling catalysts. Furthermore, the setting of DFT-D, energy cutoff, maximal force and displacement, structures, and software affect the calculation accuracy. However, it is challenging to select rational control measures for catalysts to endow excellent activation and degradation performances in experimental or calculational processes. DFT calculation parameters and software are also difficult to set to optimize the calculation accuracy. Additionally, the contribution or proportion of control measures, calculation parameters, and software is unclear due to the complexity in the entire process. It is worth to put more effect to solve those challenges in future.
Low temperature selective catalytic reduction of nitric oxide with urea over activated carbon supported metal oxide catalysts
Published in Environmental Technology, 2020
Kaijie Liu, Qingbo Yu, Baolan Wang, Qin Qin, Mengqi Wei, Qi Fu
The NO conversion of nu-AC supported catalysts with different loading of MnOX at 50°C is illustrated in Figure 13. Compared with the catalyst without loading MnOx, the catalysts showed higher catalytic activity after loading manganese oxides, which also indicated metal oxides could improve the catalytic performance of urea-SCR. Increasing the loading of active metal oxides could increase the active sites on the catalyst surface, however, more loading of active metal oxides would reduce the specific surface area of the catalyst. Besides, the load of 10% urea could cover some of the metal oxide active sites, which limited the number of active sites exposed on the catalyst surface. Thus the changes of NO conversion were not obvious with the increase of MnOX mass ratio from 15% to 20%.