scholarly journals Kinetic Study on CO-Selective Methanation over Nickel-Based Catalysts for Deep Removal of CO from Hydrogen-Rich Reformate

Catalysts ◽  
2021 ◽  
Vol 11 (12) ◽  
pp. 1429
Author(s):  
Woohyun Kim ◽  
Khaja Mohaideen Kamal ◽  
Dong Joo Seo ◽  
Wang Lai Yoon
Keyword(s):  
Kinetic Parameters ◽  
Kinetic Models ◽  
Active Sites ◽  
Solution Space ◽  
Rate Equations ◽  
Parameter Study ◽  
Large Solution ◽  
Co Methanation ◽  
Adsorption Desorption ◽  
Product Species

The CO-selective methanation process is considered as a promising CO removal process for compact fuel processors producing hydrogen, since the process selectively converts the trace of CO in the hydrogen-rich gas into methane without additional reactants. Two different types of efficient nickel-based catalysts, showing high activity and selectivity to the CO methanation reaction, were developed in our previous works; therefore, the kinetic models of the reactions over these nickel-based catalysts have been investigated adopting the mechanistic kinetic models based on the Langmuir chemisorption theory. In the methanation process, the product species can react with the reactant and also affect the adsorption/desorption of the molecules at the active sites. Thus, the kinetic parameter study should be carried out by global optimization handling all the rate equations for the plausible reactions at once. To estimate the kinetic parameters, an effective optimization algorithm combining both heuristic and deterministic methods is used due to the large solution space and the nonlinearity of the objective function. As a result, 14 kinetic parameters for each catalyst have been determined and the parameter sets for the catalysts have been compared to understand the catalytic characteristics.

scholarly journals Kinetic models for xanthan gum production using Xanthomonas campestris from molasses

2011 ◽  
Vol 17 (2) ◽  
pp. 179-187 ◽  
Author(s):  
S.L. Gilani ◽  
G.D. Najafpour ◽  
H.D. Heydarzadeh ◽  
H. Zare
Keyword(s):  
Kinetic Parameters ◽  
Kinetic Models ◽  
Xanthan Gum ◽  
Xanthomonas Campestris ◽  
Specific Growth ◽  
Dry Weight ◽  
Product Formation ◽  
Rate Equations ◽  
Agitation Rate ◽  
Consumption Rates

In process of xanthan gum production the effect of media temperature, agitation rate and molasses concentration on yield of fermentation were investigated. Xanthan gum was produced in batch fermentation by Xanthomonas campestris PTCC 1473 from molasses. At 32?C, 500 rpm and media with 30g/l of total sugar maximum production of xanthan gum (17.1g/l) was achieved. For the purity of the xanthan FTIR spectrum was obtained. The identified spectrum was compared with the commercial product. In batch culture, several kinetic models for the biochemical reactions were extensively studied. The growth kinetic parameters were evaluated by unstructured model and derived from the related equations. Based on Malthus and Logistic rate equations, the maximum specific growth rate, ?max, and initial cell dry weight, X0, were defined. Luedeking-Piret and Modified Luedeking-Piret models were applied for the product formation and substrate consumption rates. In batch experiments, the kinetic parameters for the growth associated (m, a) and non-growth associated (n, b) parameters were determined.

On the Temperature Rate Dependent Transformation Processes

2007 ◽  
Vol 537-538 ◽  
pp. 571-578
Author(s):  
Tamás Réti ◽  
Imre Czinege ◽  
Imre Felde ◽  
Lino Costa ◽  
Rafael Colás
Keyword(s):  
Kinetic Parameters ◽  
Kinetic Models ◽  
Rapid Heating ◽  
Rate Equations ◽  
Transformation Rate ◽  
Isothermal Reaction ◽  
Heating And Cooling ◽  
Rate Dependent ◽  
Temperature Rate ◽  
Transformation Processes

Kinetic models of new types are suggested which are designated primarily to predict the progress of non-isothermal transformations occurring during rapid heating and cooling in alloys. A common feature of each model outlined is that it takes into account not only the varying temperature but also the rate of temperature change on the transformation rate of the process. The two models represented by differential equations are generated by using the concept of virtual kinetic parameters, which can be determined from non-isothermal experiments only. A key property of the virtual parameter "p" involved in the transformation rate equations is that it quantitatively characterizes the temperature rate dependence of the non-isothermal reaction.

A mathematical model of the carbon metabolism in photosynthesis. Difficulties in explaining oscillations by fructose 2, 6-bisphosphate regulation

1989 ◽  
Vol 237 (1289) ◽  
pp. 389-415 ◽  
Keyword(s):  
Mathematical Model ◽  
Active Sites ◽  
Starch Synthesis ◽  
Standard Free Energy ◽  
Atp Synthesis ◽  
Rate Equations ◽  
Standard Free Energy Change ◽  
Sucrose Synthesis ◽  
Carbon Reduction ◽  
Fructose 2

A mathematical model of the pentosephosphate carbon reduction (PCR) cycle is presented. The internal structure of the model is consistent with and complements the known biochemical pathways in the PCR cycle, together with starch and sucrose synthesis. Individual enzymes are described by maximum rate ( V m ), standard free energy change (Δ G´ 0 ) and Michaelis constant ( K m ) values as parameters and rate-equations, sym­metrical for the direct and reverse reactions. Enzymic control is included in the starch synthesis pathway (activation by phosphoglycerate (PGA)), inhibition by inorganic phosphate) and in the reactions of sucrose synthesis based on fructose 2, 6-bisphosphate (F2, 6BP) as a metabolite con­trolling the cytosolic fructose bisphosphatase (FBPase) activity. The phosphate translocator carries out the exchange of triose phosphates, orthophosphate and PGA. Ionic forms of metabolites are calculated in relation to pH and assumed to be the actual reacting substances. The significant concentration of the active sites of ribulose 1, 5-bisphosphate (RuBP) carboxylase is taken into account. Light reactions are included only in the form of an ATPase the Δ G´ 0 of which is shifted towards ATP synthesis by the existing proton gradient. The behaviour of the model was studied with the aim of reproducing oscillations in photosynthesis. It is concluded that oscillations in photosynthesis cannot be caused by the fructose 2, 6-bisphosphate control of sucrose synthesis alone, but that an additional control of photosynthetic rate must also be involved.

Furfural hydrogenation over amorphous alloy catalysts prepared by different reducing agents

BioResources ◽  
2017 ◽  
Vol 12 (4) ◽  
pp. 8755-8774
Author(s):  
Haijun Guo ◽  
Hairong Zhang ◽  
Weichao Tang ◽  
Can Wang ◽  
Chao Huang ◽  
...  
Keyword(s):  
Amorphous Alloy ◽  
Active Sites ◽  
Chemical Reduction ◽  
Surface Concentration ◽  
Reducing Agents ◽  
Chemical Reduction Method ◽  
Transfer Capability ◽  
Furfural Hydrogenation ◽  
Adsorption Desorption ◽  
Alloy Catalysts

The catalytic hydrogenation of furfural was studied over a series of Ni-B, Co-B, and Ni-Co-B amorphous alloy catalysts that were prepared by the chemical reduction method using KBH4 and NaBH4 as reducing agents. These catalysts were characterized by N2 adsorption/desorption, XRD, XPS, FE-SEM, and TEM. The results showed that NaBH4 had a much stronger reduction ability to enhance the surface concentration of the metallic active sites for furfural hydrogenation and electron transfer capability, leading to much higher hydrogenation activity. In the Ni-Co-B amorphous alloy catalyst, the equilibrium between the isolated Ni-B/Co-B active sites and the combined Ni-Co-B active sites was important in regulating furfural conversion and products distribution.

Kinetic modelling of microalgal growth and fucoxanthin synthesis in photobioreactor

2021 ◽  
Vol 0 (0) ◽  
Author(s):  
Xiaojuan Zhang ◽  
Junru Zhao ◽  
Jie Zhang ◽  
Shijing Su ◽  
Luqiang Huang ◽  
...  
Keyword(s):  
Experimental Data ◽  
Mathematical Model ◽  
Kinetic Parameters ◽  
Kinetic Modelling ◽  
Inhibitory Effect ◽  
Rate Equations ◽  
Phosphorus Concentration ◽  
Model Output ◽  
Nitrogen And Phosphorus ◽  
Nitrogen Phosphorus

Abstract This paper presented a mathematical model to describe the production of fucoxanthin by alga Thalassiosira weissflogi ND-8 in photobioreactor. Our interest was focused on characterizing the effects of nitrogen and phosphorus on the growth of microalgae and on the synthesis of fucoxanthin. The rate equations of microalgal growth, fucoxanthin synthesis and substrate consumptions were formulated. Kinetic parameters of the model and their sensitivities with respect to model output were estimated. The predicted results were compared with experimental data, which showed that this model closely agrees with actual experiment and is able to reflect the growth and metabolism characteristics of microalgae. Our results also indicated that nitrogen plays a major role in the synthesis of fucoxanthin, and the synthesis of fucoxanthin is partially linearly related to the consumption of nitrogen. Phosphorus is primarily consumed in the growth and metabolism of microalgal cells, while excessive phosphorus concentration has an inhibitory effect on the growth of microalgae.

scholarly journals Porosity Design of Shaped Zeolites for Improved Catalyst Lifetime in the Methanol-to-Hydrocarbons Reaction

Catalysts ◽  
2019 ◽  
Vol 9 (6) ◽  
pp. 545 ◽  
Author(s):  
Rogéria Bingre ◽  
Renna Li ◽  
Qiang Wang ◽  
Patrick Nguyen ◽  
Thomas Onfroy ◽  
...  
Keyword(s):  
Pore Volume ◽  
Active Sites ◽  
Coke Formation ◽  
Effective Diffusivity ◽  
Nitrogen Adsorption ◽  
Breakthrough Time ◽  
Methanol To Hydrocarbons ◽  
Catalytic Stability ◽  
Temperature Programmed ◽  
Adsorption Desorption

Additional porosity, such as meso- and macropores, was introduced in zeolite extrudates with the intention intuit of improving the effective diffusivity of the catalysts. The samples were characterized in depth by nitrogen adsorption-desorption, mercury intrusion porosimetry, ammonia temperature programmed desorption and adsorption of pyridine followed by infrared spectroscopy. The results revealed no significant change in the acidity but an increase of the pore volume. According to significant improvement in the effective diffusivity, the samples were tested in the methanol-to-hydrocarbons reaction. The catalytic stability was greatly enhanced with an increase in the pore volume, demonstrating a relation between effective diffusivity and resistance to deactivation by coke formation. Further experiments also revealed a higher toluene adsorption capacity and a raise in the breakthrough time over the most porous samples due to better accessibility of toluene molecules into the active sites of the zeolite.

scholarly journals ProtMiscuity: a database of promiscuous proteins

Database ◽  
2019 ◽  
Vol 2019 ◽  
Author(s):  
Ana Julia Velez Rueda ◽  
Nicolas Palopoli ◽  
Matías Zacarías ◽  
Leandro Matías Sommese ◽  
Gustavo Parisi
Keyword(s):  
Structure Function ◽  
Kinetic Parameters ◽  
Active Sites ◽  
Online Database ◽  
Catalytic Promiscuity ◽  
External Resources ◽  
Functional Annotations ◽  
Underlying Mechanisms ◽  
Function Relationship ◽  
Derived Data

Abstract Promiscuous behaviour in proteins and enzymes remains a challenging feature to understand the structure–function relationship. Here we present ProtMiscuity, a manually curated online database of proteins showing catalytic promiscuity. ProtMiscuity contains information about canonical and promiscuous activities comprising 88 different reactions in 57 proteins from 40 different organisms. It can be searched or browsed by protein names, organisms and descriptions of canonical and promiscuous reactions. Entries provide information on reaction substrates, products and kinetic parameters, mapping of active sites to sequence and structure and links to external resources with biological and functional annotations. ProtMiscuity could assist in studying the underlying mechanisms of promiscuous reactions by offering a unique and curated collection of experimentally derived data that is otherwise hard to find, retrieve and validate from literature.

scholarly journals The ZSM-5-Catalyzed Oxidation of Benzene to Phenol with N2O: Effect of Lewis Acid Sites

Catalysts ◽  
2019 ◽  
Vol 9 (1) ◽  
pp. 44
Author(s):  
Cui Ouyang ◽  
Yingxia Li ◽  
Jianwei Li
Keyword(s):  
Active Sites ◽  
Acid Sites ◽  
X Ray Diffraction ◽  
Remarkable Feature ◽  
Chemisorbed Oxygen ◽  
Lewis Acidic Sites ◽  
Acidic Sites ◽  
Adsorption Desorption ◽  
Oxidation Of Benzene ◽  
N2o Selectivity

The oxidation of benzene to phenol (BTOP) with N2O as the oxidant has been studied with a variety of Fe/ZSM-5 catalysts. The literature has conclusively proven that Fe2+ sites are the active sites. However, some studies have suggested that the Lewis acidic sites (LAS) are responsible for the generation of the active chemisorbed oxygen. Nevertheless, there is no clear relationship between the LAS and the N2O selectivity to phenol. In an effort to elucidate the effects of LAS on BTOP with various ZSM-5 catalysts, we investigated the initial N2O selectivity to phenol. Here we show that the initial N2O selectivity to phenol is negative with the amount of LAS over a certain range. The catalyst H-ZSM-5-ST (H-ZSM-5 treated with water vapor) showed a remarkable initial N2O selectivity to phenol as high as 95.9% with a 0.021 mmol g−1 LAS concentration on the surface of the catalyst, while the Fe/ZSM-5 catalyst demonstrated the lowest initial N2O selectivity to phenol (11.7%) with the highest LAS concentration (0.137 mmol g−1). Another remarkable feature is that steaming was more effective than Fe ion exchange and high temperature calcining. The samples were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), N2-adsorption-desorption, UV-vis, NH3-TPD and pyridine Fourier transform infrared (FT-IR) techniques. Our results demonstrate how the concentration of LAS is likely to affect the initial N2O selectivity to phenol within a certain range (0.021–0.137 mmol g−1). This research has demonstrated the synergy between the active Fe2+ sites and LAS.

Tunnel-dependent supercapacitance of MnO2: effects of crystal structure

2013 ◽  
Vol 46 (4) ◽  
pp. 1128-1135 ◽  
Author(s):  
Congting Sun ◽  
Yuanjian Zhang ◽  
Shuyan Song ◽  
Dongfeng Xue
Keyword(s):  
Specific Capacitance ◽  
Active Sites ◽  
Crystal Size ◽  
Present Model ◽  
Electrode Materials ◽  
Quantitative Relationship ◽  
Charge Storage ◽  
Extraction Processes ◽  
Proportional Relationship ◽  
Adsorption Desorption

A proportional relationship between the specific capacitance of MnO2 and the percentage of effective Mn centers that act as active sites in the Faradaic charge storage has been established on the basis of a tunnel structure–crystallization behavior correlation. A quantitative relationship between the effective Mn centers at the surfaces and in the tunnels can distinguish the specific capacitance values that arise from the adsorption/desorption and insertion/extraction processes, respectively, of different MnO2 crystallographic forms in the Faradaic charge storage. The different specific capacitance values between the MnO2 crystallographic forms are mainly attributed to the different effective utilizations of Mn centers in the size-limited tunnels. The present model demonstrates that increasing the percentage of effective Mn centers via decreasing the crystal size can facilitate obtaining MnO2-based electrode materials with higher specific capacitance values.

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