scholarly journals Effect of the Preparation Method of LaSrCoFeOx Perovskites on the Activity of N2O Decomposition

2021 ◽  
Author(s):  
Nia Richards ◽  
Luke A. Parker ◽  
James H. Carter ◽  
Samuel Pattisson ◽  
David J. Morgan ◽  
...  
Keyword(s):  
Citric Acid ◽  
Active Sites ◽  
Preparation Method ◽  
N2o Decomposition ◽  
Oxygen Species ◽  
Calcination Temperatures ◽  
Highly Active ◽  
Rate Limiting Step ◽  
Enhanced Mobility ◽  
Rate Limiting

AbstractN2O remains a major greenhouse gas and contributor to global warming, therefore developing a catalyst that can decompose N2O at low temperatures is of global importance. We have investigated the use of LaSrCoFeOx perovskites for N2O decomposition and the effect of surface area, A and B site elements, Co–O bond strength, redox capabilities and oxygen mobility have been studied. It was found that by using a citric acid preparation method, perovskites with strong redox capabilities and weak Co–O bonds can be formed at relatively low calcination temperatures (550 °C) resulting in highly active catalysts. The enhanced activity is related to the presence of highly mobile oxygen species. Oxygen recombination on the catalyst surface is understood to be a prominent rate limiting step for N2O decomposition. Here the reduced strength of Co–O bonds and mobile lattice oxygen species suggest that the surface oxygen species have enhanced mobility, aiding recombination, and subsequent regeneration of the active sites. La0.75Sr0.25Co0.81Fe0.19Ox prepared by citric acid method converted 50% of the N2O in the feed (T50) at 448 °C. Graphic Abstract

scholarly journals Waste-Derived Green Nanocatalyst for Biodiesel Production: Kinetic-Mechanism Deduction and Optimization Studies

2021 ◽  
Vol 13 (11) ◽  
pp. 5849
Author(s):  
Chee Yoong Chooi ◽  
Jia Huey Sim ◽  
Shiau Foon Tee ◽  
Zhi Hua Lee
Keyword(s):  
Active Sites ◽  
Reaction Rate ◽  
Surface Reaction ◽  
Pore Diameter ◽  
Preparation Method ◽  
Kinetic Mechanism ◽  
Transesterification Reaction ◽  
Biodiesel Production ◽  
Rate Limiting Step ◽  
Rate Limiting

This research focuses on deducing the kinetic mechanism for biodiesel production catalyzed by a CaO nanocatalyst derived from waste cockle shells via thermal hydration–dehydration treatment. In addition, the CaO nanocatalyst preparation method via thermal hydration–dehydration-related parameters (hydration duration, recalcination temperature, and recalcination duration) was studied and optimized. The transesterification reaction catalyzed by the CaO nanocatalyst followed the Langmuir–Hinshelwood kinetic mechanism with surface reaction as the rate-limiting step. The relatively low activation energy (3786.7 J/mol) for a transesterification reaction offered by the CaO nanocatalyst enhanced the reaction rate to 27.3% FAME yield/hr. The optimal conditions for the thermal hydration–dehydration treatment used to develop the nano CaO catalyst were 6 h of hydration duration, 650 °C of recalcination temperature, and 3 h of recalcination duration. Of biodiesel yield, 94.13% was obtained at a moderate temperature of 60 °C and 3 h reaction time during the transesterification of palm oil catalyzed by the nano-CaO. SEM, BET, and TPD results proved that the CaO nanocatalyst had a large surface area (13.9113 m2/g) and high pore volume (0.0318 cm3/g) that were rich in active sites (1046.46 μmol CO2/g), and the pore diameter (33.17 nm) was accessible to reactants and products.

Surface Separation Equilibria and Dynamics of Cationic Dye Loaded onto Citric Acid and Sodium Hydroxide Treated Eggshells

2018 ◽  
Vol 17 (1) ◽  
Author(s):  
Elisha A. Adeniji ◽  
Temitope O. Abodunrin ◽  
Temitope A. Ogunnupebi ◽  
Babatunde A. Koiki ◽  
Abimbola M. Olatunde ◽  
...  
Keyword(s):  
Citric Acid ◽  
Diffusion Mechanism ◽  
Experiment Data ◽  
Surface Separation ◽  
Rate Limiting Step ◽  
Monolayer Adsorption ◽  
Delta G ◽  
Rate Limiting ◽  
Best Fit ◽  
Adsorption Systems

AbstractThis research enthusiastically highlights the bio-adsorption of methylene blue (MB) by local, poultry, NaOH and citric acid modified ubiquitous eggshell (LES, NLES, CLES, PES, NPES and CPES) adsorbents. The microstructures of these adsorbents indicated that they had some surface functional moieties that were responsible for the adsorption of MB. The Langmuir isotherm and PSO model best fit the experiment data. The largest Langmuir monolayer adsorption capacity${q_{max}}$, was 242.47 mg/g, with the largest MB initial concentration of 400 mg/L. This was a clear indication and a confirmation that MB adsorption by the powdered eggshells was chemisorptive. Moreover, the values of$F$, the thickness of the boundary layer/film were$\gt 0$, showing that the rate limiting step for the adsorption process was controlled by more than one diffusion mechanism. The values of$\Delta {G^\circ }$for the adsorption of MB by the adsorbents indicated that the adsorption reactions were all non-feasible and non-spontaneous. The values for$\Delta {S^\circ }$(J/K/mol) for LES, NLES and CPES for the uptake of MB showed decrease in the chaos or degree of randomness of the adsorption reactions, and the reverse was the case for PES, NPES and CLES for the uptake of MB, which showed increase in the chaos or degree of randomness of the adsorption. The adsorption of MB by LES, NLES and CPES gave$\Delta {H^\circ }$(kJ/mol) values which were indicative of endothermic nature of the adsorption systems, and the reverse was the case for the uptake of MB by PES, NPES and CLES, which was indicative of the exothermic nature of the adsorption systems.

scholarly journals Toxic Mechanisms of Aryloxyphenoxypropionates in Target and Non-target Organisms

2019 ◽  
pp. 1-11
Author(s):  
Ayokanmi Ore ◽  
Ebenezer Tunde Olayinka
Keyword(s):  
Membrane Lipids ◽  
Lipid Synthesis ◽  
Oxygen Species ◽  
Acetyl Coa Carboxylase ◽  
Rate Limiting Step ◽  
Limiting Step ◽  
Major Toxicity ◽  
Pharmacokinetic Properties ◽  
Entire Plant ◽  
Rate Limiting

Herbicides are substances used to control unwanted plants-weeds. They can be classified into several classes by mechanism of action. This review describes the members of aryloxyphenoxypropionate herbicides, their pharmacokinetic properties, metabolism and their mechanism of phytotoxicity in target weeds as well as in non-target organisms. Two major toxicity mechanisms are described. The first is by inhibition of lipid synthesis. This is achieved by inhibiting the rate limiting step of lipid biosynthesis catalyzed by acetyl CoA carboxylase. The second mechanism is by induction of oxidative stress. This is achieved by generation of reactive oxygen species which in excess can cause oxidative damage to macromolecules and cellular structures especially the membrane lipids. Loss of vital membrane lipids alters the fluidity of membrane, loss of cellular contents and eventually cell death and death of the entire plant.

scholarly journals Carbon Dioxide Reforming of Methane over Ni Supported SiO2: Influence of the Preparation Method on the Resulting Structural Properties and Catalytic Activity

Catalysts ◽  
2020 ◽  
Vol 10 (7) ◽  
pp. 795 ◽  
Author(s):  
Hua-Ping Ren ◽  
Shao-Peng Tian ◽  
Si-Yi Ding ◽  
Gui-Qiu Huang ◽  
Min Zhu ◽  
...  
Keyword(s):  
Carbon Dioxide ◽  
Particle Size ◽  
Catalytic Activity ◽  
Citric Acid ◽  
Preparation Method ◽  
Complexing Agents ◽  
Impregnation Method ◽  
Carbon Dioxide Reforming ◽  
Highly Active ◽  
Before And After

Ni-C/SiO2 and Ni-G/SiO2 catalysts were prepared by a complexed-impregnation method using citric acid and glycine as complexing agents, respectively. Ni/SiO2 was also prepared by the conventional incipient impregnation method. All the catalysts were comparatively tested for carbon dioxide reforming of methane (CDR) at P = 1.0 atm, T = 750 °C, CO2/CH4 = 1.0, and GHSV = 60,000 mL·g−1·h−1. The results showed that Ni-C/SiO2 and Ni-G/SiO2 exhibited better CDR performance, especially regarding stability, than Ni/SiO2. The conversions of CH4 and CO2 were kept constant above 82% and 87% after 20 h of reaction over Ni-C/SiO2 and Ni-G/SiO2 while they were decreased from 81% and 88% to 56% and 59%, respectively, over the Ni/SiO2. The characterization results of the catalysts before and after the reaction showed that the particle size and the distribution of Ni, as well as the interactions between Ni and the support were significantly influenced by the preparation method. As a result, an excellent resistance to the coking deposition and the anti-sintering of Ni was obtained over the Ni-C/SiO2 and Ni-G/SiO2, leading to a highly active and stable CDR performance.

scholarly journals Chemical clustering and visualization applied to macromolecular crystallography

2014 ◽  
Vol 70 (a1) ◽  
pp. C1145-C1145
Author(s):  
Andrew Bruno ◽  
Amanda Ruby ◽  
Joseph Luft ◽  
Thomas Grant ◽  
Jayaraman Seetharaman ◽  
...  
Keyword(s):  
Hierarchical Clustering ◽  
High Throughput ◽  
Active Sites ◽  
X Ray Crystallography ◽  
Rate Limiting Step ◽  
Potential Applications ◽  
Crystallization Conditions ◽  
Electron Density Map ◽  
Distance Coefficient ◽  
Rate Limiting

Many bioscience fields employ high-throughput methods to screen multiple biochemical conditions. The analysis of these becomes tedious without a degree of automation. Crystallization, a rate limiting step in biological X-ray crystallography, is one of these fields. Screening of multiple potential crystallization conditions (cocktails) is the most effective method of probing a proteins phase diagram and guiding crystallization but the interpretation of results can be consuming. To aid this empirical approach a cocktail distance coefficient was developed to quantitatively compare macromolecule crystallization conditions and outcome. These coefficients were evaluated against an existing similarity metric developed for crystallization, the C6 metric, using both virtual crystallization screens and by comparison of two related 1,536-cocktail high-throughput crystallization screens. Hierarchical clustering was employed to visualize one of these screens and the crystallization results from an exopolyphosphatase-related protein from Bacteroides fragilis, (BfR192) overlaid on this clustering. This demonstrated a strong correlation between certain chemically related clusters and crystal lead conditions. While this analysis was not used to guide the initial crystallization optimization, it led to the re-evaluation of unexplained peaks in the electron density map of the protein and the insertion and correct placement of a sodium, potassium and phosphate atoms in the structure. With these in place, the resulting structure of the putative active site demonstrated features consistent with active sites of other phosphatases which are involved in binding the phosphoryl moieties of nucleotide triphosphates. The new distance coefficient appears to be robust in this application and coupled with hierarchical clustering and the overlay of crystallization outcome reveals information of biological relevance. While tested with a single example the potential applications appear promising.

Catalytic oxidation of n-propane and methyl alcohol over nickel(II) oxide

1981 ◽  
Vol 59 (5) ◽  
pp. 865-869 ◽  
Author(s):  
I. M. Hoodless ◽  
R. A. Ross ◽  
R. Swaminathan
Keyword(s):  
Carbon Dioxide ◽  
Catalytic Oxidation ◽  
Water Vapour ◽  
Complete Oxidation ◽  
Oxygen Species ◽  
Fractional Rate ◽  
Rate Limiting Step ◽  
Adsorbed Oxygen Species ◽  
Limiting Step ◽  
Rate Limiting

The catalytic oxidation of propane over nickel(II) oxide has been studied in the temperature range 280 to 490 °C. Complete oxidation to carbon dioxide and water occurred. Fractional rate order dependencies were obtained for propane and oxygen and the reaction was inhibited by water vapour but not by carbon dioxide. It is suggested that the interaction of the adsorbed hydrocarbon with the adsorbed oxygen species, O−, is the rate-limiting step in the reaction at the lower temperature.Preliminary measurements of the oxidation of propane–methanol mixtures indicated that the alcohol supressed carbon dioxide formation. Conductivity studies have shown that, in these mixtures, methanol strongly interacts with the catalyst resulting in surface reduction.

scholarly journals A yeast TATA-binding protein mutant that selectively enhances gene expression from weak RNA polymerase II promoters.

1997 ◽  
Vol 17 (5) ◽  
pp. 2888-2896 ◽  
Author(s):  
W S Blair ◽  
B R Cullen
Keyword(s):  
Gene Expression ◽  
Rna Polymerase Ii ◽  
Transcription Initiation ◽  
Binding Protein ◽  
Tata Binding Protein ◽  
Mrna Transcription ◽  
Highly Active ◽  
Rate Limiting Step ◽  
Limiting Step ◽  
Rate Limiting

We describe a unique gain-of-function mutant of the TATA-binding protein (TBP) subunit of Saccharomyces cerevisiae TFIID that, at least in part, renders transcriptional transactivators dispensable for efficient mRNA expression. The yTBPN69S mutant enhances transcription from weaker yeast promoter elements by up to 50-fold yet does not significantly increase gene expression directed by highly active promoters. Therefore, this TBP mutant and transcriptional transactivators appear to affect a common rate-limiting step in transcription initiation. Consistent with the hypothesis that this step is TFIID recruitment, tethering of TBP to a target promoter via a heterologous DNA binding domain, which is known to bypass the need for transcriptional transactivators, also nullifies the enhancing effect exerted by the N69S mutation. These data provide genetic support for the hypothesis that TFIID recruitment represents a rate-limiting step in the initiation of mRNA transcription that is specifically enhanced by transcriptional transactivators.

scholarly journals Co-operativity in seminal ribonuclease function: binding studies

1987 ◽  
Vol 241 (2) ◽  
pp. 435-440 ◽  
Author(s):  
A Di Donato ◽  
R Piccoli ◽  
G D'Alessio
Keyword(s):  
Active Sites ◽  
Mixed Type ◽  
Equilibrium Dialysis ◽  
Binding Studies ◽  
Rate Limiting Step ◽  
Differential Spectrophotometry ◽  
Limiting Step ◽  
Binding Data ◽  
Hysteretic Effect ◽  
Rate Limiting

Binding of nucleotides to bovine seminal RNAase was studied by differential spectrophotometry and equilibrium dialysis. Cytidine 3′-phosphate, the reaction product of the hydrolytic, rate-limiting step of the reaction, was found to be capable, in contrast to related nucleotides, of discriminating between the two structurally identical active sites of the enzyme. Negative co-operativity, with a ‘half-of-sites’ reactivity, was found at lower concentrations of ligand, whereas at higher concentrations positive co-operativity was detected. These findings exclude that the non-hyperbolic kinetics previously reported for the hydrolytic step of the reaction are due to hysteretic effect. A model of mixed-type co-operativity is proposed for interpreting the binding data.

Improving photosynthesis through the enhancement of Rubisco carboxylation capacity

2021 ◽  
Author(s):  
Concepción Iñiguez ◽  
Pere Aguiló-Nicolau ◽  
Jeroni Galmés
Keyword(s):  
Active Sites ◽  
Arable Land ◽  
Small Subunit ◽  
Resource Use Efficiency ◽  
Rate Limiting Step ◽  
Promising Target ◽  
Use Efficiency ◽  
Co2 Concentrating Mechanisms ◽  
Near Future ◽  
Rate Limiting

Rising human population, along with the reduction in arable land and the impacts of global change, sets out the need for continuously improving agricultural resource use efficiency and crop yield (CY). Bioengineering approaches for photosynthesis optimization have largely demonstrated the potential for enhancing CY. This review is focused on the improvement of Rubisco functioning, which catalyzes the rate-limiting step of CO2 fixation required for plant growth, but also catalyzes the ribulose-bisphosphate oxygenation initiating the carbon and energy wasteful photorespiration pathway. Rubisco carboxylation capacity can be enhanced by engineering the Rubisco large and/or small subunit genes to improve its catalytic traits, or by engineering the mechanisms that provide enhanced Rubisco expression, activation and/or elevated [CO2] around the active sites to favor carboxylation over oxygenation. Recent advances have been made in the expression, assembly and activation of foreign (either natural or mutant) faster and/or more CO2-specific Rubisco versions. Some components of CO2 concentrating mechanisms (CCMs) from bacteria, algae and C4 plants has been successfully expressed in tobacco and rice. Still, none of the transformed plant lines expressing foreign Rubisco versions and/or simplified CCM components were able to grow faster than wild type plants under present atmospheric [CO2] and optimum conditions. However, the results obtained up to date suggest that it might be achievable in the near future. In addition, photosynthetic and yield improvements have already been observed when manipulating Rubisco quantity and activation degree in crops. Therefore, engineering Rubisco carboxylation capacity continues being a promising target for the improvement in photosynthesis and yield.

scholarly journals Validation of Flory-Huggins model for phenol adsorption by Parthenium hysterophorus in a batch system

2019 ◽  
Vol 2 (2) ◽  
Author(s):  
Zakia Latif1 ◽  
Aliya Fazal2 ◽  
Muhammad Aziz Choudhary1 ◽  
Zahoor Ahmad1 ◽  
Muhammad Aslam Mirza1
Keyword(s):  
Active Sites ◽  
Cost Effective ◽  
Toxic Waste ◽  
Parthenium Hysterophorus ◽  
Phenol Adsorption ◽  
Rate Limiting Step ◽  
Adsorbent Surface ◽  
Ft Ir ◽  
Biomass Dosage ◽  
Rate Limiting

Parthenium hysterophorus weed powder was studied as adsorbent for phenol adsorption from its aqueous standardized solution. The adsorption of pollutant was found improving with an increase of biomass dosage and contact time. The intraparticle diffusion of phenol onto adsorbent surface was identified to be the rate limiting step. Linear form of Flory-Huggins model revealed preeminence to Langmuir, Freundlich, Temkin, and Dubinin-Radushkevich due to highest value of R2. The remediation process was figured out as a physisorption rather than a chemical one based on value of E (0.21KJ/mol). Active sites of sorbent surface identified by FT-IR were oxygen containing functional groups. Recent study proposes cost effective utilization of toxic allergent for treatment of toxic waste.

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