scholarly journals Understanding CO oxidation on the Pt(111) surface based on a reaction route network

2019 ◽  
Vol 21 (26) ◽  
pp. 14366-14375 ◽  
Author(s):  
Kanami Sugiyama ◽  
Yosuke Sumiya ◽  
Makito Takagi ◽  
Kenichiro Saita ◽  
Satoshi Maeda
Keyword(s):  
Co Oxidation ◽  
Kinetic Analysis ◽  
Rate Constant ◽  
Local Minima ◽  
Reaction Route ◽  
Constant Matrix ◽  
Route Network ◽  
Matrix Contraction ◽  
The Impact ◽  
Induced Reaction

Kinetic analysis by the rate constant matrix contraction on the reaction route network of CO oxidation on the Pt(111) surface obtained by the artificial force induced reaction reveals the impact of entropic contributions arising from a variety of local minima and transition states.

scholarly journals Kinetic and Microhydrodynamic Modeling of Fenofibrate Nanosuspension Production in a Wet Stirred Media Mill

Pharmaceutics ◽  
2021 ◽  
Vol 13 (7) ◽  
pp. 1055
Author(s):  
Gulenay Guner ◽  
Dogacan Yilmaz ◽  
Ecevit Bilgili
Keyword(s):  
Rate Constant ◽  
Kinetic Models ◽  
Multiple Linear Regression Model ◽  
Empirical Correlation ◽  
P Value ◽  
Order Kinetic ◽  
Stirrer Speed ◽  
Predictive Capability ◽  
Breakage Rate ◽  
The Impact

This study examined the impact of stirrer speed and bead material loading on fenofibrate particle breakage during wet stirred media milling (WSMM) via three kinetic models and a microhydrodynamic model. Evolution of median particle size was tracked via laser diffraction during WSMM operating at 3000–4000 rpm with 35–50% (v/v) concentration of polystyrene or zirconia beads. Additional experiments were performed at the center points of the above conditions, as well as outside the range of these conditions, in order to test the predictive capability of the models. First-order, nth-order, and warped-time kinetic models were fitted to the data. Main effects plots helped to visualize the influence of the milling variables on the breakage kinetics and microhydrodynamic parameters. A subset selection algorithm was used along with a multiple linear regression model (MLRM) to delineate how the breakage rate constant k was affected by the microhydrodynamic parameters. As a comparison, a purely empirical correlation for k was also developed in terms of the process/bead parameters. The nth-order model was found to be the best model to describe the temporal evolution; nearly second-order kinetics (n ≅ 2) was observed. When the process was operated at a higher stirrer speed and/or higher loading with zirconia beads as opposed to polystyrene beads, the breakage occurred faster. A statistically significant (p-value ≤ 0.01) MLRM of three microhydrodynamic parameters explained the variation in the breakage rate constant best (R2 ≥ 0.99). Not only do the models and the nth-order kinetic–microhydrodynamic correlation enable deeper process understanding toward developing a WSMM process with reduced cycle time, but they also provide good predictive capability, while outperforming the purely empirical correlation.

scholarly journals Exploring the full catalytic cycle of rhodium(i)–BINAP-catalysed isomerisation of allylic amines: a graph theory approach for path optimisation

2017 ◽  
Vol 8 (6) ◽  
pp. 4475-4488 ◽  
Author(s):  
Takayoshi Yoshimura ◽  
Satoshi Maeda ◽  
Tetsuya Taketsugu ◽  
Masaya Sawamura ◽  
Keiji Morokuma ◽  
...  
Keyword(s):  
Graph Theory ◽  
Reaction Mechanism ◽  
Catalytic Cycle ◽  
Theory Approach ◽  
Allylic Amines ◽  
Reaction Route ◽  
Reaction Method ◽  
Mapping Strategy ◽  
Global Reaction ◽  
Induced Reaction

The reaction mechanism of the cationic rhodium(i)–BINAP complex catalysed isomerisation of allylic amines was explored using the artificial force induced reaction method with the global reaction route mapping strategy.

scholarly journals Impact of uncertainties in inorganic chemical rate constants on tropospheric composition and ozone radiative forcing

2017 ◽  
Author(s):  
Ben Newsome ◽  
Mat Evans
Keyword(s):  
Rate Constant ◽  
Atmospheric Chemistry ◽  
Rate Constants ◽  
Tropospheric Ozone ◽  
Radiative Forcing ◽  
Transport Model ◽  
Surface Ozone ◽  
Photolysis Rates ◽  
The Impact ◽  
Chemical Rate

Abstract. Chemical rate constants determine the composition of the atmosphere and how this composition has changed over time. They are central to our understanding of climate change and air quality degradation. Atmospheric chemistry models, whether online or offline, box, regional or global use these rate constants. Expert panels synthesise laboratory measurements, making recommendations for the rate constants that should be used. This results in very similar or identical rate constants being used by all models. The inherent uncertainties in these recommendations are, in general, therefore ignored. We explore the impact of these uncertainties on the composition of the troposphere using the GEOS-Chem chemistry transport model. Based on the JPL and IUPAC evaluations we assess 50 mainly inorganic rate constants and 10 photolysis rates, through simulations where we increase the rate of the reactions to the 1σ upper value recommended by the expert panels. We assess the impact on 4 standard metrics: annual mean tropospheric ozone burden, surface ozone and tropospheric OH concentrations, and tropospheric methane lifetime. Uncertainty in the rate constants for NO2 + OH    M →  HNO3, OH + CH4 → CH3O2 + H2O and O3 + NO → NO2 + O2 are the three largest source of uncertainty in these metrics. We investigate two methods of assessing these uncertainties, addition in quadrature and a Monte Carlo approach, and conclude they give similar outcomes. Combining the uncertainties across the 60 reactions, gives overall uncertainties on the annual mean tropospheric ozone burden, surface ozone and tropospheric OH concentrations, and tropospheric methane lifetime of 11, 12, 17 and 17 % respectively. These are larger than the spread between models in recent model inter-comparisons. Remote regions such as the tropics, poles, and upper troposphere are most uncertain. This chemical uncertainty is sufficiently large to suggest that rate constant uncertainty should be considered when model results disagree with measurement. Calculations for the pre-industrial allow a tropospheric ozone radiative forcing to be calculated of 0.412 ± 0.062 Wm−2. This uncertainty (15 %) is comparable to the inter-model spread in ozone radiative forcing found in previous model-model inter-comparison studies where the rate constants used in the models are all identical or very similar. Thus the uncertainty of tropospheric ozone radiative forcing should expanded to include this additional source of uncertainty. These rate constant uncertainties are significant and suggest that refinement of supposedly well known chemical rate constants should be considered alongside other improvements to enhance our understanding of atmospheric processes.

scholarly journals Perphenazine-macrocycle conjugates divert Aβ42 towards non-toxic aggregates by monomer sequestration

2020 ◽  
Author(s):  
Sarah R Ball ◽  
Julius S P Adamson ◽  
Michael A Sullivan ◽  
Manuela R Zimmermann ◽  
Victor Lo ◽  
...  
Keyword(s):  
Alzheimer’S Disease ◽  
Alzheimer's Disease ◽  
Nmr Spectroscopy ◽  
Kinetic Analysis ◽  
Amyloid Β ◽  
Dimensional Structure ◽  
Amyloid Β Peptide ◽  
Monomeric Form ◽  
Starting Point ◽  
The Impact

AbstractThe amyloid-β peptide, the main protein component of amyloid plaques in Alzheimer’s disease, plays a key role in the neurotoxicity associated with the condition through the formation of small toxic oligomer species which mediate the disruption of calcium and glutamate homeostasis. The lack of therapeutic benefit associated with removal of mature amyloid-β fibrils has focused attention on the toxic oligomeric species formed during the process of fibril assembly. Here, we present the design and synthesis of a family of perphenazine-macrocyle conjugates. We find that two-armed perphenazine-cyclam conjugates divert the monomeric form of the amyloid-β peptide away from the amyloidogenic pathway into amorphous aggregates that are not toxic to differentiated SH-SY5Y cells in vitro. This strategy prevents the formation of damaging amyloid oligomers. Kinetic analysis of the effects of these compounds on the assembly pathway, together with NMR spectroscopy, identifies rapid monomer sequestration as the underlying neuroprotective mechanism. The ability to specifically target the monomeric form of amyloid-β allows for further understanding of the impact of the multiple species formed between peptide biogenesis and plaque deposition. The modular, three-dimensional structure of these compounds provides a starting point for the design of more potent modulators of this amyloid-forming peptide, and can be adapted to probe the protein self-assembly pathways associated with other proteinopathies.Significance statementThe aggregation pathway of the amyloid-β (Aβ) peptide in Alzheimer’s disease is complex and involves multiple different species. An inability to isolate and study the impact of distinct Aβ species has undermined efforts to develop effective therapies. To address this issue, we have developed a series of molecules that specifically sequester the monomeric form of the highly aggregation-prone Aβ42 peptide. Interaction with these molecules diverts Aβ42 from the amyloidogenic pathway and prevents formation of toxic oligomeric species. We use kinetic analysis and NMR spectroscopy to identify rapid monomer sequestration as the underlying neuroprotective mechanism. Future rational development of these molecules and characterisation of their interactions with Aβ will delineate the impact of different Aβ oligomers on neurobiology and pathology.

scholarly journals Application of Potassium Ion Deposition in Determining the Impact of Support Reducibility on Catalytic Activity of Au/Ceria-Zirconia Catalysts in CO Oxidation, NO Oxidation, and C3H8 Combustion

Catalysts ◽  
2020 ◽  
Vol 10 (6) ◽  
pp. 688
Author(s):  
Ewa M. Iwanek (nee Wilczkowska) ◽  
Leonarda F. Liotta ◽  
Shazam Williams ◽  
Linjie Hu ◽  
Krishelle Calilung ◽  
...  
Keyword(s):  
Low Temperature ◽  
Co Oxidation ◽  
Gold Catalysts ◽  
Maximum Temperature ◽  
Potassium Ions ◽  
Reduction Peak ◽  
Temperature Reduction ◽  
Potassium Loading ◽  
The Impact ◽  
Low Temperature Reduction

The purpose of the study was to show how a controlled, subtle change of the reducibility of the support by deposition of potassium ions impacts the activity of gold catalysts. Since the activity of supported gold catalysts in carbon monoxide oxidation is known to strongly depend on the reducibility of the support, this reaction was chosen as the model reaction. The results of tests conducted in a simple system in which the only reagents were CO and O2 showed good agreement with the CO activity trend in tests performed in a complex stream of reagents, which also contained CH4, C2H6, C3H8, NO, and water vapor. The results of the X-ray Diffraction (XRD) studies revealed that the support has the composition Ce0.85Zr0.15O2, that its lattice constant is the same for all samples, and that gold is mostly present in the metallic phase. The reducibility of the systems was established based on Temperature Programmed Reduction (TPR) and in situ XRD measurements in H2 atmosphere. The results show that the low temperature reduction peak, which is due to the presence of gold, is shifted to a higher value by the presence of 0.3 at% potassium ions on the surface. Moreover, the increase of the potassium loading leads to a more pronounced shift. The T50 of CO oxidation in the simple model stream was found to exhibit an excellent linear correlation with the maximum temperature of the low temperature reduction peak of Au catalysts. This means that stabilizing oxygen with a known amount of potassium ions can be numerically used to estimate the T50 in CO oxidation. The results in the complex stream also showed a similar dependence of CO conversion on reducibility, though there was no substantial difference in the activity of the catalysts in other reactions regardless of the potassium loading. These studies have shown that the influence of potassium varies depending on the reaction, which highlights differences in the impact of reducibility and importance of other factors in these reactions.

scholarly journals Understanding the Impact of Defects on Catalytic CO Oxidation of LaFeO3-Supported Rh, Pd, and Pt Single-Atom Catalysts

2019 ◽  
Vol 123 (12) ◽  
pp. 7290-7298 ◽  
Author(s):  
Long Zhang ◽  
Ivo A. W. Filot ◽  
Ya-Qiong Su ◽  
Jin-Xun Liu ◽  
Emiel J. M. Hensen
Keyword(s):  
Co Oxidation ◽  
Single Atom ◽  
Catalytic Co Oxidation ◽  
The Impact
Sign in / Sign up

Export Citation Format

Share Document