scholarly journals Assessing Catalytic Rates of Bimetallic Nanoparticles with Active Site Specificity - A Case Study using NO Decomposition

2021 ◽  
Author(s):  
Joakim Halldin Stenlid ◽  
Verena Streibel ◽  
Tej S. Choksi ◽  
Frank Abild-Pedersen
Keyword(s):  
Active Sites ◽  
Bimetallic Nanoparticles ◽  
Pt Nanoparticles ◽  
Reaction Rates ◽  
Shell Nanoparticles ◽  
Wide Range ◽  
Compositional Variations ◽  
Random Alloys ◽  
The Stability ◽  
Core Shell Nanoparticles

Bimetallic alloys have emerged as an important class of catalytic materials, spanning a wide range of shapes, sizes, and compositions. The combinatorics across this wide materials space makes predicting catalytic turnovers of individual active sites challenging. Herein, we introduce the stability of active sites as a descriptor for site-resolved reaction rates. The site stability unifies structural and compositional variations in a single descriptor. We compute this descriptor using coordination-based models trained with DFT calculations. Our approach enables instantaneous predictions of catalytic turnovers for nanostructures up to 12 nm in size. Using NO dissociation as probe reaction, we identify that octahedral Au-Pt core-shell nanoparticles and 3 nm 0.5:0.5 AuPt random alloys yield greater than 10 times higher compared to monometallic Pt nanoparticles. By prescribing specific sizes, morphologies, and compositions of optimal catalytic nanoparticles, our method provides tailored guidance to experiments for rationally designing bimetallic catalysts.

scholarly journals Synthesis and Advanced Characterization of Polymer-Protein Core-Shell Nanoparticles

Catalysts ◽  
2021 ◽  
Vol 11 (6) ◽  
pp. 730
Author(s):  
Erik Sarnello ◽  
Tao Li
Keyword(s):  
Particle Size ◽  
Small Angle ◽  
Core Shell ◽  
Assembly Process ◽  
Shell Nanoparticles ◽  
X Ray ◽  
X Ray Scattering ◽  
Wide Range ◽  
Core Shell Nanoparticles ◽  
Ray Scattering

Enzyme immobilization techniques are widely researched due to their wide range of applications. Polymer–protein core–shell nanoparticles (CSNPs) have emerged as a promising technique for enzyme/protein immobilization via a self-assembly process. Based on the desired application, different sizes and distribution of the polymer–protein CSNPs may be required. This work systematically studies the assembly process of poly(4-vinyl pyridine) and bovine serum albumin CSNPs. Average particle size was controlled by varying the concentrations of each reagent. Particle size and size distributions were monitored by dynamic light scattering, ultra-small-angle X-ray scattering, small-angle X-ray scattering and transmission electron microscopy. Results showed a wide range of CSNPs could be assembled ranging from an average radius as small as 52.3 nm, to particles above 1 µm by adjusting reagent concentrations. In situ X-ray scattering techniques monitored particle assembly as a function of time showing the initial particle growth followed by a decrease in particle size as they reach equilibrium. The results outline a general strategy that can be applied to other CSNP systems to better control particle size and distribution for various applications.

scholarly journals Advanced Microfluidic Technologies for Lipid Nano-Microsystems from Synthesis to Biological Application

Pharmaceutics ◽  
2022 ◽  
Vol 14 (1) ◽  
pp. 141
Author(s):  
Bruna Carvalho ◽  
Bruno Ceccato ◽  
Mariano Michelon ◽  
Sang Han ◽  
Lucimara de la Torre
Keyword(s):  
Lipid Nanoparticles ◽  
Future Trends ◽  
Biological Applications ◽  
Biological Application ◽  
Shell Nanoparticles ◽  
Cellular Environment ◽  
Wide Range ◽  
Core Shell Nanoparticles ◽  
New Strategies ◽  
Lipid Structures

Microfluidics is an emerging technology that can be employed as a powerful tool for designing lipid nano-microsized structures for biological applications. Those lipid structures can be used as carrying vehicles for a wide range of drugs and genetic materials. Microfluidic technology also allows the design of sustainable processes with less financial demand, while it can be scaled up using parallelization to increase production. From this perspective, this article reviews the recent advances in the synthesis of lipid-based nanostructures through microfluidics (liposomes, lipoplexes, lipid nanoparticles, core-shell nanoparticles, and biomimetic nanovesicles). Besides that, this review describes the recent microfluidic approaches to produce lipid micro-sized structures as giant unilamellar vesicles. New strategies are also described for the controlled release of the lipid payloads using microgels and droplet-based microfluidics. To address the importance of microfluidics for lipid-nanoparticle screening, an overview of how microfluidic systems can be used to mimic the cellular environment is also presented. Future trends and perspectives in designing novel nano and micro scales are also discussed herein.

Tuning core–shell interactions in tungsten carbide–Pt nanoparticles for the hydrogen evolution reaction

2018 ◽  
Vol 20 (36) ◽  
pp. 23262-23271 ◽  
Author(s):  
Akash Jain ◽  
Ashwin Ramasubramaniam
Keyword(s):  
Tungsten Carbide ◽  
Hydrogen Evolution ◽  
Hydrogen Evolution Reaction ◽  
Pt Nanoparticles ◽  
Core Shell ◽  
Shell Nanoparticles ◽  
Titanium Doping ◽  
The Stability

Titanium doping enhances the stability and activity of tungsten carbide core–platinum shell nanoparticles for hydrogen evolution

scholarly journals Assessing the stability of Pd-exchanged sites in zeolites with the aid of a high throughput quantum chemistry workflow

2021 ◽  
Author(s):  
Hassan Aljama ◽  
Martin Head-Gordon ◽  
Alexis Bell
Keyword(s):  
High Throughput ◽  
High Throughput Screening ◽  
Active Sites ◽  
Density Functional ◽  
Functional Materials ◽  
No Adsorption ◽  
Functional Theory ◽  
Wide Range ◽  
The Stability ◽  
Shed Light

Abstract Cation exchanged-zeolites are functional materials with a wide range of applications from catalysis to sorbents. They present a challenge for computational studies using density functional theory due to the numerous possible active sites. From Al configuration, to placement of extra framework cation(s), to potentially different oxidation states of the cation, accounting for all these possibilities is not trivial. To make the number of calculations more tractable, most studies focus on a few active sites. We attempt to go beyond these limitations by implementing a workflow for a high throughput screening, designed to systematize the problem and exhaustively search for feasible active sites. We use Pd-exchanged CHA and BEA to illustrate the approach. After conducting thousands of individual calculations, we identify the sites most favorable for the Pd cation and discuss the results in detail. The high throughput screening identifies many energetically favorable sites that are non-trivial. Lastly, we employ these results to examine NO adsorption in Pd-exchanged CHA, which is a promising passive NOx adsorbent (PNA) during the cold start of automobiles. The results shed light on critical active sites for NOx capture that were not previously studied.

Controlled Synthesis and Characterization of Co-Au Core-shell Nanoparticles

2005 ◽  
Vol 877 ◽  
Author(s):  
Yuping Bao ◽  
Hector Calderon ◽  
Kannan M. Krishnan
Keyword(s):  
Core Shell ◽  
Gold Compound ◽  
Contrast Imaging ◽  
Shell Nanoparticles ◽  
Transmission Electron ◽  
Wide Range ◽  
High Resolution Tem ◽  
Core Shell Nanoparticles ◽  
Z Contrast ◽  
First Time

AbstractCo-Au Core-shell nanoparticles are synthesized by slowly reducing an organo-gold compound on pre-made cobalt seeds with a weak reducer at mild condition. For the first time, these coreshell nanoparticles are generated in non-polar solvent in a controlled manner. The formation theory of core-shell structure, especially the seed size effect, is addressed as well. These coreshell structures are confirmed with a wide range of transmission electron microscopy (TEM) methods, which includes routine TEM images, high resolution TEM, and z-contrast imaging.

scholarly journals Bubble nucleation and migration in a lead–iron hydr(oxide) core–shell nanoparticle

2015 ◽  
Vol 112 (42) ◽  
pp. 12928-12932 ◽  
Author(s):  
Kaiyang Niu ◽  
Timofey Frolov ◽  
Huolin L. Xin ◽  
Junling Wang ◽  
Mark Asta ◽  
...  
Keyword(s):  
Iron Hydroxide ◽  
Steel Corrosion ◽  
Elastic Interaction ◽  
Bubble Nucleation ◽  
Core Shell ◽  
In Situ Observation ◽  
Shell Nanoparticles ◽  
Wide Range ◽  
And Migration ◽  
Core Shell Nanoparticles

Iron hydroxide is found in a wide range of contexts ranging from biominerals to steel corrosion, and it can transform to anhydrous oxide via releasing O2 gas and H2O. However, it is not well understood how gases transport through a crystal lattice. Here, we present in situ observation of the nucleation and migration of gas bubbles in iron (hydr)oxide using transmission electron microscopy. We create Pb–FeOOH model core–shell nanoparticles in a liquid cell. Under electron irradiation, iron hydroxide transforms to iron oxide, during which bubbles are generated, and they migrate through the shell to the nanoparticle surface. Geometric phase analysis of the shell lattice shows an inhomogeneous stain field at the bubbles. Our modeling suggests that the elastic interaction between the core and the bubble provides a driving force for bubble migration.

scholarly journals Dehydra-Decyclization of 2-Methyltetrahydrofuran to Pentadienes on Boron-Containing Zeolites

2020 ◽  
Author(s):  
Gaurav Kumar ◽  
Dongxia Liu ◽  
Dandan Xu ◽  
Limin Ren ◽  
Michael Tsapatsis ◽  
...  
Keyword(s):  
Active Sites ◽  
Space Velocity ◽  
Reaction Rates ◽  
Reaction Conditions ◽  
Kinetic Measurements ◽  
Individual Site ◽  
Order Of Magnitude ◽  
The Stability ◽  
Total Turnover ◽  
Competing Pathways

Biomass-derived 2-methyltetrahydrofuran (2-MTHF) undergoes tandem ring-opening and dehydration (dehydra-decyclization) to linear pentadienes, namely 1,3-pentadiene and 1,4-pentadiene. It can also fragment to butenes and formaldehyde through a competing retro-Prins condensation pathway. Using detailed kinetic measurements of 2-MTHF dehydra-decyclization on zeolites with disparate acidities (boro- and alumino-silicates) and micropore environments (MFI, MWW, and BEA), weakly acidic borosilicates were shown to exhibit ca. 10-30% higher selectivity to dienes at about five-to-sixty times lower proton-normalized rates than aluminosilicates (453-573 K). Dehydra-decyclization site time yields (STYs) were invariant for aluminosilicates within the investigated frameworks, indicating the absence of pore-confinement influence. However, individual site-normalized reaction rates varied by almost an order of magnitude on borosilicates in the order MWW > MFI > BEA at a given temperature (523 K), indicating the different nature of active sites in these weak solid acids. The diene distribution remained far from equilibrium and was tuned towards the desirable conjugated diene (1,3-pentadiene) by facile isomerization of 1,4-pentadiene. This tuning capability was facilitated by high bed residence times, as well as the smaller micropore sizes among the considered zeolite frameworks. The suppression of competing pathways and promotion of 1,4-pentadiene isomerization events lead to a hitherto unreported ∼86% 1,3-pentadiene yield and an overall ∼ 89% combined linear C5 dienes’ yield at near quantitative (~98%) 2-MTHF conversion on the borosilicate B-MWW, without a significant reduction in diene selectivities for at least 80 hours time-on-stream under low space velocity (0.85 g reactant/g cat./h) and high temperature (658 K) conditions. Finally, starting with iso-conversion levels (ca. 21-26%) and using total turnover numbers (TONs) accrued over the entire catalyst lifetime as the stability criterion, borosilicates were demonstrated to be significantly more stable than aluminosilicates under reaction conditions (~3-6x higher TONs).

scholarly journals Computational Modeling Predicts the Stability of Both Pd+ and Pd2+ Ion-Exchanged into H-CHA

2020 ◽  
Author(s):  
Jeroen Van der Mynsbrugge ◽  
Martin Head-Gordon ◽  
Alexis T. Bell
Keyword(s):  
Active Sites ◽  
Nearest Neighbor ◽  
Operating Conditions ◽  
Oxidation States ◽  
Vehicle Exhaust ◽  
Reducing Conditions ◽  
Wide Range ◽  
Promising Solution ◽  
The Stability ◽  
Spectroscopy Studies

<p>Passive NO<sub>x</sub> adsorbers (PNA) using Pd/zeolites have emerged as a promising solution for the reduction of cold-start emissions from vehicle exhaust. However, the nature of the active sites and the mechanisms underlying NO<sub>x</sub> adsorption in Pd/zeolites remain a subject of ongoing investigation. In this study, we employ quantum chemical simulations to investigate the structure of Pd species in cation-exchange sites at isolated Al and Al pairs in the 6-ring and 8-ring of the CHA framework, before the introduction of NO<sub>x</sub>. Our calculations show that the speciation of Pd in these exchange sites strongly depends on the precise Al arrangement within the framework, as well as the operating conditions. Ionically dispersed Pd is found to be the most favorable species over a wide range of oxidizing and reducing conditions. Small oligomers of PdO and metallic Pd do not appear to be competitive at either isolated Al or Al pairs. Notably, our calculations show that ion exchange sites other than next-next-nearest neighbor Al pairs in the 6-ring will be preferentially occupied by Pd<sup>+</sup> instead of Pd<sup>2+</sup>. The stability of Pd<sup>+</sup> in the zeolite environment is an interesting contrast with its rareness in molecular Pd compounds. Nonetheless, a detailed analysis of the electronic structure shows that predicted Pd oxidation states are consistent with chemical intuition for all complexes investigated in this study. We also discuss the potential ambiguity in Pd characterization provided by typical experimental techniques such as XANES, EXAFS and UV-VIS, and highlight the need for additional EPR spectroscopy studies to further elucidate the initial Pd speciation in zeolites for PNA applications. </p>

scholarly journals Computational Modeling Predicts the Stability of Both Pd+ and Pd2+ Ion-Exchanged into H-CHA

2020 ◽  
Author(s):  
Jeroen Van der Mynsbrugge ◽  
Martin Head-Gordon ◽  
Alexis T. Bell
Keyword(s):  
Active Sites ◽  
Nearest Neighbor ◽  
Operating Conditions ◽  
Oxidation States ◽  
Vehicle Exhaust ◽  
Reducing Conditions ◽  
Wide Range ◽  
Promising Solution ◽  
The Stability ◽  
Spectroscopy Studies

<p>Passive NO<sub>x</sub> adsorbers (PNA) using Pd/zeolites have emerged as a promising solution for the reduction of cold-start emissions from vehicle exhaust. However, the nature of the active sites and the mechanisms underlying NO<sub>x</sub> adsorption in Pd/zeolites remain a subject of ongoing investigation. In this study, we employ quantum chemical simulations to investigate the structure of Pd species in cation-exchange sites at isolated Al and Al pairs in the 6-ring and 8-ring of the CHA framework, before the introduction of NO<sub>x</sub>. Our calculations show that the speciation of Pd in these exchange sites strongly depends on the precise Al arrangement within the framework, as well as the operating conditions. Ionically dispersed Pd is found to be the most favorable species over a wide range of oxidizing and reducing conditions. Small oligomers of PdO and metallic Pd do not appear to be competitive at either isolated Al or Al pairs. Notably, our calculations show that ion exchange sites other than next-next-nearest neighbor Al pairs in the 6-ring will be preferentially occupied by Pd<sup>+</sup> instead of Pd<sup>2+</sup>. The stability of Pd<sup>+</sup> in the zeolite environment is an interesting contrast with its rareness in molecular Pd compounds. Nonetheless, a detailed analysis of the electronic structure shows that predicted Pd oxidation states are consistent with chemical intuition for all complexes investigated in this study. We also discuss the potential ambiguity in Pd characterization provided by typical experimental techniques such as XANES, EXAFS and UV-VIS, and highlight the need for additional EPR spectroscopy studies to further elucidate the initial Pd speciation in zeolites for PNA applications. </p>

Enhanced visible-light-driven photocatalytic activity of Au@Ag core–shell bimetallic nanoparticles immobilized on electrospun TiO2 nanofibers for degradation of organic compounds

2017 ◽  
Vol 7 (3) ◽  
pp. 570-580 ◽  
Author(s):  
Mrinmoy Misra ◽  
Narendra Singh ◽  
Raju Kumar Gupta
Keyword(s):  
Photocatalytic Activity ◽  
Visible Light ◽  
Organic Compounds ◽  
Shell Thickness ◽  
Bimetallic Nanoparticles ◽  
Core Shell ◽  
Shell Nanoparticles ◽  
Tio2 Nanofibers ◽  
Visible Light Driven ◽  
Core Shell Nanoparticles

In this work, Au@Ag core–shell nanoparticles (NPs) with variable Ag shell thickness were synthesized and immobilized on TiO2 nanofibers (TNF).

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