Microwave Activation of Homogeneous and Heterogeneous Catalytic Reactions

1997 ◽  
Vol 62 (2) ◽  
pp. 347-354 ◽  
Author(s):  
Milan Hájek
Keyword(s):  
Active Sites ◽  
Specific Effect ◽  
Point Of View ◽  
Heterogeneous Reactions ◽  
Microwave Activation ◽  
Rate Enhancement ◽  
Heterogeneous Catalytic ◽  
Order Of Magnitude ◽  
And Performance ◽  
Alkylation Reactions

Microwave heating was applied in homogeneous and in heterogeneous reactions and the results were compared from the point of view of activation of chemical reactions. Reactions including the addition of halo compounds to alkenes catalyzed by copper and ruthenium complexes in different solvents and NaY zeolite catalyzed alkylation of secondary amine in the absence of solvent were studied as model reactions to compare possibilities of microwave activation of reactants and catalysts. Rate enhancement of over one order of magnitude in homogeneous reactions was caused mainly by thermal dielectric heating effect which resulted from the effective coupling of microwaves to polar solvents. Activation of reactants and catalysts was very low if any. In heterogeneously catalyzed alkylation reactions highly efficient activation of zeolite catalyst was recorded. The results indicated that the best reaction conditions were in experiments when both activation of catalyst and performance of reaction were carried out under microwave conditions. Rate enhancement was most probably caused by "hot spots" or by "selective heating" of active sites. In both homogeneous and heterogeneous reactions non-thermal activation (specific effect) was excluded.

Geometric Factor in Skeletal Reactions of 2-Methylpentane on Stepped Surfaces of Platinum Catalyst

1992 ◽  
Vol 57 (10) ◽  
pp. 2012-2020
Author(s):  
Vladimír Hejtmánek
Keyword(s):  
Active Sites ◽  
Platinum Catalyst ◽  
Point Of View ◽  
Geometric Factor ◽  
Published Data ◽  
Stepped Surfaces ◽  
Geometric Conditions ◽  
Surface Intermediates ◽  
Isomerization Mechanism

The role of geometric factor in the course of skeletal reactions (isomerization, hydrogenolysis) of 2-methylpentane on stepped (119), (557) and reconstructed R(557) surfaces of single crystals of platinum was evaluated with computer designed models. These calculations were compared with reported experimental data. It was found by analysis of geometric conditions that there are accessible active ensembles on double step of the reconstructed R(557) surface. In addition, these active sites are unsaturated in their coordination sphere and thus catalytically effective. This finding is consistent with published data, confirming higher catalytic activity of this surface. The various pathways of Bond Shift isomerization mechanism of 2-methylpentane from the point of view of steric demands of surface intermediates on differently located ensembles are discussed, too.

scholarly journals Green Nanocoatings Based on the Deposition of Zirconium Oxide: The Role of the Substrate

Materials ◽  
2021 ◽  
Vol 14 (4) ◽  
pp. 1043
Author(s):  
Vitor Bonamigo Moreira ◽  
Anna Puiggalí-Jou ◽  
Emilio Jiménez-Piqué ◽  
Carlos Alemán ◽  
Alvaro Meneguzzi ◽  
...  
Keyword(s):  
Zirconium Oxide ◽  
Active Sites ◽  
Modified Electrodes ◽  
Chemical Conversion ◽  
Ceramic Materials ◽  
Point Of View ◽  
Oxide Coatings ◽  
Alloying Element ◽  
Substrate Nature

Herein, the influence of the substrate in the formation of zirconium oxide monolayer, from an aqueous hexafluorozirconic acid solution, by chemical conversion and by electro-assisted deposition, has been approached. The nanoscale dimensions of the ZrO2 film is affected by the substrate nature and roughness. This study evidenced that the mechanism of Zr-EAD is dependent on the potential applied and on the substrate composition, whereas conversion coating is uniquely dependent on the adsorption reaction time. The zirconium oxide based nanofilms were more homogenous in AA2024 substrates if compared to pure Al grade (AA1100). It was justified by the high content of Cu alloying element present in the grain boundaries of the latter. Such intermetallic active sites favor the obtaining of ZrO2 films, as demonstrated by XPS and AFM results. From a mechanistic point of view, the electrochemical reactions take place simultaneously with the conventional chemical conversion process driven by ions diffusion. Such findings will bring new perspectives for the generation of controlled oxide coatings in modified electrodes used, as for example, in the construction of battery cells; in automotive and in aerospace industries, to replace micrometric layers of zinc phosphate by light-weight zirconium oxide nanometric ones. This study is particularly addressed for the reduction of industrial waste by applying green bath solutions without the need of auxiliary compounds and using lightweight ceramic materials.

scholarly journals Enhanced catalytic ozonation of ibuprofen using a 3D structured catalyst with MnO2 nanosheets on carbon microfibers

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Guhankumar Ponnusamy ◽  
Hajar Farzaneh ◽  
Yongfeng Tong ◽  
Jenny Lawler ◽  
Zhaoyang Liu ◽  
...  
Keyword(s):  
Removal Efficiency ◽  
Active Sites ◽  
Low Cost ◽  
Three Dimensional ◽  
Industrial Applications ◽  
Catalytic Ozonation ◽  
Heterogeneous Catalytic ◽  
Structured Catalyst ◽  
Dimensional Network ◽  
Carbon Microfibers

AbstractHeterogeneous catalytic ozonation is an effective approach to degrade refractory organic pollutants in water. However, ozonation catalysts with combined merits of high activity, good reusability and low cost for practical industrial applications are still rare. This study aims to develop an efficient, stable and economic ozonation catalyst for the degradation of Ibuprofen, a pharmaceutical compound frequently detected as a refractory pollutant in treated wastewaters. The novel three-dimensional network-structured catalyst, comprising of δ-MnO2 nanosheets grown on woven carbon microfibers (MnO2 nanosheets/carbon microfiber), was synthesized via a facile hydrothermal approach. Catalytic ozonation performance of Ibuprofen removal in water using the new catalyst proves a significant enhancement, where Ibuprofen removal efficiency of close to 90% was achieved with a catalyst loading of 1% (w/v). In contrast, conventional ozonation was only able to achieve 65% removal efficiency under the same operating condition. The enhanced performance with the new catalyst could be attributed to its significantly increased available surface active sites and improved mass transfer of reaction media, as a result of the special surface and structure properties of this new three-dimensional network-structured catalyst. Moreover, the new catalyst displays excellent stability and reusability for ibuprofen degradation over successive reaction cycles. The facile synthesis method and low-cost materials render the new catalyst high potential for industrial scaling up. With the combined advantages of high efficiency, high stability, and low cost, this study sheds new light for industrial applications of ozonation catalysts.

scholarly journals Comprehensive Thermodynamic Analysis of the Humphrey Cycle for Gas Turbines with Pressure Gain Combustion

Energies ◽  
2018 ◽  
Vol 11 (12) ◽  
pp. 3521 ◽  
Author(s):  
Panagiotis Stathopoulos
Keyword(s):  
Gas Turbine ◽  
Gas Turbines ◽  
Combustion Process ◽  
Ideal Gas ◽  
Point Of View ◽  
Pressure Gain Combustion ◽  
Combustion Technology ◽  
Secondary Air ◽  
And Performance ◽  
The Impact

Conventional gas turbines are approaching their efficiency limits and performance gains are becoming increasingly difficult to achieve. Pressure Gain Combustion (PGC) has emerged as a very promising technology in this respect, due to the higher thermal efficiency of the respective ideal gas turbine thermodynamic cycles. Up to date, only very simplified models of open cycle gas turbines with pressure gain combustion have been considered. However, the integration of a fundamentally different combustion technology will be inherently connected with additional losses. Entropy generation in the combustion process, combustor inlet pressure loss (a central issue for pressure gain combustors), and the impact of PGC on the secondary air system (especially blade cooling) are all very important parameters that have been neglected. The current work uses the Humphrey cycle in an attempt to address all these issues in order to provide gas turbine component designers with benchmark efficiency values for individual components of gas turbines with PGC. The analysis concludes with some recommendations for the best strategy to integrate turbine expanders with PGC combustors. This is done from a purely thermodynamic point of view, again with the goal to deliver design benchmark values for a more realistic interpretation of the cycle.

scholarly journals Heterogeneous Catalytic Synthesis of 2-Methylbenzimidazole from 2-Nitroaniline and Ethanol Over Mg Modified Cu-Pd/γ-Al2O3

Catalysts ◽  
2018 ◽  
Vol 9 (1) ◽  
pp. 8 ◽  
Author(s):  
Feng Feng ◽  
Yaqin Deng ◽  
Zheng Cheng ◽  
Xiaoliang Xu ◽  
Qunfeng Zhang ◽  
...  
Keyword(s):  
Active Sites ◽  
Hydrogen Transfer ◽  
High Efficiency ◽  
Simple Procedure ◽  
Direct Synthesis ◽  
Reaction System ◽  
Simple Method ◽  
Heterogeneous Catalytic ◽  
Coupled Reaction ◽  
Al2o3 Catalyst

The direct synthesis of benzimidazoles from 2-nitroaniline and ethanol over Cu-Pd/γ-Al2O3 catalysts has the advantages of requiring easily available starting materials, having high efficiency, and a simple procedure. The modification by Mg of the Cu-Pd/γ-Al2O3 catalyst could improve the catalytic activity significantly. The addition of Mg to the Cu-Pd/γ-Al2O3 catalyst could maintain and promote the formation of CuPd alloy active sites. Meanwhile, the basicity of the support was enhanced appropriately by Mg, which generated more basic sites (Al-Oδ−) to accelerate the dehydrogenation of alcohol and increased the rate of the whole coupled reaction. The 2-nitroaniline was completely converted over Cu-Pd/(Mg)γ-Al2O3 after reacting for six hours, and the yield of 2-methylbenzimidazole was 98.8%. The results of this work provide a simple method to develop a more efficient catalyst for the “alcohol-dehydrogenation, hydrogen transfer and hydrogenation” coupled reaction system.

scholarly journals Silicon Photonic Micro-Transceivers for Beyond 5G Environments

2021 ◽  
Vol 11 (22) ◽  
pp. 10955
Author(s):  
Kazuhiko Kurata ◽  
Luca Giorgi ◽  
Fabio Cavaliere ◽  
Liam O’Faolain ◽  
Sebastian A. Schulz ◽  
...  
Keyword(s):  
Quantum Dot ◽  
High Temperatures ◽  
Low Cost ◽  
Laser System ◽  
Data Rate ◽  
Ambient Temperatures ◽  
Quantum Dot Laser ◽  
Silicon Photonic ◽  
Order Of Magnitude ◽  
And Performance

Here, we report on the design and performance of a silicon photonic micro-transceiver required to operate in 5G and 6G environments at high ambient temperatures above 105 °C. The four-channel “IOCore” micro-transceiver incorporates a 1310 nm quantum dot laser system and operates at a data rate of 25 Gbps and higher. The 5 × 5 mm micro-transceiver chip benefits from a multimode coupling interface for low-cost assembly and robust connectivity at high temperatures as well as an optical redundancy scheme, which increases reliability by over an order of magnitude.

scholarly journals Detection of eye contact with deep neural networks is as accurate as human experts

2020 ◽  
Author(s):  
Eunji Chong ◽  
Elysha Clark-Whitney ◽  
Audrey Southerland ◽  
Elizabeth Stubbs ◽  
Chanel Miller ◽  
...  
Keyword(s):  
Neural Network ◽  
Eye Contact ◽  
Autism Spectrum ◽  
Point Of View ◽  
Gaze Behavior ◽  
Equivalence Tests ◽  
Social Settings ◽  
Automated Coding ◽  
Primary Means ◽  
And Performance

Eye contact is among the most primary means of social communication that humans use from the first months of life. Quantification of eye contact is valuable in various scenarios as a part of the analysis of social roles, communication skills, and medical screening. Estimating a subject's looking direction from video is a challenging task, but eye contact can be effectively captured by a wearable point-of-view camera which provides a unique viewpoint as a result of its configuration. While moments of eye contact from this viewpoint can be hand coded, such process tends to be laborious and subjective. In this work, we developed the first deep neural network model to automatically detect eye contact in egocentric video with accuracy equivalent to that of human experts. We trained a deep convolutional neural network using a dataset of 4,339,879 annotated images, consisting of 103 subjects with diverse demographic backgrounds. 57 have a diagnosis of Autism Spectrum Disorder. The network achieves overall precision 0.936 and recall 0.943 on 18 set-aside validation subjects, and performance is on par with 10 trained human coders with a mean precision 0.918 and recall 0.946. This result passes class equivalence tests in Cohen’s kappa scores (equivalence boundary of 0.025, p < .005), demonstrating that deep learning model can produce automated coding with a level of reliability comparable to human coders. The presented method will be instrumental in analyzing gaze behavior in naturalistic social settings by serving as a scalable, objective, and accessible tool for clinicians and researchers.

scholarly journals The reality of Educational accountability and its mechanisms among school leaders in public education schools in Sharourah governorate/ Najran

2019 ◽  
Vol 3 (11) ◽  
Author(s):  
Mohammed Qasim Almqablah
Keyword(s):  
Public Education ◽  
School Leaders ◽  
Point Of View ◽  
School Level ◽  
First Semester ◽  
Female Teachers ◽  
General Average ◽  
And Performance ◽  
High Degree ◽  
Academic Year

The study aimed to identify the reality of practicing accountability among school leaders in public education schools in Sharourah Governorate / Najran and the degree of accountability in the administrative and technical domains. To achieve this goal, the researcher used the analytical survey approach. The study was applied to a sample of )177 ( teachers, including (101) male teachers and (76) female teachers, in the first semester of the academic year 2018- 2019. The results of the study found that, the practice of accountability among the leaders of public education schools in Sharourah governorate / Najran from teachers point of view has got a general average (4.02), high rating, and according to the domains level, practicing accountability in administrative domain has got an average; (3.93), with a high rating, also, practicing accountability in the technical domain has got an average of (3.90) with a high degree. There were no statistically significant differences at the level of (0.05 = α) between the arithmetical averages of the total score for the degree of accountability in administrative and technical domains due to the differences in the variables of the study (years of experience and the scientific qualification). There were statistically significant differences in the degree of accountability in administrative and technical domains due to gender in favor of males; and in the variable of a school level in favor of high school. The study recommended the need to spread the culture of accountability, And to clarify the nature, methods, objectives and mechanisms for teachers, and the need to provide standards and performance indicators used in accountability process.

scholarly journals Large-area printing of ferroelectric surface and super-domains for efficient solar water splitting

2020 ◽  
Author(s):  
Yu Tian ◽  
Yaqing Wei ◽  
Minghui Pei ◽  
Rongrong Cao ◽  
Zhenao Gu ◽  
...  
Keyword(s):  
Water Splitting ◽  
Electric Fields ◽  
Electronic Structures ◽  
Active Sites ◽  
Large Area ◽  
Solar Water Splitting ◽  
High Efficient ◽  
Catalytic Sites ◽  
Order Of Magnitude ◽  
Magnitude Increase

Abstract Surface electronic structures of the photoelectrodes determine the activity and efficiency of the photoelectrochemical water splitting, but the controls of their surface structures and interfacial chemical reactions remain challenging. Here, we use ferroelectric BiFeO3 as a model system to demonstrate an efficient and controllable water splitting reaction by large-area constructing the hydroxyls-bonded surface. The up-shift of band edge positions at this surface enables and enhances the interfacial holes and electrons transfer through the hydroxyl-active-sites, leading to simultaneously enhanced oxygen and hydrogen evolutions. Furthermore, printing of ferroelectric super-domains with microscale checkboard up/down electric fields separates the distribution of reduction/oxidation catalytic sites, enhancing the charge separation and giving rise to an order of magnitude increase of the photocurrent. This large-area printable ferroelectric surface and super-domains offer an alternative platform for controllable and high-efficient photocatalysis.

Sign in / Sign up

Export Citation Format

Share Document