scholarly journals Synthesis of Mesoporous Zeolites and Their Opportunities in Heterogeneous Catalysis

Catalysts ◽  
2021 ◽  
Vol 11 (12) ◽  
pp. 1541
Author(s):  
Bhupendra Kumar Singh ◽  
Yongseok Kim ◽  
Seungdon Kwon ◽  
Kyungsu Na
Keyword(s):  
Heterogeneous Catalysts ◽  
State Of The Art ◽  
Structural Characteristics ◽  
Shape Selectivity ◽  
Zeolite Framework ◽  
Mesoporous Zeolites ◽  
Scale Size ◽  
Catalytic Sites ◽  
Methanol To Hydrocarbon ◽  
Excellent Stability

Currently, zeolites are one of the most important classes of heterogeneous catalysts in chemical industries owing to their unique structural characteristics such as molecular-scale size/shape-selectivity, heterogenized single catalytic sites in the framework, and excellent stability in harsh industrial processes. However, the microporous structure of conventional zeolite materials limits their applications to small-molecule reactions. To alleviate this problem, mesoporous zeolitic frameworks were developed. In the last few decades, several methods have been developed for the synthesis of mesoporous zeolites; these zeolites have demonstrated greater lifetime and better performance than their bulk microporous counterparts in many catalytic processes, which can be explained by the rapid diffusion of reactant species into the zeolite framework and facile accessibility to bulky molecules through the mesopores. Mesoporous zeolites provide versatile opportunities not only in conventional chemical industries but also in emerging catalysis fields. This review presents many state-of-the-art mesoporous zeolites, discusses various strategies for their synthesis, and details their contributions to catalytic reactions including catalytic cracking, isomerization, alkylation and acylation, alternative fuel synthesis via methanol-to-hydrocarbon (MTH) and Fischer–Tropsch synthesis (FTS) routes, and different fine-chemical syntheses.

Catalysts for hydrogenation of CO2 into components of motor fuels

2020 ◽  
pp. 1-18
Author(s):  
Yu.V. Bilokopytov ◽  
◽  
S.L. Melnykova ◽  
N.Yu. Khimach ◽  
◽  
...  
Keyword(s):  
Carbon Dioxide ◽  
Heterogeneous Catalysts ◽  
Fossil Fuels ◽  
Catalyst Stability ◽  
Co2 Conversion ◽  
Active Components ◽  
Synthesis Conditions ◽  
Hydrogenation Of Co2 ◽  
Mesoporous Zeolites ◽  
Motor Fuels

CO2 is a harmful greenhouse gas, a product of chemical emissions, the combustion of fossil fuels and car exhausts, and it is a widely available source of carbon. The review considers various ways of hydrogenation of carbon dioxide into components of motor fuels - methanol, dimethyl ether, ethanol, hydrocarbons - in the presence of heterogeneous catalysts. At each route of conversion of CO2 (into oxygenates or hydrocarbons) the first stage is the formation of CO by the reverse water gas shift (rWGS) reaction, which must be taken into account when catalysts of process are choosing. The influence of chemical nature, specific surface area, particle size and interaction between catalyst components, as well as the method of its production on the CO2 conversion processes is analyzed. It is noted that the main active components of CO2 conversion into methanol are copper atoms and ions which interact with the oxide components of the catalyst. There is a positive effect of other metals oxides additives with strong basic centers on the surface on the activity of the traditional copper-zinc-aluminum oxide catalyst for the synthesis of methanol from the synthesis gas. The most active catalysts for the synthesis of DME from CO2 and H2 are bifunctional. These catalysts contain both a methanol synthesis catalyst and a dehydrating component, such as mesoporous zeolites with acid centers of weak and medium strength, evenly distributed on the surface. The synthesis of gasoline hydrocarbons (≥ C5) is carried out through the formation of CO or CH3OH and DME as intermediates on multifunctional catalysts, which also contain zeolites. Hydrogenation of CO2 into ethanol can be considered as an alternative to the synthesis of ethanol through the hydration of ethylene. High activation energy of carbon dioxide, harsh synthesis conditions as well as high selectivity for hydrocarbons, in particular methane remains the main problems. Further increase of selectivity and efficiency of carbon dioxide hydrogenation processes involves the use of nanocatalysts taking into account the mechanism of CO2 conversion reactions, development of methods for removing excess water as a by-product from the reaction zone and increasing catalyst stability over time.

Dissolution and Performing Homogeneous Photocatalysis of Polymeric Carbon Nitride

2018 ◽  
Author(s):  
Chaofeng Huang ◽  
Jing Wen ◽  
Yanfei Shen ◽  
Fei He ◽  
Li Mi ◽  
...  
Keyword(s):  
Conjugated Polymer ◽  
Carbon Nitride ◽  
Heterogeneous Catalysts ◽  
Methane Sulfonic Acid ◽  
Environment Friendly ◽  
The Poor ◽  
Catalytic Sites ◽  
Homogeneous Photocatalysis ◽  
Polymeric Carbon ◽  
First Time

<a></a><a>As a metal-free conjugated polymer, carbon nitride (CN) has attracted tremendous attention as heterogeneous (photo)catalysts. </a><a></a><a>By following prototype of enzymes, making all catalytic sites of accessible via homogeneous reactions is a promising approach toward maximizing CN activity, but hindered due to </a><a></a><a>the poor insolubility of CN</a>. Herein, we report the dissolution of CN in environment-friendly methane sulfonic acid and the homogeneous photocatalysis driven by CN for the first time with the activity boosted up to 10-times, comparing to the heterogeneous counterparts. Moreover, facile recycling and reusability, the <a>hallmark</a> of heterogeneous catalysts, were kept for the homogeneous CN photocatalyst via reversible precipitation using poor solvents. It opens new vista of CN in homogeneous catalysis and offers a successful example of polymeric catalysts in bridging gaps of homo/heterogeneous catalysis.

Selective Cyclohexene Oxidation to Allylic Compounds over Cu-triazole Framework via Homolytic Activation of Hydrogen Peroxide

2021 ◽  
Author(s):  
Panyapat Ponchai ◽  
Kanyaporn Adpakpang ◽  
Sareeya Bureekaew
Keyword(s):  
Hydrogen Peroxide ◽  
Heterogeneous Catalysts ◽  
Metal Organic Frameworks ◽  
Porous Structures ◽  
Cyclohexene Oxidation ◽  
Catalytic Sites ◽  
P Utilization ◽  
Metal Organic ◽  
Activation Of Hydrogen Peroxide

Utilization of metal-organic frameworks as heterogeneous catalysts is crucial owing to their abundant catalytic sites and well-defined porous structures. Highly robust [Cu3(trz)3(μ3-OH)(OH)2(H2O)4]∙2H2O (trz = 1,2,4-triazole) was employed as a catalyst...

scholarly journals Introduction to redundancy rules: the continuous wavelet transform comes of age

2018 ◽  
Vol 376 (2126) ◽  
pp. 20170258 ◽  
Author(s):  
Paul S. Addison
Keyword(s):  
Wavelet Transform ◽  
Continuous Wavelet Transform ◽  
State Of The Art ◽  
Structural Characteristics ◽  
Continuous Wavelet ◽  
Theme Issue ◽  
Current State ◽  
Analysis Methods ◽  
Wide Range ◽  
New Form

Redundancy: it is a word heavy with connotations of lacking usefulness. I often hear that the rationale for not using the continuous wavelet transform (CWT)—even when it appears most appropriate for the problem at hand—is that it is ‘redundant’. Sometimes the conversation ends there, as if self-explanatory. However, in the context of the CWT, ‘redundant’ is not a pejorative term, it simply refers to a less compact form used to represent the information within the signal. The benefit of this new form—the CWT—is that it allows for intricate structural characteristics of the signal information to be made manifest within the transform space, where it can be more amenable to study: resolution over redundancy. Once the signal information is in CWT form, a range of powerful analysis methods can then be employed for its extraction, interpretation and/or manipulation. This theme issue is intended to provide the reader with an overview of the current state of the art of CWT analysis methods from across a wide range of numerate disciplines, including fluid dynamics, structural mechanics, geophysics, medicine, astronomy and finance. This article is part of the theme issue ‘Redundancy rules: the continuous wavelet transform comes of age’.

Towards highly active heterogeneous catalysts via a sequential noncovalent bonding strategy

2021 ◽  
Author(s):  
Ruixue Wang ◽  
Ying Yue ◽  
Huiying Wei ◽  
Jinxin Guo ◽  
Yanzhao Yang
Keyword(s):  
Catalytic Activity ◽  
Heterogeneous Catalysts ◽  
High Catalytic Activity ◽  
Synthetic Route ◽  
Surface Ligands ◽  
Highly Active ◽  
Noncovalent Bonding ◽  
Excellent Stability

Here, a novel synthetic route of ceria-based nanocatalysts with high catalytic activity and excellent stability was constructed by utilizing function groups from surface ligands. The surface of ceria nanorods were...

scholarly journals Discovering Language Properties through Corpus-Based Dictionary Data Analysis

2017 ◽  
Vol 6 (2) ◽  
pp. 61-70
Author(s):  
Paul Lyddon ◽  
Keyword(s):  
Data Analysis ◽  
Language Use ◽  
State Of The Art ◽  
Structural Characteristics ◽  
Language Teacher ◽  
Linguistic Data ◽  
Large Samples ◽  
Widespread Availability ◽  
Real Language

To reveal underlying patterns in real language use, linguists have increasingly come to rely on corpus analyses, involving the evaluation of statistical frequencies in generally sizable bodies of natural linguistic data. However, accessing and analyzing large samples of raw language is neither always practical nor even truly necessary, especially in cases pertaining to structural characteristics. In fact, the requisite data can oftentimes be gleaned from a state-of-the-art (i.e., corpus-based) dictionary. Moreover, given the widespread availability of easily searchable electronic dictionaries nowadays, almost any language teacher or learner can use one to answer a number of these types of queries. This paper illustrates this claim with a step-by-step analysis of corpus-based dictionary data for the purpose of formulating the sound-symbol relations in English words with vowels preceding –gh.

scholarly journals Coloring Graph Neural Networks for Node Disambiguation

2020 ◽  
Author(s):  
George Dasoulas ◽  
Ludovic Dos Santos ◽  
Kevin Scaman ◽  
Aladin Virmaux
Keyword(s):  
Neural Networks ◽  
Message Passing ◽  
State Of The Art ◽  
Structural Characteristics ◽  
Expressive Power ◽  
Continuous Functions ◽  
Graph Classification ◽  
Node Attributes ◽  
Graph Neural Networks ◽  
Coloring Graph

In this paper, we show that a simple coloring scheme can improve, both theoretically and empirically, the expressive power of Message Passing Neural Networks (MPNNs). More specifically, we introduce a graph neural network called Colored Local Iterative Procedure (CLIP) that uses colors to disambiguate identical node attributes, and show that this representation is a universal approximator of continuous functions on graphs with node attributes. Our method relies on separability, a key topological characteristic that allows to extend well-chosen neural networks into universal representations. Finally, we show experimentally that CLIP is capable of capturing structural characteristics that traditional MPNNs fail to distinguish, while being state-of-the-art on benchmark graph classification datasets.

scholarly journals Understanding the Catalytic Activity of Microporous and Mesoporous Zeolites in Cracking by Experiments and Simulations

Catalysts ◽  
2021 ◽  
Vol 11 (9) ◽  
pp. 1114
Author(s):  
Shih-Cheng Li ◽  
Yen-Chun Lin ◽  
Yi-Pei Li
Keyword(s):  
Catalytic Activity ◽  
Active Site ◽  
Petrochemical Industry ◽  
Molecular Level ◽  
Shape Selectivity ◽  
Zeolite Catalysts ◽  
Hydrocarbon Cracking ◽  
Mesoporous Zeolites ◽  
Secondary Reactions ◽  
Pros And Cons

Porous zeolite catalysts have been widely used in the industry for the conversion of fuel-range molecules for decades. They have the advantages of higher surface area, better hydrothermal stability, and superior shape selectivity, which make them ideal catalysts for hydrocarbon cracking in the petrochemical industry. However, the catalytic activity and selectivity of zeolites for hydrocarbon cracking are significantly affected by the zeolite topology and composition. The aim of this review is to survey recent investigations on hydrocarbon cracking and secondary reactions in micro- and mesoporous zeolites, with the emphasis on the studies of the effects of different porous environments and active site structures on alkane adsorption and activation at the molecular level. The pros and cons of different computational methods used for zeolite simulations are also discussed in this review.

Papain-like peptidases: structure, function, and evolution

2013 ◽  
Vol 4 (3) ◽  
pp. 287-308 ◽  
Author(s):  
Marko Novinec ◽  
Brigita Lenarčič
Keyword(s):  
Active Site ◽  
State Of The Art ◽  
Structural Characteristics ◽  
Extracellular Matrix Remodeling ◽  
Matrix Remodeling ◽  
Structural Elements ◽  
Processing Enzymes ◽  
Physiological Processes ◽  
Cysteine Cathepsins ◽  
Pathological Conditions

AbstractPapain-like cysteine peptidases are a diverse family of peptidases found in most known organisms. In eukaryotes, they are divided into multiple evolutionary groups, which can be clearly distinguished on the basis of the structural characteristics of the proenzymes. Most of them are endopeptidases; some, however, evolved into exopeptidases by obtaining additional structural elements that restrict the binding of substrate into the active site. In humans, papain-like peptidases, also called cysteine cathepsins, act both as non-specific hydrolases and as specific processing enzymes. They are involved in numerous physiological processes, such as antigen presentation, extracellular matrix remodeling, and hormone processing. Their activity is tightly regulated and dysregulation of one or more cysteine cathepsins can result in severe pathological conditions, such as cardiovascular diseases and cancer. Other organisms can utilize papain-like peptidases for different purposes and they are often part of host-pathogen interactions. Numerous parasites, such as Plasmodium and flukes, utilize papain-like peptidases for host invasion, whereas plants, in contrast, use these enzymes for host defense. This review presents a state-of-the-art description of the structure and phylogeny of papain-like peptidases as well as an overview of their physiological and pathological functions in humans and in other organisms.

Tracking Study on International Large Scale Centrifugal Shakers of 40g-t and Key Technology

2012 ◽  
Vol 256-259 ◽  
pp. 145-148
Author(s):  
Yong Zhi Wang ◽  
Wei Ming Wang ◽  
Xiao Ming Yuan
Keyword(s):  
Earthquake Engineering ◽  
Large Scale ◽  
State Of The Art ◽  
Structural Characteristics ◽  
The United States ◽  
Test Methods ◽  
Power Sources ◽  
Geotechnical Earthquake Engineering ◽  
The World ◽  
Support Devices

Centrifugal shakers are widely regarded as state-of-the-art testing facilities of geotechnical earthquake engineering for providing an effective solution for the unequal gravity stress between models and prototypes typically in traditional test methods. Currently only two large centrifugal shakers are in the United States and Japan respectively, whereas no one has been established in China. Such situation remarkably lags behind the serious seismic conditions and the world largest construction scale of civil engineering in China. Due to the lack of experiences and the lot of difficulty, one significant task of large scale centrifugal shaker construction is tracking study on the world advanced facilities. The paper outlines the technology parameters and components of the two existing large centrifugal shakers. Through investigating and comparing the structural characteristics of the two facilities, the differences between the two are summed up and analyzed. The analyses indicate that key technologies mainly centre upon centrifuge arms, centrifuge buckets, exciting devices, power sources and guide-support devices. The results can provide assistance and reference to the construction of foreign and domestic large scale centrifugal shakers.

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