scholarly journals Delocalized electron effect on single metal sites in ultrathin conjugated microporous polymer nanosheets for boosting CO2 cycloaddition

2020 ◽  
Vol 6 (17) ◽  
pp. eaaz4824 ◽  
Author(s):  
Xiaofei Zhang ◽  
Haitao Liu ◽  
Pengfei An ◽  
Yanan Shi ◽  
Jianyu Han ◽  
...  
Keyword(s):  
Oxidation State ◽  
Active Sites ◽  
Heterogeneous Catalysts ◽  
Acid Sites ◽  
Molecular Engineering ◽  
Reaction Conditions ◽  
Tert Butyl ◽  
Conjugated Microporous Polymer ◽  
Microporous Polymer ◽  
Delocalized Electron

CO2 cycloaddition with epoxides at low temperature and pressure has been broadly recognized as an ambitious but challenging goal, which requires the catalysts to have precisely controlled Lewis acid sites. Here, we demonstrate that both stereochemical environment and oxidation state of single cobalt active sites in cobalt tetraaminophthalocyanine [CoPc(NH2)4] are finely tuned via molecular engineering with 2,5-di-tert-butyl-1,4-benzoquinone (DTBBQ). Notably, DTBBQ incorporation not only enables formation of 5-nm-thick conjugated microporous polymer (CMP) nanosheets due to the steric hindrance effect of tert-butyl groups but also makes isolated cobalt sites with high oxidation state due to the presence of delocalized electron-withdrawing effect of alkene groups in DTBBQ via conjugated skeleton. Notably, when used as heterogeneous catalysts for CO2 cycloaddition with different epoxides, single cobalt active sites on the ultrathin CMP nanosheets exhibit unprecedentedly high activity and excellent stability under mild reaction conditions.

Salen–porphyrin-based conjugated microporous polymer supported Pd nanoparticles: highly efficient heterogeneous catalysts for aqueous C–C coupling reactions

2019 ◽  
Vol 7 (6) ◽  
pp. 2660-2666 ◽  
Author(s):  
Pengyao Ju ◽  
Shujie Wu ◽  
Qing Su ◽  
Xiaodong Li ◽  
Ziqian Liu ◽  
...  
Keyword(s):  
High Performance ◽  
Heterogeneous Catalysts ◽  
Pd Nanoparticles ◽  
Coupling Reactions ◽  
Highly Efficient ◽  
Conjugated Microporous Polymer ◽  
Microporous Polymer ◽  
Polymer Supported ◽  
Supported Pd

Salen–porphyrin-based CMP supported Pd nanoparticles were employed as high-performance heterogeneous catalysts for aqueous Suzuki–Miyaura and Heck–Mizoroki coupling reactions.

scholarly journals Critical Review of Low-Temperature CO Oxidation and Hysteresis Phenomenon on Heterogeneous Catalysts

Catalysts ◽  
2018 ◽  
Vol 8 (12) ◽  
pp. 660 ◽  
Author(s):  
Rola Al Soubaihi ◽  
Khaled Saoud ◽  
Joydeep Dutta
Keyword(s):  
Low Temperature ◽  
Co Oxidation ◽  
Active Sites ◽  
Heterogeneous Catalysts ◽  
Catalyst Activity ◽  
Cost Effective ◽  
Hysteresis Phenomenon ◽  
Reaction Conditions ◽  
Kinetic Oscillations ◽  
Low Temperature Co Oxidation

There is a growing demand for new heterogeneous catalysts for cost-effective catalysis. Currently, the hysteresis phenomenon during low-temperature CO oxidation is an important topic in heterogeneous catalysis. Hysteresis provides important information about fluctuating reaction conditions that affect the regeneration of active sites and indicate the restoration of catalyst activity. Understanding its dynamic behavior, such as hysteresis and self-sustained kinetic oscillations, during CO oxidation, is crucial for the development of cost-effective, stable and long-lasting catalysts. Hysteresis during CO oxidation has a direct influence on many industrial processes and its understanding can be beneficial to a broad range of applications, including long-life CO2 lasers, gas masks, catalytic converters, sensors, indoor air quality, etc. This review considers the most recent reported advancements in the field of hysteresis behavior during CO oxidation which shed light on the origin of this phenomenon and the parameters that influence the type, shape, and width of the conversion of the hysteresis curves.

scholarly journals Heterogeneous Catalysts for the Conversion of Glucose into 5-Hydroxymethyl Furfural

Catalysts ◽  
2021 ◽  
Vol 11 (7) ◽  
pp. 861
Author(s):  
Christiaan H. L. Tempelman ◽  
Ryan Oozeerally ◽  
Volkan Degirmenci
Keyword(s):  
Lignocellulosic Biomass ◽  
Active Sites ◽  
Heterogeneous Catalysts ◽  
Supported Catalysts ◽  
Metal Organic Frameworks ◽  
Reaction Conditions ◽  
Catalytic Systems ◽  
Hydroxymethyl Furfural ◽  
Potential Applications ◽  
Metal Organic

Lignocellulosic biomass, a cheap and plentiful resource, could play a key role in the production of sustainable chemicals. The simple sugars contained in the renewable lignocellulosic biomass can be converted into commercially valuable products such as 5-hydroxymethyl furfural (HMF). A platform molecule, HMF can be transformed into numerous chemical products with potential applications in a wide variety of industries. Of the hexoses contained in the lignocellulosic biomass, the successful production of HMF from glucose has been a challenge. Various heterogeneous catalysts have been proposed over the last decade, ranging from zeolites to metal organic frameworks. The reaction conditions vary in the reports in the literature, which makes it difficult to compare catalysts reported in different studies. In addition, the slight variations in the synthesis of the same material in different laboratories may affect the activity results, because the selectivity towards desired products in this transformation strongly depends on the nature of the active sites. This poses another difficulty for the comparison of different reports. Furthermore, over the last decade the new catalytic systems proposed have increased profoundly. In this article, we summarize the heterogeneous catalysts: Metal Organic Frameworks (MOFs), zeolites and conventional supported catalysts, that have been reported in the recent literature and provide an overview of the observed catalytic activity, in order to provide a comparison.

Fe/N-doped carbon nanofibers with Fe3O4/Fe2C nanocrystals enchased as electrocatalysts for efficient oxygen reduction reaction

2019 ◽  
Vol 6 (9) ◽  
pp. 2296-2303 ◽  
Author(s):  
Mengfei Li ◽  
Zhenyu Xiao ◽  
Lili Fan ◽  
Fengmei Wang ◽  
Xinxin Du ◽  
...  
Keyword(s):  
Oxygen Reduction Reaction ◽  
Oxygen Reduction ◽  
Carbon Nanofibers ◽  
Carbon Material ◽  
Active Sites ◽  
Reduction Reaction ◽  
Conjugated Microporous Polymer ◽  
Microporous Polymer

A Fe-based carbon material with multi active sites of Fe–Nx, Fe3O4 and Fe2C for oxygen reduction was synthesized through facile pyrolysis of a Fe–porphyrin conjugated microporous polymer.

scholarly journals Enhancing Methane Aromatization Performance by Reducing the Particle Size of Molybdenum Oxide

Nanomaterials ◽  
2020 ◽  
Vol 10 (10) ◽  
pp. 1991
Author(s):  
Jing Hu ◽  
Jinghai Liu ◽  
Jinglin Liu ◽  
Yangyang Li ◽  
Peihe Li ◽  
...  
Keyword(s):  
Molybdenum Oxide ◽  
Type Species ◽  
Active Sites ◽  
High Performance ◽  
Acid Sites ◽  
Reaction Conditions ◽  
Methane Aromatization ◽  
Synthetic Strategy ◽  
Aromatization Reaction ◽  
Molybdenum Oxide Nanoparticles

Efficient use of natural gas to produce aromatics is an attractive subject; the process requires catalysts that possess high-performance active sites to activate stable C–H bonds. Here, we report a facile synthetic strategy to modify HMCM-49 with small molybdenum oxide nanoparticles. Due to the higher sublimability of nano-MoO3 particles than commercial MoO3, they more easily enter into the channels of HMCM-49 and associate with Brønsted acid sites to form active MoCx-type species under calcination and reaction conditions. Compared with commercial MoO3 modified MCM-49, nano-MoO3 modified MCM-49 exhibits higher methane conversion (13.2%), higher aromatics yield (9.1%), and better stability for the methane aromatization reaction.

scholarly journals Design and control of Lewis acid sites in Sn-substituted microporous architectures

2016 ◽  
Vol 4 (15) ◽  
pp. 5706-5712 ◽  
Author(s):  
Khaled M. H. Mohammed ◽  
Arunabhiram Chutia ◽  
June Callison ◽  
Peter P. Wells ◽  
Emma K. Gibson ◽  
...  
Keyword(s):  
Lewis Acid ◽  
Active Sites ◽  
Heterogeneous Catalysts ◽  
Acid Sites ◽  
Bronsted Acid ◽  
Lewis Acid Sites ◽  
Brønsted Acid Sites ◽  
Brönsted Acid ◽  
Brönsted Acid Sites ◽  
And Control

Modulation of tetrahedral Sn(iv) active sites in framework architectures influences the generation of Lewis and Brønsted acid sites in heterogeneous catalysts.

What catalysis needs from the electron microscopist

1988 ◽  
Vol 46 ◽  
pp. 694-695
Author(s):  
Alexis T. Bell
Keyword(s):  
Active Sites ◽  
Heterogeneous Catalysts ◽  
Catalyst Deactivation ◽  
Surface Composition ◽  
Internal Surface ◽  
Active Phase ◽  
Atomic Scale ◽  
Metal Catalyst ◽  
Internal Surface Area ◽  
Porous Support

Heterogeneous catalysts, used in industry for the production of fuels and chemicals, are microporous solids characterized by a high internal surface area. The catalyticly active sites may occur at the surface of the bulk solid or of small crystallites deposited on a porous support. An example of the former case would be a zeolite, and of the latter, a supported metal catalyst. Since the activity and selectivity of a catalyst are known to be a function of surface composition and structure, it is highly desirable to characterize catalyst surfaces with atomic scale resolution. Where the active phase is dispersed on a support, it is also important to know the dispersion of the deposited phase, as well as its structural and compositional uniformity, the latter characteristics being particularly important in the case of multicomponent catalysts. Knowledge of the pore size and shape is also important, since these can influence the transport of reactants and products through a catalyst and the dynamics of catalyst deactivation.

scholarly journals Selective Styrene Oxidation to Benzaldehyde over Recently Developed Heterogeneous Catalysts

Molecules ◽  
2021 ◽  
Vol 26 (6) ◽  
pp. 1680
Author(s):  
Marta A. Andrade ◽  
Luísa M. D. R. S. Martins
Keyword(s):  
Heterogeneous Catalysts ◽  
Carbon Materials ◽  
Oxygen Species ◽  
Styrene Oxidation ◽  
Reaction Conditions ◽  
Reactive Metal ◽  
Catalytic Systems ◽  
Tert Butyl Hydroperoxide ◽  
Metal Organic ◽  
Important Intermediate

The selective oxidation of styrene under heterogeneous catalyzed conditions delivers environmentally friendly paths for the production of benzaldehyde, an important intermediate for the synthesis of several products. The present review explores heterogeneous catalysts for styrene oxidation using a variety of metal catalysts over the last decade. The use of several classes of supports is discussed, including metal–organic frameworks, zeolites, carbon materials and silicas, among others. The studied catalytic systems propose as most used oxidants tert-butyl hydroperoxide, and hydrogen peroxide and mild reaction conditions. The reaction mechanism proceeds through the generation of an intermediate reactive metal–oxygen species by catalyst-oxidant interactions. Overall, most of the studies highlight the synergetic effects among the metal and support for the activity and selectivity enhancement.

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