Dehydrocyclization of Diphenylamine to Carbazole Over Platinum Catalysts

2008 ◽  
Vol 73 (8-9) ◽  
pp. 1149-1160 ◽  
Author(s):  
Miroslav Vlčko ◽  
Zuzana Cvengrošová ◽  
Milan Hronec
Keyword(s):  
Citric Acid ◽  
Gas Phase ◽  
Platinum Catalysts ◽  
Pt Catalyst ◽  
Pt Catalysts ◽  
In Situ Reduction ◽  
Wet Impregnation ◽  
Very High

The gas-phase dehydrocyclization of diphenylamine (DPA) to carbazole over alumina-supported 0.4 wt.% Pt catalysts in a fix-bed reactor has been studied. The reaction was carried out at a temperature of 550 °C in the presence of hydrogen. All catalysts became well dispersed Pt after in situ reduction. Pt catalysts prepared in the presence of a competitive adsorbate (citric acid) were reasonably active during first hours on stream (DPA conversion higher than 90%). However, later, their activity decreased rapidly, except the catalyst prepared in the presence of a higher concentration of the competitive agent. The same trend was observed for the Pt catalyst prepared by wet impregnation. The activity of the catalysts prepared by a microemulsion technique was very high and stable during testing, the conversion of DPA being higher than 93%. However, the selectivities of catalysts prepared in the presence of citric acid gradually decreased with time on stream (TOS). The initial selectivityof such prepared catalysts for carbazole was about 60%. The same trend was observed for catalysts prepared by microemulsion technique. The highest selectivities, 73%, were obtained over the catalysts prepared by wet impregnation; it dropped after 6 days of testing to about 62%.

Relation Between CO2 Evolution and in situ Reduction of Nitrate in Wheat Leaves

1981 ◽  
Vol 8 (6) ◽  
pp. 515 ◽  
Author(s):  
MS Naik ◽  
DJD Nicholas
Keyword(s):  
Citric Acid ◽  
Nitrate Reduction ◽  
Citric Acid Cycle ◽  
Nitrate Assimilation ◽  
Co2 Evolution ◽  
In Situ Reduction ◽  
Acid Cycle ◽  
Nitrite Production ◽  
Wheat Leaves

In wheat leaf discs the evolution of 14CO2 from exogenously supplied 14C-labelled citric acid cycle intermediates was stimulated during the in situ anaerobic reduction of nitrate in the dark. Under these conditions, however, [1,4-14C]succinate was not metabolized. Similarly, when leaves were allowed to assimilate 14CO2 in the dark, thus producing endogenously labelled organic acids, the subsequent evolution of 14CO2 from discs prepared from these leaves was strongly dependent on nitrate reduction. A 1 : 1 stoichiometry between nitrite production and CO2 evolution was recorded during this in situ reduction of nitrate. The in situ reduction of nitrate was inhibited by malonate and D-malate and this effect was reversed by fumarate, probably by generating L-malate within the mitochondria. Mitochondrial NAD-malic enzyme (decarboxylating) (EC 1.1.1.38) was similarly inhibited competitively by malonate and D-malate, but not by succinate. These results indicate that the citric acid cycle dehydrogenases which generate CO2 supply NADH for nitrate reduction in wheat leaves. It is likely that, under anaerobic conditions, nitrate acts as an alternative oxidant to O2 for the NADH generated by the citric acid cycle dehydrogenases resulting in simultaneous evolution of CO2. This ensures that the citric acid cycle operates at the required rate for nitrate assimilation.

Carbon nanostructures formed on mesoporous silica by catalytic chemical vapor deposition of ethene

2008 ◽  
Vol 23 (2) ◽  
pp. 435-443 ◽  
Author(s):  
Lingxia Zhang ◽  
Jianlin Shi ◽  
Jiangtian Li ◽  
Zile Hua ◽  
Meiling Ruan
Keyword(s):  
Mesoporous Silica ◽  
Vapor Deposition ◽  
Carbon Nanostructures ◽  
Chemical Vapor ◽  
Coupling Agents ◽  
In Situ Reduction ◽  
Silane Coupling Agents ◽  
Wet Impregnation ◽  
Silane Coupling

Three different strategies, wet impregnation, in situ reduction, and grafting with silane coupling agents, have been used to introduce CoNi nanoparticles with different existing forms into mesoporous silica. These composites were used as catalysts to grow nanostructured carbons by catalytic chemical vapor deposition using ethene. Carbon nanotubes (CNTs) with different inner diameters can grow out of mesoporous silica particles incorporated with CoNi nanoclusters. Many fewer CNTs could be found in the pore channels of the sample prepared by using silane coupling agents than in those of the sample synthesized via wet impregnation. No CNTs formed in the pore channels of the sample prepared by in situ reduction. After the removal of silica, different carbon nanostructures have been obtained in the pore channels. Ordered graphite carbon mesostructure was obtained from the sample prepared by in situ reduction. Highly dispersed metal catalysts inside mesopore channels are favorable for the formation of graphite carbons with ordered mesostructures.

Quantitative end-group functionalization of PNIPAM from aqueous SET-LRP via in situ reduction of Cu(ii) with NaBH4

2016 ◽  
Vol 7 (29) ◽  
pp. 4802-4809 ◽  
Author(s):  
Mikhail Gavrilov ◽  
Zhongfan Jia ◽  
Virgil Percec ◽  
Michael J. Monteiro
Keyword(s):  
Click Reaction ◽  
In Situ Reduction ◽  
End Group Functionalization ◽  
Very High ◽  
End Group

Rapid in situ azidation and CuAAC ‘click’ reaction demonstrating very high chain-end functionality.

scholarly journals In Situ Observation of Electron-Beam-Induced Formation of Nano-Structures in PbTe

Nanomaterials ◽  
2021 ◽  
Vol 11 (1) ◽  
pp. 163
Author(s):  
Iryna Zelenina ◽  
Igor Veremchuk ◽  
Yuri Grin ◽  
Paul Simon
Keyword(s):  
Electron Beam ◽  
Gas Phase ◽  
Threshold Current ◽  
Threshold Current Density ◽  
Atomic Scale ◽  
In Situ Observation ◽  
Nano Structures ◽  
Transmission Electron ◽  
Initial Crystal

Nano-scaled thermoelectric materials attract significant interest due to their improved physical properties as compared to bulk materials. Well-shaped nanoparticles such as nano-bars and nano-cubes were observed in the known thermoelectric material PbTe. Their extended two-dimensional nano-layer arrangements form directly in situ through electron-beam treatment in the transmission electron microscope. The experiments show the atomistic depletion mechanism of the initial crystal and the recrystallization of PbTe nanoparticles out of the microparticles due to the local atomic-scale transport via the gas phase beyond a threshold current density of the beam.

scholarly journals Critical Dynamics of Defects and Mechanisms of Damage-Failure Transitions in Fatigue

Materials ◽  
2021 ◽  
Vol 14 (10) ◽  
pp. 2554
Author(s):  
Oleg Naimark ◽  
Vladimir Oborin ◽  
Mikhail Bannikov ◽  
Dmitry Ledon
Keyword(s):  
Fatigue Damage ◽  
Kinetic Equations ◽  
Experimental Methodology ◽  
Preliminary Deformation ◽  
Scaling Properties ◽  
In Situ Data ◽  
Number Of Cycles ◽  
Fish Eye ◽  
Very High

An experimental methodology was developed for estimating a very high cycle fatigue (VHCF) life of the aluminum alloy AMG-6 subjected to preliminary deformation. The analysis of fatigue damage staging is based on the measurement of elastic modulus decrement according to “in situ” data of nonlinear dynamics of free-end specimen vibrations at the VHCF test. The correlation of fatigue damage staging and fracture surface morphology was studied to establish the scaling properties and kinetic equations for damage localization, “fish-eye” nucleation, and transition to the Paris crack kinetics. These equations, based on empirical parameters related to the structure of the material, allows us to estimate the number of cycles for the nucleation and advance of fatigue crack.

scholarly journals A Pixel Design of a Branching Ultra-Highspeed Image Sensor

Sensors ◽  
2021 ◽  
Vol 21 (7) ◽  
pp. 2506
Author(s):  
Nguyen Hoai Ngo ◽  
Kazuhiro Shimonomura ◽  
Taeko Ando ◽  
Takayoshi Shimura ◽  
Heiji Watanabe ◽  
...  
Keyword(s):  
Image Sensor ◽  
Frame Rate ◽  
Front Side ◽  
Digital Signals ◽  
Memory Element ◽  
Image Capture ◽  
Readout Circuits ◽  
Pros And Cons ◽  
Very High

A burst image sensor named Hanabi, meaning fireworks in Japanese, includes a branching CCD and multiple CMOS readout circuits. The sensor is backside-illuminated with a light/charge guide pipe to minimize the temporal resolution by suppressing the horizontal motion of signal carriers. On the front side, the pixel has a guide gate at the center, branching to six first-branching gates, each bifurcating to second-branching gates, and finally connected to 12 (=6×2) floating diffusions. The signals are either read out after an image capture operation to replay 12 to 48 consecutive images, or continuously transferred to a memory chip stacked on the front side of the sensor chip and converted to digital signals. A CCD burst image sensor enables a noiseless signal transfer from a photodiode to the in-situ storage even at very high frame rates. However, the pixel count conflicts with the frame count due to the large pixel size for the relatively large in-pixel CCD memory elements. A CMOS burst image sensor can use small trench-type capacitors for memory elements, instead of CCD channels. However, the transfer noise from a floating diffusion to the memory element increases in proportion to the square root of the frame rate. The Hanabi chip overcomes the compromise between these pros and cons.

Catalytic dehydrogenation of amines to imines and the in-situ reduction of sulfoxides into sulfides

2021 ◽  
Author(s):  
Xixi Liu ◽  
Yanxin Wang ◽  
Bo Li ◽  
Bing Liu ◽  
Wei Wang ◽  
...  
Keyword(s):  
Catalytic Dehydrogenation ◽  
In Situ Reduction

scholarly journals An Atmospheric Origin for HCN-Derived Polymers on Titan

Processes ◽  
2021 ◽  
Vol 9 (6) ◽  
pp. 965
Author(s):  
Zoé Perrin ◽  
Nathalie Carrasco ◽  
Audrey Chatain ◽  
Lora Jovanovic ◽  
Ludovic Vettier ◽  
...  
Keyword(s):  
Chemical Composition ◽  
Gas Phase ◽  
Formation Process ◽  
Upper Atmosphere ◽  
Gas Mixture ◽  
Space Probe ◽  
Atmospheric Haze ◽  
Formation And Evolution ◽  
Haze Formation

Titan’s haze is strongly suspected to be an HCN-derived polymer, but despite the first in situ measurements by the ESA-Huygens space probe, its chemical composition and formation process remain largely unknown. To investigate this question, we simulated the atmospheric haze formation process, experimentally. We synthesized analogues of Titan’s haze, named Titan tholins, in an irradiated N2–CH4 gas mixture, mimicking Titan’s upper atmosphere chemistry. HCN was monitored in situ in the gas phase simultaneously with the formation and evolution of the haze particles. We show that HCN is produced as long as the particles are absent, and is then progressively consumed when the particles appear and grow. This work highlights HCN as an effective precursor of Titan’s haze and confirms the HCN-derived polymer nature of the haze.

Physicochemical properties of geopolymer composites with DFT calculations of in-situ reduction of graphene oxide

2021 ◽  
Author(s):  
Amun Amri ◽  
Ahmad Ainun Najib ◽  
Monita Olivia ◽  
Mohammednoor Altarawneh ◽  
Aman Syam ◽  
...  
Keyword(s):  
Graphene Oxide ◽  
Dft Calculations ◽  
Physicochemical Properties ◽  
In Situ Reduction ◽  
Geopolymer Composites

scholarly journals Influence of Hydrogeochemistry on Tunnel Drainage in Evaporitic Formations: El Regajal Tunnel Case Study (Aranjuez, Spain)

2021 ◽  
Vol 13 (3) ◽  
pp. 1505
Author(s):  
Ignacio Menéndez Pidal ◽  
Jose Antonio Mancebo Piqueras ◽  
Eugenio Sanz Pérez ◽  
Clemente Sáenz Sanz
Keyword(s):  
High Speed ◽  
Civil Engineering ◽  
Saturation Index ◽  
The Subject ◽  
Under Construction ◽  
Underground Flow ◽  
Very High ◽  
Over Time

Many of the large number of underground works constructed or under construction in recent years are in unfavorable terrains facing unusual situations and construction conditions. This is the case of the subject under study in this paper: a tunnel excavated in evaporitic rocks that experienced significant karstification problems very quickly over time. As a result of this situation, the causes that may underlie this rapid karstification are investigated and a novel methodology is presented in civil engineering where the use of saturation indices for the different mineral specimens present has been crucial. The drainage of the rock massif of El Regajal (Madrid-Toledo, Spain, in the Madrid-Valencia high-speed train line) was studied and permitted the in-situ study of the hydrogeochemical evolution of water flow in the Miocene evaporitic materials of the Tajo Basin as a full-scale testing laboratory, that are conforms as a whole, a single aquifer. The work provides a novel methodology based on the calculation of activities through the hydrogeochemical study of water samples in different piezometers, estimating the saturation index of different saline materials and the dissolution capacity of the brine, which is surprisingly very high despite the high electrical conductivity. The circulating brine appears unsaturated with respect to thenardite, mirabilite, epsomite, glauberite, and halite. The alteration of the underground flow and the consequent renewal of the water of the aquifer by the infiltration water of rain and irrigation is the cause of the hydrogeochemical imbalance and the modification of the characteristics of the massif. These modifications include very important loss of material by dissolution, altering the resistance of the terrain and the increase of the porosity. Simultaneously, different expansive and recrystallization processes that decrease the porosity of the massif were identified in the present work. The hydrogeochemical study allows the evolution of these phenomena to be followed over time, and this, in turn, may facilitate the implementation of preventive works in civil engineering.

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