scholarly journals Escaping undesired gas-phase chemistry: Microwave-driven selectivity enhancement in heterogeneous catalytic reactors

2019 ◽  
Vol 5 (3) ◽  
pp. eaau9000 ◽  
Author(s):  
A. Ramirez ◽  
J. L. Hueso ◽  
M. Abian ◽  
M. U. Alzueta ◽  
R. Mallada ◽  
...  
Keyword(s):  
Gas Phase ◽  
Solid Phase ◽  
Catalyst Support ◽  
Accurate Estimation ◽  
Gas Phase Reactions ◽  
Catalytic Reactors ◽  
Heterogeneous Catalytic ◽  
Catalyst Composition ◽  
Heterogeneous Catalytic Processes ◽  
Phase Chemistry

Research in solid-gas heterogeneous catalytic processes is typically aimed toward optimization of catalyst composition to achieve a higher conversion and, especially, a higher selectivity. However, even with the most selective catalysts, an upper limit is found: Above a certain temperature, gas-phase reactions become important and their effects cannot be neglected. Here, we apply a microwave field to a catalyst-support ensemble capable of direct microwave heating (MWH). We have taken extra precautions to ensure that (i) the solid phase is free from significant hot spots and (ii) an accurate estimation of both solid and gas temperatures is obtained. MWH allows operating with a catalyst that is significantly hotter than the surrounding gas, achieving a high conversion on the catalyst while reducing undesired homogeneous reactions. We demonstrate the concept with the CO2-mediated oxidative dehydrogenation of isobutane, but it can be applied to any system with significant undesired homogeneous contributions.

scholarly journals Application of carbonized ion exchange resin beads as catalyst support for gas phase hydrogenation processes

2019 ◽  
Vol 129 (1) ◽  
pp. 85-94 ◽  
Author(s):  
Ádám Prekob ◽  
Viktória Hajdu ◽  
Gábor Muránszky ◽  
István Kocserha ◽  
Béla Fiser ◽  
...  
Keyword(s):  
Ion Exchange ◽  
Gas Phase ◽  
Exchange Resin ◽  
Catalyst Surface ◽  
Catalyst Support ◽  
Pd Nanoparticles ◽  
Ion Exchange Resin ◽  
X Ray ◽  
Heterogeneous Catalytic ◽  
Resin Beads

Abstract Carbonized ion exchange resin beads were prepared as catalyst for gas phase hydrogenation processes. Amberlite IR 120 polystyrene based sulfonated ion exchange beads were carbonized at 900 °C. The process of carbonization was monitored by FTIR combined thermogravimetric analysis. During the carbonization formed sulfur dioxide, carbon dioxide and organic compounds. The carbon pearls were used as catalyst support for Pd nanoparticles. The catalyst was characterized by scanning electron microscopy and X-ray diffractometry. The diameters of the palladium nanoparticles on the catalyst surface were between 15 and 50 nm, but bigger aggregates were also detected. The catalyst was tested during the gas phased heterogeneous catalytic hydrogenation of 1-butene. The hydrogenation process was followed by FTIR measurements, 93% conversion was reached after 10 min.

Si + SiH4 Reactions and Implications for Hot-Wire CVD of a-Si:H: Computational Studies

2000 ◽  
Vol 609 ◽  
Author(s):  
Richard P. Muller ◽  
Jason K. Holt ◽  
David G. Goodwin ◽  
William A. Goddard
Keyword(s):  
Quantum Chemistry ◽  
Amorphous Silicon ◽  
Gas Phase ◽  
Computational Studies ◽  
Hot Wire ◽  
Gas Phase Reactions ◽  
High Quality ◽  
Gas Phase Chemistry ◽  
Si Films ◽  
Phase Chemistry

ABSTRACTGas phase chemistry is believed to play an important role in hot-wire CVD of amorphous silicon, serving to convert the highly-reactive atomic Si produced at the wire into a less-reactive species by reaction with ambient SiH4. In this paper, we use quantum chemistry computations (B3LYP/cc-pvTZ) to examine the energetics and rates of possible gas-phase reactions between Si and SiH4. The results indicate that formation of disilyne (Si2H2) is energetically favorable. Unlike other products of this reaction, Si2H2 does not require collisional stabilization, and thus this species is the most likely candidate for a benevolent precursor that participates in the growth of high-quality Si films.

Oxidative dealkylation of aromatic amines by "bare" FeO+ in the gas phase

1999 ◽  
Vol 77 (5-6) ◽  
pp. 774-780 ◽  
Author(s):  
Mark Brönstrup ◽  
Detlef Schröder ◽  
Helmut Schwarz
Keyword(s):  
Gas Phase ◽  
Bond Activation ◽  
Isotope Effects ◽  
Gas Phase Reactions ◽  
Electron Transfer Mechanism ◽  
Gas Phase Chemistry ◽  
Kinetic Isotope ◽  
Phase Chemistry ◽  
Cytochrome P 450 ◽  
Mass Spectrometric Techniques

The gas-phase oxidations of aniline, N-methylaniline, and N,N-dimethylaniline by FeO+ cation are examined by using mass spectrometric techniques. Although bare FeO+ is capable of hydroxylating aromatic C—H bonds, the fate of the oxidation of arylamines is determined by docking of the FeO+ unit at nitrogen. The major reactions of the metastable aniline/FeO+ complex are losses of molecular hydrogen, ammonia, and water, all involving at least one N-H proton. N-alkylation results in a complete shift of the course of the reaction. The unimolecular processes observed can be regarded as initial steps of an oxidative dealkylation of the amines mediated by FeO+. More detailed mechanistic insight is obtained by examining the C—H(D) bond activation of N-methyl-N-([D3]-methyl)aniline by bare and ligated FeO+ species. The gas-phase reactions of FeO+ with methylanilines show some similarities to the enzymatic dealkylation of amines by cytochrome P-450. The kinetic isotope effects observed experimentally suggest an electron transfer mechanism for the gas-phase reaction.Key words: mass spectrometry, gas-phase chemistry, iron, dealkylation, N,N-dimethylaniline.

Selective oxidations in micro-structured catalytic reactors—For gas-phase reactions and specifically for fuel processing for fuel cells

2007 ◽  
Vol 120 (1) ◽  
pp. 2-20 ◽  
Author(s):  
G. Kolb ◽  
V. Hessel ◽  
V. Cominos ◽  
C. Hofmann ◽  
H. Löwe ◽  
...  
Keyword(s):  
Fuel Cells ◽  
Gas Phase ◽  
Gas Phase Reactions ◽  
Catalytic Reactors ◽  
Fuel Processing

scholarly journals The Effect of an Inert Solid Reservoir on Molecular Abundances in Dense Interstellar Clouds

2012 ◽  
Vol 21 (4) ◽  
Author(s):  
Juris Kalvāns ◽  
Ivar Shmeld
Keyword(s):  
Gas Phase ◽  
Reference Model ◽  
Solid Phase ◽  
Chemical Species ◽  
Interstellar Gas ◽  
Interstellar Clouds ◽  
Major Chemical ◽  
Molecular Abundances ◽  
Phase Chemistry ◽  
Grain Surface

AbstractThe question, what is the role of freeze-out of chemical species in determining the molecular abundances in the interstellar gas is a matter of debate. We investigate a theoretical case of a dense interstellar molecular cloud core by time-dependent modeling of chemical kinetics, where grain surface reactions deliberately are not included. That means, the gas-phase and solid-phase abundances are influenced only by gas reactions, accretion on grains and desorption. We compare the results to a reference model where no accretion occurs, and only gas-phase reactions are included. We can trace that the purely physical processes of molecule accretion and desorption have major chemical consequences on the gas-phase chemistry. The main effect of introduction of the gas-grain interaction is long-term molecule abundance changes that come nowhere near an equilibrium during the typical lifetime of a prestellar core.

Investigations into the Mechanisms of Flame Retardation on Wool

1977 ◽  
Vol 47 (11) ◽  
pp. 699-711 ◽  
Author(s):  
P. G. Gordon ◽  
D. T. W. McMahon ◽  
L. J. Stephens
Keyword(s):  
Hydrochloric Acid ◽  
Boric Acid ◽  
Gas Phase ◽  
Solid Phase ◽  
Preliminary Investigation ◽  
Sulfamic Acid ◽  
Antimony Oxide ◽  
Gas Phase Reactions ◽  
System A ◽  
Flame Retardation

A number of flame-retardant systems have been applied to wool, and their flame-inhibiting efficiencies in atmospheres containing oxygen and nitrous oxide have been compared in order to explore the mechanisms by which they operate. The retardant systems investigated include phosphoric acid, sulfuric acid, sulfamic acid, and their ammonium salts, hexafluorophosphate, borax, boric acid, fluoroborate, antimony oxide/hydrochloric acid, hexafluorozirconate, hexafluorotitanate, hexafluorostannate, and dichromate. Most of the systems apparently operate in the solid phase though by different mechanisms. The antimony-based system inhibits in the gas phase. The chromium system, as well as catalyzing the thermal decomposition of wool, also inhibits gas-phase reactions, probably by a heterogeneous mechanism. Fluorostannate when padded onto wool also exhibits gase-phase inhibition properties, but when exhausted onto wool it appears to inhibit in the solid phase. The fluorotitanate treatment shows a dependence on the nature of the oxidizing atmosphere, but this may be due to the fact that a metal oxide-oxygen species complex is necessary for retardation. Fluorozirconate does not show the same dependence, though it is closely related chemically to the fluorotitanate system. A preliminary investigation has been made into the effectiveness of combinations of the padded fluorozirconate system with the sulfamic acid, fluoroborate, boric acid, and antimony oxide/hydrochloric acid systems.

MOVPE GaN Gas-Phase Chemistry for Reactor Design and Optimization

1996 ◽  
Vol 449 ◽  
Author(s):  
S. A. Safvi ◽  
J. M. Redwing ◽  
A. Thon ◽  
J. S. Flynn ◽  
M. A. Tischler ◽  
...  
Keyword(s):  
Growth Rate ◽  
Gas Phase ◽  
Growth Rates ◽  
Operating Conditions ◽  
Gas Phase Reactions ◽  
Group V ◽  
Group Iii ◽  
Design And Optimization ◽  
Gas Phase Chemistry ◽  
Phase Chemistry

ABSTRACTThe results of gas phase decomposition studies are used to construct a chemistry model which is compared to data obtained from an experimental MOVPE reactor. A flow tube reactor is used to study gas phase reactions between trimethylgallium (TMG) and ammonia at high temperatures, characteristic to the metalorganic vapor phase epitaxy (MOVPE) of GaN. Experiments were performed to determine the effect of the mixing of the Group III precursors and Group V precursors on the growth rate, growth uniformity and film properties. Growth rates are predicted for simple reaction mechanisms and compared to those obtained experimentally. Quantification of the loss of reacting species due to oligmerization is made based on experimentally observed growth rates. The model is used to obtain trends in growth rate and uniformity with the purpose of moving towards better operating conditions.

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