The State of Hydrogen Desorbing from Intermediates Formed by Ammonia Interaction with Tungsten Surfaces

1974 ◽  
Vol 52 (7) ◽  
pp. 1147-1154 ◽  
Author(s):  
Y. K. Peng ◽  
P. T. Dawson
Keyword(s):  
Hydrogen Atom ◽  
Atomic Hydrogen ◽  
Surface Concentration ◽  
Hydrogen Desorption ◽  
Pure Hydrogen ◽  
Adsorbed Hydrogen ◽  
Tungsten Filament ◽  
Hydrogen Atoms ◽  
Ionization Source ◽  
Hydrogen Desorbing

Ammonia interaction with a tungsten surface can generate dense adlayers containing nitrogen and hydrogen, i.e. an η-species of surface stoichiometry Ws2N3H. In thermal desorption mass spectrometry experiments, hydrogen desorbing from the η-species interacts with the glass wall in a manner similar to that previously observed for atomic hydrogen. This paper describes two mass spectrometric techniques designed to confirm this conclusion directly. The first method uses a line-of-sight geometry between the tungsten filament and the ionization source of the mass spectrometer and the results indicate that, at least, part of the hydrogen desorbing from the η-species does so atomically. In the second method a multiple wall collision geometry is used but prior saturation of the wall with D atoms will result in an HD+ ion current for desorbing H atoms. The results suggest that 26% of the hydrogen desorbs atomically. Hydrogen atom desorption from the η-species occurs at tungsten filament temperatures below those required for hydrogen atom evaporation from a pure hydrogen adlayer. It is proposed that a reduced binding energy for adsorbed hydrogen atoms and a reduced mobility of these adatoms arises from the presence of a large surface concentration of nitrogen. This will result in the rates of atomic hydrogen desorption and bimolecular recombination becoming comparable at temperatures lower than is the case for pure hydrogen interaction with tungsten. The implications of these results for the ammonia synthesis reaction are discussed.

Surface Luminescence of Polycrystalline Zinc Oxide Excited by Hydrogen Atoms

2006 ◽  
Vol 957 ◽  
Author(s):  
Michael Sushchikh ◽  
Vladislav Styrov ◽  
Vladimir Tyutunnikov ◽  
Nick Cordella
Keyword(s):  
Atomic Hydrogen ◽  
Hydrogen Atmosphere ◽  
Adsorbed Hydrogen ◽  
Hydrogen Atoms ◽  
Long Wavelength ◽  
Pl Spectra ◽  
Zno Powders ◽  
Exothermic Chemical Reaction ◽  
Heterogeneous Chemiluminescence ◽  
Surface Luminescence

ABSTRACTExcitation of a luminescence by highly exothermic chemical reaction on the surface of a luminophore provides a unique opportunity to separate surface luminescence from the bulk luminescence. This enables studies of the electronic properties of the semiconductor surfaces even if the surfaces are of complicate shapes. We have studied heterogeneous chemiluminescence (HCL) of ZnO powders. The luminescence was excited by a release of chemical energy, namely by catalytic recombination of hydrogen atoms. The HCL spectra were compared to the photoluminescence (PL) spectra. The HCL spectra were sensitive to the details of preparation and treatment whereas PL spectra almost did not change. HCL spectra of powder samples pretreated for enhancing “green” luminescence exhibited long-wavelength tail (up to 800 nm) and their maximum was blue-shifted as compared with PL spectra. Different HCL bands forming long-wavelength tail were isolated by changing the temperature of the samples. Additional milling of ZnO led to amplification of the HCL-specific surface bands. Pure ZnO showed neither PL nor HCL; however we were able to observe HCL surface bands with maxima at 610 nm and 730 nm after treatment of the sample in atomic hydrogen atmosphere at 570 K. Remarkably, such treatment did not cause appearance of the PL. The HCL in the presence of atomic hydrogen was steady in time and was caused by an abstraction of adsorbed hydrogen by incident hydrogen atoms, i.e. the reaction followed Eley-Rideal mechanism. The HCL can be utilized for in situ monitoring of the growth and evolution of ZnO in controlled atmosphere.

The kinetics of the interaction of atomic hydrogen with olefines. V. Results obtained for a further series of compounds

1950 ◽  
Vol 202 (1069) ◽  
pp. 181-202 ◽  
Keyword(s):  
Double Bond ◽  
Hydrogen Atom ◽  
Atomic Hydrogen ◽  
Methyl Radicals ◽  
Hydrogen Atoms ◽  
Alkyl Radicals ◽  
Kinetics Of ◽  
Interesting Generalization

In this paper the efficiency of interaction of a hydrogen atom with a series of olefines has been determined, the olefines being members of the series obtained by progressively replacing the hydrogen atoms of ethylene by methyl radicals. The interesting generalization which emerges from this is that the efficiency of interaction does not vary very much with the nature of the alkyl substituents in the molecule, and calculations involving the heats of addition of a hydrogen atom to a double bond confirm this generalization. The data presented here are discussed critically in relation to information available on the reaction of CCl 3 radicals with olefines and of alkyl radicals with olefines, complete general agreement being demonstrated.

The dissociation of hydrogen by tungsten

1936 ◽  
Vol 32 (4) ◽  
pp. 648-652 ◽  
Author(s):  
G. Bryce
Keyword(s):  
Tungsten Oxide ◽  
Constant Temperature ◽  
Atomic Hydrogen ◽  
Square Root ◽  
Tungsten Filament ◽  
Hydrogen Atoms ◽  
Production Of Hydrogen

The dissociation of hydrogen by a hot tungsten filament has been studied under conditions such that all the atomic hydrogen produced is effectively removed by reaction with molybdenum or tungsten oxide. The rate of production of atomic hydrogen is many times greater than was inferred from earlier work. With the tungsten at constant temperature the rate of dissociation is proportional to the square root of the pressure. A formula is given for the rate of production of hydrogen atoms per sq. cm. of the tungsten per second.

Hydrogen elimination from the dissociation of methyl-substituted silanes on tungsten and tantalum surfaces

2016 ◽  
Vol 94 (4) ◽  
pp. 265-272 ◽  
Author(s):  
R. Toukabri ◽  
Y.J. Shi
Keyword(s):  
Vacuum Ultraviolet ◽  
Single Photon ◽  
Bond Cleavage ◽  
Bond Rupture ◽  
Ionization Mass ◽  
Adsorbed Hydrogen ◽  
Methyl Radical ◽  
Hydrogen Atoms ◽  
Ionization Source ◽  
Hydrogen Elimination

The elimination of H2 from the dissociation of four methyl-substituted silane molecules, including monomethylsilane (MMS), dimethylsilane (DMS), trimethylsilane (TriMS), and tetramethylsilane (TMS), on a heated tungsten or tantalum filament surface has been studied using laser ionization mass spectrometry. Two complementary ionization methods, i.e., single photon ionization (SPI) using a vacuum ultraviolet wavelength at 118 nm (10.5 eV) and a dual ionization source incorporating both 10.5 eV SPI and laser-induced electron ionization, were employed to detect the production of H2. Examination of the intensity of the H2+ peak from the four molecules has shown that it increases with temperature until reaching a plateau at around 2000−2100 °C on both tungsten and tantalum filaments. These methyl-substituted silanes are dissociatively adsorbed on tungsten and tantalum surfaces by Si−H bond cleavage, and as the temperature is raised, by C−H bond rupture. Experiments with the isotopomers of MMS, DMS, and TriMS have shown that the formation of H2 follows the Langmuir−Hinshelwood mechanism where two adsorbed hydrogen atoms on metal surfaces recombine to produce H2. The determined activation energy (Ea) for H2 formation from MMS, DMS, and TriMS, in the range of 58.2−93.4 kJ mol−1, has been found to increase with the number of methyl substitutions in the precursor molecule. Comparison of these Ea values with the reported values of 51.1−78.8 kJ mol−1 for the methyl radical formation from the same three precursor molecules has led to the conclusion that the initial Si−H bond cleavage in the dissociative adsorption of MMS, DMS, and TriMS is the rate-limiting step for the formation of both H2 molecules and ·CH3 radicals.

MICROSCOPIC MODEL OF ASSOCIATIVE DESORPTION FOR HYDROGEN ON Mo(110)

2006 ◽  
Vol 13 (04) ◽  
pp. 375-386 ◽  
Author(s):  
I. N. YAKOVKIN ◽  
V. D. OSOVSKII ◽  
N. V. PETROVA ◽  
Yu. G. PTUSHINSKII
Keyword(s):  
Hydrogen Desorption ◽  
Microscopic Model ◽  
Adsorbed Hydrogen ◽  
Hydrogen Atoms ◽  
Microscopic Description ◽  
High Hydrogen ◽  
Molecular Formation ◽  
Temperature Programmed ◽  
Insight Into ◽  
Good Agreement

Adsorbed hydrogen layers on the Mo (110) surface have been investigated both experimentally by temperature programmed desorption (TPD) method and theoretically by means of DFT-based optimization of surface structures. We suggest a novel microscopic model of the associative hydrogen desorption, which explains essential features of the process. In this model, the process of hydrogen desorption can be described as association of hydrogen atoms on the surface, but molecular formation is actually accomplished while the molecule moves away from the surface. We also suggest a new algorithm for realistic Monte Carlo simulations of associative desorption, which implements the microscopic description of the association of hydrogen adatoms into a molecule with activation energy, found from the DFT calculations. Good agreement between simulated and experimental TPD spectra gives insight into different behavior of the spectra, obtained for low and high hydrogen coverages on the Mo (110) surface.

scholarly journals The kinetics of the interaction of atomic hydrogen with olefines III. Theory and technique involved in the use of the oxides of molybdenum and tungsten as hydrogen atom removers

1949 ◽  
Vol 196 (1047) ◽  
pp. 479-493 ◽  
Keyword(s):  
Hydrogen Atom ◽  
Molybdenum Oxide ◽  
Atomic Hydrogen ◽  
Colorimetric Method ◽  
Oxide Surface ◽  
Hydrogen Atoms ◽  
Alkyl Radicals ◽  
Kinetics Of ◽  
And Tungsten

The colorimetric method of estimating the rate of addition of hydrogen atoms to the oxides of molybdenum and tungsten is discussed in detail. It is also shown that alkyl radicals are efficiently removed by molybdenum oxide, and allowance is made for the effect of their presence on the blueing rate of the oxide surface. The method of evaluating collision efficiencies from the data obtained is indicated in full, and the construction and operation of a calculator to assist in the computation is described.

scholarly journals The mechanism of the steam-carbon reaction

1948 ◽  
Vol 193 (1034) ◽  
pp. 377-399 ◽  
Keyword(s):  
Carbon Dioxide ◽  
Carbon Monoxide ◽  
Hydrogen Atom ◽  
Active Carbon ◽  
Active Sites ◽  
Adsorbed Oxygen ◽  
Adsorbed Hydrogen ◽  
Hydrogen Atoms ◽  
Exponential Factor ◽  
Gaseous Carbon Monoxide

The detailed mechanism of the reaction between steam and coconut shell charcoal has been studied by the method described in the preceding paper. The temperature has been varied in the range 680 to 800° C and the pressures of the gases from 10 to 760 mm. Steam first reacts with the carbon to give oxygen and hydrogen atoms separately adsorbed on neighbouring sites. An initial dissociation into an adsorbed hydrogen atom and an adsorbed hydroxyl radical is probably followed by the more rapid transfer of the second hydrogen atom to the carbon. Only about 2% of the total surface takes part in the reaction; these sites are distinct from the smaller group which reacts with carbon dioxide, but they are also thought to be atoms at the edges of lattice planes. The rate of the first stage can be accounted for by assuming that reaction occurs in those collisions in which the combined energy of the incident steam molecule and the two active carbon atoms exceeds 75 kcal. Adsorbed hydrogen evaporates rapidly, but in the steady state much remains on the surface. A close correlation has been observed between the fraction of the active sites occupied by hydrogen and the extent to which the reaction is retarded by that gas. Adsorbed oxygen reacts much more slowly to form gaseous carbon monoxide; the latter, which has no retarding effect, is not appreciably adsorbed by the sites accessible to steam. The activation energy for the conversion of an adsorbed oxygen atom into gaseous carbon monoxide is found to be 55 kcal., and the non- exponential factor to be 10 11±1.7 sec. -1 which may be compared with the value of 10 13 sec. -1 predicted by simple theory. As the active carbon atoms are thought to be exerting less than their maximum valency, it is suggested that the two types differ in the number of extra bonds which they can form. Energetic considerations show that whereas those which can form a single bond should react with steam, only the relatively few capable of forming a double bond should react with carbon dioxide. This theory also explains why hydrogen is strongly adsorbed by both the steam and the carbon dioxide sites, but carbon monoxide only by the latter type. The relation of these views to outstanding problems of the oxygen-carbon and nitrous oxide-carbon reactions is discussed, and an explanation of the main kinetic features of those processes is given.

Effect of Atomic Hydrogen Concentration in the Study of Adsorption on Graphene

2011 ◽  
Vol 465 ◽  
pp. 211-214
Author(s):  
A.V. Pak ◽  
Nikolay G. Lebedev
Keyword(s):  
Band Structure ◽  
Russian Federation ◽  
Atomic Hydrogen ◽  
Function Method ◽  
Hydrogen Adsorption ◽  
Adsorbed Hydrogen ◽  
Hydrogen Atoms ◽  
Statistical Research ◽  
Graphene Surface ◽  
Quantum Statistical

The results of theoretical quantum-statistical research of atomic hydrogen adsorption on the graphene surface within the framework of the periodic Anderson’s model have been presented. The band structure of graphene with adsorbed hydrogen atoms is calculated by the Green's function method. The work is supported by The Education Ministry of Russian Federation (project No. NK-16(3)).

Density Functional Theory Calculations of Atomic Hydrogen Adsorption on (3, 3) Single-Wall Carbon Nanotubes with Vacancy Defects

2014 ◽  
Vol 687-691 ◽  
pp. 4315-4318
Author(s):  
Zong Sheng Li
Keyword(s):  
Carbon Nanotubes ◽  
Density Functional Theory ◽  
Hydrogen Atom ◽  
Density Functional ◽  
Single Wall Carbon Nanotubes ◽  
Adsorbed Hydrogen ◽  
Hydrogen Atoms ◽  
Functional Theory ◽  
Vacancy Defects ◽  
Single Wall Carbon

In this paper, we have employed density functional theory (DFT) to investigate the adsorption mechanisms of atomic hydrogens on the sidewalls of (3, 3) single-wall carbon nanotubes (CNTs) which have vacancy defects. All the calculations were performed using the generalized gradient approximation (GGA) with the Perdew, Burke and Ernzerhof (PBE) correlation functional.Our results show that hydrogen atoms can chemically adsorb on the defective nanotube. Bonding energy of per hydrogen atom decreases with the number of adsorbed hydrogen atoms. The hydrogen atoms will enhance the electrical conductivity of the (3, 3) nanotube. Besides one hydrogen atom adsorbing on the nanotube with a vacancy defect (MVD), hydrogen atoms move towards the MVD of the nanotube.

scholarly journals The reaction of atomic hydrogen with hydrazine

1940 ◽  
Vol 175 (961) ◽  
pp. 164-186 ◽  
Keyword(s):  
Hydrogen Atom ◽  
Gas Phase ◽  
Atomic Hydrogen ◽  
Ammonia Molecule ◽  
Para Hydrogen ◽  
Hydrogen Atoms ◽  
Stationary Concentration ◽  
Essential Step ◽  
Photochemical Decomposition ◽  
The Subject

The reason for studying the reaction of hydrogen atoms with hydrazine is that a controversy has arisen in attempting to elucidate the mechanism of the photochemical decomposition of ammonia. It has been generally agreed that the ammonia molecule is decomposed to a hydrogen atom and an amine radical when it absorbs light around 2000° A. Presuming that the atomic hydrogen combines on the walls or in the gas phase it is possible to calculate what its stationary concentration ought to be under any given set of conditions. If, however, the stationary concentration is actually measured by using para-hydrogen as a detector, as was done by Farkas and Harteck (1934), it is found that the measured value is lower than the value calculated from the above assumptions. A number of suggestions, discussed in detail in the following paper, were made to explain this discrepancy, and among the most reasonable was that of Mund and van Tiggelen (1937) who suggested that the hydrazine known to be formed in the system removed such atoms more rapidly than would occur in the ordinary course of events. The result of their suggestion was the invention of elaborate schemes to explain the mechanism of the ammonia photolysis. As a further essential step in the ammonia problem it therefore seemed necessary to measure the efficiency of the reaction between hydrogen atoms and hydrazine. At the same time further information was also desirable about the photochemistry of hydrazine itself. This paper will therefore be concerned with this aspect of the subject. The results will then be discussed in the following paper together with a number of new experiments on ammonia in order that the mechanism of the ammonia reaction may be more fully established.

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