Activation of Alkanes by Transition Metal Nitrides and Carbides

1998 ◽  
Vol 549 ◽  
Author(s):  
C. A. Bennett ◽  
M. K. Neylon ◽  
H. H. Kwon ◽  
S. Choi ◽  
K. E. Curry ◽  
...  
Keyword(s):  
Metal Atom ◽  
Catalytic Properties ◽  
Lattice Structure ◽  
Reaction Rates ◽  
Transition Metal Nitrides ◽  
Atom Type ◽  
Group Vi ◽  
Group V ◽  
Dehydrogenation Reactions ◽  
Temperature Programmed Reaction

AbstractGroup V and VI nitrides and carbides were synthesized by the temperature programmed reaction of metal oxides with ammonia or an equimolar mixture of methane/hydrogen. The synthesis protocols were developed using thermogravimetric techniques. The resulting nitrides and carbides were primarily mesoporous and possessed surface areas in the range of 11 – 81 m2/g. Their alkane activation rates were comparable to a Pt-Sn/AL20 3 dehydrogenation catalyst and the surface area normalized reaction rates decreased in the following order: Mo2N > W2C > WC > W2N > WC1−x > VCoa0.05N > MO2C > VN = VC > NbMo0.01 N > NbMo0.05 > NbN = NbC. The activities measured at 450°C ranged between 1011 – 1013 molecules/cm2/s for n-butane and 1012 – 1013 molecules/cm2/s for n-hexane. The Group VI nitrides and carbides were far more active than the Group V materials. The Group VI materials catalyzed the hydrogenolysis and dehydrogenation reactions with similar activities whereas the Group V materials were more than 98% selective to dehydrogenation. While the metal atom type had the most significant effect on the catalytic properties, the lattice structure of the material also played a role. In particular, we observed that WC (hex) was almost twice as active as WC1-x (fcc). Nitrides and carbides of the same metal and lattice structure possessed similar catalytic properties, implying that the effect of the non-metal atom type was minimal. The W2N catalyst was found to be highly selective towards n-butane isomerization. The multimetallic nitrides each demonstrated some form of synergy.

Electronic properties of transition-metal nitrides: The group-V and group-VI nitrides VN, NbN, TaN, CrN, MoN, and WN

1985 ◽  
Vol 31 (2) ◽  
pp. 752-761 ◽  
Author(s):  
D. A. Papaconstantopoulos ◽  
W. E. Pickett ◽  
B. M. Klein ◽  
L. L. Boyer
Keyword(s):  
Transition Metal ◽  
Electronic Properties ◽  
Metal Nitrides ◽  
Transition Metal Nitrides ◽  
Group Vi ◽  
Group V

scholarly journals First principles computation of composition dependent elastic constants of omega in titanium alloys: implications on mechanical behavior

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
R. Salloom ◽  
S. A. Mantri ◽  
R. Banerjee ◽  
S. G. Srinivasan
Keyword(s):  
Mechanical Properties ◽  
Young’S Modulus ◽  
First Principles ◽  
Young's Modulus ◽  
Group Vi ◽  
Group V ◽  
Β Phase ◽  
Ti Alloys ◽  
Ω Phase ◽  
Stabilizer Concentration

AbstractFor decades the poor mechanical properties of Ti alloys were attributed to the intrinsic brittleness of the hexagonal ω-phase that has fewer than 5-independent slip systems. We contradict this conventional wisdom by coupling first-principles and cluster expansion calculations with experiments. We show that the elastic properties of the ω-phase can be systematically varied as a function of its composition to enhance both the ductility and strength of the Ti-alloy. Studies with five prototypical β-stabilizer solutes (Nb, Ta, V, Mo, and W) show that increasing β-stabilizer concentration destabilizes the ω-phase, in agreement with experiments. The Young’s modulus of ω-phase also decreased at larger concentration of β-stabilizers. Within the region of ω-phase stability, addition of Nb, Ta, and V (Group-V elements) decreased Young’s modulus more steeply compared to Mo and W (Group-VI elements) additions. The higher values of Young’s modulus of Ti–W and Ti–Mo binaries is related to the stronger stabilization of ω-phase due to the higher number of valence electrons. Density of states (DOS) calculations also revealed a stronger covalent bonding in the ω-phase compared to a metallic bonding in β-phase, and indicate that alloying is a promising route to enhance the ω-phase’s ductility. Overall, the mechanical properties of ω-phase predicted by our calculations agree well with the available experiments. Importantly, our study reveals that ω precipitates are not intrinsically embrittling and detrimental, and that we can create Ti-alloys with both good ductility and strength by tailoring ω precipitates' composition instead of completely eliminating them.

scholarly journals Electrolyte-Assisted Hydrogen Cycling in Lithium and Sodium Alanates at Low Pressures and Temperatures

Energies ◽  
2020 ◽  
Vol 13 (22) ◽  
pp. 5868
Author(s):  
Jason Graetz ◽  
John J. Vajo
Keyword(s):  
Growth Parameters ◽  
Reaction Times ◽  
Hydrogen Uptake ◽  
Hydrogen Desorption ◽  
Reaction Rates ◽  
Rate Coefficients ◽  
Aluminum Hydrides ◽  
Dehydrogenation Reactions ◽  
Low Pressures ◽  
Sodium Alanates

An investigation of electrolyte-assisted hydrogen storage reactions in complex aluminum hydrides (LiAlH4 and NaAlH4) reveals significantly reduced reaction times for hydrogen desorption and uptake in the presence of an electrolyte. LiAlH4 evolves ~7.8 wt% H2 over ~3 h in the presence of a Li-KBH4 eutectic at 130 °C compared to ~25 h for the same material without the electrolyte. Similarly, NaAlH4 exhibits 4.8 wt% H2 evolution over ~4 h in the presence of a diglyme electrolyte at 150 °C compared to 4.4 wt% in ~15 h for the same material without the electrolyte. These reduced reaction times are composed of two effects, an increase in reaction rates and a change in the reaction kinetics. While typical solid state dehydrogenation reactions exhibit kinetics with rates that continuously decrease with the extent of reaction, we find that the addition of an electrolyte results in rates that are relatively constant over the full desorption window. Fitting the kinetics to an Avrami-Erofe’ev model supports these observations. The desorption rate coefficients increase in the presence of an electrolyte, suggesting an increase in the velocities of the reactant-product interfaces. In addition, including an electrolyte increases the growth parameters, primarily for the second desorption steps, resulting in the observed relatively constant reaction rates. Similar effects occur upon hydrogen uptake in NaH/Al where the presence of an electrolyte enables hydrogenation under more practical low temperature (75 °C) and pressure (50 bar H2) conditions.

scholarly journals Influence of Fiber Inserts, Type of Composite, and Gingival Margin Location on the Microleakage in Class II Resin Composite Restorations

2014 ◽  
Vol 39 (1) ◽  
pp. E9-E15 ◽  
Author(s):  
V Dhingra ◽  
S Taneja ◽  
M Kumar ◽  
M Kumari
Keyword(s):  
Resin Composite ◽  
Class Ii ◽  
Blue Dye ◽  
Group Vi ◽  
Group V ◽  
Gingival Margin ◽  
Composite Restorations ◽  
Group I ◽  
Distal Side ◽  
Fiber Inserts

SUMMARY This study evaluated the influence of fiber inserts, type of composites, and location of the gingival seat on microleakage in Class II resin composite restorations. Fifty noncarious human third molars were selected for the study. Standardized Class II box type cavities were prepared on the mesial and distal side of 45 teeth. The gingival margin was placed above the cementoenamel junction (CEJ) on the mesial side and below the CEJ on the distal side. The remaining five teeth received no cavity preparations. The prepared samples were divided randomly on the basis of type of composite and presence or absence of fiber inserts, into four experimental groups of 10 teeth each and two control groups of five teeth each. The groups were defined as follows: group I (n=10) – Z350 XT; group II (n=10) – Z350 XT with fibers; group III (n=10) – P90; group IV (n=10) – P90 with fibers; and group V (n=5) – positive controls, cavities were not restored; group VI (n=5) – negative controls, no cavities were prepared. The samples were stored in distilled water in incubator at 37°C for 24 hours and then subjected to 500 cycles of thermocycling (5°C and 55°C) with a dwell time of 15 seconds. They were then placed in a 2% methylene blue dye solution for 24 hours at 37°C. Samples were sectioned longitudinally and evaluated for microleakage at the occlusal and gingival margin under a stereomicroscope at 20× magnification. Kruskal-Wallis and Mann-Whitney U-tests were used to compare the mean leakage scores. Restorations with gingival margins in enamel showed significantly less microleakage. Significant reduction in microleakage was observed in groups restored with P90 composite than those restored with Z350 XT. No improvement in microleakage was observed with the use of fiber inserts (p>0.05).

scholarly journals Effect of a Diet Composed of Genetically Modified Feed Components on the Selected Immune Parameters in Pigs, Cattle, and Poultry

2013 ◽  
Vol 57 (2) ◽  
pp. 209-217 ◽  
Author(s):  
Dariusz Bednarek ◽  
Katarzyna Dudek ◽  
Krzysztof Kwiatek ◽  
Małgorzata Świątkiewicz ◽  
Sylwester Świątkiewicz ◽  
...  
Keyword(s):  
Soybean Meal ◽  
Genetically Modified ◽  
Group Iv ◽  
Group Vi ◽  
Group V ◽  
Group Iii ◽  
Immune Parameters ◽  
Group I ◽  
Toxin Protein ◽  
Gm Soybean

Abstract The aim of the study was to evaluate the immune effects of genetically modified (GM), insect resistant corn (MON810) expressing toxin protein of Bacillus thuringiensis, and glyphosate-tolerant soybean meal (Roundup Ready MON-40-30-2), which are used as the feed mixture components in domestic animals. The study was conducted on 60 pigs (36 fatteners and 24 sows), 20 calves, 40 broilers, and 40 laying hens. Each species was divided into four basic nutritional groups: group I (control) - conventional feed, group II - feed consisted of GM soybean meal and non-modified corn, group III - non-modified soybean meal and GM corn, group IV - GM soybean meal and GM corn. Moreover, in the experiment on fatteners two additional groups were formed: group V - animals fed both conventional soybean meal and bruised grain, and group VI - GM soybean meal and conventional bruised grain. The results of study did not reveal any significant effect of feed mixtures containing GM components on the immune response in all animals regardless of their species and technological producing groups.

Antihyperglycaemic Effect of Laser Acupuncture Treatment at Bl20 in Diabetic Rats

2014 ◽  
Vol 32 (6) ◽  
pp. 486-494 ◽  
Author(s):  
Jorge Cornejo-Garrido ◽  
Flavia Becerril-Chávez ◽  
Gabriel Carlín-Vargas ◽  
Juan Manuel Ordoñez-Rodríguez ◽  
María del Carmen Abrajan-González ◽  
...  
Keyword(s):  
Acupuncture Treatment ◽  
Morphological Changes ◽  
Intraperitoneal Administration ◽  
Diabetic Rats ◽  
Laser Acupuncture ◽  
Group Vi ◽  
Group V ◽  
Glucose Levels ◽  
Lower Glucose ◽  
Healthy Adult Male

Objective To investigate the antihyperglycaemic activity of laser acupuncture stimulation at 650 and 980 nm at BL20 in streptozotocin (STZ)-induced diabetic rats. Methods Seventy healthy adult male albino Wistar rats weighing 250±50 g were divided into seven groups of 10 animals each. Groups I–III comprised healthy control rats which were untreated (I) or stimulated with laser acupuncture at 650 nm (II) and 980 nm (III), respectively. Groups IV–VII underwent induction of diabetes with a single intraperitoneal administration of STZ at 50 mg/kg. Animals with blood glucose levels of ≥200 mg/dL on the fifth day were used for the experiments and were left untreated (group IV), treated with glibenclamide (group V) or stimulated with laser acupuncture at 650 nm (group VI) and 980 nm (group VII), respectively. Laser acupuncture was applied at BL20 on alternate days for a total of 12 sessions over a 28-day period. Results After 28 days of treatment, STZ-induced diabetic rats stimulated with laser acupuncture at 650 and 980 nm had significantly lower glucose levels compared with untreated diabetic rats (242.0±65.0 and 129.8±33.2 vs 376.5±10.0 mg/dL, both p≤0.05). Treatment at 980 nm also attenuated the increase in glucose between day 1 and day 28 compared with the glibenclamide-treated diabetic group (41.5±19.6 mg/dL vs 164.1±13.7 g/dL, p<0.05). Laser acupuncture treatment did not affect the blood count or biochemical profile and was not associated with any morphological changes in the pancreas, liver, kidney or spleen. Conclusions Stimulation with laser acupuncture at 650 and 980 nm at BL20 in STZ-induced diabetic rats has antihyperglycaemic activity. The results support further evaluation of laser acupuncture as an alternative or complementary treatment for the control of hyperglycaemia.

First Principles Calculations of Helium Solution Energies in BCC Transition Metals

2006 ◽  
Vol 981 ◽  
Author(s):  
François Willaime ◽  
Chu Chun FU
Keyword(s):  
Transition Metals ◽  
Density Functional ◽  
Tetrahedral Site ◽  
Density Functional Theory Calculations ◽  
Interstitial Site ◽  
Group Vi ◽  
Functional Theory ◽  
Group V ◽  
Substitutional Site ◽  
Exchange Correlation

AbstractDensity functional theory calculations of the solution energies of helium in substitutional, tetrahedral and octahedral sites have been performed for all BCC transition metals: V, Nb, Ta, Cr, Mo, W and Fe. The effects of exchange correlation functional and of pseudopotential have been investigated in Fe; they are relatively small. The solution energies are found to be weakly dependent on the element for the substitutional site whereas for the interstitial sites they are much smaller in group V than in group VI and they decrease from 3d to 4d and 5d metals. As a result an inversion is observed from V, Nb and Ta - which tend to favor the interstitial site - to Mo and W, which favor the substitutional one, with an intermediate behavior for Cr and Fe. Finally, the results indicate that the tetrahedral site is always energetically more favorable than the octahedral one by 0.2 to 0.3 eV.

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