558-20-3Relevant academic research and scientific papers
Effects of rhodium dispersion on catalytic behavior of Rh/active-carbon catalysts for H/D exchange reaction between and CH4 and D2
Sakagami,Ogata,Takahashi,Matsuda
, p. 1930 - 1934 (2001)
The H/D exchange reaction between CH4 and D2 was carried out over Rh/active-carbon catalysts, which were prepared from RhCl3 and Rh(NO3)3. In the case of the catalysts prepared from RhCl3, Rh species were homogeneously dispersed on the support from external surface to the inside of pores. Metallic particles of Rh were found to be the predominant species on the catalysts prepared from Rh(NO3)3 in the low Rh-loading region of 2 wt.%. The reaction rate per unit gram of catalyst and the product distribution in methane reflected well the Rh-dispersion on the catalysts. The catalysts which contained the highly dispersed Rh species as predominant species were found to be more active for the H/D exchange reaction than the catalysts with relatively large metal particles of Rh. On the former, the ratio of CH3D/CD4 was observed to be much higher than that on the latter.
High-temperature Shilov-type methane conversion reaction: Mechanistic and kinetic studies
Kang, Shujuan,Ma, Qisheng,Chen, Weiqun,Chen, Guanyi,Tang, Yongchun
, p. 1777 - 1784 (2015)
Traditional Shilov reactions (performed in aqueous solution with a PtCl2 catalyst) for methane conversion suffer from catalyst deactivation at high temperatures (> 100 °C), therefore only very low conversion rates have been achieved. In this paper, we show that Shilov-type C-H activations are achievable at much higher temperatures (～200 °C) by addition of concentrated aqueous solutions of Cl- to inhibit Pt catalyst precipitation. Various chloride-based ionic liquids also stabilized the Pt catalyst at mild reaction temperatures (～140 °C). Under high-pressure conditions (> 25.5 MPa), achieved using a specially designed sealed gold-tube reactor, very high methane conversion rates (> 90%) were obtained; this is attributed to the improved methane solubility in aqueous solution. Deuterium isotope (H/D) exchange between methane and water was used to examine the reaction reactivity and selectivity. Multiply D-substituted products were observed, indicating that multiple C-H activations occurred. A comprehensive network reaction that included all the chain reactions was set up to clarify the reactivities and product selectivities of the methane activation reactions. The reaction network consisted of a series of parallel first-order reactions, which can be described by the Arrhenius equation. The kinetic parameters such as the frequency factor, activation energies, and stoichiometric coefficients were obtained by fitting the experimental data. Because all four C-H bonds in a methane molecule are equivalent, multiple substitutions during methane conversion cannot be avoided. Our studies indicate that mono-substituted and di-substituted methane isotopologue generations have similar activation energies, suggesting that the highest mono-substitution selectivity cannot be greater than 50%.
Methane hydrogenation and confirmation of CHx intermediate species on NaY encapsulated cobalt clusters and Co/SiO2 catalysts: EXAFS, FTIR, UV characterization and catalytic performances
Shen, Guo-Cheng,Ichikawa, Masaru
, p. 1185 - 1193 (1997)
The adsorption of Co2(CO)8 onto dehydrated NaY powder under an N2 atmosphere predominantly yielded supported Co4(CO)12. The molecular cobalt carbonyl clusters and their decarbonylated products have been structurally characterized by in situ IR, extended X-ray absorption fine structure (EXAFS) and diffuse reflectance spectroscopies. The IR spectrum assigned to the species Co4(CO)12/NaY is shifted significantly from that observed for externally supported analogues on NaY and for this cluster in solution, which indicates that the cobalt carbonyl clusters occurring on the NaY are similar to those occurring in weakly basic solution. EXAFS coordination numbers (N) show that the successively decarbonylated samples maintain small cluster sizes, which depend on the temperature-programmed oxidation of the precursor. Methane hydrogenation was carried out on intrazeolitic cobalt clusters using a two-step process. It showed a relatively higher activity and selectivity to C2+ hydrocarbons in comparison with Co/SiO2 catalysts. On the basis of IR (νC-H 2960, 2880 cm-1 and δC-H 1520, 1393 cm-1) spectroscopy, mass spectrometry and reaction studies, one can conclude that CHx (x = 0, 1 or 2) surface carbonaceous species were generated by CH4 dissociation on the activated cobalt catalyst; the CH2 species was quite reactive, and propagated higher hydrocarbons.
Effect of Pt Particle Size on H/D Exchange of Methane over Alumina- and Zeolite-supported Catalysts
Khodakov, Andrei,Barbouth, Nisso,Berthier, Yves,Oudar, Jacques,Schulz, Philippe
, p. 569 - 574 (1995)
Deuterium exchange in methane was studied over a series of Pt/Al2O3 and Pt/mazzite catalysts.The reaction proceeds by a simple stepwise mechanism with CH3D being the primary product.Large and small metal particles located in zeolite and alumina catalysts have different catalytic activity with respect to deuterium exchange in methane.The rate of reaction per Pt atom was the same on the catalysts investigated for particles >15-20 Angstroem and considerably lower than the rate of reaction on samples with smaller Pt clusters.The activity of small clusters of Pt (diameter 15-20 Angstroem) depended on the nature of the support.
Platinum catalyzed c-h activation and the effect of metal-support interactions
Sattler, Aaron,Paccagnini, Michele,Lanci, Michael P.,Miseo, Sabato,Kliewer, Chris E.
, p. 710 - 720 (2020)
Catalytic C-H bond activation of methane and ethane on a series of silica supported platinum catalysts (Pt/SiO2) was studied by using hydrogen/deuterium (H/D) exchange. Kinetic experiments demonstrate that under the reaction conditions studied, the rate of C-H bond activation shows approximate first order dependence in alkane and inverse first order dependence in D2. The rate of C-H activation is affected by the presence of sodium on the silica support, where sodium-free supports have the fastest rates of C-H activation, as assessed by H/D exchange. CO adsorption and FTIR studies indicate that the Pt particles on the sodium-free support are more electron-deficient, having the most blue-shifted linear CO stretch, while sodium-containing supports are more electron-donating, having the most red-shifted linear CO stretch. It is proposed, based on the results described in this article and previous work in the literature, that more electron-donating supports cause the Pt particles to be more electron-rich and to adsorb D? (or H*) more strongly, thereby stabilizing the ground state and resting state of the catalyst, resulting in a decreased rate of C-H activation.
Exchange Reactions of Hydrocarbons on Silica-supported Rh-Pt Bimetallic Catalysts
Oliver, James A.,Kemball, Charles,Brown, Ronald,Jamieson, Edward W.
, p. 1871 - 1882 (1985)
A series of silica-supported rhodium-platinum catalysts containing 10E-1 mol metal g-1 silica have been shown to be well dispersed by temperature-programmed reduction.Exchange reactions with deuterium of methane (463 K), 2,2-dimethylpropane (323 K) and n-butane (311 K) were followed using most of the catalysts in the series.Two patterns of activity against composition curve were found.For methane and 2,2-dimethylpropane, i.e. molecules containing only primary C-H bonds which cannot form α,β-diadsorbed species, platinum was as effective if not more effective than rhodium.However, for the exchange of n-butane (and also propane) rhodium was some 20-30 times more active than platinum.The extent of multiple exchange increased with rhodium content.There was some evidence for the importance of electronic effects from the variations of activity and selectivity with metal composition.
Isotopic Excange in the Sonolysis of Aqueous Solutions Containing D2 and CH4
Hart, Edwin J.,Fischer, Ch.-Herbert,Henglein, Arnim
, p. 4166 - 4169 (1987)
Water was insonated under an argon atmosphere which contained various amounts of a D2-CH4 (2:1 vol percent) mixture.Maximum yield for the formation of CH3D, CH2D2, CHD3 and CD4 was observed at 40 vol percent argon.Ethane, ethylene, acetylene, and many higher hydrocarbons were also produced with about one third of the deuterated methane yield.In addition, some H/D exchange took place between D2 and H2O, and H2 was formed from water.Carbon monoxide and carbon were produced, too.A mechanism involving free radicals and atoms is discussed to explain these observations.
Reactions of Hydrocarbons over Ru/SiO2: Exchange with Deuterium and the Onset of Hydrogenolysis
Brown, Ronald,Kemball, Charles
, p. 585 - 594 (1993)
Exchange reactions with deuterium of a number of hydrocarbons, chosen to provide evidence about the nature of the intermediates, have been followed mass spectrometrically over a ruthenium-silica catalyst.The selected hydrocarbons were methane, propane, 2-methylpropane (2MP), 2,2-dimethylpropane (DMP), and 2,2,3,3-tetramethylbutane (TMB).Products from the reaction of propane and 2MP were analysed by deuterium NMR spectroscopy.The extent of multiple exchange increased with temperature and mechanisms involving αα- or αδ-adsorbed intermediates were favoured.The hydrogenolyses of DMP and TMB were followed at higher temperature with emphasis on the selectivity of the reaction and the change of the pattern of products with contact time.Subsidiary experiments to learn more about the course of the reactions with TMB were carried out with 2,2,3-trimethylbutane (TriMB) and 2,3-dimethylbutane (23DMB).There was evidence for a strong hydrocarbon-ruthenium interaction leading to a sequence of events with increase of temperature, relatively easy exchange but with self-poisoning, followed by moderately easy hydrogenolysis, again subject to self-poisoning.The sequence suggested the formation in turn of reversibly adsorbed hydrocarbon intermediates, more strongly adsorbed species leading to hydrogenolysis and finally carbonaceous residues.
Catalytic activity of systems based on supported potassium salts of transition metal carbonyl hydrides in hydrogen-deuterium exchange of hydrocarbons
Yunusov,Rummel,Herrmann,Kalyuzhnaya,Shur
, p. 1191 - 1194 (2013)
The deposition of K2[Ru4(CO)13], K 2[Os3(CO)11], K2[Fe 2(CO)8], and K[Re(CO)5] onto graphite-like carbon Sibunit followed by the thermal decomposition of the supported carbonylmetallate in a flow of dihydrogen or argon affords systems capable of activating C-H bonds of methane, ethylene, and acetylene and of introducing them into hydrogen-deuterium exchange reactions. In the case of ethylene and acetylene, the isotope exchange proceeds at room temperature, while in the case of methane reaction temperatures not lower than 150 C are needed.
Dynamics of the formation of CD4 from the direct reaction of incident D atoms with CD3/Cu(111)
Rettner,Auerbach,Lee
, p. 10115 - 10122 (1996)
Using molecular beam techniques we find that incident D atoms can abstract CD3 from a Cu(111) surface to yield CD4 in a direct (Eley-Rideal) gas-surface reaction with a cross section of ～10-16 cm2/D atom. Dynamical evidence for a direct reaction includes the observation of an extremely sharp angular distribution that is clearly displaced from the surface normal, and the determination of a very high translational energy of the product, Ef, which is ～2 eV. For a 0.25 eV D-atom beam incident at 45° on a 95 K surface, this energy varies with the detection angle, θf, as Ef(θf) = (1.8+θf/45) eV, where θf0° in the "backscattering'' direction. For these conditions, the angular distribution approximately follows the function cos70(θf-5.5), being peaked 5.5° from the normal with a full width at half maximum of 60(θf-1.5). The reaction with 0.25 eV H incident at 45° gives a similar distribution peaked at ～3.5° from the normal. The shifts in the angular distributions are approximately consistent with parallel momentum conservation. The CD3/Cu(111) surface was prepared by thermal dissociation of CD3I on the surface or by adsorbing CD3 directly from a CD3 beam produced by the pyrolvsis of azomethane.
