Partial Pressure Of CH Research Articles

Kinetic investigation of CO 2 reforming of CH 4 over La–Ni based perovskite

The kinetic behavior of the LaNiO 3 catalyst in the reforming reaction of methane with carbon dioxide was investigated as a function of temperature and partial pressures of CH 4 and CO 2. There are two kinds of active sites on the catalyst surface. In the first Ni reacts with CH 4 and in the second kind La 2O 3 reacts with CO 2. XRD pattern of the spent catalyst has shown that the phase La 2O 2CO 3 has formed which confirmed displayed mechanism. A reaction rate based on the mechanistic results was developed which predicts the experimental reaction rate with a good accuracy. Moreover, the kinetic behavior of LaNiO 3 was compared with the Ni/La 2O 3, Rh/La 2O 3 catalysts in the reforming reaction of methane with carbon dioxide at different temperatures and partial pressures of CH 4 and CO 2. These three catalysts have shown the same mechanism and the coefficients of rate equation for each one has been estimated by genetic algorithm. The results showed that Rh/La 2O 3 and LaNiO 3 posses more activity than Ni/La 2O 3at higher range of reaction temperature.

Infrared transmission properties of germanium carbon thin films deposited by reactive RF magnetron sputtering

Germanium carbon (GeC) thin films were prepared on ZnS substrates by reactive RF magnetron sputtering in Ar and CH 4 mixtures with a Ge disc as the target. H content in the films was studied as a function of the deposition parameters and low H content GeC film was obtained. RF power had a little effect on IR absorptions, hence had a little effect on H content. IR absorption of the GeC film increased a little with the increase in partial pressure of CH 4 as well as total pressure of gas mixture. Increase in substrate temperature decomposed CH 4 and CH x in the GeC film into C and H and H was desorbed from the film, lowering the IR absorption. However, high substrate temperature prevented CH 4 or CH x from adsorbing onto the substrate, which decreased C content in the GeC film and increased the film's refractive index. Higher annealing temperature of the GeC film reduced H content, but high annealing temperature (500 °C) caused the graphitization of the GeC film and destroyed its continuity.

Boron doped amorphous carbon thin films grown by r.f. PECVD under different partial pressure

Boron doped hydrogenated amorphous carbon (a-C) thin films have been deposited by r.f.-plasma CVD with a frequency of 13.56 MHz at room temperature using pure methane as a precursor of carbon source mixed with hydrogen (H 2) as a carrier gas. The films were prepared by varying the r.f. power, different flow rates of CH 4, and partial pressure of mixed gas (CH 4/H 2) using solid boron as a target. The thickness, structural, bonding and optical properties of the as-deposited films were studied by Alpha step surface profiler, Raman, FT-IR, XPS and UV–visible spectroscopy. It was found that changing the deposition pressure in presence of solid boron dopant in the r.f. PECVD process has a profound effect on the properties of the deposited films, as evidenced from their Raman scattering and optical results. The grown p-C: B films were found very smooth and thickness in the range of 240 to 360 nm for 1 h deposition. Films deposited at lower pressure appear brownish color whereas those deposited at higher pressure appear pale yellowish. The as-deposited film is found to be dominated by sp 2 rather than sp 3, which might be due to the formation of small crystallites. The optical band gap is found to be reduced from 2.60∼1.58 eV as the partial pressure of CH 4/H 2 gas is reduced.

PHOTOCATALYTIC CONVERSION OF METHANE INTO METHANOL OVER THE MoO3(010) SURFACE USING A SIMULATION METHOD

In this investigation, we have studied the kinetics and mechanism of photocatalytic conversion of methane into methanol reaction over the MoO 3(010) surface using a computer simulation method. Methane and oxygen as the reactants are used at room temperature and atmospheric pressure under UV photoirradiation of the catalyst. According to our data analysis, the order of methanol formation reaction with respect to CH 4 and O 2 was determined to be l=0.30 and m=-1.03, respectively. The highest methanol formation rate (TOF) value was obtained at about 0.05 molecule/s.site in a range of 25–35 W/cm2 incident light intensity with energy hν≥Eg. The selectivity of CH 3 OH was increased with increasing partial pressure of CH 4, while the selectivity of CHOH was decreased. The effect of light intensity on the CH 3 OH selectivity was also studied under different P CH 4/P O 2 ratios, namely 0.9, 1.5 and 2.6. The highest CH 3 OH selectivity was obtained at 1.5 ratio.

Kinetic study of the catalytic reforming of methane with carbon dioxide to synthesis gas over Ni/La 2O 3 catalyst

The kinetic behavior of the Ni/La 2O 3 catalyst in the reforming reaction of methane with carbon dioxide was investigated as a function of temperature and partial pressures of CH 4 and CO 2. The apparent activation energy of the reforming reaction was estimated to be 13.2 kcal/mol. It was also found that increase of the H 2 partial pressure leads to a continuous enhancement of the rate of CO formation, due to the simultaneous occurrence of the water-gas shift reaction. The mechanism of the CH 4/CO 2 reaction has been investigated using steady-state isotopic tracing and transient experiments, as well as FTIR, XRD, XPS and HR-TEM techniques. Based on the mechanistic results, a kinetic model was developed, which was found to predict satisfactorily the kinetic measurements. Methane cracking and the surface reaction between C and oxycarbonate species, are suggested to be the rate determining steps of the CH 4/CO 2 reaction over the Ni/La 2O 3 catalyst.

Oxidation of methane with nitrous oxide on calcium hydroxyapatites in the presence and absence of tetrachloromethane

The reactions of N 2O and CH 4 have been studied on calcium hydroxyapatite with various stoichiometries at 973 and 1023 K, partial pressures of CH 4, 28.7 kPa and of N 2O, 4.1 and 12.3 kPa, 30 ml min −1 and catalyst masses of 0.25, 0.5 and 0.75 g. On CaHAp with Ca/P from 1.59 to 1.72 the conversion of N 2O was 80±5% while that of CH 4 was 4±1%, regardless of Ca/P. The introduction of tetrachloromethane (TCM), with partial pressures: 0.085, 0.17 and 0.34 kPa, to the feedstream resulted in decreases in the conversions of both N 2O and CH 4 and increases in the selectivities to C 2 hydrocarbons and CO, apparently due to the formation of chlorapatite and/or nonstructural chlorine species in the catalysts.

Inhibition of methanogenesis by methyl fluoride: studies of pure and defined mixed cultures of anaerobic bacteria and archaea

Methyl fluoride (fluoromethane [CH(inf3)F]) has been used as a selective inhibitor of CH(inf4) oxidation by aerobic methanotrophic bacteria in studies of CH(inf4) emission from natural systems. In such studies, CH(inf3)F also diffuses into the anaerobic zones where CH(inf4) is produced. The effects of CH(inf3)F on pure and defined mixed cultures of anaerobic microorganisms were investigated. About 1 kPa of CH(inf3)F, similar to the amounts used in inhibition experiments, inhibited growth of and CH(inf4) production by pure cultures of aceticlastic methanogens (Methanosaeta spp. and Methanosarcina spp.) and by a methanogenic mixed culture of anaerobic microorganisms in which acetate was produced as an intermediate. With greater quantities of CH(inf3)F, hydrogenotrophic methanogens were also inhibited. At a partial pressure of CH(inf3)F of 1 kPa, homoacetogenic, sulfate-reducing, and fermentative bacteria and a methanogenic mixed culture of anaerobic microorganisms based on hydrogen syntrophy were not inhibited. The inhibition by CH(inf3)F of the growth and CH(inf4) production of Methanosarcina mazei growing on acetate was reversible. CH(inf3)F inhibited only acetate utilization by Methanosarcina barkeri, which is able to use acetate and hydrogen simultaneously, when both acetate and hydrogen were present. These findings suggest that the use of CH(inf3)F as a selective inhibitor of aerobic CH(inf4) oxidation in undefined systems must be interpreted with great care. However, by a careful choice of concentrations, CH(inf3)F may be useful for the rapid determination of the role of acetate as a CH(inf4) precursor.

Laser Assisted Deposition of Amorphous Hydrogen Containing Carbon at Room Temperature

ABSTRACTHydrogen-containing amorphous carbon films were produced from CH,I, by photolytical laser assisted chemical vapour deposition at room temperture. An Ar+ laser operated in the ultraviolet spectral region (351 and 364 nm) was used as the excitation source. The beam was focused in parallel to the Si(lOO) substrate. The deposition process was studied for different partial pressures of CH,I2 and for different heights of the laser beam above the substate surface. The mass thickness of the film was determined by energy dispersive X-ray spectrometry. The hydrogen content of the carbon films was determined by nuclear reaction analysis and the iodine content in the films was obtained by Auger electron spectroscopy and energy dispersive X-ray spectrometry. Carbon hybridization was investigated by Raman and infrared spectroscopy while morphology was examined by atomic force microscopy.

Structure of reactively sputtered chromium-carbon films

Chromium films having a thickness of a few microns have been prepared on stainless steel substrates maintained at different temperatures by reactive sputtering in different partial pressures of methane (CH 4) and argon. The composition of these films has been determined by electron microprobe analysis (EPMA). EPMA study of these films revealed that the carbon content in the film increases with increase in the partial pressure of CH 4. Electron diffraction study of the films revealed the normal b.c.c. structure of chromium. However, electron diffraction study of the films prepared at 500°C showed some extra reflections corresponding to d values of 2.33 and 1.77 Å. Electron microscopy study of the films revealed crystallites of chromium and the crystallite size of chromium in the film decreases with increase in the partial pressure of CH 4. However, the films prepared at a higher partial pressure of CH 4 (2.7 × 10 -1 Pa) exhibited an amorphous phase together with small crystallites of chromium. The films prepared at 250°C showed a strained structure when examined by transmission electron microscopy. The film prepared at 500°C did not show any strained structure.