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1.
The oxidative coupling of methane (OCM) was studied on BaF2/ LaOF and good catalytic results were obtained. Under the conditions of GHSV = 15 000 h−1 and a reaction temperature of 1043 K, a C 2 yield of 20.66% with a CH 4 conversion of 33.08% and a C 2 selectivity of 62.47% was achieved at CH4: O2 = 3:1, and high C 2 selectivities of 81.20% and 84.55% with a CH 4 conversion of 19.53% and 16.54% were obtained at CH 4:O 2 ratios of 6:1 and 9:1, respectively. X-ray diffraction results showed that only tetragonal LaOF existed in the BaF2/ LaOF catalysts with BaF 2 content below 18 mol-%, but a contracted BaF 2 phase was also observed at higher BaF 2 content (above 18 mol-%). 相似文献
2.
A series of bifunctional Ni-H 3PW 12O 40/SiO 2 catalysts for the hydrocracking of n-decane were designed and prepared. The evaluation results of the catalysts show that Ni-H 3PW 12O 40/SiO 2 catalysts possess a high activity for hydrocracking of n-decane and an excellent tolerance to the sulfur and nitrogen compounds in the feedstock. Under the reaction conditions: reaction temperature 300 °C; H 2/ n-decane volume ratio of 1500; total pressure of 2 Mpa and the LHSV 2 h −1, the conversion of n-decane over reduced 5%Ni-50%H 3PW 12O 40/SiO 2 catalysts is as high as 90%, the C 5+ selectivity equal to 70%. In order to reveal the structure and nature of the catalysts, a number of characterizations including XRD, Raman, H 2-TPD, NH 3-TPD, XPS and FT-IR of pyridine adsorption were carried out. The characteristic results show that the high activity of the catalysts and high C 5+ selectivity can be related to the unique structure of the H 3PW 12O 40 and its suitable acidity. 相似文献
3.
The oxidative coupling of methane over Li/MgO and BaBiO 3 - x catalysts irradiated by microwaves and classically heated is reported. Enhanced selectivities in C 2+ products are observed at lower temperatures under microwave conditions, especially with the Li/MgO catalyst. The complex permittivity measurements of BaBiO3 - x show that the regeneration of the active oxygen species on the surface is lower under microwave irradiation than classical heating. X-ray diffraction analyses of the catalyst before and after catalytic reaction, when it is classically heated and when it is heated by microwave irradiation, corroborate these results. Therefore, the CH3− carbanions are less oxidated at the catalyst surface under microwave irradiation. On the other hand, the quenching of the output gas probably decreases the oxidation of CH°3 radicals in the gas phase when the Li/MgO catalyst is irradiated by microwaves. The quenching of the output gas is a unique consequence of microwave irradiation which heats the catalyst without heating the wall of the reactor. 相似文献
4.
Pulse reaction method and in situ IR spectroscopy were used to characterize the active oxygen species for oxidative coupling of methane (OCM) over SrF 2/Nd 2O 3 catalyst. It was found that OCM activity of the catalyst was very low in the absence of gas phase oxygen, which indicated that lattice oxygen species contributed little to the yield of C 2 hydrocarbons. IR band of superoxide species (O 2−) was detected on the O 2-preadsorbed SrF 2/Nd 2O 3. The substitution of 18O 2 isotope for 16O 2 caused the IR band of O 2− at 1128 cm −1 to shift to lower wavenumbers (1094 and 1062 cm −1), consistent with the assignment of the spectra to the O 2− species. A good correlation between the rate of disappearance of surface O 2− and the rate of formation of gas phase C 2H 4 was observed upon interaction of CH 4 with O 2-preadsorbed catalyst at 700 °C. The O 2− species was also observed on the catalyst under working condition. These results suggest that O 2− species is the active oxygen species for OCM reaction on SrF 2/Nd 2O 3 catalyst. 相似文献
5.
A dense membrane tube made of Ba 0.5Sr 0.5Co 0.8Fe 0.2O 3−δ (BSCF) was prepared by plastic extrusion from BSCF oxide synthesized by the complexing EDTA-citrate method. The membrane tube was used in a catalytic membrane reactor for oxidative coupling of methane (OCM) to C 2 without an additional catalyst. At high methane concentration (93%), about 62% C 2 selectivity was obtained, which is higher than that achieved in a conventional reactor using the BSCF as a catalyst. The dependence of the OCM reaction on temperature and methane concentration indicates that the C 2 selectivity in the BSCF membrane reactor is limited by high ion recombination rates. If an active OCM catalyst (La-Sr/CaO) was packed in the membrane tube, C 2 selectivity and CH 4 conversion increased compared to the blank run. The highest C 2 yield in the BSCF membrane reactor in presence of the La-Sr/CaO catalyst was about 15%, similar to that in a packed-bed reactor with the same catalyst under the same conditions. However, the ratio of C 2H 4/C 2H 6 in the membrane reactor was much higher than that in the packed-bed reactor, which is an advantage of the membrane reactor. 相似文献
6.
Mn effect and characterization on γ-Al 2O 3-, -Al 2O 3- and SiO 2-supported Ru catalysts were investigated for Fischer–Tropsch synthesis under pressurized conditions. In the slurry phase Fischer–Tropsch reaction, γ-Al 2O 3 catalysts showed higher performance on CO conversion and C 5+ selectivity than -Al 2O 3 and SiO 2 catalysts. Moreover, Ru/Mn/γ-Al 2O 3 exhibited high resistance to catalyst deactivation and other catalysts were deactivated during the reaction. From characterization results on XRD, TPR, TEM, XPS and pore distribution, Ru particles were clearly observed over the catalysts, and γ-Al 2O 3 catalysts showed a moderate pore and particle size such as 8 nm, where -Al 2O 3 and SiO 2 showed highly dispersed ruthenium particles. The addition of Mn to γ-Al 2O 3 enhanced the removal of chloride from RuCl 3, which can lead to the formation of metallic Ru with moderate particle size, which would be an active site for Fischer–Tropsch reaction. Concomitantly, manganese chloride is formed. These schemes can be assigned to the stable nature of Ru/Mn/γ-Al 2O 3 catalyst. 相似文献
7.
Selective catalytic reduction (SCR) of NO with methane in the presence of excess oxygen has been investigated over a series of Mn-loaded sulfated zirconia (SZ) catalysts. It was found that the Mn/SZ with a metal loading of 2–3 wt.% exhibited high activity for the NO reduction, and the maximum NO conversion over the Mn/SZ catalyst was higher than that over Mn/HZSM-5. NH 3–TPD results of the catalysts showed that the sulfation process of the supports resulted in the generation of strong acid sites, which is essential for the SCR of NO with methane. On the other hand, the N 2 adsorption and the H 2–TPR of the catalysts demonstrated that the presence of the SO 42− species promoted the dispersion of the metal species and made the Mn species less reducible. Such an increased dispersion of metal species suppressed the combustion reaction of CH 4 by O 2 and increased the selectivity towards NO. The Mn/SZ catalysts prepared by different methods exhibited similar activities in the SCR of NO with methane, indicating the importance of SO 42−. The most attractive feature of the Mn/SZ catalysts was that they were more tolerant to water and SO 2 poisoning than Mn/HZSM-5 catalysts and exhibited higher reversibility after removal of SO 2. 相似文献
8.
Alkali halide added transition metal oxides produced ethylene selectively in oxidative coupling of methane. The role of alkali halides has been investigated for LiCl-added NiO (LiCl/NiO). In the absence of LiCl the reaction over NiO produced only carbon oxides (CO 2 + CO). However, addition of LiCl drastically improved the yield of C 2 compounds (C 2H 6 + C 2H 4). One of the roles of LiCl is to inhibit the catalytic activity of the host NiO for deep oxidation of CH 4. The reaction catalyzed by the LiCl/NiO proceeds stepwise from CH 4 to C 2H 4 through C 2H 6 (2CH 4 → C 2H 6 → C 2H 4). The study on the oxidation of C 2H 6 over the LiCl/NiO showed that the oxidative dehydrogenation of C 2H 6 to C 2H 4 occurs very selectively, which is the main reason why partial oxidation of CH 4 over LiCl/NiO gives C 2H 4 quite selectively. The other role of LiCl is to prevent the host oxide (NiO) from being reduced by CH 4. The catalyst model under working conditions was suggested to be the NiO covered with molten LiCl. XPS studies suggested that the catalytically active species on the LiCl/NiO is a surface compound oxide which has higher valent nickel cations (Ni (2+δ)+ or Ni 3+). The catalyst was deactivated at the temperatures>973 K due to vaporization of LiCl and consumption of chlorine during reaction. The kinetic and CH 4---CD 4 exchange studies suggested that the rate-determining step of the reaction is the abstraction of H from the vibrationally excited methane by the molecular oxygen adsorbed on the surface compound oxide. 相似文献
9.
CH 4/CO 2 reforming over La 2NiO 4 and 10%NiO/CeO 2–La 2O 3 catalysts under the condition of supersonic jet expansion was studied via direct monitoring of the reactants and products using the sensitive technique of cavity ring-down spectroscopy. Vibration–rotational absorption lines of CH 4, H 2O, CO 2 and CO molecules were recorded in the near infrared spectral region. Our results indicated that La 2NiO 4 is superior to 10%NiO/CeO 2–La 2O 3 in performance. In addition, we observed enhanced reverse-water-gas-shift reaction at augmented reaction temperature. The formation of reaction intermediates was also investigated by means of time-of-flight mass spectrometry and there was the detection of CH x+, OH + and H + species. 相似文献
10.
The homogeneous gas phase O 2-based oxidation of methane was studied in the temperature range, from 500°C to 750°C at methane partial pressures ranging from 3 bar to 40 bar. At the lower end of the temperature range methanol, formaldehyde, and CO represent the main products, while at temperatures exceeding 650° C/C-coupled products, C 2H 6, C 2H 4, C 3H 6 and C 3H 8 predominate. The change in selectivity as function of the temperature is well explained based on a free radical chain mechanism with degenerate branching, initiated by the gas phase reaction, CH 4+O 2→CH ·3+HO ·2. Bringing in basic catalysts known to catalyze the system at low methane partial pressures, in the reactor e.g. SrCO 3, BaCO 3, and 7% Li/MgO resulted in reduced rates of methane and oxygen conversions, and only minor changes in the selectivity to coupled products were observed. 相似文献
11.
Small Co clusters ( d<10 nm) supported over mixed La–Co–Fe perovskites were successfully synthesized. These catalysts were active for Fischer–Tropsch (FT). Depending on the Co to Fe ratios the mixed perovskite exhibited two different forms: the rhombohedral phase of LaCoO 3 is maintained for the mixed perovskite when x>0.5, the orthorhombic phase of LaFeO 3 is found for x<0.5. Interestingly only one of these structures is active for the FT reaction: the orthorhombic structure. This is most likely due to the capacity of this material to maintain its structure even with a high number of cation vacancies. These cations (mostly Co) were on purpose extracted and reduced. Magnetic measurements clearly showed their metallic nature. Rhombohedral Co–Fe mixed perovskites ( x≥0.5) cannot be used as precursors for Fischer–Tropsch catalysts: their partial reduction only consists in a complete reduction of Co 3+ into Co 2+. The partial reduction of orthorhombic perovskites (x<0.5) leads to active Fischer–Tropsch (FT) catalysts by formation of a metal phase well dispersed on a cation-deficient perovskite. The FT activity is related to the stability of the precursor perovskite. When initially calcined at 600 °C, a maximum of 8.6 wt.% of Co0 can be extracted from LaCo0.40Fe0.60O3 (compared to only 2 wt.% after calcination at 750 °C). The catalyst is then composed of Co0 particles of 10 nm on a stable deficient perovskite LaCo0.053+Fe0.603+O2.40. Catalytic tests showed that up to 70% in the molar selectivity for hydrocarbons was obtained at 250 °C, 40% of which was composed of the C2–C4 fraction. 相似文献
12.
The selective catalytic reduction (SCR) of NO by hydrocarbon is an efficient way to remove NO emission from lean-burn gasoline and diesel exhaust. In this paper, a thermally and hydrothermally stable Al–Ce-pillared clay (Al–Ce-PILC) was synthesized and then modified by SO 42−, whose surface area and average pore diameter calcined at 773 K were 161 m 2/g and 12.15 nm, respectively. Copper-impregnated Al–Ce-pillared clay catalyst (Cu/SO 42−/Al–Ce-PILC) was applied for the SCR of NO by C 3H 6 in the presence of oxygen. The catalyst 2 wt% Cu/SO 42−/Al–Ce-PILC showed good performance over a broad range of temperature, its maximum conversion of NO was 56% at 623 K and remained as high as 22% at 973 K. Furthermore, the presence of 10% water slightly decreased its activity, and this effect was reversible following the removal of water from the feed. Py-IR results showed SO 42− modification greatly enhanced the number and strength of Brönsted acidity on the surface of Cu/SO 42−/Al–Ce-PILC, which played a vital role in the improvement of NO conversion. TPR and XPS results indicated that both Cu + and isolated Cu 2+ species existed on the optimal catalyst, mainly Cu +, as Cu content increased to 5 wt%, another species CuO aggregates which facilitated the combustion of C 3H 6 were formed. 相似文献
13.
Li-doped sulfated-zirconia catalysts were found to be effective for oxidative coupling of methane (OCM). The catalyst performances depend on the sulfate content and calcination temperature. A maximum C 2 yield is attained over the catalysts, which contain 6 wt.% sulfate and calcined at 923–973 K, being closely related to the preparation conditions of sulfated-ZrO 2 as solid super-acids. When the performances of the Li-doped sulfated-ZrO 2 (Li/SZ) catalysts were tested at 1023 K as a function of reaction time, both the C 2 and CO x selectivities remained constant over the range of 8 h, but the CH 4 conversion decreased from 17.5% to 11.9%. The nature of Li/SZ catalysts for the OCM was investigated by X-ray diffraction, XPS, and NH 3 and CO 2 TPD measurements. It could be postulated that the sulfated-ZrO 2 surface could play an important role in the formation of a catalytically active structure by Li-doping. 相似文献
14.
The pulse corona plasma has been used as an activation method for reaction of methane and carbon dioxide, the product was C 2 hydrocarbons and by-products were CO and H 2. Methane conversion and the yield of C 2 hydrocarbons were affected by the carbon dioxide concentration in the feed. The conversion of methane increased with increasing carbon dioxide concentration in the feed whereas the yield of C 2 hydrocarbons decreased. The synergism of La 2O 3/γ-Al 2O 3 and plasma gave methane conversion of 24.9% and C 2 hydrocarbons yield of 18.1% were obtained at the power input of plasma was 30 W. The distribution of C 2 hydrocarbons changed by using Pd-La 2O 3/γ-Al 2O 3 catalyst, the major C 2 product was ethylene. 相似文献
15.
A series of CoO x/Al 2O 3 catalysts was prepared, characterized, and applied for the selective catalytic reduction (SCR) of NO by C 3H 8. The results of XRD, UV–vis, IR, Far-IR and ESR characterizations of the catalysts suggest that the predominant oxidation state of cobalt species is +2 for the catalysts with low cobalt loading (≤2 mol%) and for the catalysts with 4 mol% cobalt loading prepared by sol–gel and co-precipitation. Co 3O 4 crystallites or agglomerates are the predominant species in the catalysts with high cobalt loading prepared by incipient wetness impregnation and solid dispersion. An optimized CoO x/Al 2O 3 catalyst shows high activity in SCR of NO by C 3H 8 (100% conversion of NO at 723 K, GHSV: 10,000 h −1). The activity of the selective catalytic reduction of NO by C 3H 8 increases with the increase of cobalt–alumina interactions in the catalysts. The influences of cobalt loading and catalyst preparation method on the catalytic performance suggest that tiny CoAl 2O 4 crystallites highly dispersed on alumina are responsible for the efficient catalytic reduction of NO, whereas Co 3O 4 crystallites catalyze the combustion of C 3H 8 only. 相似文献
16.
In order to examine the importance of the further oxidation of the desired C 2 products in the oxidative coupling of methane, ethylene and ethane have been added to the feed (containing methane and oxygen) to a Li/MgO or Ca/Sm 2O 3 catalyst. The results of these measurements show that neither of these C 2 molecules is stable under these conditions with either of the catalysts. Additionally, the rates of the oxidation of ethane and of ethylene alone have been measured using a gradientless reactor for both catalysts as well as for a quartz bed. It was found that the Ca/Sm 2O 3 material had higher activities for the oxidation of C 2H 6 and C 2H 4 (and also of CH 4) than had the Li/MgO material. These higher activities result in a lower optimal reaction temperature for the oxidative coupling of methane and are (at least partially) responsible for the lower selectivity to C 2 products observed with the Ca/Sm 2O 3 catalyst compared to that with the Li/MgO catalyst. 相似文献
17.
The activity of several catalysts are studied in the soot combustion reaction using air and NO/air as oxidising agents. Over Al 2O 3-supported catalysts NO (g) is a promoter for the combustion reaction with the extent of promotion depending on the Na loading. Over these catalysts SO 42− poisons this promotion by preventing NO oxidation through a site blocking mechanism. SiO 2 is unable to adsorb NO or catalyse its oxidation and over SiO 2-supported Na catalysts NO (g) inhibits the combustion reaction. This is ascribed to a competition between NO and O 2. Over Fe-ZSM-5 catalysts the presence of a NO x trapping component does not increase the combustion of soot in the presence of NO (g) and it is proposed that this previously reported effect is only seen under continuous NO x trap operation as NO 2 is periodically released during regeneration and thus available for soot combustion. Experiments during which the [NO] (g) is varied show that CO, rather than an adsorbed carbonyl-like intermediate, is formed upon reaction between NO 2 (the proposed oxygen carrier) and soot. 相似文献
18.
The direct partial oxidation of hydrocarbons offers promising alternatives to chemical synthesis. By replacing endothermic processes such as steam reforming and steam cracking, fast and exothermic oxidation reactions should require much smaller and simpler reactors. However, direct oxidation reactions are much more difficult to manage because of potential heat release in total oxidation and hazardous because of the possibility of homogeneous reactions which are nonselective and can produce flames and explosions. We describe experiments in which monolith catalysts are used for partial oxidation of CH 4 and C 2H 6 to produce synthesis gas or alkenes by direct oxidation at or above atmospheric pressure in pure O 2 in nearly adiabatic reactors operating at 1000°C with very high flowrates (space velocities of 10 6h −1 and residence times of 10 −3 s). With methane oxidation we obtain over 90% selectivities to synthesis gas (a 2:1 H 2:CO mixture) with> 90% conversion of the methane and complete conversion of O 2 on Rh coated ceramic monoliths with contact times of 10 −3 s. With Pt catalysts under the same conditions, the H 2 selectivity drops to 70%; while with Pd, the catalyst rapidly forms carbon. This process appears to be primarily a surface reaction in which CH4 pyrolyzes on the hot Rh surface and the H atoms dimerize and the carbon is oxidized to CO. A model has been constructed which accurately predicts the conversions and selectivities and the variations between Rh and Pt. With higher alkanes, synthesis gas is produced on Rh with comparable selectivities and conversions on metal-coated monoliths. However, with Pt we observe up to 70% selectivity to alkenes with 80% conversion of alkanes at adiabatic temperatures near 1000°C with approximately 5 ms contact times. These results can be explained as occurring by predominantly surface reactions in which the alkane adsorbs to form the alkyl by H abstraction with adsorbed O atoms. Then the adsorbed alkyls undergo primarily β-elimination reactions on Pt to produce alkenes. These products are therefore far from thermodynamic equilibrium at these very short contact times, even though the temperatures are very high. The use of very short contact times and high temperatures promises to provide new routes to production of partial oxidation products with very small adiabatic reactors and thus opens up new types of reactions and reactors for chemical synthesis. 相似文献
19.
The decomposition of N 2O, and the catalytic reduction by NH 3 of N 2O and N 2O + NO, have been studied on Fe-BEA, -ZSM-5 and -FER catalysts. These catalysts were prepared by classical ion exchange and characterized by TPR after various activation treatments. Fe-FER is the most active material in the catalytic decomposition because “oxo-species” reducible at low temperature, appearing upon interaction of Fe II-zeolite with N 2O (-oxygen), are formed in largest amounts with this material. The decomposition of N 2O is promoted by addition of NH 3, and even more with NH 3 + NO in the case of Fe-FER and -BEA. It is proposed that the NO-promoted reduction of N 2O originated from the fast surface reaction between -oxygen O * and NO * to yield NO 2*, which in turn reacts immediately with NH 3. 相似文献
20.
Three supported La 0.8Sr 0.2MnO 3+x catalysts were prepared, one supported on lanthanum-stabilised alumina and two supported on a NiAl 2O 4 spinel. The catalysts were characterised using X-ray diffraction, transmission electron microscopy and surface area measurements following heat-treatments at temperatures up to 1200°C in air. In the alumina-supported catalyst, a reaction occurred between the active phase and the support at high temperatures, indicating that these materials would be unsuitable for high temperature catalytic combustion. Only in the NiAl 2O 4-supported catalysts were the supported perovskite phases found to be stable at high temperature. These catalysts showed good methane combustion activity. 相似文献
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