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1.
The oxy-CO 2 methane reforming reaction (OCRM) has been investigated over CoO x supported on a MgO precoated highly macroporous silica–alumina catalyst carrier (SA-5205) at different reaction temperatures (700–900 °C), O 2/CH 4 ratios (0.3–0.45) and space velocites (20,000–100,000 cc/g/h). The reaction temperature had a profound influence on the OCRM performance over the CoO/MgO/SA-5205 catalyst; the methane conversion, CO 2 conversion and H 2 selectivity increased while the H 2/CO ratio decreased markedly with increasing reaction temperature. While the O 2/CH 4 ratio did not strongly affect the CH 4 and CO 2 conversion and H 2 selectivity, it had an intense influence on the H 2/CO ratio. The CH 4 and CO 2 conversion and the H 2 selectivity decreased while the H 2/CO increased with increasing space velocity. The O 2/CH 4 ratio and the reaction temperature could be used to manipulate the heat of the reaction for the OCRM process. Depending on the O 2/CH 4 ratio and temperature the OCRM process could be operated in a mildly exothermic, thermal neutral or mildly endothermic mode. The OCRM reaction became almost thermoneutral at an OCRM reaction temperature of 850 °C, O 2/CH 4 ratio of 0.45 and space velocity of 46,000 cc/g/h. The CH 4 conversion and H 2 selectivity over the CoO/MgO/SA-5205 catalyst corresponding to thermoneutral conditions were excellent: 95% and 97%, respectively with a H 2/CO ratio of 1.8. 相似文献
2.
The optimization of process parameters and catalyst compositions for the CO 2 oxidative coupling of methane (CO 2-OCM) reaction over CaO–MnO/CeO 2 catalyst was developed using Response Surface Methodology (RSM). The relationship between the responses, i.e. CH 4 conversion, C 2 hydrocarbons selectivity or yield, with four independent variables, i.e. CO 2/CH 4 ratio, reactor temperature, wt.% CaO and wt.% MnO in the catalyst, were presented as empirical mathematical models. The maximum C 2 hydrocarbons selectivity and yields of 82.62% and 3.93%, respectively, were achieved by the individual-response optimization at the corresponding optimal process parameters and catalyst compositions. However, the CH 4 conversion was a saddle function and did not show a unique optimum as revealed by the canonical analysis. Moreover pertaining to simultaneous multi-responses optimization, the maximum C 2 selectivity and yield of 76.56% and 3.74%, respectively, were obtained at a unique optimal process parameters and catalyst compositions. It may be deduced that both individual- and multi-responses optimizations are useful for the recommendation of optimal process parameters and catalyst compositions for the CO 2-OCM process. 相似文献
3.
Potassium-promoted β-Mo 2C catalysts were prepared and their performances in CO hydrogenation were investigated. The main products over β-Mo 2C catalyst were C 1-C 4 hydrocarbons, only ∼4 C-atom% alcohols were obtained. The products of hydrocarbons and alcohols obeyed traditional linear Anderson-Schultz-Flory (A-S-F) distribution. However, modification with K 2CO 3 resulted in a remarkable selectivity shift from hydrocarbons to alcohols. Moreover, it was found that potassium promoter enhanced the ability of chain propagation of β-Mo 2C catalysts and resulted in a higher selectivity to C 2+OH. For K/β-Mo 2C catalysts, the hydrocarbon products also obeyed traditional linear A-S-F plots, whereas alcohols gave a unique linear A-S-F distribution with remarkable deviation of methanol compared with that on β-Mo 2C catalyst. It could be concluded that potassium promoter might exert a prominent function on the whole chain propagation to produce alcohols. A surface phase on the K/β-Mo 2C catalysts such as the “K-Mo-C” explained the higher value for C 2+OH, especially could promote the step of C 1OH to C 2OH, or could have a role in producing directly C 2OH, but again this would be speculative. At the same time, the influence of the loadings of K 2CO 3 on the performances of β-Mo 2C catalyst was investigated and the results revealed that the maximum yield of alcohol was obtained at K/Mo molar ratio of 0.2. 相似文献
4.
In the hydrogenation of CO at atmospheric pressure, unsupported molybdenum carbide catalyst produced mostly C 1-C 5 paraffins. Promotion of the catalyst with K 2CO 3 yielded C 2-C 5 hydrocarbons consisting of 80–100% olefins and reduced the methane selectivity. The selectivity of C 2-C 5 olefins among all hydrocarbon products was 50–70 wt% at CO conversions up to 70%.This work has been supported by Korean Science and Engineering Foundation through a contract 88-03-1302. 相似文献
5.
CO hydrogenation using cobalt/ manganese oxide catalysts is described and discussed. These catalysts are known to give low methane selectivity with high selectivity to C 3 hydrocarbons at moderate reaction conditions (GHSV < 500 h –1, < 600 kPa). In this study the effect of reaction conditions more appropriate to industrial operation are investigated. CO hydrogenation at 1–2 MPa using catalyst formulations with Co/Mn = 0.5 and 1.0 gives selectivities to methane that are comparable to those observed at lower pressures. At the higher pressure the catalyst rapidly deactivates, a feature that is not observed at lower pressures. However, prior to deactivation rates of CO + CO 2 conversion > 8 mol/1-catalyst h can be observed. Co-feeding ethene during CO hydrogenation is investigated by the reaction of 13C0- 12C 2H 4-H 2 mixtures and a significant decrease in methane selectivity is observed but the hydrogenation of ethene is also a dominant reaction. The results show that the co-fed ethene can be molecularly incorporated but in addition it can generate a C, species that can react further to form methane and higher hydrocarbons. 相似文献
6.
The reaction path of isoalkanes formation via CO 2 hydrogenation was studied over the Fe–Zn–Zr/HY composite catalyst, which gives high selectivity to isoalkanes. The results indicate that the reverse water–gas shift reaction is not the indispensable step for the synthesis of hydrocarbons. And i-C 4 ( iso-butane) is formed from propylene and methanol through MTG (methanol to gasoline) reaction and i-C 5 ( iso-pentane) obtained from the reaction of C 2 and C 3 through the additive dimerization. A part of C 1, C 4 is formed on the sole Fe–Zn–Zr catalyst from methanol for the CO 2 hydrogenation over Fe–Zn–Zr/HY composite catalyst. 相似文献
7.
The effects of CO 2, CO and H 2 co-reactants on CH 4 pyrolysis reactions catalyzed by Mo/H-ZSM-5 were investigated as a function of reaction temperatures and co-reactant and CH 4 concentrations. Total CH 4 conversion rates were not affected by CO 2 co-reactants, except at high CO 2 pressures, which led to the oxidation of the active MoC
x
species, but CH
x
intermediates formed in rate-determining C–H bond activation steps increasingly formed CO instead of hydrocarbons as CO 2 concentrations increased. CO formation rates increased with increasing CO 2 partial pressure; all entering CO 2 molecules reacted with CH 4 within the catalyst bed to form two CO molecules at 950-1033 K. In contrast, hydrocarbon formation rates decreased linearly with increasing CO 2 partial pressure and reached undetectable levels at CO 2/CH 4 ratios above 0.075 at 950 K. CO formation continued for a short period of time at these CO 2/CH 4 molar ratios, but then all catalytic activity ceased, apparently as a result of the conversion of active carbide structures to MoO
x
. The removal of CO 2 from the CH 4 stream led to gradual catalyst reactivation via reduction-carburization processes similar to those observed during the initial activation of MoO
x
/H-ZSM-5 precursors in CH 4. The CO 2/CH 4 molar ratios required to inhibit hydrocarbon synthesis were independent of CH 4 pressure because of the first-order kinetic dependencies of both CH 4 and CO 2 activation steps. These ratios increased from 0.075 to 0.143 as reaction temperatures increased from 950 to 1033 K. This temperature dependence reflects higher activation energies for reductant (CH 4) than for oxidant (CO 2) activation, leading to catalyst oxidation at higher relative oxidant concentrations as temperature increases. The scavenging of CH
x
intermediates by CO 2-derived species leads also to lower chain growth probabilities and to a significant inhibition of catalyst deactivation via oligomerization pathways responsible for the formation of highly unsaturated unreactive deposits. CO co-reactants did not influence the rate or selectivity of CH 4 pyrolysis reactions on Mo/H-ZSM-5; therefore, CO formed during reactions of CO 2/CH 4 mixtures are not responsible for the observed effects of CO 2 on reaction rates and selectivities, or in catalyst deactivation rates during CH 4 reactions. H 2 addition studies showed that H 2 formed during CH 4/CO 2 reactions near the bed inlet led to inhibited catalyst deactivation in downstream catalyst regions, even after CO 2 co-reactants were depleted. 相似文献
8.
This paper reports on notable promotion of C 2 + hydrocarbons formation from CO 2 hydrogenation induced by combining Fe and a small amount of selected transition metals. Al 2O 3-supported bimetallic Fe–M (M = Co, Ni, Cu, Pd) catalysts as well as the corresponding monometallic catalysts were prepared, and examined for CO 2 hydrogenation at 573 K and 1.1 MPa. Among the monometallic catalysts, C 2 + hydrocarbons were obtained only with Fe catalyst, while Co and Ni catalysts yielded higher CH 4 selectively than other catalysts. The combination of Fe and Cu or Pd led to significant bimetallic promotion of C 2 + hydrocarbons formation from CO 2 hydrogenation, in addition to Fe–Co formulation discovered in our previous work. CO 2 conversion on Ni catalyst nearly reached equilibrium for CO 2 methanation which makes this catalyst suitable for making synthetic natural gas. Fe–Ni bimetallic catalyst was also capable of catalyzing CO 2 hydrogenation to C 2 + hydrocarbons, but with much lower Ni/(Ni+Fe) atomic ratio compared to other bimetallic catalysts. The addition of a small amount of K to these bimetallic catalysts further enhanced CO 2 hydrogenation activity to C 2 + hydrocarbons. K-promoted Fe–Co and Fe–Cu catalysts showed better performance for synthesizing C 2 + hydrocarbons than Fe/K/Al 2O 3 catalyst which has been known as a promising catalyst so far. 相似文献
9.
A monolithic electropromoted reactor (MEPR) with up to 22 thin Rh/YSZ/Pt or Cu/TiO 2/YSZ/Au plate cells was used to investigate the hydrogenation of CO 2 at atmospheric pressure and temperatures 220–380 °C. The Rh/YSZ/Pt cells lead to CO and CH 4 formation and the open-circuit selectivity to CH 4 is less than 5%. Both positive and negative applied potentials enhance significantly the total hydrogenation rate but the selectivity to CH 4 remains below 12%. The Cu/TiO 2/YSZ/Au cells produce CO, CH 4 and C 2H 4 with selectivities to CH 4 and C 2H 4 up to 80% and 2%. Both positive and negative applied potential significantly enhance the hydrogenation rate and the selectivity to C 2H 4. It was found that the addition of small (0.5 kPa) amounts of CH 3OH in the feed has a pronounced promotional effect on the reaction rate and selectivity of the Cu/TiO 2/YSZ/Au cells. The selective reduction of CO 2 to CH 4 starts at 220 °C (vs 320 °C in absence of CH 3OH) with near 100% CH 4 selectivity at open-circuit and under polarization conditions at temperatures 220–380 °C. The results show the possibility of direct CO 2 conversion to useful products in a MEPR via electrochemical promotion at atmospheric pressure. 相似文献
10.
The synthesis and characterization of an inexpensive porous MoxCy/SiO2 material is presented, which was obtained by mixing ammonium hexamolybdate, sucrose, and a mesoporous silica (SBA-15), with a subsequent heat treatment under inert atmosphere. This porous material presented a specific surface area of 170 m2/g. The catalytic behavior in CO2 hydrogenation was compared with that of Mo2C and α-MoC1?x obtained from ammonium hexamolybdate and sucrose, using different Mo/C ratios. CO2 hydrogenation tests were performed at moderate (100 kPa) and high pressures (2.0 MPa), and it was found that only CO, H2O and CH4 are formed at moderate pressures by the three materials, while at higher pressures, methanol and hydrocarbons (C2H6, C3H8) are also obtained. Differences in selectivity were observed at the high pressure tests. Mo2C presented higher selectivity to CO and methanol compared with MoC1?x, which showed preferential selectivity to hydrocarbons (CH4, C2H6). The porous MoxCy/SiO2 material showed the highest CO2 hydrogenation activity at high temperatures (270 and 300 °C), being a promising material for the conversion of CO2 to CO and CH4. 相似文献
11.
The hydrogenation of CO 2 has been studied over Fe/alumina and Fe-K/alumina catalysts. The addition of potassium increases the chemisorption ability of CO 2 but decreases that of H 2. The catalytic activity test at high pressure (20 atm) reveals that remarkably high activity and selectivity toward light olefins and C 2+ hydrocarbons can be achieved with Fe-K/alumina catalysts containing high concentration of K (K/Fe molar ratio = 0.5, 1.0). In the reaction at atmospheric pressure, the highly K-promoted catalysts give much higher CO formation rate than the unpromoted catalyst. It is deduced that the remarkable catalytic properties in the presence of K are attributable to the increase in the ability of CO 2 chemisorption and the enhanced activity for CO formation, which is the preceding step of C 2+ hydrocarbon formation. 相似文献
12.
Biomass gasification and subsequent conversion of this syngas to liquid hydrocarbons using Fischer–Tropsch (F–T) synthesis is a promising source of hydrocarbon fuels. However, biomass-derived syngas is different from syngas obtained from other sources such as steam reforming of methane. Specifically the H 2/CO ratio is less than 1/1 and the CO 2 concentrations are somewhat higher. Here, we report the use of Fe-based F–T catalysts for the conversion of syngas produced by the air-blown, atmospheric pressure gasification of southern pine wood chips. The syngas from the gasification step is compressed and cleaned in a series of sorbents to produce the following feed to the F–T step: 2.78 % CH 4, 11 % CO 2, 15.4 % H 2, 21.3 % CO, and balance N 2. The relatively high level of CO 2 suggests the need to use catalysts that are active for CO 2 hydrogenation as well is resistant to oxidation in presence of high levels of CO 2. The work reported here focuses on the effect of these different structural promoters on iron-based F–T catalysts with the general formulas 100Fe/5Cu/4K/15Si, 100Fe/5Cu/4K/15Al and 100Fe/5Cu/4K/15Zn. Although the effect of Si, Al or Zn on iron-based F–T catalysts has been examined previously for CO+CO 2 hydrogenation, we have found no direct comparison of these three structural promoters, nor any studies of these promoters for a syngas produced from biomass. Results show that catalysts promoted with Zn and Al have a higher extent of reduction and carburization in CO and higher amount of carbides and CO adsorption as compared to Fe/Cu/K/Si. This resulted in higher activity and selectivity to C 5+ hydrocarbons than the catalyst promoted with silica. 相似文献
13.
A batch reactor directly combined with an ultrahigh vacuum apparatus, which is equipped with facilities for catalyst preparation and Auger electron spectroscopy, was used to answer some questions which had arisen in recent studies concerning carbon dioxide hydrogenation on pure metallic and supported Co catalysts. Both oxygen incorporated during oxidation/reduction cycles and carbon deposited when CO 2 is hydrogenated penetrate deep into the bulk. This kind of carbon can easily be hydrogenated. CO strongly hinders the reduction of the oxidized Co surface in the H 2/CO 2 reaction mixture (4 : 1). CO hydrogenation is favoured over CO 2 hydrogenation and leads to a higher percentage of C 2 to C 4 hydrocarbons as compared with CH 4 formation. 相似文献
14.
Hydroformylation of ethylene and CO hydrogenation were studied over cobalt-based catalysts derived from reaction of Co 2(CO) 8 with ZnO, MgO and La 2O 3 supports. At 433 K a similar activity sequence was reached for both reactions: Co/ ZnO > Co/La 2O 3 > Co/MgO. This confirms the deep analogy between hydroformylation and CO hydrogenation into alcohols. In the CO hydrogenation the selectivity towards alcohol mixture (C 1-C 3) was found to be near 100% at 433 K for a conversion of 6% over the Co/ZnO catalyst; this catalyst showed oxo selectivity higher than 98% in the hydroformylation of ethylene. Magnetic experiments showed that no metallic cobalt particles were formed at 433 K. It is suggested that the active site for the step that is common to both reactions is related to the surface homonuclear Co 2+/[Co(CO) 4] – ion-pairing species. 相似文献
15.
The hydrogenation of C, CO, and CO 2 has been studied on polycrystalline cobalt foils using a combination of UHV studies and atmospheric pressure reactions in temperature range from 475 to 575 K at 101 kPa total pressure. The reactions produce mainly methane but with selectivities of 98, 80, and 99 wt% at 525 K for C, CO, and CO 2, respectively. In the C and CO 2 hydrogenation the rest is ethane, whereas in CO hydrogenation hydrocarbons up to C 4 were detected. The activation energies of methane formation are 57, 86, and 158 kJ/mol from C, CO, and CO 2, respectively. The partial pressure dependencies of the CO and CO 2 hydrogenation indicate roughly first order dependence on hydrogen pressure (1.5 and 0.9), negative first order on CO (–0.75) and zero order on CO 2 (–0.05). Post reaction spectroscopy revealed carbon deposition from CO and oxygen deposition from CO 2 on the surface above 540 K. The reduction of cobalt oxide formed after dissociation of C-O bonds on the surface is proposed to be the rate limiting step in CO and CO 2 hydrogenation. 相似文献
16.
In the production of higher hydrocarbons, combining oxidative coupling of methane (OCM) with hydrogenation of the formed carbon oxides in a separate reactor provides an alternative to the currently applied methane conversion to syngas followed by Fischer‐Tropsch synthesis. The effects of CH 4:O 2 feed ratio in the OCM reactor and partial pressures of H 2 or/and H 2O in the hydrogenation reactor were analyzed to maximize production of C 2+ hydrocarbons and reduce CO x formation. The highest C 2+ yield was achieved with low CH 4:O 2 feed ratio for OCM and removal of the formed water before entering the hydrogenation reactor. 相似文献
17.
The hydrogenation of CO 2 was investigated over a Rh catalyst prepared from an amorphous Rh 20Zr 80 alloy. After the reaction, the catalyst was regenerated by oxidation in air and reduction in H 2. It was observed that the reaction activity increased with the repetition of regeneration. We also prepared the Rh/ZrO 2 catalyst by the conventional impregnation method. The difference in the turnover frequency between the alloy-precursor catalyst and the conventionally prepared catalyst was small. For the alloy-precursor catalyst, however, the conversion and CH 4 selectivity were stable at 723 K, whereas the conversion and CH 4 selectivity decreased with time-on-stream even at 673 K for the catalyst prepared by the conventional impregnation method. 相似文献
18.
Pulse studies of the interaction of CH 4 and NiO/Al 2O 3 catalysts at 500°C indicate that CH 4 adsorption on reduced nickel sites is a key step for CH 4 oxidative conversion. On an oxygen-rich surface, CH 4 conversion is low and the selectivity of CO 2 is higher than that of CO. With the consumption of surface oxygen, CO selectivity increases while the CO 2 selectivity falls. The conversion of CH 4 is small at 500°C when a pulse of CH 4/O 2 (CH 4O 2=21) is introduced to the partially reduced catalyst, indicating that CH 4 and O 2 adsorption are competitive steps and the adsorption of O 2 is more favorable than CH 4 adsorption 相似文献
19.
Almost 100% CO selectivity was achieved with small pulses of CH 4/O 2 (2/1), using very short residence times over a reduced NiO/La 2O 3 catalyst. One concludes that CH 4 conversion depends on its dissociation, whereas CO selectivity is mainly dependent on the strength of oxygen binding to the catalyst. Over the reduced catalyst, the oxygen species oxidize with difficulty (because of their strong binding to metal Ni) CO to CO 2, whereas over the unreduced catalyst (which contains Ni oxide), the oxygen species easily oxidize (because they are weakly adsorbed) CO to CO 2. 相似文献
20.
The influence of CO 2 on the deactivation of Co/γ-Al 2O 3 Fischer–Tropsch (FT) catalyst in CO hydrogenation has been investigated. The presence of CO 2 in the feed stream reveals a negative effect on catalyst stability and in the formation of heavy hydrocarbons. The CO 2 acts as a mild oxidizing agent on cobalt metal during Fischer–Tropsch synthesis. During FT synthesis on Co/γ-Al 2O 3 of 70 h, the CO conversion and C 5+ selectivity in the presence of CO 2 decreased more significantly than in the absence of CO 2. CO 2 is found to be responsible for the partial oxidation of surface cobalt metal at FT synthesis environment with the co-existence of generated water. 相似文献
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