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1.
The catalytic reduction of N 2O by CH 4, CO, and their mixtures has been comparatively investigated over steam-activated FeZSM-5 zeolite. The influence of the molar feed ratio between N 2O and the reducing agents, the gas-hourly space velocity, and the presence of O 2 on the catalytic performance were studied in the temperature range of 475–850 K. The CH 4 is more efficient than CO for N 2O reduction, achieving the same degree of conversion at significantly lower temperatures. The apparent activation energy for N 2O reduction by CH 4 was very similar to that of direct N 2O decomposition (140 kJ mol −1), being much lower for the N 2O reduction by CO (60 kJ mol −1). This suggests that the reactions have a markedly different mechanism. Addition of CO using equimolar mixtures in the ternary N 2O + CH 4 + CO system did not affect the N 2O conversion with respect to the binary N 2O + CH 4 system, indicating that CO does not interfere in the low-temperature reduction of N 2O by CH 4. In the ternary system, CO contributed to N 2O reduction when methane was the limiting reactant. The conversion and selectivity of the reactions of N 2O with CH 4, CO, and their mixtures were not altered upon adding excess O 2 in the feed. 相似文献
2.
The NO-H 2-O 2 reaction was studied over supported bimetallic catalysts, Pt-Mo and Pt-W, which were prepared by coexchange of hydrotalcite-like Mg-Al double layered hydroxides by Pt(NO 2) 42−, MoO 42−, and/or WO 42− and subsequent heating at 600 °C in H 2. The Pt–Mo interaction could obviously be seen when the catalyst after reduction treatment was exposed to a mixture of NO and H 2 in the absence of O 2. The Pt-HT catalyst showed the almost complete NO conversion at 70 °C, whereas the Pt-Mo-HT showed a negligible conversion. Upon exposure to O 2, however, Pt-Mo-HT exhibited the NO conversion at the lowest temperature of ≥30 °C, compared to ≥60 °C required for Pt-HT. EXAFS/XANES, XPS and IR results suggested that the role of Mo is very sensitive to the oxidation state, i.e., oxidized Mo species residing in Pt particles are postulated to retard the oxidative adsorption of NO as NO 3 and promote the catalytic conversion of NO to N 2O at low temperatures. 相似文献
3.
Both NO decomposition and NO reduction by CH 4 over 4%Sr/La 2O 3 in the absence and presence of O 2 were examined between 773 and 973 K, and N 2O decomposition was also studied. The presence of CH 4 greatly increased the conversion of NO to N 2 and this activity was further enhanced by co-fed O 2. For example, at 773 K and 15 Torr NO the specific activities of NO decomposition, reduction by CH 4 in the absence of O 2, and reduction with 1% O 2 in the feed were 8.3·10 −4, 4.6·10 −3, and 1.3·10 −2 μmol N 2/s m 2, respectively. This oxygen-enhanced activity for NO reduction is attributed to the formation of methyl (and/or methylene) species on the oxide surface. NO decomposition on this catalyst occurred with an activation energy of 28 kcal/mol and the reaction order at 923 K with respect to NO was 1.1. The rate of N 2 formation by decomposition was inhibited by O 2 in the feed even though the reaction order in NO remained the same. The rate of NO reduction by CH 4 continuously increased with temperature to 973 K with no bend-over in either the absence or the presence of O 2 with equal activation energies of 26 kcal/mol. The addition of O 2 increased the reaction order in CH 4 at 923 K from 0.19 to 0.87, while it decreased the reaction order in NO from 0.73 to 0.55. The reaction order in O 2 was 0.26 up to 0.5% O 2 during which time the CH 4 concentration was not decreased significantly. N 2O decomposition occurs rapidly on this catalyst with a specific activity of 1.6·10 −4 μmol N 2/s m 2 at 623 K and 1220 ppm N 2O and an activation energy of 24 kcal/mol. The addition of CH 4 inhibits this decomposition reaction. Finally, the use of either CO or H 2 as the reductant (no O 2) produced specific activities at 773 K that were almost 5 times greater than that with CH 4 and gave activation energies of 21–26 kcal/mol, thus demonstrating the potential of using CO/H 2 to reduce NO to N 2 over these REO catalysts. 相似文献
4.
The objective of this work was to study the promotional effect of Pt on Co-zeolite (viz. mordenite, ferrierite, ZSM-5 and Y-zeolite) and Co/Al 2O 3 on the selective catalytic reduction (SCR) of NO x with CH 4 under dry and wet reaction stream. After being reduced in H 2 at 350°C, the PtCo bimetallic zeolites showed higher NO to N 2 conversion and selectivity than the monometallic samples, as well as a combination of the latter samples such as mechanical mixtures or two-stage catalysts. After the same pretreatment, under wet reaction stream, the bimetallic samples were also more active. Among the other catalysts studied with 5% of water in the feed, (NO = CH 4 = 1000 ppm, O 2 = 2%), the NO conversion dropped to zero over Co 2.0Mor at 500°C and GHSV = 30,000 h −1, whereas it is 20% in Pt 0.5Co 2.0Mor. In Pt/Co/Al 2O 3 the NO x conversion dropped below 5% with only 2% of water under the same reaction conditions. The specific activity given as molecules of NO converted per total metal atom per second were 16.5 × 10 −4 s −1 for Pt 0.5Co 2.0Fer, 13 × 10 −4 s −1 for Pt 0.5Co 2.0Mor, 4.33 × 10 −4 s −1 for Pt 0.5Co 2.0ZSM-5 and 0.5 × 10 −4 s −1 for Pt/Co/Al 2O 3. The Y-zeolite-based samples were inactive in both mono and bimetallic samples. The species initially present in the solid were Pt° and Co°, together with Co 2+ and Pt 2+ at exchange positions. Co° seems not to participate as an active site in the SCR of NO x. Those species remained after the reaction but some reorganization occurred. A synergetic effect among the different species that enhances both the NO to NO 2 reaction, the activation of CH 4 and also the ability of the catalyst to adsorb NO, could be responsible for the high activity and selectivity of the bimetallic zeolites. 相似文献
5.
The reactions of ethanol over Rh/CeO 2 have been investigated using the techniques of temperature programmed desorption (TPD) and FT-IR spectroscopy, in addition to steady state catalytic tests. A comparison with previous studies of ethanol adsorption over Pd/CeO 2 [J. Catal. 186 (1999) 279] and Pt/CeO 2 [J. Catal. 191 (2000) 30] catalysts is presented. The apparent activation energy for the reaction was 49, 40, and 43 kJ mol −1 for Rh/CeO 2, Pd/CeO 2 and Pt/CeO 2, respectively, while the turnover number (TON) at 400 K was 5.9, 8.6 and 2.6, respectively. Surface compositions of catalysts were characterised by XPS. A decrease of the atomic O(1s)/Ce(3d) ratio of the CeO 2 support indicates its partial reduction upon addition of the noble metal. The extent of reduction per metal atom was in the following order: Pt>Pd>Rh. FT-IR and TPD studies have shown that dehydrogenation of ethanol to acetaldehyde occurred over Pd/CeO 2, Pt/CeO 2 and Rh/CeO 2. Moreover, Rh/CeO 2 readily dissociated the C–C bond of ethanol at room temperature to form adsorbed CO (IR bands at 1904–2091 cm −1). This was corroborated by the low desorption temperature of CH 4 over Rh/CeO 2 (450 K) when compared to that of Pd/CeO 2 (550 K) or Pt/CeO 2 (585 K). 相似文献
6.
Indirect partial oxidation (IPOX) of propane was studied over bimetallic 0.2 wt.% Pt–15 wt.% Ni/δ-Al 2O 3 catalyst in the 623–743 K temperature range. The unreduced and reduced forms of the catalyst were characterized by ESEM–EDAX and X-ray diffraction (XRD). In the IPOX tests, the effects of steam to carbon ratio (S/C), carbon to oxygen ratio (C/O 2) and residence time ( W/ F (g cat h/mol HC)) on the hydrogen production activity, selectivity and product distribution were studied in detail. The effect of temperature program applied (increasing from 623 to 743 K, ITP; decreasing from 743 to 623 K, DTP) during reaction was also tested. The results showed that the Pt–Ni bimetallic system has superior performance characteristics compared to the monometallic catalysts reported in literature. The reason is thought to be the utilization of the catalyst particles as micro heat exchangers during IPOX; the heat generated by Pt sites during exothermic total oxidation (TOX) being readily transferred through the catalyst particles acting as micro heat exchangers to the Ni sites, which promote endothermic steam reforming (SR). The optimal conditions were found as S/C = 3, C/O 2 = 2.70 and W/ F = 0.51 g cat h/mol HC for IPOX of propane on the basis of high hydrogen productivity and selectivity between 623 and 748 K for the experimental conditions tested. The thermo-neutral points obtained showed the sustainability of reaction in terms of energy. 相似文献
7.
A kinetic study on CH 4 combustion over a PdO/ZrO 2 (10%, w/w) catalyst has been performed in a temperature range between 400 and 550 °C by means of an annular catalytic microreactor. The role of mass transfer phenomena including diffusion in the catalyst pore, gas–solid diffusion and axial diffusion in the gas phase, has been preliminary addressed by means of mathematical modeling. Simulation results have pointed out the key role of internal diffusion showing that thicknesses of the active catalyst layer as thin as 10–15 μm are required to minimize the impact of mass transfer limitations. The thermal behavior of the reactor has been also addressed by means of catalytic combustion tests with CH4 and CO–H2 mixtures as fuels. The results have demonstrated the possibility to obtain nearly isothermal temperature profiles under severe conditions (up to 3% of CH4) thanks to effective dissipation of reaction heat by radiation from the catalyst outer skin. Finally the effect of reactants (CH4 and O2) and products (H2O and CO2) on CH4 combustion rate has been addressed. The results have shown that both H2O and CO2 markedly inhibit the reaction up to 550 °C. The data have been fitted by the following simple power law expression r=krPCH4PH2O−0.32PCO2−0.25 with an apparent activation energy of 108 kJ/mol. Evidences have been found and discussed indicating a key role of the support on the extent of such inhibition effects. 相似文献
8.
A new proton-conductive composite of NH 4PO 3–(NH 4) 2Mn(PO 3) 4 was synthesized and characterized as a potential electrolyte for intermediate temperature fuel cells that operated around 250 °C. Thermal gravimetric analysis and X-ray diffraction investigation showed that (NH 4) 2Mn(PO 3) 4 was stable as a supporting matrix for NH 4PO 3. The composite conductivity, measured using impedance spectroscopy, improved with increasing the molar ratio of NH 4PO 3 in both dry and wet atmospheres. A conductivity of 7 mS cm −1 was obtained at 250 °C in wet hydrogen. Electromotive forces measured by hydrogen concentration cells showed that the composite was nearly a pure protonic conductor with hydrogen partial pressure in the range of 10 2–10 5 Pa. The proton transference number was determined to be 0.95 at 250 °C for 2NH 4PO 3–(NH 4) 2Mn(PO 3) 4 electrolyte. Fuel cells using 2NH 4PO 3–(NH 4) 2Mn(PO 3) 4 as an electrolyte and the Pt–C catalyst as an electrode were fabricated. Maximum power density of 16.8 mW/cm 2 was achieved at 250 °C with dry hydrogen and dry oxygen as the fuel and oxidant, respectively. However, the NH 4PO 3–(NH 4) 2Mn(PO 3) 4 electrolyte is not compatible with the Pt–C catalyst, indicating that it is critical to develop new electrode materials for the intermediate temperature fuel cells. 相似文献
9.
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
10.
Coupled semiconductor (CS) Cu/CdS–TiO 2/SiO 2 photocatalyst was prepared using a mutli-step impregnation method. Its optical property was characterized by UV–vis spectra. BET, XRD, Raman and IR were used to study the structure of the photocatalyst. Fine CdS was found dispersed over the surface of anatase TiO 2/SiO 2 substrate. Chemisorption and IR analysis showed methane absorbed in the molecular state interacted weakly with the surface of catalyst, and the interaction of CO 2 with CS produced various forms of absorbed CO 2 species that were primarily present in the form of formate, bidentate and linear absorption species. Photocatalytic direct conversion of CH 4 and CO 2 was performed under the operation conditions: 373 K, 1:1 of CO 2/CH 4, 1 atm, space velocity of 200 h −1 and UV intensity of 20.0 mW/cm 2. The conversion was 1.47% for CH 4 and 0.74% for CO 2 with a selectivity of acetone up to 92.3%. The reaction mechanisms were proposed based on the experimental observations. 相似文献
11.
ZrO 2–TiO 2 mixed oxides, prepared using the sol–gel method, were used as supports for platinum catalysts. The effects of catalyst pre-reduction and surface acidity on the performance of Pt/ZT catalysts for the reduction of NO with CH 4 were studied. The diffuse reflectance infrared Fourier transformed (DRIFT) spectra of CO adsorbed on the Pt/ZT catalysts, and also on the Pt/T and Pt/Z references, pre-reduced at 773 K in hydrogen, revealed that an SMSI state is developed in the Ti-rich oxide-supported platinum catalysts. However, no shift in the binding energy of Pt 4f 7/2 level for Pt/T and Pt deposited on Ti-rich support counterparts pre-reduced at 773 K was found by photoelectron spectroscopy. The DRIFT spectra of the catalysts under the NO+O 2 co-adsorption revealed the appearance of nitrite/nitrate species on the surface of the Zr-containing catalysts, which displayed acidic properties, but were almost absent in the Pt/T catalyst. The intensity of these bands reached a maximum for the Pt/ZT(1:1) catalyst, which in turn exhibited a larger specific area. In the absence of oxygen in the feed stream, the NO+CH 4 reaction showed DRIFT spectra assigned to surface isocyano species. Since the intensity of this band is higher for the Pt/ZT (9:1) catalyst, it seems that such species are developed at the Pt–support interface. 相似文献
12.
Influence of time-on-stream (0.5–15 h), CH 4/O 2 ratio in feed (1.8–8.0), space velocity (6000–510,000 cm 3 g −1 h −1), catalyst particle size (22–70 mesh), and catalyst dilution by inert solid particles (diluent/catalyst weight ratio=4) on the performance at different temperatures (600–900°C) of the NiO/MgO solid solution deposited on SA-5205 [which is a low surface area macroporous silica-alumina catalyst carrier] in the oxidative conversion of methane to syngas (a mixture of CO and H 2) has been investigated. The dependence of conversion and selectivity on the space velocity is strongly influenced by the temperature. Both the conversion and selectivity for H 2 and CO are decreased markedly by increasing the CH 4/O 2 ratio in the feed. The catalyst dilution resulted in a small but significant decrease in both the conversion and selectivity for H 2 and CO. The increase in the catalyst particle size had also a small but significant effect on both the conversion and selectivity in the oxidative conversion process. Both the heat and mass transfer processes seem to play significant roles in the oxidative conversion of methane to syngas at a very low contact time or very high space velocity (5.1×10 5 cm 3 g −1 h −1). 相似文献
13.
The electrical conductivity of TiO 2 single crystal (rutile) was determined within the n–p transition regime in the temperature range 985–1387 K and p(O 2) 1–10 5 Pa. The determined values of the p(O 2) exponent differ from those predicted by defect disorder models (in both n- and p-type regimes), which were derived assuming validity of ionic charge compensation. This difference allows the evaluation of the ionic conductivity. The ionic component thus determined within the n–p transition regime exhibits an activation energy of E a=158 kJ mol −1. It was found that the ionic transfer number for undoped TiO 2 at the n–p transition is approximately 0.5. The electronic conductivity component was used to determine the width of the forbidden gap of TiO 2 (E g=2.86 eV). 相似文献
14.
Dispersing La 2O 3 on δ- or γ-Al 2O 3 significantly enhances the rate of NO reduction by CH 4 in 1% O 2, compared to unsupported La 2O 3. Typically, no bend-over in activity occurs between 500° and 700°C, and the rate at 700°C is 60% higher than that with a Co/ZSM-5 catalyst. The final activity was dependent upon the La 2O 3 precursor used, the pretreatment, and the La 2O 3 loading. The most active family of catalysts consisted of La 2O 3 on γ-Al 2O 3 prepared with lanthanum acetate and calcined at 750°C for 10 h. A maximum in rate (mol/s/g) and specific activity (mol/s/m 2) occurred between the addition of one and two theoretical monolayers of La 2O 3 on the γ-Al 2O 3 surface. The best catalyst, 40% La 2O 3/γ-Al 2O 3, had a turnover frequency at 700°C of 0.05 s −1, based on NO chemisorption at 25°C, which was 15 times higher than that for Co/ZSM-5. These La 2O 3/Al 2O 3 catalysts exhibited stable activity under high conversion conditions as well as high CH 4 selectivity (CH 4 + NO vs. CH 4 + O 2). The addition of Sr to a 20% La 2O 3/γ-Al 2O 3 sample increased activity, and a maximum rate enhancement of 45% was obtained at a SrO loading of 5%. In contrast, addition of SO =4 to the latter Sr-promoted La 2O 3/Al 2O 3 catalyst decreased activity although sulfate increased the activity of Sr-promoted La 2O 3. Dispersing La 2O 3 on SiO 2 produced catalysts with extremely low specific activities, and rates were even lower than with pure La 2O 3. This is presumably due to water sensitivity and silicate formation. The La 2O 3/Al 2O 3 catalysts are anticipated to show sufficient hydrothermal stability to allow their use in certain high-temperature applications. 相似文献
15.
The gas phase catalytic hydrodechlorination (HDC) of mono- and di-chlorobenzenes (423 K ≤ T ≤ 593 K) over unsupported and silica supported Mo carbide (Mo 2C) is presented as a viable means of detoxifying Cl-containing gas streams for the recovery/reuse of valuable chemical feedstock. The action of Mo 2C/SiO 2 is compared with MoO 3/SiO 2 and Ni/SiO 2 (an established HDC catalyst). The pre- and post-HDC catalyst samples have been characterized in terms of BET area, TG-MS, TPR, TEM, SEM, H 2 chemisorption/TPD and XRD analysis. Molybdenum carbide was prepared via a two step temperature programmed synthesis where MoO 3 was first subjected to a nitridation in NH 3 followed by carbidization in a CH 4/H 2 mixture to yield a face-centred cubic (-Mo 2C) structure characterized by a platelet morphology. Pseudo-first order kinetic analysis was used to obtain chlorobenzene HDC rate constants and the associated temperature dependences yielded apparent activation energies that decreased in the order MoO 3/SiO 2 (80 ± 5 kJ mol −1) ≈ MoO 3 (78 ± 8 kJ mol −1) > Ni/SiO 2 (62 ± 3 kJ mol −1) ≈ -Mo 2C (56 ± 6 kJ mol −1) ≈ -Mo 2C/SiO 2 (53 ± 3 kJ mol −1). HDC activity was lower for the dechlorination of the dichlorobenzene reactants where steric hindrance influenced chloro-isomer reactivity. Supporting -Mo 2C on silica served to elevate HDC performance, but under identical reaction conditions, Ni/SiO 2 consistently delivered a higher initial HDC activity. Nevertheless, the decline in HDC performance with time-on-stream for Ni/SiO 2 was such that activity converged with that of -Mo 2C/SiO 2 after three reaction cycles. A temporal loss of HDC activity (less extreme for the carbides) was observed for each catalyst that was studied and is linked to a disruption to supply of surface active hydrogen as a result of prolonged Cl/catalyst interaction. 相似文献
16.
Autothermal reforming of CH 4 has been studied under both periodic and steady state conditions. The investigation was conducted over Co–NiO in a fluidised bed reactor at 873 K and 101.32 kPa. Cycle periods of 1–40 min were used whilst the cycle split, Sox (with respect to the O 2-rich cycle) was varied from 0.1 to 0.9. Generally, CH 4 oxidation stimulated CO formation, however, steam reforming yielded predominantly CO 2 and H 2. Although O 2-rich cycling ( Sox≥0.5) was detrimental to H 2 formation, H 2O-rich cycling resulted in a 15% improvement in steady state H 2 formation. Theoretical as well as experimental investigations pointed to a resonant frequency of about 6.7 mHz for CH 4 oxidation to produce super steady state H 2 yields. By periodic operation, it is possible to tune H 2/CO ratios over the range 2.5–7 for the same feed composition. Interestingly, Sox=0.1 yielded the highest ratios, whereas the lowest ratios were attained at Sox=0.9. Periodic composition cycling introduces a more flexible approach to reactor operation — H 2/CO can be easily modulated by varying the cycle parameters — compared to steady state operation. 相似文献
17.
A series of CuO–ZnO/Al 2O 3 solids were prepared by wet impregnation using Al(OH) 3 solid and zinc and copper nitrate solutions. The amounts of copper and zinc oxides were varied between 10.3 and 16.0 wt% CuO and between 0.83 and 7.71 wt% ZnO. The prepared solids were subjected to thermal treatment at 400–1000°C. The solid–solid interactions between the different constituents of the prepared solids were studied using XRD analysis of different calcined solids. The surface characteristics of various calcined adsorbents were investigated using nitrogen adsorption at −196°C and their catalytic activities were determined using CO-oxidation by O 2 at temperatures ranged between 125°C and 200°C. The results showed that CuO interacts with Al2O3 to produce copper aluminate at ≥600°C and the completion of this reaction requires heating at 1000°C. ZnO hinders the formation of CuAl2O4 at 600°C while stimulates its production at 800°C. The treatment of CuO/Al2O3 solids with different amounts of ZnO increases their specific surface area and total pore volume and hinders their sintering (the activation energy of sintering increases from 30 to 58 kJ mol−1 in presence of 7.71 wt% ZnO). This treatment resulted in a progressive decrease in the catalytic activities of the investigated solids but increased their catalytic durability. Zinc and copper oxides present did not modify the mechanism of the catalyzed reaction but changed the concentration of catalytically active constituents (surface CuO crystallites) without changing their energetic nature. 相似文献
18.
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
19.
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
20.
An evaluative investigation of the Fischer–Tropsch performance of two catalysts (20%Co/Al 2O 3 and 10%Co:10%Mo/Al 2O 3) has been carried out in a slurry reactor at 2 MPa and 220–260 °C. The addition of Mo to the Co-catalyst significantly increased the acid-site strength suggesting strong electron withdrawing character in the Co-Mo catalyst. Analysis of steady-state rate data however, indicates that the FT reaction proceeds via a similar mechanism on both catalysts (carbide mechanism with hydrogenation of surface precursors as the rate-determining step). Although chain growth, , on both catalysts were comparable ( 0.6), stronger CH 2 adsorption on the Co-Mo catalyst and lower surface concentration of hydrogen adatoms as a result of increased acid-site strength was responsible for the lower individual hydrocarbons production rate compared to the Co catalyst. The activation energy, E, for Co (96.6 kJ mol −1), is also smaller than the estimate for the Co-Mo catalyst (112 kJ mol −1). Transient hydrocarbon rate profiles on each catalyst are indicative of first-order processes, however the associated surface time constants are higher for alkanes than alkenes on individual catalysts. Even so, for each homologous class, surface time constants for paraffins are greater for Co-Mo than Co, indicative that the adsorption of CH 2 species on the Co-Mo surface is stronger than on the monometallic Co catalyst. 相似文献
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