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1.
Effect of additives, In 2O 3, SnO 2, CoO, CuO and Ag, on the catalytic performance of Ga 2O 3–Al 2O 3 prepared by sol–gel method for the selective reduction of NO with propene in the presence of oxygen was studied. As for the reaction in the absence of H 2O, CoO, CuO and Ag showed good additive effect. When H 2O was added to the reaction gas, the activity of CoO-, CuO- and Ag-doped Ga 2O 3–Al 2O 3 was depressed considerably, while an intensifying effect of H 2O was observed for In 2O 3- and SnO 2-doped Ga 2O 3–Al 2O 3. Of several metal oxide additives, In 2O 3-doped Ga 2O 3–Al 2O 3 showed the highest activity for NO reduction by propene in the presence of H 2O. Kinetic studies on NO reduction over In 2O 3–Ga 2O 3–Al 2O 3 revealed that the rate-determining step in the absence of H 2O is the reaction of NO 2 formed on Ga 2O 3–Al 2O 3 with C 3H 6-derived species, whereas that in the presence of H 2O is the formation of C 3H 6-derived species. We presumed the reason for the promotional effect of H 2O as follows: the rate for the formation of C 3H 6-derived species in the presence of H 2O is sufficiently fast compared with that for the reaction of NO 2 with C 3H 6-derived species in the absence of H 2O. Although the retarding effect of SO 2 on the activity was observed for all of the catalysts, SnO 2–Ga 2O 3–Al 2O 3 showed still relatively high activity in the lower temperature region. 相似文献
2.
采用共沉淀法合成一系列具有不同Ce/Zr物质的量比的铈锆固溶体Ce xZr 1-xO 2,考察Ce/Zr比例对H 2S选择氧化反应催化活性的影响。通过XRD、BET、Raman、XPS、CO 2-TPD、O 2-TPD、H 2-TPR等手段对铈锆固溶体的晶体结构、表面性质、碱性位以及氧化还原性等进行表征。结果表明,所有的铈锆固溶体催化剂均可以在化学计量比的氧气下具有优良的低温催化活性,催化活性随着Ce/Zr比例的提高而增加,其中Ce 0.9Zr 0.1O 2活性最高,(160~260) ℃转化率均保持在95%以上,在180 ℃时硫收率可达到97%,这主要是因为Ce 0.9Zr 0.1O 2具有最多的中度碱性位、活性位数量和强的氧化还原性。同时推测Ce 4+为催化反应的活性位,并遵循氧化还原机理。此外,催化剂的失活主要是由于催化剂表面生成硫酸盐物种,消耗了活性组分Ce 4+。 相似文献
3.
MgO-promoted Ni/Al 2O 3 catalysts have been investigated with respect to catalytic activity and coke formation in combined steam and carbon dioxide reforming of methane (CSCRM) to develop a highly active and stable catalyst for gas to liquid (GTL) processes. Ni/Al 2O 3 catalysts were promoted through varying the MgO content by the incipient wetness method. X-ray diffraction (XRD), BET surface area, H 2-temperature programmed reduction (TPR), H 2-chemisorption and CO 2-temperature programmed desorption (TPD) were used to observe the characteristics of the prepared catalysts. The coke formation and amount in used catalysts were examined by SEM and TGA, respectively. H 2/CO ratio of 2 was achieved in CSCRM by controlling the feed H 2O/CO 2 ratio. The catalysts prepared with 20 wt.% MgO exhibit the highest catalytic performance and have high coke resistance in CSCRM. MgO promotion forms MgAl 2O 4 spinel phase, which is stable at high temperatures and effectively prevents coke formation by increasing the CO 2 adsorption due to the increase in base strength on the surface of catalyst. 相似文献
4.
The vapor-phase selective oxidation of propylene (H 2CCHCH 3) to acrolein (H 2CCHCHO) was investigated over supported V 2O 5/Nb 2O 5 catalysts. The catalysts were synthesized by incipient wetness impregnation of V-isopropoxide/isopropanol solutions and calcination at 450 °C. The catalytic active vanadia component was shown by in situ Raman spectroscopy to be 100% dispersed as surface VO x species on the Nb 2O 5 support in the sub-monolayer region (<8.4 V/nm 2). Surface allyl species (H 2CCHCH 2*) were observed with in situ FT-IR to be the most abundant reaction intermediates. The acrolein formation kinetics and selectivity were strongly dependent on the surface VO x coverage. Two surface VO x sites were found to participate in the selective oxidation of propylene to acrolein. The reaction kinetics followed a Langmuir–Hinshelwood mechanism with first-order in propylene and half-order in O 2 partial pressures. C 3H 6-TPSR spectroscopy studies also revealed that the lattice oxygen from the catalyst was not capable of selectively oxidizing propylene to acrolein and that the presence of gas phase molecular O 2 was critical for maintaining the surface VO x species in the fully oxidized state. The catalytic active site for this selective oxidation reaction involves the bridging VONb support bond. 相似文献
5.
Ag-based catalysts supported on various metal oxides, Al 2O 3, TiO 2, and TiO 2–Al 2O 3, were prepared by the sol–gel method. The effect of SO 2 on catalytic activity was investigated for NO reduction with propene under lean burn condition. The results showed the catalytic activities were greatly enhanced on Ag/TiO 2–Al 2O 3 in comparison to Ag/Al 2O 3 and Ag/TiO 2, especially in the low temperature region. Application of different characterization techniques revealed that the activity enhancement was correlated with the properties of the support material. Silver was highly dispersed over the amorphous system of TiO 2–Al 2O 3. NO 3− rather than NO 2− or NO x reacted with the carboxylate species to form CN or NCO. NO 2 was the predominant desorption species in the temperature programmed desorption (TPD) of NO on Ag/TiO 2–Al 2O 3. More amount of formate (HCOO −) and CN were generated on the Ag/TiO 2–Al 2O 3 catalyst than the Ag/Al 2O 3 catalyst, due to an increased number of Lewis acid sites. Sulfate species, resulted from SO 2 oxidation, played dual roles on catalytic activity. On aged samples, the slow decomposition of accumulated sulfate species on catalyst surface led to poor NO conversion due to the blockage of these species on active sites. On the other hand, catalytic activity was greatly enhanced in the low temperature region because of the enhanced intensity of Lewis acid site caused by the adsorbed sulfate species. The rate of sulfate accumulation on the Ag/TiO 2–Al 2O 3 system was relatively slow. As a consequence, the system showed superior capability for selective adsorption of NO and SO 2 toleration to the Ag/Al 2O 3 catalyst. 相似文献
6.
The role of La 2O 3 loading in Pd/Al 2O 3-La 2O 3 prepared by sol–gel on the catalytic properties in the NO reduction with H 2 was studied. The catalysts were characterized by N 2 physisorption, temperature-programmed reduction, differential thermal analysis, temperature-programmed oxidation and temperature-programmed desorption of NO. The physicochemical properties of Pd catalysts as well as the catalytic activity and selectivity are modified by La2O3 inclusion. The selectivity depends on the NO/H2 molar ratio (GHSV = 72,000 h−1) and the extent of interaction between Pd and La2O3. At NO/H2 = 0.5, the catalysts show high N2 selectivity (60–75%) at temperatures lower than 250 °C. For NO/H2 = 1, the N2 selectivity is almost 100% mainly for high temperatures, and even in the presence of 10% H2O vapor. The high N2 selectivity indicates a high capability of the catalysts to dissociate NO upon adsorption. This property is attributed to the creation of new adsorption sites through the formation of a surface PdOx phase interacting with La2O3. The formation of this phase is favored by the spreading of PdO promoted by La2O3. DTA shows that the phase transformation takes place at temperatures of 280–350 °C, while TPO indicates that this phase transformation is related to the oxidation process of PdO: in the case of Pd/Al2O3 the O2 uptake is consistent with the oxidation of PdO to PdO2, and when La2O3 is present the O2 uptake exceeds that amount (1.5 times). La2O3 in Pd catalysts promotes also the oxidation of Pd and dissociative adsorption of NO mainly at low temperatures (<250 °C) favoring the formation of N2. 相似文献
7.
An In 2O 3/Al 2O 3 catalyst shows high activity for the selective catalytic reduction of NO with propene in the presence of oxygen. The presence of SO 2 in feed gas suppressed the catalytic activity dramatically at high temperatures; however it was enhanced in the low temperature range of 473–573 K. In TPD and FT-IR studies, the formation of sulfate species on the surface of the catalyst caused an inhibition of NO X adsorption sites, and the absorbance ability of NO was suppressed by the presence of SO 2, and the amount of ad-NO 3− species decreased obviously. This leads to a decrease of catalytic activity at higher temperatures. However, addition of SO 2 enhanced the formation of carboxylate and formate species, which can explain the promotional effect of SO 2 at low temperature, because active C 3H 6 (partially oxidized C 3H 6) is crucial at low temperature. 相似文献
8.
The effects of cobalt and manganese oxides-doping on surface and catalytic properties of Cr 2O 3/MgO system have been investigated. The dopant concentration was changed between 1 and 5 mol% cobalt and manganese oxides. Pure and variously doped solids were subjected to heat treatment at 400 and 700 °C. The techniques employed were X-ray diffraction (XRD), nitrogen adsorption at –196 °C, catalytic conversion of iso-propanol at 200–400 °C using flow technique and catalytic decomposition of H 2O 2 at 20–40 °C. The results revealed that the doping process of the system investigated followed by calcinations at 400 or 700 °C, enhanced the solid–solid interactions between catalyst constituents yielding (-MgCrO 4, β-MgCrO 4) and MgCr 2O 4, respectively. Furthermore, manganese and cobalt oxide-doping for Cr 2O 3/MgO system increased its catalytic activity much towards H 2O 2-decomposition. The increase was, however, more pronounced in the case of manganese-doping. Opposite results have been observed in the case of iso-propanol conversion, which proceeds via dehydrogenation and dehydration reaction. The SBET of the investigated system was found to decrease by increasing the dopant concentration. The doping process did not modify the activation energy of the catalyzed reaction, but rather changed the concentration of the catalytically active constituents without changing their energetic nature. 相似文献
9.
Combined effect of H 2O and SO 2 on V 2O 5/AC the activity of catalyst for selective catalytic reduction (SCR) of NO with NH 3 at lower temperatures was studied. In the absence of SO 2, H 2O inhibits the catalytic activity, which may be attributed to competitive adsorption of H 2O and reactants (NO and/or NH 3). Although SO 2 promotes the SCR activity of the V 2O 5/AC catalyst in the absence of H 2O, it speeds the deactivation of the catalyst in the presence of H 2O. The dual effect of SO 2 is attributed to the SO 42− formed on the catalyst surface, which stays as ammonium-sulfate salts on the catalyst surface. In the absence of H 2O, a small amount of ammonium-sulfate salts deposits on the surface of the catalyst, which promote the SCR activity; in the presence of H 2O, however, the deposition rate of ammonium-sulfate salts is much greater, which results in blocking of the catalyst pores and deactivates the catalyst. Decreasing V 2O 5 loading decreases the deactivation rate of the catalyst. The catalyst can be used stably at a space velocity of 9000 h −1 and temperature of 250 °C. 相似文献
10.
The selective catalytic reduction of NO by H 2 under strongly oxidizing conditions (H 2-SCR) in the low-temperature range of 100–200 °C has been studied over Pt supported on a series of metal oxides (e.g., La 2O 3, MgO, Y 2O 3, CaO, CeO 2, TiO 2, SiO 2 and MgO-CeO 2). The Pt/MgO and Pt/CeO 2 solids showed the best catalytic behavior with respect to N 2 yield and the widest temperature window of operation compared with the other single metal oxide-supported Pt solids. An optimum 50 wt% MgO-50wt% CeO 2 support composition and 0.3 wt% Pt loading (in the 0.1–2.0 wt% range) were found in terms of specific reaction rate of N 2 production (mols N 2/g cat s). High NO conversions (70–95%) and N 2 selectivities (80–85%) were also obtained in the 100–200 °C range at a GHSV of 80,000 h −1 with the lowest 0.1 wt% Pt loading and using a feed stream of 0.25 vol% NO, 1 vol% H 2, 5 vol% O 2 and He as balance gas. Addition of 5 vol% H 2O in the latter feed stream had a positive influence on the catalytic performance and practically no effect on the stability of the 0.1 wt% Pt/MgO-CeO 2 during 24 h on reaction stream. Moreover, the latter catalytic system exhibited a high stability in the presence of 25–40 ppm SO 2 in the feed stream following a given support pretreatment. N 2 selectivity values in the 80–85% range were obtained over the 0.1 wt% Pt/MgO-CeO 2 catalyst in the 100–200 °C range in the presence of water and SO 2 in the feed stream. The above-mentioned results led to the obtainment of patents for the commercial exploitation of Pt/MgO-CeO 2 catalyst towards a new NO x control technology in the low-temperature range of 100–200 °C using H 2 as reducing agent. Temperature-programmed desorption (TPD) of NO, and transient titration of the adsorbed surface intermediate NO x species with H 2 experiments, following reaction, have revealed important information towards the understanding of basic mechanistic issues of the present catalytic system (e.g., surface coverage, number and location of active NO x intermediate species, NO x spillover). 相似文献
11.
The catalytic generation of H 2O 2 from H 2 and O 2 has been studied over zeolite beta-supported Pd and zeolite beta-adsorbed organic compounds such as 1,4-benzoquinone (BQ), hydroquinone (HQ), azobenzene (AB) and hydrazobenzene (HAB). According to catalytic results, zeolite beta-supported Pd catalysts display effective performance relative to those prepared from other types of zeolites reported and Pd-loaded zeolite beta-adsorbed HQ catalysts show enhanced activity compared to zeolite beta-supported Pd catalysts. In situ UV–Vis spectroscopic study indicates that HQ can readily be converted to BQ reversibly under H 2 and air inside zeolite beta only in the presence of Pd. The results suggest that HQ acts as a strong hydrogen transfer agent to promote the production of H 2O 2 from H 2 and O 2 in cooperation with a Pd catalyst. By contrast, adsorption of BQ, AB and HAB induces suppression of the catalytic properties of Pd/zeolite beta. 相似文献
12.
This work investigates performances of supported transition-metal oxide catalysts for the catalytic reduction of SO 2 with C 2H 4 as a reducing agent. Experimental results indicate that the active species, the support, the feed ratio of C 2H 4/SO 2, and pretreatment are all important factors affecting catalyst activity. Fe 2O 3/γ-Al 2O 3 was found to be the most active catalyst among six γ-Al 2O 3-supported metal oxide catalysts tested. With Fe 2O 3 as the active species, of the supports tested, CeO 2 is the most suitable one. Using this Fe 2O 3/CeO 2 catalyst, we found that the optimal Fe content is 10 wt.%, the optimal feed ratio of C 2H 4/SO 2 is 1:1, and the catalyst presulfidized by H 2+H 2S exhibits a higher performance than those pretreated with H 2 or He. Although the feed concentrations of C 2H 4:SO 2 being 3000:3000 ppm provide a higher conversion of SO 2, the sulfur yield decreases drastically at temperatures above 300 °C. With higher feed concentrations, maximum yield appears at higher temperatures. The C 2H 4 temperature-programmed desorption (C 2H 4-TPD) and SO 2-TPD desorption patterns illustrate that Fe 2O 3/CeO 2 can adsorb and desorb C 2H 4 and SO 2 more easily than can Fe 2O 3/γ-Al 2O 3. Moreover, the SO 2-TPD patterns further show that Fe 2O 3/γ-Al 2O 3 is more seriously inhibited by SO 2. These findings may properly explain why Fe 2O 3/CeO 2 has a higher activity for the reduction of SO 2. 相似文献
13.
以γ-Al_2O_3为载体,负载Zr OCl_2和H_2SO_4制备Zr OCl_2-H_2SO_4/γ-Al_2O_3催化剂,并用于1-丁烯齐聚反应。采用气相色谱在线分析,确定产物组成,考察制备条件对催化剂催化活性的影响,通过1-丁烯转化率和主产物选择性确定适宜的反应条件。结果表明,在Zr OCl_2和H_2SO_4负载质量分数为4.5%和焙烧温度500℃条件下制备的催化剂,在反应温度140℃、1-丁烯液时空速2 h-1和N2分压1.4 MPa条件下,表现出较好的催化活性,1-丁烯转化率96.77%,产物以二聚体(C8)为主,选择性85.99%。该催化剂失活后容易再生,且催化活性良好,1-丁烯转化率92.73%,C8选择性86.73%。 相似文献
14.
A series of CeO 2 promoted cobalt spinel catalysts were prepared by the co-precipitation method and tested for the decomposition of nitrous oxide (N 2O). Addition of CeO 2 to Co 3O 4 led to an improvement in the catalytic activity for N 2O decomposition. The catalyst was most active when the molar ratio of Ce/Co was around 0.05. Complete N 2O conversion could be attained over the CoCe0.05 catalyst below 400 °C even in the presence of O 2, H 2O or NO. Methods of XRD, FE-SEM, BET, XPS, H 2-TPR and O 2-TPD were used to characterize these catalysts. The analytical results indicated that the addition of CeO 2 could increase the surface area of Co 3O 4, and then improve the reduction of Co 3+ to Co 2+ by facilitating the desorption of adsorbed oxygen species, which is the rate-determining step of the N 2O decomposition over cobalt spinel catalyst. We conclude that these effects, caused by the addition of CeO 2, are responsible for the enhancement of catalytic activity of Co 3O 4. 相似文献
15.
The effects of nickel loading, calcination temperature, support, and basic additives on Ni-based catalyst structure and reactivity for CH 4 reforming with CO 2 were investigated. The results show that the structure of the nickel active phase strongly depends on the interactions of the metal and the support, which are related to the support properties, the additives and the preparation conditions. “Free” Ni species can be formed when the interaction is weak and their mobility makes them easily deactivated by coking and sintering. The effect of strong metal-support interaction (SMSI effect) is different for various supports. The formation of solid solution of Ni–Mg–O 2 and the blocking of TiO x by the partially reduced TiO 2 can both decrease the availability of Ni active sites in Ni/MgO and Ni/TiO 2. The spinel NiAl 2O 4 formed in Ni/γ-Al 2O 3 might be responsible for its high activity and resistance to coking and sintering because it can produce a highly dispersed active phase and a large active surface area as bound-state Ni species when the catalyst is prepared at high calcined temperatures or with low nickel loading. The addition of La 2O 3 or MgO as alumina modifiers can also be beneficial for the performance of the Ni/γ-Al 2O 3 catalyst. 相似文献
16.
The selective catalytic reduction (SCR) of NO by C 3H 6 in excess oxygen was evaluated and compared over Ag/Al 2O 3 and Cu/Al 2O 3 catalysts. Ag/Al 2O 3 showed a high activity for NO reduction. However, Cu/Al 2O 3 showed a high activity for C 3H 6 oxidation. The partial oxidation of C 3H 6 gave surface enolic species and acetate species on the Ag/Al 2O 3, but only an acetate species was clearly observed on the Cu/Al 2O 3. The enolic species is a more active intermediate towards NO + O 2 to yield—NCO species than the acetate species on the Ag/Al 2O 3 catalyst. The Ag and Cu metal loadings and phase changes on Al 2O 3 support can affect the activity and selectivity of Ag/Al 2O 3 and Cu/Al 2O 3 catalysts, but the formation of enolic species is the main reason why the activity of the Ag/Al 2O 3 catalyst for NO reduction is higher than that of the Cu/Al 2O 3 catalyst. 相似文献
17.
Selective catalytic reduction of NO x by C 3H 6 in the presence of H 2 over Ag/Al 2O 3 was investigated using in situ DRIFTS and GC–MS measurements. The addition of H 2 promoted the partial oxidation of C 3H 6 to enolic species, the formation of –NCO and the reactions of enolic species and –NCO with NO x on Ag/Al 2O 3 surface at low temperatures. Based on the results, we proposed reaction mechanism to explain the promotional effect of H 2 on the SCR of NO x by C 3H 6 over Ag/Al 2O 3 catalyst. 相似文献
18.
The catalytic performance of some metal oxides in the selective oxidation of H 2S in the stream containing water vapor and ammonia was investigated in this study. Among the catalysts tested, V 2O 5/SiO 2 and Fe 2O 3/SiO 2 catalyst showed good conversion of H 2S with very low selectivity to undesired SO 2. Hydrogen sulfide could be recovered as harmless solid products (elemental sulfur and various ammonium salts), and distribution of solid products was varied with types of catalyst and compositions of reactant. XRD and FT-IR analysis revealed that the salt was mixture of ammonium–sulfur–oxygen compounds. It was noteworthy that V 2O 5/SiO 2 catalyst produced elemental sulfur and ammonium thiosulfate, and that elemental sulfur was principal product on Fe 2O 3/SiO 2 catalyst. Small amount of ammonium sulfate was obtained with the Fe 2O 3/SiO 2 catalyst. In order to elucidate the reaction path, the effects of O 2/H 2S ratio and concentration of NH 3 and H 2O are also studied with the V 2O 5/SiO 2 catalyst. 相似文献
19.
H 3PMo 12O 40 catalyst was chemically immobilized on the surface modified CMK-3 (SM-CMK-3) support as a charge compensating component, by taking advantage of the overall negative charge of [PMo 12O 40] 3−. The supported H 3PMo 12O 40/SM-CMK-3 catalyst was characterized to have high surface area (≈1000 m 2/g) and relatively large pore volume (0.83 cm 3/g). The H 3PMo 12O 40/SM-CMK-3 catalyst was applied to the vapor-phase 2-propanol conversion reaction. The H 3PMo 12O 40/SM-CMK-3 catalyst exhibited higher 2-propanol conversion than the unsupported H 3PMo 12O 40 and the impregnated H 3PMo 12O 40 on CMK-3. Furthermore, the PMo 12/SM-CMK-3 catalyst showed the enhanced oxidation activity (acetone formation) and the suppressed acid catalytic activity (propylene formation) compared to the other two catalysts. It is believed that [PMo 12O 40] 3− species were chemically and finely immobilized on the SM-CMK-3 support as charge matching species, and thus, the PMo 12/SM-CMK-3 catalyst showed an excellent oxidation activity. 相似文献
20.
Ethanol steam reforming was studied over Ni/Al 2O 3 catalysts. The effect of support (- and γ-Al 2O 3), metal loading and a comparison between conventional H 2 reduction with an activation method employing a CH 4/O 2 mixture was investigated. The properties of catalysts were studied by N 2 physisorption, X-ray diffraction (XRD) and temperature programmed reduction (TPR). After activity tests, the catalysts were analyzed by scanning electron microscopy (SEM) and thermogravimetric analysis (TG/DTA). Ni supported on γ-Al 2O 3 was more active for H 2 production than the catalyst supported on -Al 2O 3. Metal loading did not affect the catalytic performance. The alternative activation method with CH 4/O 2 mixture affected differently the activity and stability of the Ni/γ-Al 2O 3 and the Ni/-Al 2O 3 catalyst. This activation method increased significantly the stability of Ni/-Al 2O 3 compared to H 2 reduction. SEM and TG/DTA analysis indicate the formation of filamentous carbon during the CH 4/O 2 activation step, which is associated with the increasing catalyst activity and stability. The effect of temperature on the type of carbon formed was investigated; indicating that filamentous coke increased activity while encapsulating coke promoted deactivation. A discussion about carbon formation and the influence on the activity is presented. 相似文献
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