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1.
通过等体积浸渍法制备单贵金属Pt/γ-Al 2O 3和双金属Pt-Ce/γ-Al 2O 3催化剂,考察Ce对催化剂活性的影响,确定催化剂最优配比。结果表明,当Pt的负载量为质量分数0.5%时,Pt/γ-Al 2O 3催化活性最高;当Pt的负载量为质量分数0.2%,Ce的负载量为质量分数1.0%时,Pt-Ce/γ-Al 2O 3催化剂的催化活性最高。Pt-Ce/γ-Al 2O 3催化剂的甲苯转化率高于Pt/γ-Al 2O 3催化剂。随着Pt负载量增大,催化剂孔容、孔径减小。粉体式催化剂性能优于整体式催化剂,但差别不大;Ce的添加有助于催化剂活性的提升。 相似文献
2.
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
3.
Ag-modified La 0.6Sr 0.4MnO 3-based catalysts with the perovskite-type structure were prepared by using a citric acid sol–gel method, and their catalytic performance for complete oxidation of methanol and ethanol was evaluated and compared with that of the γ-Al 2O 3-supported catalysts, Ag/γ-Al 2O 3, Pt/γ-Al 2O 3, and Pd/γ-Al 2O 3. The results showed that the Ag-modified La 0.6Sr 0.4MnO 3-based catalysts with the perovskite-type structure displayed the activity significantly higher than that of the supported precious metal catalysts, 0.1%Pd/γ-Al 2O 3 and 0.1%Pt/γ-Al 2O 3 in the temperature range of 370–573 K. Over a 6%Ag/20%La 0.6Sr 0.4MnO 3/γ-Al 2O 3 catalyst, the T95 temperature for methanol oxidation can be as low as 413 K. Even at such low reaction temperature, there were little HCHO and CO detected in the reaction exit-gas. However, for the 0.1%Pd/γ-Al 2O 3 and 0.1%Pt/γ-Al 2O 3 catalysts, the HCHO content in the reaction exit-gas reached 200 and 630 ppm at their T95 temperatures. Over a 6%Ag/La 0.6Sr 0.4MnO 3 catalyst, the T95 temperature for ethanol oxidation can be as low as 453 K, with a corresponding content of CH 3CHO in the exit-gas at 782 ppm; when ethanol oxidation is performed at 493 K, the content of acetaldehyde in the exit-gas can be below 1 ppm. Characterization of the catalysts by X-ray diffraction (XRD), TEM, XPS, laser Raman spectra (LRS), hydrogen temperature-programmed reduction (H 2-TPR) and oxygen temperature-programmed desorption (O 2-TPD) methods revealed that both the surface and the bulk phase of the perovskite La 0.6Sr 0.4MnO 3 played important roles in the catalytic oxidation of the alcohols, and that γ-Al 2O 3 as the bottom carrier could be beneficial in creating a large surface area of catalyst. Moreover, a small amount of Ag + doped onto the surface of La 0.6Sr 0.4MnO 3 was able to partially occupy the positions of La 3+ and Sr 2+ due to their similar ionic radii, and thus, became stabilized by the perovskite lattice, which would be in favor of preventing the aggregation of the Ag species on the surface and enhancing the stability of the catalyst. On the other hand, modification of the Ag + to the surface of La 0.6Sr 0.4MnO 3 resulted in an increase in relative content of the surface O 22−/O − species highly reactive toward the alcohols and aldehydes as well as CO. Besides, solution of low-valence metal oxides SrO and Ag 2O with proper amounts in the lattice of the trivalent metal perovskite-type oxide LaMnO 3 would also lead to an increase in the content of the reducible Mn n+ and the formation of anionic vacancies, which would be favorable for the adsorption-activation of oxygen on the functioning catalyst and the transport of the lattice and surface oxygen species. All these factors would contribute to the pronounced improvement of the catalyst performance. 相似文献
4.
采用铝箔盐酸回流-油柱成型法制备了不同Sn掺杂量的Sn(x)-θ-Al 2O 3载体,并采用真空浸渍法制备了Pt/Sn(x)-θ-Al 2O 3催化剂。对制备的催化剂进行XRD、N 2物理吸附-脱附、NH 3-TPD、H 2-TPR和TG-DTA表征,研究了在载体中掺入助剂Sn对Pt/Sn(x)-θ-Al 2O 3催化剂结构及丙烷脱氢催化反应性能的影响。结果表明,在载体制备过程中掺入Sn,可以提高催化剂反应活性和产物选择性,当Sn掺杂质量分数为1.0%时,催化剂具有最优的丙烷脱氢反应性能,15 h的平均丙烷转化率为32.4%,平均丙烯选择性为95.5%。 相似文献
5.
采用水热处理对γ-Al2O3载体改性,并进行XRD、N2物理吸附-脱附、热重、NH3-TPD及H2-TPR表征。结果表明,γ-Al2O3经过"再水合-焙烧"过程,晶型变好,表面总酸量降低,Pt-Al2O3相互作用增加,提高了Pt Sn K/Al2O3催化剂的丙烷脱氢转化率、选择性及稳定性。其中,140℃处理4 h时,氧化铝负载的Pt Sn K催化剂表现出最优的丙烷脱氢性能,100 h内平均转化率为33.6%,平均选择性97.3%,失活参数为15.9%。 相似文献
6.
Direct formation of isobutene from n-butane was investigated over zeolite TON and γ-Al 2O 3 supported platinum and platinum–copper catalysts. Addition of Cu decreases Pt dispersion, irrespective of preparation methods and nature of catalyst supports. The presence of potassium was found to reduce acidity and Pt dispersion. The experiments were performed in a fixed-bed microreactor system operating at 673 K and atmospheric pressure. Changing the support from γ-Al 2O 3 to TON, shows that n-butane conversion is almost independent of acidity. However, significant changes in products selectivities are observed. The selectivities to isobutene, C 1–C 3 fractions, and aromatics increases drastically from 3.5 to 32.6%, 20.3 to 27.2%, and 3.0 to 20.6%, respectively, for the TON-supported catalyst whereas dehydrogenation is largely predominant when γ-Al 2O 3 is used as support. Addition of Cu, as expected, has an adverse effect on n-butane conversion as less active sites are available due to the reduction in Pt dispersion. Though Cu addition has marginal effect on isobutene selectivity, it certainly suppresses hydrogenolysis which evidences a reduction in size of the Pt ensembles at the surface of the Pt particles. 相似文献
7.
Catalytic performance of Sn/Al 2O 3 catalysts prepared by impregnation (IM) and sol–gel (SG) method for selective catalytic reduction of NO x by propene under lean burn condition were investigated. The physical properties of catalyst were characterized by BET, XRD, XPS and TPD. The results showed that NO 2 had higher reactivity than NO to nitrogen, the maximum NO conversion was 82% on the 5% Sn/Al 2O 3 (SG) catalyst, and the maximum NO 2 conversion reached nearly 100% around 425 °C. Such a temperature of maximum NO conversion was in accordance with those of NO x desorption accompanied with O 2 around 450 °C. The activity of NO reduction was enhanced remarkably by the presence of H 2O and SO 2 at low temperature, and the temperature window was also broadened in the presence of H 2O and SO 2, however the NO x desorption and NO conversion decreased sharply on the 300 ppm SO 2 treated catalyst, the catalytic activity was inhibited by the presence of SO 2 due to formation of sulfate species (SO 42−) on the catalysts. The presence of oxygen played an essential role in NO reduction, and the activity of the 5% Sn/Al 2O 3 (SG) was not decreased in the presence of large oxygen. 相似文献
8.
以浸渍法制备VMo/γ-Al 2O 3和VMoMg/γ-Al 2O 3催化剂,考察其催化丙烷氧化脱氢制丙烯的反应活性,采用XRD、UV-Vis DRS和In suit IR对催化剂进行表征。结果表明,V负载质量分数为3%、Mo负载质量分数为7%时的3V7Mo/γ-Al 2O 3催化剂表现出较好的催化性能;添加Mg后催化剂的催化性能有所改善,反应温度500 ℃时,丙烷转化率为18.19%,丙烯选择性74.76%。丙烷和丙烯在3V7Mo/γ-Al 2O 3和3V 7Mo 4Mg/γ-Al 2O 3催化剂上吸附后,C—H键的H与催化剂活性中心的晶格氧发生作用形成H—O键,且3V 7Mo 4Mg/γ-Al 2O 3催化剂上出现C—O键的温度比3V 7Mo/γ-Al 2O 3催化剂高,表明加入Mg有利于提高丙烯选择性。 相似文献
9.
Zirconium sulfate supported on γ-Al 2O 3 catalysts were prepared by impregnation of powdered γ-Al 2O 3 with zirconium sulfate aqueous solution followed by calcining in air at high temperature. For Zr(SO 4) 2/γ-Al 2O 3 samples, no diffraction line of zirconium sulfate was observed up to 50 wt.%, indicating good dispersion of Zr(SO 4) 2 on the surface of γ-Al 2O 3. The acidity of catalysts increased in proportion to the zirconium sulfate content up to 40 wt.% of Zr(SO 4) 2. 40-Zr(SO 4) 2/γ-Al 2O 3 calcined at 400 °C exhibited maximum catalytic activities for 2-propanol dehydration and cumene dealkylation. The catalytic activities for both reactions, 2-propanol dehydration and cumene dealkylation were correlated with the acidity of catalysts measured by ammonia chemisorption method. 相似文献
10.
Several solid catalysts (Co 3O 4/γ-Al 2O 3, Fe 2O 3/γ-Al 2O 3, Mn 2O 3/γ-Al 2O 3, Zn–Fe–Mn–Al–O, Pt/γ-Al 2O 3, Ru/CeO 2, Ru/C) have been prepared and used to remove N-containing organic contaminants while processing toxic and hazardous industrial waste waters using wet oxidation by air (WAO). The autoclave tests of catalysts were done to reveal the main advantages of catalysts in water presence at high pressures and temperatures. Catalyst activity was determined with regard to oxygen interaction with model mixtures (water–organic contaminant: acetonitrile, carbamide, dimethyl formamide, or multi-component mixture of aliphatic alcohols). Activity tests were done in a static reactor under ideal mixing regime. Reagents and products were monitored using gas chromatograph Cvet-560, Millichrom-1 HPLC, and routine chemical analysis. Optimum process conditions for the best catalyst (Ru/graphite-like carbon) are as follows: partial oxygen pressure – 1.0 MPa, temperature – 473–513 K. At 0.5–5.0 MPa total pressure and 433–523 K catalysts show high water-resistance and high activity level (residual content of toxic compounds is less than 1%, and no NO x and NH 3 are detected). There are no legal restrictions on catalysts operation, since they are harmless to environment. 相似文献
11.
Oxidation of propene and propane to CO 2 and H 2O has been studied over Au/Al 2O 3 and two different Au/CuO/Al 2O 3 (4 wt.% Au and 7.4 wt.% Au) catalysts and compared with the catalytic behaviour of Au/Co 3O 4/Al 2O 3 (4.1 wt.% Au) and Pt/Al 2O 3 (4.8 wt.% Pt) catalysts. The various characterization techniques employed (XRD, HRTEM, TPR and DR-UV–vis) revealed the presence of metallic gold, along with a highly dispersed CuO (6 wt.% CuO), or more crystalline CuO phase (12 wt.% CuO). A higher CuO loading does not significantly influence the catalytic performance of the catalyst in propene oxidation, the gold loading appears to be more important. Moreover, it was found that 7.4Au/CuO/Al2O3 is almost as active as Pt/Al2O3, whereas Au/Co3O4/Al2O3 performs less than any of the CuO-containing gold-based catalysts. The light-off temperature for C3H8 oxidation is significantly higher than for C3H6. For this reaction the particle size effect appears to prevail over the effect of gold loading. The most active catalysts are 4Au/CuO/Al2O3 (gold particles less than 3 nm) and 4Au/Co3O4/Al2O3 (gold particles less than 5 nm). 相似文献
12.
The photocatalytic properties of sulphated MoO x/γ-Al 2O 3 catalysts in cyclohexane oxidative dehydrogenation have been determined in a two-dimensional fluidized bed photoreactor and compared to those of sulphated MoO x/TiO 2 catalysts. Photocatalytic tests on MoO x/γ-Al 2O 3 at 8 wt% MoO 3 and various sulphate contents showed the selective (100%) formation of cyclohexene, without production of benzene, as instead found with MoO x/TiO 2. These results show that the selectivity of photocatalytic cyclohexane oxydehydrogenation is dramatically influenced by the catalyst support. Maximum cyclohexane conversion and cyclohexene yield of 11% were obtained for SO4 content of 2.6 wt% at 120 °C. Physico-chemical characterisation of catalysts indicates the presence of both octahedral polymolybdate and sulphate species on alumina surface, as previously found for titania. Increasing sulphate load, thermogravimetry evidenced the presence of up to three sulphate species at different thermal stability. The lower activity observed at high sulphate content is likely due to polymolybdate decoration by sulphates. 相似文献
13.
The performance of the active catalyst 5%V 2O 5-1.9%MgO/TiO 2 in propane oxidative dehydrogenation is investigated under various reactant contact modes: co-feed and redox decoupling using fixed bed and co-feed using fluid bed. Using fixed bed reactor under co-feed conditions, propane is activated easily on the catalyst surface with selectivities ranging from 30 to 75% depending on the degree of conversion. Under varying oxygen partial pressures, especially for higher than the stoichiometric ratio O 2/C 3H 8 = 1/2, nor the propane conversion or the selectivities to propene and COx are affected. The performance of the catalyst in the absence of gas phase oxygen was tested at 400 °C. It was confirmed that the catalyst surface oxygen participates to the activation of propane forming propene and oxidation products with similar selectivities as those obtained under co-feed conditions. The ability of the catalyst to fully restore its activity by oxygen treatment was checked in repetitive reduction–oxidation cycles. Fluid bed reactor using premixed propane–oxygen mixtures was also employed in the study. The catalyst was proved to be very active in the temperature range 300–450 °C attaining selectivities comparable to those of fixed bed. 相似文献
14.
The catalytic partial oxidation of propane in supercritical carbon dioxide has been investigated in a stirred batch reactor. Various metals (oxides) have been used as supported catalysts with respect to their activity and selectivity for the formation of oxygenates. The reactions run with a 1:2.3–2.9:68–108 molar ratio of propane:synthetic air:CO 2 at 453–573 K and 80–100 bar. Using a precipitated 2.4 wt.% Co 3O 4–SiO 2 catalyst at 573 K, a total oxygenate (i.e. acetic acid, acetone, acetaldehyde, methanol) selectivity of 59% and a propene selectivity of 21% were obtained at a propane conversion of 12 mol%. The same catalyst has been used to investigate the influence of the supercritical conditions and initial feed composition on the reaction, varying the density of CO 2 and the concentration of synthetic air, respectively. 相似文献
15.
The distribution of gaseous products and the nature of the surface species generated during the selective catalytic reduction of NO with C 3H 6 in the presence of excess O 2 (i.e. C 3H 6-SCR) were studied over both a 0.4% Co/γ-Al 2O 3 catalyst and a sulphated 1.2% Ag/γ-Al 2O 3 catalyst. The results were compared with those previously reported for the C 3H 6-SCR over 1.2% Ag/γ-Al 2O 3 and γ-Al 2O 3. High concentrations of NO 2 were observed in the product stream of the SCR reaction over the 0.4% Co/γ-Al 2O 3 and sulphated 1.2% Ag/γ-Al 2O 3 materials. The results show that (as in the case of the γ-Al 2O 3 and also probably that of the 1.2% Ag/γ-Al 2O 3) the NO 2 was formed via an alternative route to the direct oxidation of NO with O 2. The yields of NO 2 were higher over the Co/γ-Al 2O 3 than over the other materials and in contrast to the other materials, no NH 3 was produced over the Co/γ-Al 2O 3 catalyst. Based on these results and those of in situ DRIFTS experiments, a global reaction scheme incorporating organo-nitrogen species as key intermediates is proposed. In this scheme, NO, propene and oxygen react to form organo-nitro and/or organo-nitrito adsorbed species, the reaction products of which combine to yield N 2. The results reported here suggest that Co preferentially promotes the formation of nitrito-compounds which can readily decompose to NO 2, whereas Ag preferentially promotes the formation of nitro-compounds (from reaction of strongly bound ad-NO x species) which can decompose to isocyanates and ammonia. The sulphation of the 1.2% Ag/γ-Al 2O 3 reduced the surface concentration of strongly bound ad-NO x species which were thought to react with the reductant or derived species to yield the organo-nitrogen species. 相似文献
16.
Polycylic aromatic hydrocarbons (PAHs) are listed as carcinogenic and mutagenic priority pollutants, belonging to the environmental endocrine disrupters. Most PAHs in the environment stem from the atmospheric deposition and diesel emission. Consequently, the elimination of PAHs in the off-gases is one of the priority and emerging challenges. Catalytic oxidation has been widely used in the destruction of organic compounds due to its high efficiency (or conversion of reactants), its economic benefits and good applicability. This study investigates the application of the catalytic oxidation using Pt/γ-Al2O3 catalysts to decompose PAHs and taking naphthalene (the simplest and least toxic PAH) as a target compound. It studies the relationships between conversion, operating parameters and relevant factors such as treatment temperatures, catalyst sizes and space velocities. Also, a related reaction kinetic expression is proposed to provide a simplified expression of the relevant kinetic parameters. The results indicate that the Pt/γ-Al2O3 catalyst used accelerates the reaction rate of the decomposition of naphthalene and decreases the reaction temperature. A high conversion (over 95%) can be achieved at a moderate reaction temperature of 480 K and space velocity below 35,000 h−1. Non-catalytic (thermal) oxidation achieves the same conversion at a temperature beyond 1000 K. The results also indicate that Rideal–Eley mechanism and Arrhenius equation can be reasonably applied to describe the data by using the pseudo-first-order reaction kinetic equation with activation energy of 149.97 kJ/mol and frequency factor equal to 3.26 × 1017 s−1. 相似文献
17.
The influences of calcination temperatures and additives for 10 wt.% Cu/γ-Al 2O 3 catalysts on the surface properties and reactivity for NO reduction by C 3H 6 in the presence of excess oxygen were investigated. The results of XRD and XPS show that the 10 wt.% Cu/γ-Al 2O 3 catalysts calcined below 973 K possess highly dispersed surface and bulk CuO phases. The 10 wt.% Cu/γ-Al 2O 3 and 10 wt.% Mn–10 wt.% Cu/γ-Al 2O 3 catalysts calcined at 1073 K possess a CuAl 2O 4 phase with a spinel-type structure. In addition, the 10 wt.% La–10 wt.% Cu/γ-Al 2O 3 catalyst calcined at 1073 K possesses a bulk CuO phase. The result of NO reduction by C 3H 6 shows that the CuAl 2O 4 is a more active phase than the highly dispersed and bulk CuO phase. However, the 10 wt.% Mn–10 wt.% Cu/γ-Al 2O 3 catalyst calcined at 1073 K possesses significantly lower reactivity for NO reduction than the 10 wt.% Cu/γ-Al 2O 3 catalyst calcined at 1073 K, although these catalysts possess the same CuAl 2O 4 phase. The low reactivity for NO reduction for 10 wt.% Mn–10 wt.% Cu/γ-Al 2O 3 catalyst calcined at 1073 K is attributed to the formation of less active CuAl 2O 4 phase with high aggregation and preferential promotion of C 3H 6 combustion to CO x by MnO 2. The engine dynamometer test for NO reduction shows that the C 3H 6 is a more effective reducing agent for NO reduction than the C 2H 5OH. The maximum reactivity for NO reduction by C 3H 6 is reached when the NO/C 3H 6 ratio is one. 相似文献
18.
Polychlorinated benzenes (PhCl x) are formed as byproducts in the combustion of chlorobenzene on Pt supported on γ-Al 2O 3, SiO 2, SiO 2–Al 2O 3, or ZrO 2. The congener and isomer distribution of the PhCl x differs for the various supports. The amounts of PhCl x correlate with the dispersion of platinum. Thus, a Pt/γ-Al 2O 3 catalyst calcined at 500°C to yield very small Pt crystallites was more active in PhCl x formation than Pt/γ-Al 2O 3 calcined at 800°C. In all cases T50% for chlorobenzene conversion is close to 300°C and appears to be independent of the crystallite size of the platinum. Replacing platinum by palladium led to lower rates of combustion and to more byproducts. These results lead us to propose that, in the presence of Cl and higher oxygen concentrations, small Pt crystallites are converted more easily into Pt(IV) species. These are less efficient in combustion, but can be more active in chlorination. 相似文献
19.
The catalytic oxidation of unsymmetrical dimethylhydrazine (UDMH) by air has been studied in a vibro-fluidized catalyst bed laboratory kinetic setup over catalysts Cu xMg 1−xCr 2O 4/γ-Al 2O 3, 32.9%Ir/γ-Al 2O 3 and β-Si 3N 4 in a temperature range 150–400 °C. The catalyst Cu xMg 1−xCr 2O 4/γ-Al 2O 3 was found to be optimal regarding high yields of CO 2 and low yields of NO x. A probable mechanism of UDMH heterogeneous catalytic oxidation is proposed. Catalyst Cu xMg 1−xCr 2O 4/γ-Al 2O 3 has been further used in the pilot plant specially designed for the destruction of UDMH. Results of testing the main fluidized bed catalytic reactor for UDMH oxidation and the reactor for selective catalytic reduction of NO x with NH 3 are presented. These results prove that the developed UDMH destruction technology is highly efficient and environmentally safe. 相似文献
20.
A method to quantify DRIFT spectral features associated with the in situ adsorption of gases on a NO x adsorber catalyst, Pt/K/Al 2O 3, is described. To implement this method, the multicomponent catalyst is analysed with DRIFT and chemisorption to determine that under operating conditions the surface comprised a Pt phase, a pure γ-Al 2O 3 phase with associated hydroxyl groups at the surface, and an alkalized-Al 2O 3 phase where the surface –OH groups are replaced by –OK groups. Both DRIFTS and chemisorption experiments show that 93–97% of the potassium exists in this form. The phases have a fractional surface area of 1.1% for the 1.7 nm-sized Pt, 34% for pure Al 2O 3 and 65% for the alkalized-Al 2O 3. NO 2 and CO 2 chemisorption at 250 °C is implemented to determine the saturation uptake value, which is observed with DRIFTS at 250 °C. Pt/Al 2O 3 adsorbs 0.087 μmol CO 2/m 2and 2.0 μmol NO 2/m 2, and Pt/K/Al 2O 3 adsorbs 2.0 μmol CO 2/m 2and 6.4 μmol NO 2/m 2. This method can be implemented to quantitatively monitor the formation of carboxylates and nitrates on Pt/K/Al 2O 3 during both lean and rich periods of the NO x adsorber catalyst cycle. 相似文献
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