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1.
《Catalysis communications》2001,2(11-12):369-374
Platinum and Platinum–tin bimetallic catalysts supported on alumina were prepared by co-impregnation of both metallic precursors on the support and used as catalysts for the oxidation of SO2. Platinum dispersion was determined by means of H2–O2 titration. Tin addition (1 and 2 wt%) only slightly decreased the exposed platinum atoms suggesting that tin is mainly over the support. At temperatures lower than 300 °C, SO2 did not react with oxygen. Nevertheless, when the temperature was increased, the SO2 oxidation began. The ignition temperatures for SO2 oxidation (taken at 50% conversion) were 345 °C for 1% Pt/Al2O3 and 520 °C for 1% Pt–2% Sn/Al2O3. The strong displacement on activity suggests that tin plays an important role as inhibitor of the SO2 oxidation reaction. 相似文献
2.
采用负载型Rh/MgO/γ-Al2O3催化剂研究了毫秒级甲烷蒸汽重整过程,在水碳比为1和3的条件下,详细考察了反应温度、空速和催化剂Rh含量对反应转化率和选择性的影响。研究结果表明,Rh/MgO/γ-Al2O3催化剂在毫秒级操作条件下具有良好的催化性能,使用5%(质量分数)Rh催化剂,在水碳比3、反应温度1150 K、空速641.11 L8226;(g cat)-18226;h-1时,CH4转化率约90%,CO2选择性约20%,毫秒级接触时间反应行为即可接近热力学平衡。高温有利于毫秒级甲烷蒸汽重整过程。 相似文献
3.
Macro-porous monolithic γ-Al2O3 was prepared by using macro-porous polystyrene monolith foam as the template and alumina sol as the precursor. Platinum and potassium were loaded on the support by impregnation method. TG, XRD, N2 adsorption–desorption, SEM, TEM, and TPR techniques were used for catalysts characterization, and the catalytic performance of macro-porous monolithic Pt/γ-Al2O3 and K–Pt/γ-Al2O3 catalysts were tested in hydrogen-rich stream for CO preferential oxidation (CO-PROX). SEM images show that the macropores in the macro-porous monolithic γ-Al2O3 are interconnected with the pore size in the range of 10 to 50 μm, and the monoliths possess hierarchical macro-meso(micro)-porous structure. The macro-porous monolithic catalysts, although they are less active intrinsically than the particle ones, exhibit higher CO conversion and higher O2 to CO oxidation selectivity than particle catalysts at high reaction temperatures, which is proposed to be owing to its hierarchical macro-meso(micro) -porous structure. Adding potassium lead to marked improvement of the catalytic performance, owing to intrinsic activity and platinum dispersion increase resulted from K-doping. CO in hydrogen-rich gases can be removed to 10 ppm over monolithic K–Pt/γ-Al2O3 by CO-PROX. 相似文献
4.
《Applied Catalysis A: General》1999,176(1):17-26
A series of NiMoNx/γ-Al2O3 catalysts with various Ni contents were prepared by a topotactic reaction between their corresponding precursors NiO·MoO3/γ-Al2O3 and NH3. The catalysts were characterized using BET, XRD, and H2-TPR techniques, and the HDN activity of pyridine over these catalysts was tested. XRD patterns show that metallic Ni, Mo2N and a new phase of Ni3Mo3N exist in NiMoNx/γ-Al2O3 catalyst. H2-TPR studies indicate that the presence of Ni lowers the reduction temperature of the passivated surface layer of nitrided Mo/γ-Al2O3. The HDN activity for NiMoNx/γ-Al2O3 is much higher than that for NiMoSx/γ-Al2O3. The nitride catalyst with about 5.0 wt% NiO and 15.0 wt% MoO3 in its precursor has the highest specific denitrogenation activity. The appearance of Ni3Mo3N and the synergy between metallic Ni and nitrided Mo are probably responsible for the high activity of NiMoNx/γ-Al2O3 catalyst. The role of Ni in HDN reaction was also investigated. The activities decrease in the order: reduced Ni/γ-Al2O3≥nitrided Ni/γ-Al2O3>partially reduced Ni/γ-Al2O3 and sulfided Ni/γ-Al2O3. 相似文献
5.
G. Capannelli A. Bottino G. Gao A. Grosso A. Servida G. Vitulli A. Mastantuono R. Lazzaroni P. Salvadori 《Catalysis Letters》1993,20(3-4):287-297
The opportunity of using mesitylene solvated Pt atoms for the deposition of Pt catalyst on inorganic membranes is shown. The catalytic activity of the membrane reactor has been tested using the hydrogenation of benzene as model reaction. The performance of the membrane reactor has been compared with that of a conventional packed bed using -Al2O3 powder impregnated with Pt. The effect of the feeding configuration has been investigated, and the results show a membrane effect due to the different degrees of accessibility of pores of different size. For alumina powder we have obtained an activation energy of 12.9 kcal/mol, which well agrees with the data reported in literature. The membrane reactor, instead, exhibited an activation energy ca. 60% lower. The preliminary porometry results have shown a slight effect of the platinum deposition process on membrane permeability. 相似文献
6.
Autothermal reforming (ATR) of methane over the synthesized catalysts of 10Ni-2La/γ-Al2O3, 10Ni-2Ce/γ-Al2O3, 10Ni-2Co/γ-Al2O3 was investigated in the temperature range of 600-800 oC for the hydrogen production. The sequence of 2 wt% metal loading on nickel alumina support in relation to their catalytic performance was observed as La>Ce>Co. The excellent activity and selectivity of 10Ni-2La/γ-Al2O3 was superior to other catalysts owing to little carbon deposition (~2.23 mg coke/gcath), high surface area and good dispersion and stability in the alumina support. The reforming of methane was inferred to be initiated by the decomposition of hydrocarbon at the inlet zone, preceded by the reforming reactions in the catalyst bed. Our result shows that it can be possible to achieve the H2/CO ratio optimal to the GTL processes by controlling the O2/CH4 ratio of the feed inlet. The addition of oxygen to the feed inlet enhanced conversion efficiency substantially; probably, it favors the re-oxidation of carbonaceous residues formed over the catalyst surfaces, avoiding the catalyst deactivation and hence promoting catalyst stability. 相似文献
7.
In the current paper, a strategy for catalytic degradation of benzene over Pd/γ-Al2O3 catalysts via different atmospheres (H2, N2, He and air) pretreatment was carried out in a fixed bed reactor. The experimental results indicated that H2, N2, and He pretreatments have a significant positive effect on the initial activity of the catalyst compared to air. We have also investigated the effects of pretreatment atmospheres on the catalytic performance for benzene degradation through the information on the chemical state and crystal structure of the catalysts using X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), high resolution transmission electron microscopy (HRTEM), and CO chemisorption measurements techniques. The chemical state of Pd species decreased via H2 pretreatment, leading to the increase of the initial catalytic activity, while chemical state increased accompanying with a decrease in degradation benzene via air pretreatment. There is no change in the chemical state of Pd species using inert atmosphere (N2 and/or He) pretreatment, but the initial activity of the catalyst improved significantly due to the modified crystal structure of Pd species in the catalysts, with the crystalline PdO being transformed to amorphous state. 相似文献
8.
The kinetic isotope effect for combustion of a C6H5Cl/C6D5Cl mixture on Pt/-Al2O3 was found to be close to unity between 520 and 580 K. However, in the presence of an excess of heptane, an isotope effect of 1.5 was found between 460 and 490 K. For the combustion of a C6H6/C6D6 mixture the kH/kD value was around 2 between 404 and 439 K. The results show that in the combustion of chlorobenzene per se, C–H bond activation is not a rate-determining step. On Pt sites, C–Cl bond scission probably occurs already at low temperatures. The chlorine and the phenyl group cannot easily react further. Chlorine on the surface is active in chlorination, which is shown by the formation of C6D5Cl in an experiment with C6H5Cl and C6D6. Only at a certain temperature is the chlorine removed, partly as polychlorinated benzenes. The removal of chlorine from the catalyst allows oxygen to take part in the reaction, which determines the rate of the combustion of chlorobenzene. When heptane is present, Cl is removed from the surface and C–H bond scission can become rate determining, as is also the case in the combustion of C6H6/C6D6. Upon (partial) combustion of C6H5Cl/C6D5Cl and C6H6/C6D6 mixtures on a Pt/-Al2O3 catalyst, hydrogen–deuterium exchange occurs on the -Al2O3 support. 相似文献
9.
Abolfazl Samavati Moslem Fattahi Farhad Khorasheh 《Korean Journal of Chemical Engineering》2013,30(1):55-61
A reduction in catalyst activity with time-on-stream and formation of side products are the major problems associated with catalytic propane dehydrogenation. Coke formation on the catalyst surface is the most important cause for catalyst deactivation. Experiments have indicated that the presence of very small amounts of oxygenated additives such as water can reduce the amount of coke accumulated on the catalyst surface and enhance catalyst activity. Addition of water beyond an optimum level, however, would result in a loss of activity due to sintering of catalyst. Propane dehydrogenation over a Pt-Sn/γ-Al2O3 catalyst in the temperature range of 575 to 620 °C was investigated in the presence of small amounts of water added to the feed. A monolayer-multilayer mechanism was used to model the coke growth kinetics. Coke deposition and catalyst sintering were considered in a catalyst deactivation model to explain the observed optimum level in the amounts of water added to the feed. The model predictions for both propane conversion and coke formation with time-on-stream were in good agreement with experimental data. 相似文献
10.
Ryan M. Ravenelle John R. Copeland Adam H. Van Pelt John C. Crittenden Carsten Sievers 《Topics in Catalysis》2012,55(3-4):162-174
The stability of a Pt/??-Al2O3 catalyst in liquid water and aqueous solutions of 5?wt% glycerol or sorbitol at 225?°C is examined using a variety of physicochemical methods. It is demonstrated that the presence of glycerol and sorbitol significantly reduces the hydration of ??-Al2O3 to form boehmite as compared to treatment in pure water. The stability against hydration increases with increasing carbon chain length. Treatment with polyol solutions also results in reduced agglomeration of supported metal particles. The prevention of boehmite formation and agglomeration of metal particles are attributed to the formation of carbonaceous species on the surface. In addition to these effects, the deposits block a considerable portion of active metal surface area. IR spectroscopic analysis indicates that dehydration reactions play an important role in the formation of the carbonaceous deposits. The present results illustrate that water and dissolved biomass compounds can strongly affect the stability of heterogeneous catalysts under reaction conditions. 相似文献
11.
Gas-phase dehydration of glycerol to produce acrolein was investigated over commercial catalysts based onγ-Al2O3, viz. A-64, A-56, I-62, AP-10, AP-56, AP-64 and KR-104. To understand the effect of Cl?anions, HCl-impregnated sup-ports have been investigated in the dehydration reaction of glycerol at 375 °C. For comparison, various H-zeolites were also examined. It was found that the glycerol conversion over the solid acid catalysts was strongly dependent on their acidity and surface area. And the relationship between the catalytic activity and the acidity of the catalysts was discussed. The outstanding properties of Pt/γ-Al2O3 catalyst systems for the dehydration of glycerol were revealed. Pt/γ-Al2O3 catalyst (AP-64) showed the highest catalytic activity after 50 h of reaction with an acrolein selectivity of 65%at a conversion of glycerol of 90%. Based on these results, catalysts based onγ-Al2O3 appear to be most promising for gas phase dehydration of glycerol. 相似文献
12.
Véronique Jollet Flora Chambon Franck Rataboul Amandine Cabiac Catherine Pinel Emmanuelle Guillon Nadine Essayem 《Topics in Catalysis》2010,53(15-18):1254-1257
The dissolution of cellulose under 5 MPa of H2 in the absence of catalyst is temperature and time dependant. The presence of Pt/γ-Al2O3 increases the initial rate of dissolution. The presence of H2/Pt is essential although its exact role has not been well elucidated. 相似文献
13.
《Catalysis communications》2009,10(15):2601-2605
The catalytic oxidation of low concentration of methane (2000 ppmV) in excess oxygen was investigated over unsulfated and pre-sulfated Pt/γ-Al2O3 catalysts. Over unsulfated samples, catalyst activity increased slightly with Pt concentration and with catalyst loading in the reactor. This enhancement was stronger over pre-sulfated catalyst relative to unsulfated samples. The results suggest that the new catalytic sites generated during sulfation (formed by the interaction between surface support sulfates and highly oxidized Pt atom at the edge of the platinum particle) may activate the almost non-polar C–H bonds of methane through a dissociate adsorption of CH4, thus the increase in the sulfated catalyst loading results in the increase in the number of the catalytic sites generated during sulfation. The probability of the initial C–H activation of CH4 increases and may lead to the observed increase in the oxidation rate for CH4O2 reaction. 相似文献
14.
We show that butanone can be reacted to form n-butane in an isothermal reactor containing a 1 wt.% Pt/γ-Al2O3 and an HZSM-5 catalyst (total mass of 12–400 mg, Si/Al = 11.5) below 160 °C with up to 99% selectivity and 67% yield. The catalyst loading (12–400 mg) and temperature (100–250 °C) were varied to obtain primary products whose selectivities decreased with conversion and secondary/tertiary products whose selectivities increased with conversion. As conversion increased, the selectivities of butanol and butene decreased, showing the formation of butane from butanone through a series reaction pathway: butanone → 2-butanol → butene → butane. Butane selectivity increased as the temperature was increased from 100 to 200 °C when compared at similar conversions due to higher dehydration rates over the zeolite. Processing ketones at low temperatures over bifunctional catalysts may be an efficient means of obtaining high yields of stable paraffins from reactive oxygenates. 相似文献
15.
Enantioselective hydrogenation of ethyl-2-oxo-4-phenylbutyrate (EOPB) on a cinchonidine-modified Pt/-Al2O3 catalyst was carried out using a fixed-bed reactor to obtain the chiral product, (R)-(+)-ethyl-2-hydroxy-4-phenylbutyrate ((R)-(+)-EHPB). About 95% conversion and 68% ee of the (R)-(+)-EHPB were obtained for the cinchonidine-modified Pt/-Al2O3 catalyst in a continuous-flow reaction system with a fixed-bed reactor. It is observed that the ee of (R)-(+)-EHPB strongly depends on the different solvent and hydrogen pressure. The competitive adsorption between the solvent and reactant molecule plays an important role in determining the ee value of (R)-(+)-EHPB. This study also shows that a compact adsorption of chiral modifiers on the platinum surface is beneficial to the higher enantioselectivity. 相似文献
16.
NiFe bimetallic catalyst shows an excellent activity and selectivity for the hydrodeoxygenation (HDO) of three typical model compounds of bio-oil. The conversion of furfuryl alcohol, benzene alcohol and ethyl oenanthate is 100, 95.48 and 97.89% at 400 °C and the yield to 2-methylfuran, toluene and heptane is 98.85, 93.49 and 96.11% at 0.1 ml/min flow speed and atmospheric pressure. It indicates that the major reaction pathway is the cleavage of C–O rather than C–C. After the catalytic HDO of bio-oil over NiFe/Al2O3 catalyst, the heating value changes from 37.8 to 43.9 MJ/kg, the pH changes from 6.65 to 7.50. 相似文献
17.
Co/γ-Al2O3 and CoRe/γ-Al2O3 catalysts have been studied by the steady-state isotopic transient kinetic analysis (SSITKA) technique. It was found that
neither the CO partial pressure, the temperature nor the space velocity influences the in situ CO adsorption. The space velocity, H2/CO ratio and temperature was found to affect the intrinsic activity (
) slightly, while the total pressure and syngas partial pressure had only a negligible effect. The surface concentrations
and coverages were, however, unaffected by the space velocity, temperature, total pressure, syngas partial pressure and H2/CO ratio. All changes, however, affected the methane selectivity, indicating that the methane selectivity was not a function
of the surface inventory of methane precursors. 相似文献
18.
《Ceramics International》2019,45(16):19956-19961
In this work, CNTs and short carbon fiber reinforced α-Al2O3 matrix composites (i.e., Cnt/α-Al2O3 and Cnt-Csf/α-Al2O3) were prepared by sol-gel dispersing method followed by hot pressing process. Effects of CNTs content on the mechanical properties of Cnt/α-Al2O3 and Cnt-Csf/α-Al2O3 composites were investigated and the inter- and transgranular fracture mechanisms in Cnt-Csf/α-Al2O3 composites were analyzed. The hardness and relative density of Cnt/α-Al2O3 and Cnt-Csf/α-Al2O3 composites slightly decrease as CNTs content increases. The flexural strength and fracture toughness monotonically increase with the increase in Cnt content for both Cnt/α-Al2O3 and Cnt-Csf/α-Al2O3 composites. Addition of Csf and CNTs into α-Al2O3 matrix results in a bimodal grain size microstructure of Cnt-Csf/α-Al2O3 composites, which accounts for the unique fractograph and the enhanced toughness of Cnt-Cf/α-Al2O3 composites. The flexural strength and fracture toughness of Csf5-nt06 composite are 465 MPa and 7.08 MPa/m2, 37% and 13% higher than that of Cnt06, and 42% and 34% higher than that of Csf5, respectively. 相似文献
19.
The conversion of benzene-containing gasoline fractions on the bifunctional Pt/SO 4 2? -ZrO2-Al2O3 catalytic system with different compositions of the support is studied. Using the results from hydroisomerization of a heptane-benzene model mixture, it is shown that a system with 67.8 wt % of aluminum oxide in its support has the best catalytic properties. For the IBP-85°C industrial benzene-containing fraction (23.7 wt % of benzene), it is established that the given catalyst ensures the complete removal of arenes from the benzene-containing fraction while raising its research octane number by 2.2–3.3 points and retaining a high yield of liquid products at levels of 98.7 wt % and higher. 相似文献
20.
《Applied catalysis》1987,29(1):125-140
The Australian brown coal-derived oil mixed with a hydrogenated creosote oil was hydrotreated over NiMo and CoMoγAl2O3 catalysts. The initial catalytic activities varied with the reaction for each catalyst: converting of the hexane-insolubles to the hexane-soluble oils(HDHI) > hydrodesulfurization(HDS) > hydrodenitrogenation(HDN) > hydroconverting of the 623 K+ residues to the 623 K− oils(HDC). A NiMo catalyst showed higher activities than a CoMo catalyst did. The initial catalyst deactivation was significant in the order of HDC > HDN > HDS > HDHI for each catalyst. The degrees of the deactivation were larger for a CoMo catalyst. The analyses of the spent catalysts showed that the pore volumes and the surface areas were decreased markedly by the carbonaceous deposits, in which higher amounts of the N- and O-containing compounds accumulated. The XPS and elemental analyses of the spent catalysts indicated that the decreases in the amounts of sulfur during the course of run were linked with the decreases in the sulfidic states of molybdenum(Mo4+ species) and the promoters. These carbonaceous deposits and the changes in chemical states of the supported metals were interpreted as the main reasons for the initial catalyst deactivation. 相似文献