共查询到20条相似文献,搜索用时 31 毫秒
1.
A polymer-based catalytic membrane reactor was developed and applied for hydrodechlorination of chlorobenzene as a model compound of ground and waste water contaminants. The catalytically active membrane consists of a non-porous, thin film (about 3–7 μm) of poly(dimethylsiloxane) (PDMS) loaded with nano-sized Pd clusters. They were built-in either directly or as nano-sized, supported catalysts. A composite membrane, consisting of porous poly(acrylonitrile) (PAN) support and a Pd-loaded thin PDMS film, was fabricated on a coating machine. Defect-free membrane envelopes of 0.1 m 2 were produced and fitted into a membrane test cell. Gaseous hydrogen as reductant for hydrodechlorination is fed from the membrane’s back side directly to the catalyst, embedded in the PDMS layer. The chemical reactions at the Pd surface are accompanied by absorption of chlorobenzene from the water phase into the PDMS layer and desorption of benzene and HCl back to the water phase. The specific activity of supported catalysts decreased only slightly by PDMS incorporation, e.g., from 31 l/g(Pd) min for Pd/Fe on titania to 16 l/g(Pd) min for the same catalyst built-in a 7 μm thick supported PDMS membrane and measured in the membrane test cell. Directly built-in Pd clusters are less active and more difficult to prepare on a larger scale. Some catalyst deactivation was observed and may be balanced by development of more suited nano-sized supported catalysts. 相似文献
2.
This work investigates the effects of Au 3+/Au 0 ratio or distribution of gold oxidation states in Au/ZrO 2 catalysts of different gold loadings (0.01–0.76% Au) on CO oxidation and 1,3-butadiene hydrogenation by regulating the temperature of catalyst calcination (393–673 K) and pre-reduction with hydrogen (473–523 K). The catalysts were prepared by deposition–precipitation and were characterized with elemental analysis, nitrogen adsorption/desorption, TEM, XPS and TPR. The catalytic data showed that the exposed metallic Au 0 atoms at the surface of Au particles were not the only catalytic sites for the two reactions, isolated Au 3+ ions at the surface of ZrO 2, such as those in the catalysts containing no more than 0.08% Au were more active by TOF. For 0.76% Au/ZrO 2 catalysts having coexisting Au 3+ and Au 0, the catalytic activity changed differently with varying the Au 3+/Au 0 ratio in the two reactions. The highest activity for the CO oxidation reaction was observed over the catalyst of Au 3+/Au 0 = 0.33. However, catalyst with a higher Au 3+/Au 0 ratio showed always a higher activity for the hydrogenation reaction; co-existance of Au 0 with Au 3+ ions lowered the catalyst activity. Moreover, the coexisting Au particles changed the product selectivity of 1,3-butadiene hydrogenation to favor the formation of more trans-2-butene and butane. It is thus suggested that for better control of the catalytic performance of Au catalyst the effect of Au 3+/Au 0 ratio on catalytic reactions should be investigated in combination with the particle size effect of Au. 相似文献
3.
0.5 wt% palladium supported on exchanged BEA and FAU zeolites were prepared, characterized and tested in the total oxidation of volatile organic compounds (VOCs). The BEA and FAU zeolites were exchanged with different cations to study the influence of alkali metal cations (Na +, Cs +) and H + in Pd-based catalysts on propene and toluene total oxidation. The exchange with different cations (Na +, Cs +) and H + led to a decrease of the surface area and the micropore volume. All Pd/BEA and Pd/FAU zeolites were found to be powerful catalysts for the total oxidation of VOCs. They were active at low temperature and totally selective for CO 2 and H 2O. However, their activity depends significantly on the type of zeolite and on the nature of the charge-compensating cation. The activity order for propene and toluene oxidation on FAU catalysts, Pd/CsFAU > Pd/NaFAU > Pd/HFAU, is the reverse of the activity order on BEA catalysts: Pd/HBEA > Pd/NaBEA > Pd/CsBEA. The catalytic activities can be rationalized in terms of the influence of the electronegativity of the charge-compensating cation on the Pd particles, the Pd dispersion, the PdO reducibility and the adsorption energies for VOCs. 相似文献
4.
采用负载法制备了一系列纳米ZrO 2负载金属Ni、Pd催化剂,通过XRD、TEM和SEM等技术对催化剂进行了表征,并以氯苯的加氢脱氯为探针反应,考察了催化剂的加氢脱氯性能和反应温度、碱的用量、催化剂镍的含量等因素对催化活性的影响。结果发现,在80 ℃、NaOH和氯苯物质的量的比为1的反应条件下,Ni质量分数为10%和Pd为0.05%的Pd-Ni/ZrO 2催化剂效果最佳,反应9 h后氯苯的转化率可达到100%。 相似文献
5.
The performance of four different alumina-supported noble metal catalysts (0.5% of Pd, Pt, Rh and Ru, respectively) for the deep oxidation of trichloroethene (1000–2500 ppmV, WHSV = 55 h −1) in air was studied in this work. Experiments were carried out at both dry and wet (20,000 ppm of H 2O) conditions. Catalysts were compared in terms of activity, selectivity for the different reaction products (CO 2, HCl, Cl 2, C 2Cl 4, CCl 4 and CHCl 3), and stability at reaction conditions. As general trend, the activity of the catalysts decreases in the order Ru Pd > Rh > Pt. Concerning to the effect of the water addition, no important effect on the catalyst activity was observed, except in the case of Pt, for which an increase of the catalytic activity was observed. Reaction mechanism (and hence product distribution) is very similar for Rh, Pd and Pt, being in these cases C2Cl4 the only organochlorinated by-product detected. In the case of Ru, the reaction mechanism seems to be quite different, CCl4 and CHCl3 being the main organic by-products. Simple power-law kinetic expressions (first order on trichloroethene concentration for Pd, Rh and Ru, and zeroth order for Pt) provide fairly good fits for catalytic performance of the studied catalysts. Finally, deactivation studies show that both formation of active metal chlorides (especially in the case of Rh) and fouling (especially for Pd and Pt) are the main deactivation causes. 相似文献
6.
Palladium (Pd) supported on CeO 2-promoted γ-Al 2O 3 with various CeO 2 (ceria) crystallinities, were used as catalysts in the methane steam reforming reaction. X-ray diffraction (XRD) analysis, FTIR spectroscopy of adsorbed CO, and X-ray photoelectron spectroscopy (XPS) were employed to characterize the samples in terms of Pd and CeO 2 structure and dispersion on the γ-Al 2O 3 support. These results were correlated with the observed catalytic activity and deactivation process. Arrhenius plots at steady-state conditions are presented as a function of CeO 2 structure. Pd is present on the oxidized CeO 2-promoted catalysts as Pd 0, Pd + and Pd 2+, at ratios strongly dependent on CeO 2 structure. XRD measurements indicated that Pd is well dispersed (particles <2 nm) on crystalline CeO 2 and is agglomerated as large clusters (particles in 10–20 nm range) on amorphous CeO 2. FTIR spectra of adsorbed CO revealed that after pre-treatment under H 2 or in the presence of amorphous CeO 2, partial encapsulation of Pd particles occurs. CeO 2 structure influences the CH 4 steam reforming reaction rates. Crystalline CeO 2 and dispersed Pd favor high reaction rates (low activation energy). The presence of CeO 2 as a promoter conferred high catalytic activity to the alumina-supported Pd catalysts. The catalytic activity is significantly lower on Pd/γ-Al 2O 3 or on amorphous (reduced) CeO 2/Al 2O 3 catalysts. The reaction rates are two orders of magnitude higher on Pd/CeO 2/γ-Al 2O 3 than on Pd/γ-Al 2O 3, which is attributed to a catalytic synergism between Pd and CeO 2. The low rates on the reduced Pd/CeO 2/Al 2O 3 catalysts can be correlated with the loss of Pd sites through encapsulation or particle agglomeration, a process found mostly irreversible after catalyst regeneration. 相似文献
7.
The catalytic performance of mono- and bimetallic Pd (0.6, 1.0 wt.%)–Pt (0.3 wt.%) catalysts supported on ZrO 2 (70, 85 wt.%)–Al 2O 3 (15, 0 wt.%)–WO x (15 wt.%) prepared by sol–gel was studied in the hydroisomerization of n-hexane. The catalysts were characterized by N 2 physisorption, XRD, TPR, XPS, Raman, NMR, and FT-IR of adsorbed pyridine. The preparation of ZrW and ZrAlW mixed oxides by sol–gel favored the high dispersion of WO x and the stabilization of zirconia in the tetragonal phase. The Al incorporation avoided the formation of monoclinic-WO 3 bulk phase. The catalysts increased their SBET for about 15% promoted by Al 2O 3 addition. Various oxidation states of WO x species coexist on the surface of the catalysts after calcination. The structure of the highly dispersed surface WO x species is constituted mainly of isolated monotungstate and two-dimensional mono-oxotungstate species in tetrahedral coordination. The activity of Pd/ZrW catalysts in the hydroisomerization of n-hexane is promoted both with the addition of Al to the ZrW mixed oxide and the addition of Pt to Pd/ZrAlW catalysts. The improvement in the activity of Pd/ZrAlW catalysts is ascribed to a moderated acid strength and acidity, which can be correlated to the coexistence of W 6+ and reduced-state WO x species (either W 4+ or W 0). The addition of Pt to the Pd/ZrAlW catalyst does not modify significantly its acidic character. Selectivity results showed that the catalyst produced 2MP, 3MP and the high octane 2,3-dimethylbutane (2,3-DMB) and 2,2-dimethylbutane (2,2-DMB) isomers. 相似文献
8.
Catalytic hydrodehalogenation is presented as a viable approach in the non-destructive treatment of concentrated halogenated aromatic gas streams to generate reusable raw material. Nickel loaded (from 1.5 to 20.3% w/w) silica catalysts have been used to hydrotreat a range of halogenated feedstock, where 473 K≤ T≤573 K: chlorobenzene, chlorotoluene, chlorophenol, bromobenzene, dichlorobenzene, dichlorophenol, trichlorophenol, pentachlorophenol. The long term (up to 800 h-on-stream) stability of these catalysts has been assessed where the changes in nickel particle size and morphology as a result of the prolonged catalytic step was probed by TEM; each catalyst irrespective of any loss of initial activity was fully selective in solely promoting dehalogenation. In the case of a polychlorinated feedstock, dechlorination can proceed in a stepwise manner to generate a partially dechlorinated product. Hydrodehalogenation appears to occur via an electrophilic mechanism where the presence of electron-donating substituents on the benzene ring enhances the rate of reaction. The reaction is shown to be structure sensitive over Ni/SiO 2 where the hydrodechlorination rates and ultimate yield of the parent aromatic from a polychlorinated reactant is favored by larger nickel particle sizes. A direct contact of the freshly activated catalyst with HCl or HBr gas induced an appreciable growth of the supported metal crystallites. Chlorobenzene hydrodechlorination was suppressed on a HCl or HBr treated Ni/SiO 2 which promoted instead the unexpected growth of highly ordered carbon filaments; this carbon growth is characterized by TEM and SEM. The dependence of the experimental hydrodechlorination and hydrodebromination rates on the gas phase aromatic partial pressure (in the range 0.02–0.1 atm) is adequately represented by a kinetic model involving a non-competitive adsorption of hydrogen and halogenated aromatic where the incoming aromatic reactant must displace the hydrogen halide from the catalyst surface. 相似文献
9.
This study reports the influence of palladium salt precursor on the catalytic activity of palladium-doped hexaaluminate catalysts for the combustion of 1 vol% CH 4 in the presence of CO 2 and H 2O as inhibitors. Thermal stability of the catalysts is evaluated in long-term catalytic test at 700 °C. The hexaaluminate supports were synthesized using two different procedures: conventional coprecipitation and solid/solid diffusion procedure. Palladium impregnation was carried out by two different routes using Pd(NO 3) 2 in water or Pd(acac) 2 in toluene as impregnation solution. It was observed that using Pd(acac) 2 as precursor allows to attain higher dispersion of the active phase (Pd particles size <3 nm). Compared to the catalysts obtained by impregnation of Pd(NO 3) 2, higher catalytic activities are then obtained. Nevertheless, a deactivation of the samples obtained using Pd(acac) 2 is observed. At the end of the stability test, almost similar catalytic activity is obtained whatever the palladium precursor. Reduction–reoxidation experiment showed that this deactivation is irreversible, and TEM analysis suggest that this deactivation is related to the sintering of Pd particles under reaction over samples synthesized using Pd(acac) 2 as precursor. 相似文献
10.
In this work, different procedures, namely carbonate coprecipitation and modified solid–solid diffusion, were used to prepare hexaaluminate samples, unsupported or supported onto θ-Al 2O 3. These samples were used as catalyst for the methane total oxidation as synthesized or after impregnation of 1 wt% Pd. It was observed that the modified solid–solid diffusion procedure is an efficient method to obtain the hexaaluminate structure. At a theoretical ratio x of hexaaluminate onto Al 2O 3 less than 0.6 ( xLa 0.2Sr 0.3Ba 0.5MnAl 11O 19 + (1− x)·Al 2O 3, with x = 0.25, 0.60), samples with high specific surface area and θ-Al 2O 3 structure are then obtained. Large differences in catalytic activity can be observed among the series of sample synthesized. All the pure oxide samples (i.e. without palladium) present low catalytic activity for methane total oxidation compared to a reference Pd/Al 2O 3 catalyst. The highest activity was obtained for the samples presenting a θ-Al 2O 3 structure (with x = 0.60) and a high surface area. Impregnation of 1 wt% palladium resulted in an increase in catalytic activity, for all the solids synthesized in this work. Even if the lowest light-off temperature was obtained on the reference sample, similar methane conversions at high temperature (700 °C) were obtained on the stabilized θ-Al 2O 3 solids ( x = 0.25, 0.60). Moreover, the reference sample is found to strongly deactivate with reaction time at the temperature of test (700 °C), due to a progressive reduction of the PdO x active phase into the less active Pd° phase, whereas excellent stabilities in reaction were obtained on the pure and palladium-doped hexaaluminate and supported θ-Al 2O 3 samples. This clearly showed the beneficial effect of the support for the stabilization of the PdO x active phase at high reaction temperature. These properties are discussed in term of oxygen transfer from the support to the palladium particle. Oxygen transfer is directly related to the Mn 3+/Mn 2+ redox properties (in the case of the hexaaluminate and stabilized θ-Al 2O 3 samples), that allows a fast reoxidation of the metal palladium sites since palladium sites reoxidation cannot occur directly by gaseous dioxygen adsorption and dissociation on the surface. 相似文献
11.
Calcined and reduced catalysts Pd/LaBO 3 (B = Co, Fe, Mn, Ni) were used for the total oxidation of toluene. Easiness of toluene destruction was found to follow the sequence based on the T50 values (temperature at which 50% of toluene is converted): Pd/LaFeO 3 > Pd/LaMnO 3+δ > Pd/LaCoO 3 > Pd/LaNiO 3. In order to investigate the activation process (calcination and reduction) in detail, the reducibility of the samples was evaluated by H 2-TPR on the calcined catalysts. Additionally, characterization of the Pd/LaBO 3 (B = Co, Fe) surface was carried out by X-ray photoelectron spectroscopy (XPS) at each stage of the global process, namely after calcination, reduction and under catalytic reaction at either 150 or 200 °C for Pd/LaFeO 3 and either 200 or 250 °C for LaCoO 3. The different results showed that palladium oxidized entities were totally reduced after pre-reduction at 200 °C for 2 h (2 L/h, 1 °C/min). As LaFeO 3 was unaffected by such a treatment, for the other perovskites, the cations B are partially reduced as B 3+ (B = Mn) or B 2+ even to B 0 (B = Co, Ni). In the reactive stream (0.1% toluene in air), Pd 0 reoxidized partially, more rapidly over Co than Fe based catalysts, to give a Pd 2+/Pd 4+ and Pd 0/Pd 2+/Pd 4+ surface redox states, respectively. Noticeably, reduced cobalt species are progressively oxidized on stream into Co 3+ in a distorted environment. By contrast, only the lines characteristic of the initial perovskite lattice were detected by XRD studies on the used catalysts. The higher activity performance of Pd/LaFeO 3 for the total oxidation of toluene was attributed here to a low temperature of calcination and to a remarkable high stability of the perovskite lattice whatever the nature of the stream which allowed to keep a same palladium dispersion at the different stages of the process and to resist to the oxidizing experimental conditions. On the contrary, phase transformations for the other perovskite lattices along the process were believed to increase the palladium particle size responsible of a lower activity. 相似文献
12.
A series of alumina supported Pd catalysts were prepared by the novel deposition-precipitation method adopting the chloride
precursor (DP-Cl) of Pd and varying the metal content from 0.25 to 1.0 wt%. The catalytic properties of prepared catalysts
were studied by various characterization techniques such as N 2 adsorption, CO chemisorption, TPR, XRD, XPS, and TEM techniques. The activity and stability of the catalysts were evaluated
for the gas phase hydrodechlorination (HDC) of chlorobenzene operating at atmospheric pressure. At 1 wt% of Pd the catalyst
showed higher chlorobenzene conversion with good stability when tested for a period of 25 h, whereas the other catalysts exhibited
a loss in activity with time. In order to elucidate the exceptional activity and stability of this catalyst, a few more catalysts
with 1 wt% Pd were prepared by impregnation technique and also using a non-chloride precursor, palladium nitrate. The 1 wt%
DP-Cl catalyst again was found to be the best among the others. The activity and stability of the DP-Cl catalyst was also
found to be superior to two low-dispersed catalysts, each with 10 wt% Pd, prepared by conventional impregnation method using
the chloride and nitrate as the precursors. The characterization results reveal that the high activity and stability of the
DP-Cl catalyst is related to the formation of electron deficient Pd species and its stabilization in the octahedral vacancies
of alumina. 相似文献
13.
La xSr 2−xMnO 4 (0 ≤ x ≤ 0.8) oxides were synthesized and single-phase K 2NiF 4-type oxides were obtained in the range of 0.1 ≤ x < 0.5. The catalytic activity of La xSr 2−xMnO 4 for NO–CO reaction increased with increasing x in the range of solubility limit of La. La 0.5Sr 1.5MnO 4 showed the highest activity among La xSr 2−xMnO 4 prepared in this study, but its activity was inferior to perovskite-type La 0.5Sr 0.5MnO 3. Among the Pd-loaded catalysts, however, Pd/La 0.8Sr 1.2MnO 4 showed the higher activity and the selectivity to N 2 than Pd/La 0.5Sr 0.5MnO 3 and Pd/γ-Al 2O 3. The excellent catalytic performance of Pd/La 0.2Sr 1.2MnO 4 could be ascribable to the formation of SrPd 3O 4 which was detected by XRD in the catalyst but not in the other two catalysts. 相似文献
14.
H-AITS-1 zeolite with Si/Ti = 50 and Si/Al = 50 was employed in preparing catalyst samples by ion-exchange and impregnation with a copper nitrate solution to obtain 0.24–1.15 wt.% and 1.5, 2 and 2.5 wt.% Cu loading, respectively. The catalytic properties for the NO decomposition were compared with that of Cu-ZSM-5 (Si/Al = 25 with 2 wt.% Cu loading) and similarity was found between the AITS-1 based samples and Cu-ZSM-5. Due to the higher acidity, the activity at 500°C per total copper atoms (an apparent turnover frequency, TOF) was significantly higher over Cu based AITS-1 samples being 2–3 × 10 −3 s −1 as compared to 1 × 10 −3 s −1 measured on Cu-ZSM-5. For the ion-exchanged Cu-AITS-1 there was an increase in TOF with increasing copper content, whereas on the impregnated samples a decrease in TOF was found. On all catalysts there was a maximum in the NO conversion at 500–550°C. The amount of NO per copper atom measured by temperature programmed desorption (TPD) was about the same as that on Cu-ZSM-5 and the features of the TPD were also similar. At the first contact of the catalyst at 500°C with the 2 vol% NO/Ar gas a transient N 2O formation and a considerable delay in the O 2 formation was observed. This could, however, be reproduced only on fresh catalyst, while all further transients showed different but reproducible features using the same sample. 相似文献
15.
采用浸渍法制备系列不同助剂修饰的Pd/C催化剂,并考察不同助剂对2,6-二氯吡啶加氢脱氯性能的影响。结果表明,助剂Sn使催化剂活性明显下降,Fe、Mg对催化剂活性影响不大,少量Ba的修饰可以提高Pd/C催化剂活性。Ba质量分数为1.0%时,2,6-二氯吡啶完全转化,催化剂可多次重复使用。 相似文献
16.
The use of glass fibers in the form of woven cloth (GFC), as a new type of catalytic support, was studied for the reduction of aqueous nitrate solutions using a Pd/Cu–GFC catalyst. The activity (per gram Pd) and selectivity to nitrogen were found to be comparable with those found for Pd–Cu catalysts supported on the other carriers. The maximal initial removal activity was found for a catalyst with a Pd/(Pd+Cu) ratio of 0.81. The corresponding activity was 0.7 mmol min −1 (g Pd) −1, and the selectivity was 97 mol% at 25°C and pH 6.5 for initial nitrate concentration of 100 mg l −1. The selectivity to nitrogen declined at high conversions of nitrate and high pH. 相似文献
17.
The liquid phase hydrodechlorination (HDC) of 2-chlorophenol (2-CP) and 2,4-dichlorophenol (2,4-DCP) has been studied over 1% (w/w) Pd/C and Pd/Al 2O 3 under conditions of minimal mass transport constraints. The HDC of 2,4-DCP generated HCl and 2-CP as the only intermediate partially dechlorinated product which reacts further to yield phenol; cyclohexanone was formed over Pd/Al 2O 3, but not over Pd/C, prior to complete dechlorination. Pd/Al 2O 3 is characterized (on the basis of TEM analysis) by a narrow distribution of smaller Pd particles to give a surface area weighted mean particle DIAMETER = 2.4 nm that is appreciably lower than the value of 13.2 nm established for Pd/C, where the latter is characterized by a broader distribution of larger (spherical) particles. The addition of NaOH served to increase fractional dechlorination by suppressing HDC inhibition due to the HCl that is generated. Reuse of the catalysts revealed an appreciable deactivation of Pd/C and a limited loss of activity in the case of Pd/Al 2O 3. Deactivation of Pd/C can be linked to a decrease (up to ca. 60%) in the initial BET surface area allied to appreciable leaching (up to ca. 40%) of the starting Pd content through the corrosive action of HCl and, while the average Pd diameter is essentially unaffected, there is evidence of a preferred leaching of larger Pd particles. The stronger metal/support interactions prevalent in Pd/Al 2O 3 results in limited Pd leaching and comparable initial HDC activities during catalyst reuse with/without NaOH addition. Inclusion of HCl in the reaction mixture (pH 5–1.5) resulted in a marked decline in the initial HDC rate associated with Pd/Al 2O 3 and a lesser drop in HDC activity for Pd/C. The difference in response to bulk solution pH variations are discussed in terms of the nature of the reactive species in solution and the amphoteric behavior of the Pd supports. 相似文献
18.
The hydrodechlorination of CF 3CCl 2F over Pd and Pt supported on β-AlF 3 and MgF 2 with D 2 gas has been investigated employing temperature programmed isotope exchange (TPIE) under static conditions. The isotope exchange observed between the H-loaded metal catalyst and the D 2 gas phase demonstrates the significantly higher hydrogen uptake capability of Pd-based catalysts. Both Pd and Pt on β-AlF 3, show significantly higher hydrogen/deuterium uptake and isotope exchange activity as compared with the MgF 2 support, probably due to the presence of hexagonal channels in β-AlF 3 and its higher Lewis acidity. The combination of these properties make Pd/β-AlF 3 a superior catalyst for selective hydrodechlorination of CF 3CCl 2F. Based on the results of the hydrodechlorination of CF 3CCl 2F with D 2, a competitive rather than a consecutive mechanism is proposed. The data from H/D-TPIE are best interpreted by the formation of surface carbene species as intermediates. 相似文献
19.
Hydrodechlorination of chlorobenzenes on platinum (Pt)-supported γ-alumina and alumina Lewis superacid (AmLSA) catalysts was carried out at room temperature and ambient pressure using a fixed bed flow reactor and a semi-batch reactor. Both the catalysts indicated good activity for the hydrodechlorination, but the former was superior to the latter. The hydrodechlorinations of reactants C 6H 6−xCl x ( x=1, 2, 3) proceeded step-wisely to benzene and then cyclohexane via C 6H 6−yCl y ( y= x−1). The reactions seem to be promoted by the contribution of spillover hydrogen formed on the Pt-supported catalysts. The catalysts deactivated with reaction time and the amount of chlorine that accumulated on the Pt-supported γ-alumina catalyst in the hydrodechlorination of 1,4-dichlorobenzene for 3 h was near to that estimated from the converted reactant molecules. When the deactivated catalysts were treated in a stream of hydrogen above 503 K, the original activity was completely restored, but the deactivation phenomenon with reaction time was observed again. 相似文献
20.
The effect of the Pd addition method into the fresh Pd/(OSC + Al 2O 3) and (Pd + OSC)/Al 2O 3 catalysts (OSC material = Ce xZr 1−xO 2 mixed oxides) was investigated in this study. The CO + NO and CO + NO + O 2 model reactions were studied over fresh and aged catalysts. The differences in the fresh catalysts were insignificant compared to the aged catalysts. During the CO + NO reaction, only small differences were observed in the behaviour of the fresh catalysts. The light-off temperature of CO was about 20 °C lower for the fresh Pd/(OSC + Al 2O 3) catalyst than for the fresh (Pd + OSC)/Al 2O 3 catalyst during the CO + NO + O 2 reaction. For the aged catalysts lower NO reduction and CO oxidation activities were observed, as expected. Pd on OSC-containing alumina was more active than Pd on OSC material after the agings. The activity decline is due to a decrease in the number of active sites on the surface, which was observed as a larger Pd particle size for aged catalysts than for fresh catalysts. In addition, the oxygen storage capacity of the aged Pd/(OSC + Al 2O 3) catalyst was higher than that of the (Pd + OSC)/Al 2O 3 catalyst. 相似文献
|