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1.
Abstract The price of iridium currently trends at about half the cost of platinum, the latter being a typical reduction promoter for
Co/Al 2O 3 Fischer–Tropsch (FT) synthesis catalysts in gas-to-liquids (GTL) technology. In the current contribution, both fixed-bed
catalytic FT and TPR-EXAFS/XANES experiments were carried out over 0.1% iridium-doped 25% Co/Al 2O 3 catalysts in order to (1) assess the effectiveness of Ir as a promoter of cobalt oxide reduction and (2) evaluate the effectiveness
of the incipient wetness impregnation (IWI) technique for adding the Ir precursor by comparing a catalyst prepared by IWI
to one prepared by atomic layer deposition (ALD). Ir was demonstrated to be an effective promoter for facilitating the second
step of cobalt oxide reduction, CoO to Co 0, and the IWI method was found to be superior to ALD. 相似文献
2.
X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) have been used to characterize a series of Cu/Ce/Al 2O 3 catalysts. Catalysts were prepared by incipient wetness impregnation using metal nitrate and alkoxide precursors. Catalyst
loadings were held constant at 12 wt% CuO and 5.1 wt% CeO 2. Mixed oxide catalysts were prepared by impregnation of cerium first, followed by copper. The information obtained from surface
and bulk characterization has been correlated with CO and CH 4 oxidation activity of the catalysts. Cu/Al 2O 3 catalysts prepared using Cu(II) nitrate (CuN) and Cu(II) ethoxide (CuA) precursors consist of a mixture of copper surface
phase and crystalline CuO. The CuA catalyst shows higher dispersion, less crystalline CuO phase, and lower oxidation activity
for CO and CH 4 than the CuN catalyst. For Cu/Ce/Al 2O 3 catalysts, Ce has little effect on the dispersion and crystallinity of the copper species. However, Cu impregnation decreases
the Ce dispersion and increases the amount of crystalline CeO 2 present in the catalysts, particularly in Ce modified alumina prepared using cerium alkoxide precursor (CeA). Cerium addition
dramatically increases the CO oxidation activity, however, it has little effect on CH 4 oxidation.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
3.
Different Pt/KL catalysts containing rare earth (RE; Ce and Yb) promoters were prepared by two techniques, incipient wetness impregnation (IWI) and vapor phase impregnation (VPI). The catalysts were tested for the activity and the selectivity of n-hexane aromatization to benzene under clean, sulfur-containing, and water-containing feeds at 500 °C. It was observed that the catalysts prepared by the VPI technique exhibited much higher activity and selectivity than those prepared by IWI. It was also found that although under clean conditions, the addition of Ce or Yb caused a decrease in activity, in the presence of sulfur the addition of Ce and to a lesser extent Yb, significantly inhibited catalyst deactivation. The influence of water in the feed was investigated by contacting the catalysts for 1 h to a feed containing 3 mol.% water. After this treatment, all the catalysts exhibited a significant activity loss. This loss was more pronounced for the catalyst prepared by the VPI method. The catalyst prepared by IWI already had suffered a significant deactivation before the water treatment, so the activity drop was not so pronounced. The sample prepared by VPI not only showed a drop in activity immediately after the water treatment but it became more susceptible to deactivation afterwards. By contrast, the Ce-promoted catalyst showed a more stable activity after the water treatment. All catalysts were characterized before and after reaction by a number of techniques. In agreement with previous studies, FT-IR of adsorbed CO and chemisorption results indicated that the VPI method resulted in higher Pt dispersion than that obtained by the IWI method. After reaction in the presence of sulfur, the Ce-promoted Pt/KL catalyst showed a higher resistance to metal agglomeration and a lower rate of coke formation than the unpromoted Pt/KL. On all the catalysts, the amount of carbon deposits was greater in the presence of sulfur and after exposure to water vapor than under the reaction with clean feeds. This difference is explained in terms of metal particle growth and location in the zeolite. 相似文献
4.
The effect of preparation method on the catalytic performance of V-promoted Ni/Al 2O 3 catalysts for synthetic natural gas (SNG) production via CO methanation has been investigated. The Ni-V/Al 2O 3 catalysts were prepared by co-impregnation (CI) method, deposition precipitation (DP) method as well as two sequential impregnation (SI) methods with different impregnation sequence. Among the prepared catalysts, the one prepared by CI method exhibited the best catalytic performance due to its largest H 2 uptake and highest metallic Ni dispersion. In a 91h-lifetime test, this catalyst showed high stability at high temperature and weight hourly space velocity. This work demonstrates that the catalytic performance of the V-promoted Ni/Al 2O 3 catalysts can be improved by carefully controlling the preparation method/conditions. 相似文献
5.
Series of Rh/SBA-15 catalysts were prepared by impregnation and grafting method applying different Rh precursors. The catalytic behaviors of N 2O decomposition over these catalysts were tested in an automated eight flow reactor system. The catalysts were characterized by X-ray fluorescence spectroscopy (XRF), X-ray diffraction (XRD), N 2 adsorption/desorption, transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS) techniques. The results showed that the dispersion of Rh species on the catalysts is closely related to the molecular size and the hydrophobic property of the precursors comparing to the hydrophilic support, better dispersion results were found in catalysts by impregnation of smaller precursors, while by grafting better dispersion resulted from big precursor. On the other hand, the activities of the catalysts match well with the Rh dispersion status. Rh/SBA-15-CDCR starting from [(CO) 2RhCl] 2 showed good dispersion and gave the best N 2O decomposition activity. 相似文献
6.
Abstract Carbon nanotube supported nano-size monometallic and noble metal (Pt and Ru) promoted cobalt catalysts were prepared by incipient
wetness impregnation (IWI) using solution of cobalt nitrate and characterized by nitrogen adsorption isotherm, X-ray diffraction
(XRD), temperature programmed reduction, in situ magnetic method and TEM. Analysis of the magnetization and H 2-TPR data suggested promotion with platinum and ruthenium significantly decreased the cobalt species reduction temperature.
TEM and XRD results showed that the presence of noble metal promoters had no significant effect on the size of cobalt for
carbon naotube as catalytic support. Promotion of cobalt carbon nanotube-supported catalysts with small amounts of Pt and
Ru resulted in slight increase in Fischer–Tropsch cobalt time yield. The Pt and Ru promoted cobalt catalyst exhibited carbon
monoxide conversion of 37.1 and 31.4, respectively. C 5+ hydrocarbon selectivity was attained at 80.0%. The Pt promoted cobalt supported on carbon nanotube yielded better catalytic
stability than that of the monometallic cobalt catalyst. 相似文献
7.
Fuel-cell electrode catalysts with improved electrochemical properties have been prepared by dispersing Pt nanoparticles onto carbon nanotubes (CNT) using a chemical vapor deposition (CVD) method. (Trimethyl)methylcyclopentadienyl platinum (MeCpPtMe 3) has been used as a Pt precursor in the CVD process and the CVD conditions have been optimized to disperse small Pt particles onto the CNT. Pt particles synthesized by CVD have a relatively uniform size of approximately 1 nm, which is substantially smaller than in the case of a commercial Pt/carbon black catalyst (?4.5 nm) prepared by wet impregnation. The dispersion of Pt, estimated by CO chemisorption, is also more than 14% greater than the commercial catalyst with these smaller particles. The electrochemically active surface area (ESA), measured by cyclic voltammetry (CV), and the long-time durability of the surface area of Pt/CNT prepared by CVD are higher than those of the commercial catalyst. Consequently, the single cell performance of the former catalyst is superior to that of the latter one. 相似文献
8.
Sintering behaviors of the Pt particles of Pt/Al 2O 3 catalyst prepared using different preparation methods (microemulsion, sol–gel, and impregnation methods) were investigated. It was found that the catalyst prepared by microemulsion had a higher resistance to sintering than did the sol–gel and impregnation catalysts. To limit the sintering even more, the catalysts were pressed. The resistance to sintering in all the catalysts was improved by pressing. The pressed microemulsion catalyst was little deactivated in the NO–CO reaction by thermal treatment at 700 °C for 12 h, and had a high activity relative to that of the sol–gel and impregnation catalysts. 相似文献
9.
Palladium catalysts supported on α-Si 3N 4 were prepared by impregnation with Pd(II)-acetate dissolved either in toluene or in water. The mean metal particle size of ~0.5 wt% Pd catalysts was similar (~5 nm) and independent of the way of preparation. Nevertheless, the two catalysts present very different chemisorption behaviour chemisorptive and catalytic properties. Fourier transformed infrared (FTIR) spectra of adsorbed CO at different temperatures (ranging from room temperature to 300 °C) show a very different behaviour for both catalysts. While the CO adsorption states on the Pd/α-Si 3N 4 prepared in toluene are very similar to those generally measured for silica and/or alumina supported palladium catalysts, CO chemisorbs less strongly on Pd/α-Si 3N 4 prepared in water and on different adsorption sites. The Pd/α-Si 3N 4 catalyst obtained by aqueous impregnation is much less efficient for the methane total oxidation. It is less active and less stable: it deactivates strongly after 3 h on stream at 650 °C. The two catalysts present about the same activity for the 1,3-butadiene hydrogenation after stabilisation at 20 °C. But, the catalyst prepared in water shows a much better selectivity to butenes. The results are discussed in terms of the possible migration of silicon atoms from the silicon nitride support to the surface of the palladium particles, when the catalyst is prepared in water. This is not the case when prepared in an organic solvent. 相似文献
10.
以SiC为载体、Pt为活性组分、过渡金属Fe、Co和Ni为助剂,采用浸渍法制备CO氧化催化剂。考察浸渍方法、助剂及其负载量、空速和催化剂焙烧温度等对Pt/SiC催化剂性能的影响。结果表明,助剂的加入提高了活性组分Pt在载体表面的分散度,并产生一定的相互作用,从而提高了催化剂活性,其中,铁助剂的助催化效果较好。共浸渍法制备的催化剂的催化活性优于分步浸渍法,Pt-Fe/SiC催化剂制备中焙烧温度500 ℃时,催化剂活性较佳,适量Fe助剂的添加能够显著提高Pt/SiC催化剂的活性。 相似文献
11.
The selective production of hydrogen via steam reforming of methanol (SRM) was performed using prepared catalysts at atmospheric
pressure over a temperature range 200–260 ∘C. Reverse water gas shift reaction and methanol decomposition reactions also take place simultaneously with the steam reforming
reaction producing carbon monoxide which is highly poisonous to the platinum anode of PEM fuel cell, therefore the detailed
study of effect of catalyst preparation method and of different promoters on SRM has been carried out for the minimization
of carbon monoxide formation and maximization of hydrogen production. Wet impregnation and co-precipitation methods have been
comparatively examined for the preparation of precursors to Cu(Zn)(Al 2O 3) and Cu(Zn)(Zr)(Al 2O 3). The catalyst preparation method affected the methanol conversion, hydrogen yield and carbon monoxide formation significantly.
Incorporation of zirconia in Cu(Zn)(Al 2O 3) catalyst enhanced the catalytic activity, hydrogen selectivity and also lower the CO formation. Catalyst Cu(Zn)(Zr)(Al 2O 3) with composition Cu/Zn/Zr/Al:12/4/4/80 prepared by co-precipitation method was the most active catalyst giving methanol
conversion up to 97% and CO concentration up to 400 ppm. Catalysts were characterized by atomic absorption spectroscopy (AAS),
Brunauer-Emett-Teller (BET) surface area, pore volume, pore size and X-ray powder diffraction (XRPD). The XRPD patterns revealed
that the addition of zirconia improves the dispersion of copper which resulted in the better catalytic performance of Cu(Zn)(Zr)(Al 2O 3). The time-on-stream (TOS) catalysts stability test was also conducted for which the Cu(Zn)(Zr)(Al 2O 3) catalyst gave the consistent performance for a long time compared to other catalysts. 相似文献
12.
The selective production of hydrogen via steam reforming of methanol (SRM) was performed using prepared catalysts at atmospheric pressure over a temperature range 200–260 °C. Reverse water gas shift reaction and methanol decomposition reactions also take place simultaneously with the steam reforming reaction producing carbon monoxide which is highly poisonous to the platinum anode of PEM fuel cell, therefore the detailed study of effect of catalyst preparation method and of different promoters on SRM has been carried out for the minimization of carbon monoxide formation and maximization of hydrogen production. Wet impregnation and co-precipitation methods have been comparatively examined for the preparation of precursors to Cu(Zn)(Al 2O 3) and Cu(Zn)(Zr)(Al 2O 3). The catalyst preparation method affected the methanol conversion, hydrogen yield and carbon monoxide formation significantly. Incorporation of zirconia in Cu(Zn)(Al 2O 3) catalyst enhanced the catalytic activity, hydrogen selectivity and also lower the CO formation. Catalyst Cu(Zn)(Zr)(Al 2O 3) with composition Cu/Zn/Zr/Al:12/4/4/80 prepared by co-precipitation method was the most active catalyst giving methanol conversion up to 97% and CO concentration up to 400 ppm. Catalysts were characterized by atomic absorption spectroscopy (AAS), Brunauer-Emett-Teller (BET) surface area, pore volume, pore size and X-ray powder diffraction (XRPD). The XRPD patterns revealed that the addition of zirconia improves the dispersion of copper which resulted in the better catalytic performance of Cu(Zn)(Zr)(Al 2O 3). The time-on-stream (TOS) catalysts stability test was also conducted for which the Cu(Zn)(Zr)(Al 2O 3) catalyst gave the consistent performance for a long time compared to other catalysts. 相似文献
13.
The selective CO methanation (CO-SMET) process via Ru?CAl 2O 3 catalysts was investigated as a tool for complete CO removal in fuel processors, when the H 2-rich gas so produced is employed for PEM-FCs applications to vehicles, boats, yachts and residential co-generators. CO-SMET seems, in fact, to be a good alternative to the most widely used CO preferential oxidation (CO-PROX) process. The performance of Ru-based catalysts on alumina carrier for efficient CO removal through CO-SMET was studied, exploring the role of two different Ru precursors (chloride and nitrate), and the doping effect of chloride and of Ru load (1%, 3% and 5%). First, two catalytic families (Ru?CAl 2O 3_Cl and Ru?CAl 2O 3_NO 3) were prepared by incipient wetness impregnation of alumina powder synthesized via solution combustion synthesis, by varying the Ru load. Then, based on the best obtained results, a third catalytic family was prepared adding chloride to Ru?CAl 2O 3_NO 3 catalysts by impregnation. The CO removal performance was determined at catalyst powder level in a fixed bed micro reactor. Better performances were exhibited when Ru was deposited from chloride precursor, but the post-addition of chlorine to fresh Ru?CAl 2O 3 catalysts prepared with nitrate precursor tremendously improved their selectivity toward CO methanation. In particular, with both 1% and 3% Ru?CAl_NO 3 catalyst chlorine doped, complete CO conversion was reached in a proper temperature range where the CO 2 methanation was suitably kept at a low acceptable level. 相似文献
14.
Supported Pt/C catalyst with 3.2 nm platinum crystallites was prepared by the impregnation—reduction method. The various preparation conditions, such as the reaction temperature, the concentration of precursor H 2PtCl 6 solution and the different reducing agents, and the relationship between the preparation conditions and the catalyst performance were studied. The carbon black support after heat treatment in N 2 showed improved platinum dispersion. The particle size and the degree of dispersion of Pt on the carbon black support were observed by transmission electron microscopy (TEM). The crystal phase composition of Pt in the catalyst was determined by X-ray diffraction (XRD). The surface characteristics of the carbon black support and the Pt/C catalyst were studied by X-ray photoelectron spectroscopy (XPS). The electrochemical characteristics of the Pt/C catalysts were evaluated from current—voltage curves of the membrane electrode assembly (MEA) in a proton exchange membrane fuel cell. 相似文献
15.
A unique carbon-silica (30 wt%) material was prepared by H 2O activation at 700 °C for 8 h with the carbon derived from SiC-Si sludge and the in-situ hydrolysis of the SiCl 4 trapped in the pores of the carbon into silica. The BET surface area of the carbon-silica was 1,750 m 2/g and the pore volume by QSDFT was 1.13 cm 3/g, 40% of which stemmed from micropores smaller than 2 nm with 60% from mesopores between 2 nm and 50 nm. The activated carbon-silica was loaded with Fe by means of chemical vapor infiltration (CVI) and incipient wetness impregnation (IWI). A hydrogen temperature-programmed reduction test showed that the activated carbon-silica is a prospective support material for Fe catalysts and that the dispersion of Fe in the carbon-silica is higher with CVI than with IWI. 相似文献
16.
The cryogel catalyst of platinum on alumina was prepared from aluminum sec-butoxide and H 2PtCl 6 through the sol-gel technique and subsequent freeze drying. The cryogel catalyst showed higher thermal stability of platinum
than the corresponding xerogel or impregnation catalysts, which was ascribed to the more intimately developed platinum-alumina
interaction accompanied by the encapsulation of the metal into the alumina cryogel. It was also shown that platinum accessibility
was higher on the cryogel than on the xerogel despite the higher thermal stability of the metal on the formed than on the
latter. For the VOC combustion, the cryogel exhibited higher activity than the xerogel and impregnation catalysts. Also for
the methane combustion the cryogel showed higher activity, although it showed lower activity than the impregnation catalysts
above 600 °C. By the addition of ceria as an additive to the cryogel catalyst, the CH 4 combustion activity was improved especially in the temperature region above 600 °C. 相似文献
17.
Sonochemically synthesized MoS 2/Al 2O 3, which had a hydrodesulfurization (HDS) activity that was significantly greater than that of a catalyst prepared by impregnation, exhibited low thermal stability due to sintering of MoS 2 crystallites at high temperatures. The thermal stability was improved when the catalyst was promoted with Ni. In this study, we compared the activity and thermal stability of different Ni-promoted MoS 2 catalysts, which were prepared by addition of Ni to MoS 2 using either impregnation (IMP) or chemical vapor deposition (CVD). After use in the HDS of dibenzothiophene (DBT) at 673 K for 2 h, the initial activity of the un-promoted catalyst was partially lost, while that of the Ni-promoted catalysts was preserved. Ni added by CVD interacted more intimately with MoS 2 than Ni added by impregnation because CVD allowed selective deposition of Ni on the MoS 2 edge sites. Another advantage of the CVD method over the impregnation method is that Ni(CO) 4, which was used as the Ni precursor in the former method, could be decomposed at much lower temperatures than in the case of Ni(NO 3) 2, which was used in the impregnation method. As a result, Ni-promoted catalysts prepared using Ni-CVD showed superior HDS activity compared with those prepared using Ni-impregnation. 相似文献
18.
This paper is concerned with the study of size effects in reactions of low-temperature CO oxidation on the catalysts Au/γ-Al 2O 3 and Au/δ-Al 2O 3 and complete oxidation of methane on the catalysts Pt/γ-Al 2O 3. For the synthesis of gold catalysts, four techniques have been applied: ionic adsorption, deposition-precipitation, chemical liquid-phase grafting, and decomposition of volatile gold complexes. Platinum catalysts have been prepared by aluminum oxide impregnation with aqueous solutions of H 2[Pt(OH) 6] that, depending on preparation conditions, contained mono- or oligonuclear hydroxocomplexes of platinum. Series of catalyst samples with a narrow size distribution of particles and a mean size variation from 0.5–1 to 20–25 nm have been prepared. The study of the catalytic properties of the prepared catalysts has shown that a decrease in mean size of supported metal particles leads to a sharp increase in specific catalytic activity in both systems. The activity maximum has been achieved for active component particles of 2–3 nm. A conclusion has been made that the application of nanosize catalysts is promising for the cleaning of air in closed rooms and vehicle exhaust gases from CO, for the utilization of methane, and for the obtaining of energy by the combustion of natural gas. 相似文献
19.
Co 3O 4/NP-ZrO 2, Co 3O 4/NP-CeO 2 and Co 3O 4/NP-Ce 0.8Zr 0.2O 2 catalysts were prepared via a reverse microemulsion/incipient wetness impregnation (RM–IWI) method. The catalytic properties for CO preferential oxidation (CO PROX) reaction in H 2-rich stream were investigated. The Co 3O 4/NP-Ce 0.8Zr 0.2O 2 catalyst with 1.8 wt.% Co 3O 4 loading has exhibited higher catalytic activity than that of the other two catalysts. The higher catalytic activity might be attributed to the combination effect of the highly dispersed cobalt oxide, the improvement in CeO 2 reducibility due to ZrO 2 incorporation in CeO 2 structures, and the strong cobalt oxide-support interaction. 相似文献
20.
Medium‐temperature shift reaction (MTS, 280–340 °C) has received much attention for use in fuel processors. In this study, bifunctional Pt‐Ni/CeO 2 catalysts were prepared by different Pt (0.1–0.5 %) and Ni (5–20 %) loadings, and investigated for MTS reaction. X‐ray diffraction, N 2 adsorption and temperature‐programmed reduction tests were used to characterize the prepared samples. The results showed that Pt‐Ni bimetallic catalysts have higher CO conversion in comparison to Pt/CeO 2 monometallic catalyst. Furthermore, the sequential synthesis method of Pt and Ni impregnation was preferred to the simultaneous one, which is due to the better Pt dispersion on catalytic surface. Steam to carbon ratio variations study showed the maximum CO conversion to be in the range of 4.5. 相似文献
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