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1.
An as-synthesized 8.8wt% Pd/ZnO/Al 2O 3 catalyst was either pretreated under O 2 at 773 K followed by H 2 at 293 K or under H 2 at 773 K to obtain, respectively, a supported metallic Pd° catalyst (Pd°/ZnO/Al 2O 3) or a supported PdZn alloy catalyst (PdZn/ZnO/Al 2O 3). Both catalysts were studied by CO adsorption using FTIR spectroscopy. For the supported PdZn alloy catalyst (PdZn/ZnO/Al 2O 3), exposure to a mixture of methanol and steam, simulating methanol steam reforming reaction conditions, does not change the
catalyst surface composition. This implies that the active sites are PdZn alloy like structures. The exposure of the catalyst
to an oxidizing environment (O 2 at 623 K) results in the break up of PdZn alloy, forming a readily reducible PdO with its metallic form being known as much
less active and selective for methanol steam reforming. However, for the metallic Pd°/ZnO/Al 2O 3 catalyst, FTIR results indicate that metallic Pd° can transform to PdZn alloy under methanol steam reforming conditions. These
results suggest that PdZn alloy, even after an accidental exposure to oxygen, can self repair to form the active PdZn alloy
phase under methanol steam reforming conditions. Catalytic behavior of the PdZn/ZnO/Al 2O 3 catalyst also correlates well with the surface composition characterizations by FTIR/CO spectroscopy. 相似文献
2.
A combination of various transient and steady-state kinetic experiments was used to provide evidence for dynamical changes in a Cu/ZnO/Al 2O 3 catalyst of industrial interest. From these it can be deduced that the reversible structural alterations strongly depend on the reaction conditions as well as on the pretreatment. The pretreatment was found to induce changes in the morphology of the metallic Cu particles to some extent, and surface alloying under more severe reducing conditions. 相似文献
3.
Pd/Al 2O 3, Pd/CeO 2 and Pd/ZrO 2 diesel oxidation catalysts and their washcoat materials were studied after sulphur treatment. The catalytic activities were analysed in simplified diesel exhaust gas composition by FT-IR technique. ICP-OES or XRF, physisorption and CO chemisorption was used to catalyst characterisation. The result shows that the sulphur treatment clearly deactivates the studied catalysts. 相似文献
4.
A novel gel-network-coprecipitation process has been developed to prepare ultrafine Cu/ZnO/Al 2O 3 catalysts for methanol synthesis from CO 2 hydrogenation. It is demonstrated that the gel-network-coprecipitation method can allow the preparation of the ultrafine Cu/ZnO/Al 2O 3 catalysts by homogeneous coprecipitation of the metal nitrate salts in the gel network formed by gelatin solution, which makes the metallic copper in the reduced catalyst exist in much smaller crystallite size and exhibit a much higher metallic copper-specific surface area. The effect of the gel concentration of gelatin on the structure, morphology and catalytic properties of the Cu/ZnO/Al 2O 3 catalysts for methanol synthesis from hydrogenation of carbon dioxide was investigated. The Cu/ZnO/Al 2O 3 catalysts prepared by the gel-network-coprecipitation method exhibit a high catalytic activity and selectivity in CO 2 hydrogenation to methanol. 相似文献
6.
The gas‐phase hydrogenolysis of dimethyl maleate at 10 bar and 513 K was investigated over a series of co‐precipitated Cu/ZnO/Al 2O 3 catalysts. High copper surface areas were obtained with a molar Al content of 5 % in the catalysts. Upon variation of composition at fixed alumina content, copper surface areas increased until the molar ratio exceeded Cu/Zn = 2:1. At the given reaction conditions, dimethyl maleate was completely converted to dimethyl succinate, which further reacted to methanol, γ‐butyrolactone, tetrahydrofuran, and water over all catalysts. Initial deactivation of catalysts was mainly caused by a loss of copper surface area. The catalyst with a molar Cu/Zn ratio of 1:2 was found to be most active and stable under reaction conditions. 相似文献
7.
The effect of preparation methods on the Cu/ZnO/Al 2O 3 catalyst structure and catalytic activity on liquid glycerol hydrogenolysis to 1,2-propanediol has been investigated. The physicochemical properties of the catalysts were characterized by BET, XRD, TG/DTA, NH 3-TPD and TPR. The experimental results showed that the catalyst prepared by an oxalate gel–coprecipitation had the highest activity. At 200 °C and 400 psi hydrogen pressure, the glycerol conversion and 1,2-propanediol selectivity catalyzed by the Cu/ZnO/Al 2O 3 catalyst prepared via oxalate gel–coprecipitation were 92.3 and 94.5 % respectively. It was found that the 1,2-propanediol selectivity was dependent on hydrogen pressure and the un-desired by-products were mainly due to the side reactions caused by the presence of the intermediate acetol. 相似文献
8.
The effect of preparation methods on the Cu/ZnO/Al2O3 catalyst structure and catalytic activity on liquid glycerol hydrogenolysis to 1,2-propanediol has been investigated. The physicochemical properties of the catalysts were characterized by BET, XRD, TG/DTA, NH3-TPD and TPR. The experimental results showed that the catalyst prepared by an oxalate gel–coprecipitation had the highest activity. At 200 °C and 400 psi hydrogen pressure, the glycerol conversion and 1,2-propanediol selectivity catalyzed by the Cu/ZnO/Al2O3 catalyst prepared via oxalate gel–coprecipitation were 92.3 and 94.5 % respectively. It was found that the 1,2-propanediol selectivity was dependent on hydrogen pressure and the un-desired by-products were mainly due to the side reactions caused by the presence of the intermediate acetol. 相似文献
9.
Fourth generation poly(amidoamine) dendrimers have been used to template and stabilize Ru nanoparticles in solution. UV-visible spectroscopic results indicate that Ru 3+ ions from a RuCl 3 precursor can complex with functional groups within the dendrimer structure. Subsequent reduction of the Ru 3+ ions yields finely dispersed Ru nanoparticles with a narrow particle size distribution. These dendrimer-stabilized nanoparticles were deposited onto an alumina support and thermally activated to remove the dendrimer “shell”, as indicated by in situ Fourier transform infrared (FTIR) spectroscopic measurements. High resolution transmission electron microscopy (HRTEM) measurements indicate that the resulting Ru/Al 2O 3 catalyst has a smaller mean metal particle size and a narrower particle size distribution than a similar catalyst prepared by a traditional wet impregnation from the same RuCl 3 precursor. 相似文献
10.
Modification of supported Pt catalysts with thiols has recently been shown to improve the hydrogenation selectivity of α,β-unsaturated aldehydes to unsaturated alcohols. Here, we apply a variety of organic thiol coatings to Pd/Al2O3 catalysts that typically have a much lower intrinsic selectivity for desired product formation. Thiol monolayers were found to increase hydrogenation selectivity to cinnamyl alcohol; however, unlike with Pt catalysts, the increase was independent of the identity of the organic tail. 相似文献
11.
Modification of supported Pt catalysts with thiols has recently been shown to improve the hydrogenation selectivity of α,β-unsaturated aldehydes to unsaturated alcohols. Here, we apply a variety of organic thiol coatings to Pd/Al 2O 3 catalysts that typically have a much lower intrinsic selectivity for desired product formation. Thiol monolayers were found to increase hydrogenation selectivity to cinnamyl alcohol; however, unlike with Pt catalysts, the increase was independent of the identity of the organic tail. 相似文献
12.
This work investigates the regeneration of S-poisoned Pd/Al 2O 3 and Pd/CeO 2/Al 2O 3 catalysts under different CH 4 containing atmospheres. Under lean combustion conditions in the presence of excess O 2, partial regeneration took place for both systems only above 750 °C after decomposition of stable sulphate species adsorbed
on the support. Under alternate lean combustion/CH 4-reducing pulse regeneration is markedly anticipated down to 550–600 °C. Experiments evidenced an effective role of ceria
in preventing PdO from sulphation and in promoting regeneration via sulphates decomposition under reducing conditions. 相似文献
13.
An efficient methodology to synthesize highly active Pd nanoparticles using a single-site photocatalyst under UV-light irradiation has been developed for the synthesis of hydrogen peroxide (H 2O 2) from H 2 and O 2. By the photo-assisted deposition (PAD) method, Pd precursor can be deposited directly on the photo-excited tetrahedrally coordinated metal-oxide moiety within the silica frameworks, and subsequently transformed into Pd nanoparticles by H 2 reduction. The mean diameter of the deposited Pd particles determined by CO adsorption and the catalytic activities in the direct synthesis of H 2O 2 were strongly dependent on the preparation method and kind and/or amount of metal-oxide moieties. Here, the use of Ti-containing mesoporous silica (Ti/Si = 0.01) acted as a most efficient support for the above reaction. The PAD method also provides PdAu bimetallic nanoparticles from an aqueous solution of mixture of PdCl 2 and HAuCl 4. The PdAu/Ti-MCM-41 catalyst prepared by the PAD method was shown to perform significantly better activity than the pure Pd/Ti-MCM-41. 相似文献
14.
考查了用于环己酮二聚物脱氢制备邻苯基苯酚(OPP)的Pt/Al2O3催化剂的改性研究。针对脱氢反应体系所存在的副反应特点,采用了载体碱改性〔使用了含钾矿物(KM)以及3种Mg-Al复合载体〕与助剂改性(使用K盐类)两种手段,开发出了二者结合的复合改性工艺。研究表明,矿物KM的载体改性效果较好(OPP选择性>80%),助剂改性以K2CO3的性能较好(OPP选择性>90%),而复合改性的Pt-K2CO3/KM-Al2O3〔w(Pt)=0.5%,w(K2O)=3.0%,w(KM)=15%〕催化剂在选定的反应条件下,最高活性可达二聚物转化率95.2%、OPP选择性95.0%,在100 h内,环己酮二聚物转化率和OPP选择性可分别保持在95.0%与92.0%以上。 相似文献
15.
Thermites prepared from nanoparticles are currently the subject of growing interest due to their increased performances compared to classical micrometer‐sized thermites. Here, we studied the combustion behavior of energetic composite composed of Al and chromium (III) oxide (Cr 2O 3) as function of the oxide particle size. Homogeneous composites were prepared by mixing Al nanoparticles ( Φ≈50 nm) with Cr 2O 3 micro‐ and nanoparticles ( Φ≈20 nm), respectively, in hexane solution. The dried Cr 2O 3/Al composite powders were ignited by using a CO 2 laser beam. The use of nanosized Cr 2O 3 particles incontestably improves the energetic performances of the Al/Cr 2O 3 thermite since the ignition delay time was shortened by a factor 3.5 (16±2 vs 54±4 ms) and the combustion rate (340±10 mm s −1) was significantly accelerated in contrast to those reported until now. Interestingly, the sensitivity to friction of the Al‐based thermites formulated from Cr 2O 3 is two orders of magnitude lower than the thermite prepared from other metal oxide nanoparticles (MnO 2, WO 3). Finally, our study shows that the decrease of Cr 2O 3 particle size has an interesting and beneficial effect on the energetic properties of Cr 2O 3/Al thermites and appears as an alternative to tune the properties of these energetic materials. 相似文献
16.
The addition of B 2O 3 to a Cu/ZnO/Al 2O 3 catalyst increased the activity of the catalyst for methanol synthesis after an induction period during the reaction. The
stability of the B 2O 3-containing Cu/ZnO/Al 2O 3 catalyst was greatly improved by the addition of a small amount of colloidal silica to the catalyst.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
17.
The influence of impurities in steel mill exhaust gases on ternary Cu/ZnO/Al 2O 3 catalysts was studied for conventional methanol synthesis, which is one of the central reactions within the cross-industrial approach of Carbon2Chem®. A series of hydrocarbons was identified as inert spectators for methanol synthesis. Several catalyst poisons like N-containing compounds or O 2 show reversible characteristics at low pressure. However, by increasing the partial pressure of O 2, poisoning becomes irreversible, indicating different poisoning mechanisms concerning the reversibility of deactivation. 相似文献
18.
The effects of gallia addition on the Pt dispersion and the activity for ethylene hydrogenation at 0 °C were studied for Pt-supported catalysts as a function of the reduction temperature (350, 450, and 550 °C). The catalysts contained 0.5 wt.% Pt and were prepared by successive incipient wetness impregnations with Ga(NO 3) 3 and H 2PtCl 6 aqueous solutions. CO and H 2 chemisorption data indicated that, the addition of small amount of Ga 2O 3 caused an increase of the Pt dispersion and a decrease of ethylene conversion. Both of them decreased appreciably when Ga 2O 3 addition was increased, particularly, for the case where β-Ga 2O 3 was used as a support. The increase in reduction temperature magnified the negative effects of the gallia addition on dispersion and activity, although the addition of small amount of gallia improved the resistance to metal sintering. Results were interpreted in terms of the presence of reduced Ga species, which can encapsulate Pt particles. 相似文献
19.
The hydrogenation of CO 2 was investigated on Ga 2O 3-promoted Pd/SiO 2 catalyts and mechanical mixtures of Ga 2O 3/SiO 2 and Pd/SiO 2 catalysts (H 2/CO 2 = 3; P = 3.0 MPa; T = 523 K). By means of the latter it was possible to demonstrate that atomic hydrogen, H s, can be generated by Pd 0 far from Ga 2O 3, and move (spill-over) there to reach the other reactive species (formates) and complete the reaction cycle. The reaction results indicate that (as also evidenced by in situ FTIR) the Ga 2O 3-Pd/SiO 2 catalyst works as a true bi-functional system. The metal-promoter intimacy is not decisive in terms of the catalytic chemistry of the system, but the closeness between the Pd crystallites and the Ga 2O 3 surface patches boost the activity, owing to a minimized effort in the H s supply to the latter. 相似文献
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