共查询到20条相似文献,搜索用时 375 毫秒
1.
The partial oxidation of methane was studio on Pt/Al 2O 3, Pt/ZrO 2, Pt/CeO 2 and Pt/Y 2O 3 catalysts. For Pt/Al 2O 3, Pt/ZrO 2 and Pt/CeO 2, temperature programmed surface reaction (TPSR) studies showed partial oxidation of methane comprehends two steps: combustion
of methane followed by CO 2 and steam reforming of unreacted methane, while for Pt/Y 2O 3 a direct mechanism was observed. Oxygen Storage Capacity (OSC) evaluated the reducibility and oxygen transfer capacity of
the catalysts. Pt/CeO 2 catalyst showed the highest stability on partial oxidation. The results were explained by the higher reducibility and oxygen
storage/release capacity which allowed a continuous removal of carbonaceous deposits from the active sites, favoring the stability
of the catalyst. For Pt/Al 2O 3 and Pt/ZrO 2 catalysts the increase of carbon deposits around or near the metal particle inhibits the CO 2 dissociation on CO 2 reforming of methane. Pt/Y 2O 3 was active and stable for partial oxidation of methane and its behaviour was explained by a change in the reaction mechanism. 相似文献
2.
Catalytic oxidation activity of carbon-black (CB) simulating the soot of diesel particulate matters to CO 2 over 3Pt/Al 2O 3, 3Pt5Mn/Al 2O 3 and 3Pt/30Ba–Al 2O 3 catalysts is investigated with model gases of diesel emission. In case of the large amount of CB compared to the amount of catalyst (3/1, w/w) in the mixture sample, insufficient oxygen at the point of sudden increase in the amount of CO 2 is leaded to the partial oxidation using the lattice oxygen of the catalyst. And the peaks of CO 2 after the first peak were attributed to the regional combustion of the CB, which was not in contact with catalyst particles. The fresh 3Pt5Mn was estimated to the oxidation states on the catalyst surface by XPS. For used sample at 700 °C, the BEs of Pt 4d5 was revealed to metallic state Pt(0) (314.4 eV) in a predominant levels compared with Pt(II) (317.3 eV). While BEs of Mn 2p were similar to that obtained from the fresh 3Pt5Mn. It is suggested that Pt is in charge of the roles in CB-oxidation, using the lattice oxygen of the catalyst. Two-stage catalytic system with the strategies of promoting the soot oxidation and NO x reduction, simultaneously, were composed of the CB oxidation catalyst and the diesel oxidation catalyst. The catalytic oxidation of CB was accelerated by activated oxidants and exothermic reaction resulted from the diesel oxidation catalyst, which lies in upstream of two-stage. But the system with the CB oxidation catalyst sited in the upstream showed the initiation of CB oxidation at a lower temperature than the other case. Two-stage catalytic system composed of 3Pt5Mn with CB in the upstream and DOC in the downstream showed high oxidation activity with 95% consumption rate of CB to the total loaded CB in the range of 100–500 °C during the TPR process. 相似文献
3.
An investigation was conducted of noble metal and metal oxide catalysts deposited on Al 2O 3. The noble metals Pt, Pd, Rh the metal oxides CuO, SnO 2, CoO, Ag 2O, In 2O 3, catalysts were examined. Also investigated were noble metal Pt, Pd, Rh-doped In 2O 3/Al 2O 3 catalysts prepared by single sol–gel method. Both were studied for their capability to reduce NO by propene under lean conditions. In order to improve the catalytic activity and the temperature window, the intermediate addition propene between a Pt/Al 2O 3 oxidation and metal oxide combined catalyst system was also studied. Pt/Al 2O 3 and In 2O 3/Al 2O 3 combined catalyst showed high NO reduction activity in a wider temperature window, and more than 60% NO conversion was observed in the temperature range of 300–550 °C. 相似文献
4.
An investigation was conducted of noble metal and metal oxide catalysts deposited on Al2O3. The noble metals Pt, Pd, Rh the metal oxides CuO, SnO2, CoO, Ag2O, In2O3, catalysts were examined. Also investigated were noble metal Pt, Pd, Rh-doped In2O3/Al2O3 catalysts prepared by single sol–gel method. Both were studied for their capability to reduce NO by propene under lean conditions. In order to improve the catalytic activity and the temperature window, the intermediate addition propene between a Pt/Al2O3 oxidation and metal oxide combined catalyst system was also studied. Pt/Al2O3 and In2O3/Al2O3 combined catalyst showed high NO reduction activity in a wider temperature window, and more than 60% NO conversion was observed in the temperature range of 300–550 °C. 相似文献
5.
Phosphomolybdic acid (H 3PMo 12O 40, POM) was attempted to be used as the energy‐storage agent in this paper to avoid some problems of the direct methanol fuel cell (DMFC), such as catalyst poisoning and methanol permeation. Catalytic oxidation of methanol by aqueous POM on Al 2O 3 supported catalysts with Pt and Ru active metal was evaluated in the presence of liquid water. The process takes advantage of the high catalytic activities of platinum for methanol oxidation. The effects of temperature, reaction time, and methanol concentration on activity were observed. The catalytic activity of Pt/Al 2O 3 is better than that of Ru/Al 2O 3 for the oxidation of methanol by POM. The methanol conversion rate reached 93.55% on the Pt/Al 2O 3 at 80 °C after reaction for 1 h. The electrochemical experiments indicate that POM shows a larger current density in redox processes on an Au electrode than methanol. The redox process of reduced POM is a reversible multi‐electron transfer process. 相似文献
6.
The partial oxidation of methane was studied on Pt/Al 2O 3, Pt/ZrO 2, Pt/CeO 2 and Pt/Y 2O 3 catalysts. For Pt/Al 2O 3, Pt/ZrO 2 and Pt/CeO 2, temperature programmed surface reaction (TPSR) studies showed partial oxidation of methane comprehends two steps: combustion
of methane followed by CO 2, and steam reforming of unreacted methane, while for Pt/Y 2O 3 a direct mechanism was observed. Oxygen Storage Capacity (OSC) evaluated the reducibility and oxygen transfer capacity of
the catalysts. Pt/CeO 2 catalyst showed the highest stability on partial oxidation. The results were explained by the higher reducibility and oxygen
storage/release capacity which allowed a continuous removal of carbonaceous deposits from the active sites, favoring the stability
of the catalyst, For Pt/Al 2O 3 and Pt/ZrO 2 catalysts the increase of carbon deposits around or near the metal particle inhibits the CO 2 dissociation on CO 2 reforming of methane. Pt/Y 2O 3 was active and stable for partial oxidation of methane, and its behavior was explained by a change in the reaction mechanism. 相似文献
7.
The catalytic activity of Pt catalysts supported on high surface area tin(IV) oxide in the complete oxidation of CH 4 traces under lean conditions at low temperature was studied in the absence and in the presence of water (10 vol.%) or H 2S (100 vol.ppm). Their catalytic properties were compared to those of Pd/Al 2O 3 and Pt/Al 2O 3. In the absence of H 2S in the feed, Pt/SnO 2appears as a very promising catalyst for CH 4 oxidation, being even significantly more active under wet conditions than the best reference catalyst, Pd/Al 2O 3. Catalysts steamed-aged at 873 K were also studied in order to simulate long term ageing in real lean-burn NGV exhaust conditions. To this respect, Pt/SnO 2 is slightly less resistant than Pd/Al 2O 3. In the presence of H 2S, Pt/SnO 2catalysts are rapidly and almost completely poisoned, comparably to Pd/Al 2O 3and the catalytic activity is hardly restored upon oxidising treatment below 773 K. A synergetic effect between Pt and specific surface SnO 2sites active in CH 4oxidation is proposed to explain the superior catalytic behaviour of Pt/SnO 2. 相似文献
8.
Pt(0.3)/Ni(10)/Al 2O 3, prepared by a sequential impregnation method, exhibited a more excellent performance in methane reforming with CO 2 and O 2 in terms of the catalytic activity and the temperature profile of the catalyst bed than Pt(0.3) + Ni(10)/Al 2O 3 prepared by a coimpregnation method, Ni(10)/Al 2O 3, Pt(0.3)/Al 2O 3, and Pt(10)/Al 2O 3. It is thought that this is because the surface Pt atoms on Ni catalyst can contribute to the enhancement of the catalyst reducibility. 相似文献
9.
The SSITKA measurements were performed in the steady state of complete methane oxidation on the Pd/Al 2O 3 and Pt/Al 2O 3 catalysts. It was found that the number of intermediates and their average life-time on the catalyst surface changes with
the increase of reaction temperature. On the Pd/Al 2O 3 catalyst there is larger number of active centres than on Pt/Al 2O 3 catalyst which permits the course of methane oxidation at lower temperatures. 相似文献
10.
The roles and effects of Fe on the catalytic performance and physicochemical properties of a PtPd diesel oxidation catalyst prepared by three different methods were investigated by CO oxidation reaction, X-ray diffraction, temperature-programmed reduction (TPR), temperature-programmed oxidation, and BET surface area. It was found that the roles of Fe depended strongly on the sequential order of Fe introduction during the preparation of the PtPd catalyst. The Fe/PtPd/Al 2O 3 catalyst was prepared by introducing Fe onto the PtPd/Al 2O 3, and the PtPd/Fe/Al 2O 3 catalyst was obtained by loading the PtPd onto the Fe/Al 2O 3. The former had a superior activity. From the TPR results, the catalytic activity of CO oxidation was correlated with the oxygen mobility of the iron oxides. For PtPd/Fe/Al 2O 3, the iron interacted preferentially with the alumina support forming FeAlO 3, which resulted in the stabilization of the support and a reduction in the surface area. The major role of Fe was to promote the enhancement of the catalytic activity of PtPd through an intimate interaction between the PtPd and iron oxides, which had lattice oxygens to generate oxygen with oxidation abilities. 相似文献
11.
Catalytic activity of platinum catalysts such as Pt/graphite, Pt/TiO 2, Pt/Al 2O 3, and Pt/active carbon was studied using a slurry phase CSTR. Three model reactions, namely, phenol, maleic acid, and malonic acid oxidation were investigated in the temperature range from 120 to 170 °C and at a total reactor pressure of 1.7 MPa. Platinum on graphite was found to be most suitable for aqueous phase oxidation of phenol, maleic acid, and malonic acid. Complete conversion for both phenol oxidation as well as maleic acid oxidation to CO 2 was observed with Pt/graphite at stoichiometric oxygen excess close to 0% and at 150 °C. Deactivation due to over-oxidation is gradual for Pt/graphite with a metal dispersion of 5.3% as compared to Pt/TiO 2, Pt/Al 2O 3 and Pt/AC, which have metal dispersions of 15.3%, 19.5% and 19.0%, respectively. It was further found that in the presence of Pt/graphite catalyst and oxygen, malonic acid reaction proceeds via non-catalysed decarboxylation, and catalytic decarboxylation to CO 2 and acetic acid, and catalytic oxidation to CO 2 and H 2O. Acetic acid was found to be difficult to oxidise at temperatures below 200 °C. 相似文献
12.
The catalytic oxidation of toluene, chosen as VOC probe molecule, was investigated over Co 3O 4, CeO 2 and over Co 3O 4–CeO 2 mixed oxides and compared with the catalytic behavior of a conventional Pt(1 wt%)/Al 2O 3 catalyst. Complete toluene oxidation to carbon dioxide and water was achieved over all the investigated systems at temperatures below 500 °C. The most efficient catalyst, Co 3O 4(30 wt%)–CeO 2(70 wt%), showed full toluene conversion at 275 °C, comparing favorably with Pt/Al 2O 3 (100% toluene conversion at 225 °C). 相似文献
13.
The effect of a commercial Pt/Al 2O 3 catalyst on the oxidation by NO 2 and O 2 of a model soot (carbon black) in conditions close to automotive exhaust gas aftertreatment is investigated. Isothermal oxidations of a physical mixture of carbon black and catalyst in a fixed bed reactor were performed in the temperature range 300–450 °C. The experimental results indicate that no significant effect of the Pt catalyst on the direct oxidation of carbon by O 2 and NO 2 is observed. However, in presence of NO 2–O 2 mixture, it is found that besides the well established catalytic reoxidation of NO into NO 2, Pt also exerts a catalytic effect on the cooperative carbon–NO 2–O 2 oxidation reaction. An overall mechanism involving the formation of atomic oxygen over Pt sites followed by its transfer to the carbon surface is established. Thus, the presence of Pt catalyst increases the surface concentration of –C(O) complexes which then react with NO 2 leading to an enhanced carbon consumption. The resulting kinetic equation allows to model more precisely the catalytic regeneration of soot traps for automotive applications. 相似文献
14.
An economical method was proposed to develop an efficient alumina-supported manganese (Mn) and copper (Cu) oxides (Mn-Cu-O/Al 2O 3) catalyst with a high surface area, 184.06 cm 2 g ?1. The catalyst was utilized for degradation refinery wastewater by heterogeneous catalytic ozonation. The effects of various operating variables including pH, ozone and catalyst dosages, and temperature were systematically investigated in detail to obtain the optimized conditions for accelerated degradation of refinery wastewater. The optimum values were as follows: ozone dose 50.0 mg L ?1, catalyst dose 3.0 g L ?1, initial pH = 6.8, T = 17 °C. Refinery wastewater samples were analyzed by chemical oxygen demand (COD) and the results indicated that kinetics of COD followed a pseudo–first-order degradation. Moreover, hydroxyl radical mechanism rather than absorption was proposed, indicating that the surface hydroxyl groups were the active sites that played a significant role in catalytic ozonation. 相似文献
15.
The ignition processes for the catalytic partial oxidation of methane (POM) to synthesis gas over oxidic nickel catalyst (NiO/Al 2O 3), reduced nickel catalyst (Ni 0/Al 2O 3), and Pt-promoted oxidic nickel catalyst (Pt–NiO/Al 2O 3) were studied by the temperature-programmed surface reaction (TPSR) technique. The complete oxidation of methane usually took place on the NiO catalyst during the CH 4/O 2 reaction, even with a pre-reduced nickel catalyst, and Ni 0 is inevitably first oxidized to NiO if the temperature is below the ignition temperature. It is above a certain temperature that Ni 0 is formed again, which leads to the start of the POM. The POM can be initiated at a much lower temperature on a Pt–NiO catalyst because of Pt promotion of the reduction of NiO. The POM in a fluidized bed can be easily initiated due to the addition of Pt. 相似文献
16.
Pt/CoAl 2O 4/Al 2O 3, Pt/CoO x/Al 2O 3, CoAl 2O 4/Al 2O 3 and CoO x/Al 2O 3 catalysts were studied for combination CO 2 reforming and partial oxidation of CH 4. The results indicate that Pt/CoAl 2O 4/Al 2O 3 is the most effective, and XRD results indicate that Pt species are well dispersed over the Pt/CoAl 2O 4/Al 2O 3. High dispersion is related to the presence of CoAl 2O 4, formed during calcining at high temperature before Pt addition. In the presence of Pt, CoAl 2O 4 in the catalyst could be reduced partially at 973 K. Based on these results, it appears that zerovalent platinum with high dispersion and zerovalent cobalt resulting from CoAl 2O 4 reduction are responsible for high activity in the Pt/CoAl 2O 4/Al 2O 3 catalyst. 相似文献
17.
The present work has been undertaken to tailor Pt/Al 2O 3 catalysts active for NO oxidation even after severe heat treatments in air. For this purpose, the addition of Pd has been attempted, which is less active for this reaction but can effectively suppress thermal sintering of the active metal Pt. Various Pd-modified Pt/Al 2O 3 catalysts were prepared, subjected to heat treatments in air at 800 and 830 °C, and then applied for NO oxidation at 300 °C. The total NO oxidation activity was shown to be significantly enhanced by the addition of Pd, depending on the amount of Pd added. The Pd-modified catalysts are active even after the severe heat treatment at 830 °C for a long time of 60 h. The optimized Pd-modified Pt/Al 2O 3 catalyst can show a maximum activity limited by chemical equilibrium under the conditions used. The bulk structures of supported noble metal particles were examined by XRD and their surface properties by CO chemisorption and EDX-TEM. From these characterization results as well as the reaction ones, the size of individual metal particles, the chemical composition of their surfaces, and the overall TOF value were determined for discussing possible reasons for the improvement of the thermal stability and the enhanced catalytic activity of Pt/Al 2O 3 catalysts by the Pd addition. The Pd-modified Pt/Al 2O 3 catalysts should be a promising one for NO oxidation of practical interest. 相似文献
18.
Intrinsic catalytic activities (TOF values) in CH 4 complete oxidation under lean conditions were estimated as a function of Pt and Pd particle sizes (d m) for two series of Pt/Al 2O 3 and Pd/Al 2O 3 catalysts. Comparison of TOF ~ f(d m) relationships revealed significant difference between Pt and Pd catalysts. For Pt catalyst TOF showed tendency to increase by 2–3 times with increasing particle size from 1 to ca 3 nm and remained constant, when Pt particles became larger than 3 nm. On the other hand, for Pd catalyst TOF increased almost linearly when particle size grew from 1 to 20 nm. These different tendencies were attributed to the different mechanisms of CH 4 oxidation over Pt and Pd catalysts: Langmuir–Hinshelwood and Mars-Van Krevelen respectively. 相似文献
19.
Dehydrogenation of propane on Pt or PtSn catalyst over Al 2O 3 or SBA-15 support was investigated. The catalysts were characterized by CO-pulse chemisorption, thermogravimetry, temperature-programmed-reduction of H 2, and diffuse reflectance infrared Fourier transform spectroscopy of absorbed CO. The results show that the platinum species is in oxidation state in the catalyst on Al 2O 3 support, so the catalyst must be reduced in H 2 before dehydrogenation reaction. Addition of Sn improves the Pt dispersion, but the catalyst deactivates rapidly because of the coke formation. The interaction of Pt and Al 2O 3 is strong. On SBA-15 support, the platinum species is completely reduced to Pt 0 in the calcination process, so the reduction is not needed. Addition of Sn improves the activity and selectivity of the catalyst. The interaction of Pt and SBA-15 is weak, so it is easy for Pt particles to sinter. 相似文献
20.
Supported bimetallic PtFe catalyst is one of the most promising candidates for preferential CO oxidation (PROX) in H 2 for fuel cells. We are interested in developing novel PtFe catalysts which have special architectures and are more excellent in catalytic performance for the PROX reaction. In the present study, three kinds of novel alumina-supported PtFe, PtFe 2 and PtFe 3 alloy nanoparticles were prepared from Pt(acac) 2 and Fe(acac) 3 reduced by ethylene glycol in Ar atmosphere at 185 °C. The catalytic experiments showed that the three materials were more active for the PROX reaction under pretreatment both in He and H 2 atmospheres as compared to that of Pt/Al 2O 3 prepared by the same chemical route. Their structural property and iron state were investigated by X-ray diffraction and 57Fe Mössbauer spectroscopy. The obtained results proved that the novel as-prepared PtFe/Al 2O 3, PtFe 2/Al 2O 3 and PtFe 3/Al 2O 3 materials are clearly different in the architecture and the oxidation state of iron as compared to the conventionally prepared one. 相似文献
|