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71.
72.
Synthesis, structure and catalytic properties of Fe-substituted barium hexaaluminates 总被引:7,自引:0,他引:7
Daoud Naoufal Jean-Marc Millet Edouard Garbowski Yes Brullé Michel Primet 《Catalysis Letters》1998,54(3):141-148
A sol–gel method using Ba and Al isopropylates and iron nitrate has been used to synthesise barium hexaaluminate partially substituted with iron. After calcination under oxygen at 1200°C the -alumina structure was obtained. Formation of the mixed BaFexAl12-xO19 phase occurred for x=1–4. XRD measurements showed a good crystallinity of the structure and expansion of unit cell parameters due to the presence of larger Fe3+ ions substituting Al3+ ones in octahedral sites only. Mössbauer spectroscopy revealed that Fe3+ ions are present in four different octahedral sites slightly distorted. Catalytic activity in methane combustion showed that an optimum was obtained for solid containing 2 Fe ions per unit cell: the increase of the amount of introduced iron was counterbalanced by the decrease of specific surface area. Intrinsic activities have been calculated for the four solids in both the fresh and aged states. It is observed that increasing iron content increases relative activities in the same ratio as the populations of iron located in two sites as deduced from Mössbauer spectroscopy. It is then tentatively assumed that activity is attributed to octahedrally coordinated Fe3+ ions in some specific sites. 相似文献
73.
The catalytic activity of Pt catalysts supported on high surface area tin(IV) oxide in the complete oxidation of CH4 traces under lean conditions at low temperature was studied in the absence and in the presence of water (10 vol.%) or H2S (100 vol.ppm). Their catalytic properties were compared to those of Pd/Al2O3 and Pt/Al2O3. In the absence of H2S in the feed, Pt/SnO2appears as a very promising catalyst for CH4 oxidation, being even significantly more active under wet conditions than the best reference catalyst, Pd/Al2O3. 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/SnO2 is slightly less resistant than Pd/Al2O3. In the presence of H2S, Pt/SnO2catalysts are rapidly and almost completely poisoned, comparably to Pd/Al2O3and the catalytic activity is hardly restored upon oxidising treatment below 773 K. A synergetic effect between Pt and specific surface SnO2sites active in CH4oxidation is proposed to explain the superior catalytic behaviour of Pt/SnO2. 相似文献
74.
Nanocomposite Ni/ZrO2-AN catalyst consisting of comparably sized Ni metal and ZrO2 nanoparticles is studied in comparison with zirconia- and alumina-supported Ni catalysts (Ni/ZrO2-CP and commercial Ni/Al2O3-C) for steam reforming of methane (SRM) and for combined steam and CO2 reforming of methane (CSCRM). The reactions are performed under atmospheric pressure with stoichiometric amounts of H2O and CH4 or (H2O + CO2) and CH4 at 1073 K. Under a wide range of methane space velocity (gas hourly space velocity of methane GHSVCH4 = 12,000–96,000 ml/(h gcat.), the nanocomposite Ni/ZrO2-AN catalyst always shows higher activity and stability for both SRM and CSCRM reactions. The two supported Ni catalysts (Ni/ZrO2-CP and Ni/Al2O3-C) exhibit fairly stable catalysis under low GHSVCH4 but they are easily deactivated under high GHSVCH4 and become completely inactive when they are reacted for ca.100 h at GHSVCH4 = 48,000 ml/(h gcat.). The CSCRM reaction is carried out with different H2O/CO2 ratios in the reaction feed while keeping the molar ratio (H2O + CO2)/CH4 = 1.0, the results prove that the nanocomposite Ni/ZrO2-AN catalyst can be highly promising in enabling a catalytic technology for the production of syngas with flexible H2/CO ratios (ca. H2/CO = 1.0–3.0) to meet the requirements of various downstream chemical syntheses. 相似文献
75.
Methane has been selectively converted to synthesis gas using a two-zone fixed bed of a Ni/Al2O3 catalyst inside a modified ceramic membrane. The first zone of the reactor was surrounded by an impervious wall, and therefore behaved as a conventional fixed bed reactor. In the second zone, some of the reaction products could preferentially diffuse out of the reactor, which yielded higher than equilibrium methane conversions. The influence of the different operating conditions has been studied, and the performance of the membrane reactor has been compared to that of a fixed bed reactor. The membrane reactor has also been used at pressures above atmospheric (2 bar), with good conversions and selectivities. 相似文献
76.
Methane oxidative coupling in the presence of the catalyst 1% Au/5% La2O3/CaO and gas-phase initiator hydrogen peroxide at the temperature 700–800°C under normal pressure has been studied. It has been shown that hydrogen peroxide remarkably increases the yield of C2+ products without the loss of selectivity. The maximal yield of C2+ products under the conditions studied was 27% with the formation of a noticeable quantity of benzene. It has been proposed, that the observed effect is due to hydroxyl radical formation from hydrogen peroxide, which could be essential under definite conditions also in a conventional catalytic methane oxidative coupling. 相似文献
77.
中国煤层气加工利用发展趋势分析 总被引:1,自引:0,他引:1
随着煤层气大量开发,中国煤层气利用将由民用为主逐渐转变为工业利用为主,煤层气主要用于炭黑、甲醇、发电等工业生产。 相似文献
78.
Samples of palladium supported on-alumina and a palladium foil were used as catalysts for methane oxidation at 550° C. The samples were quenched quickly in the reaction chamber to room temperature in flowing Ar and then transferred in vacuo for XPS analysis. Structure sensitivity was manifest from an increase in PdO stability and a decrease in carbon deposition relative to Pd with increasing particle size. The results were compared with recent ellipsometric data. 相似文献
79.
阐述了利用二甲基二硫在相转移催化剂作用下,于盐酸介质中经氯气直接氧化,一步合成甲烷磺酰氯的工艺过程,讨论了几个主要反应因素对产物收率的影响,确定了适宜的工艺条件。表明了产品的检测方法 相似文献
80.
D. Miceli F. Arena A. Parmaliana M. S. Scurrell V. Sokolovskii 《Catalysis Letters》1993,18(3):283-288
Precipitated silica catalysts loaded with either MoO3 (0.2–4.0 wt%) or V2O5 (0.2–5.3 wt%) have been studied in the selective partial oxidation of methane to formaldehyde with molecular oxygen at 520 °C. The functionality of the SiO2 surface towards the formation of HCHO is significantly promoted by V2O5, while it is depressed by the MoO3. 相似文献