共查询到20条相似文献,搜索用时 15 毫秒
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Stanislava Andonova Valentina Marchionni Luca Lietti Louise Olsson 《Topics in Catalysis》2013,56(1-8):68-74
The overall NSR operation was tested over a bimetallic Pt/Rh–BaO lean NO x trap (LNT) catalyst in the range of 473–673 K with simulated diesel exhausts and compared to monometallic 1 wt% Pt/BaO/γ-Al2O3 and 0.5 wt% Rh/BaO/γ-Al2O3 samples. The results showed the beneficial effect of the simultaneous presence of 0.5 wt% Pt and 0.25 wt% Rh on the catalytic performance under lean-burn conditions at low temperatures. It was observed that both Pt/BaO/γ-Al2O3 and Rh/BaO/γ-Al2O3, which both were mildly aged, have limited NO x reduction capacity at 473 K. However, combining Pt and Rh in the NO x storage catalyst assisted the NO x reduction process to occur at lower temperatures (473 K). One possible reason could be that the combined Pt and Rh sample was more resistant to aging. In addition, the NO2-TPD data showed that the presence of Rh into the Pt/BaO/γ-Al2O3 system has a considerable effect on the spill-over process of NO x , accelerating the release of NO x at lower temperatures. These results were in a good agreement with the observed higher rate of oxygen release of the bimetallic Pt/Rh catalyst, leaving a significant number of noble metal sites available for adsorption at lower temperatures than that of the monometallic Pt sample. The superior NSR performance of the bimetallic Pt/Rh/BaO/γ-Al2O3 catalyst under lean-burn conditions suggested the existence of synergetic promotion effect between the Pt and Rh components, increasing the NO x reduction efficiency in comparison with that of the monometallic Pt and Rh–BaO LNT catalysts. 相似文献
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G. Di Carlo L. F. Liotta G. Pantaleo A. M. Venezia G. Deganello 《Topics in Catalysis》2009,52(13-20):1826-1831
Co/Al2O3 and Co/Al2O3–BaO catalysts with low cobalt loading (0.1, 0.3 and 1 wt%) for the selective catalytic reduction (SCR) of NO x by C3H6 were prepared. The distribution of cobalt species was investigated by UV–vis diffuse reflectance spectroscopy and by H2-TPR in order to identify the active cobalt species in hydrocarbons (HC)-selective catalytic reduction (SCR). It was found that the nature of cobalt species strongly depends on the cobalt loading as well as on the properties of the support. The barium addition to the alumina slows down solid state diffusion processes, improving the thermal stability of the support and preventing diffusion of cobalt into the bulk. Highly dispersed surface Co2+ species over alumina were identified as active sites in the NO-SCR process. Accordingly, a high concentration of surface Co2+ sites in Co 1 wt%/Al2O3 improves the catalytic performance in NO-SCR, the long term stability as well as the water tolerance. On the contrary, the formation of Co3O4 particles in Co 1 wt%/Al2O3–BaO promotes the propylene oxidation by oxygen, decreasing the activity and selectivity of the catalyst in NO reduction. 相似文献
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n-Pentane Isomerization Over Pt- and Ni–Pt-Promoted Sulfated Zirconia Catalysts Supported on Alumina
M. Pérez-Luna A. Cosultchi J. A. Toledo-Antonio M. A. Cortés-Jácome 《Catalysis Letters》2009,131(1-2):285-293
Two series of sulfated zirconia catalysts promoted with Pt and Pt–Ni, respectively, were prepared and extruded with different amount of alumina binder (0, 20, 33, and 60 wt%). The catalytic activities of the two series of catalysts, SZPtA and SZNiPtA, were measured for n-pentane isomerization reaction. The reaction reaches its maximum conversion at 20 wt% of alumina for both catalyst series. Adding alumina beyond 20 wt% reduces the overall conversion and modifies the selectivity for both catalysts series from i-C4 towards i-C5 suggesting that the reaction mechanism changed from a monomolecular to a bimolecular one. However, only SZNiPtA catalysts maintain a higher catalytic activity at higher amounts of alumina. Such difference between the two catalyst series can be attributed to the combining effect of Ni and Pt promotion of the SZNiPtA catalysts and not to their acidic properties. 相似文献
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D. William Brookshear Ke Nguyen Todd J. Toops Bruce G. Bunting William F. Rohr 《Topics in Catalysis》2013,56(1-8):62-67
A single-cylinder diesel engine was used to investigate the impact of Na on Cu–zeolite SCR catalysts using 20 % bio- and petrol-diesel fuel blend (B20) with elevated levels of Na. The Na exposure was performed on light-duty (DOC–SCR–DPF) and heavy-duty (DOC–DPF–SCR) configurations of the diesel emissions control devices. The accelerated Na aging is achieved by exposing the system to elevated levels of Na that represent full useful life exposure (700,000 km) and periodically increasing the exhaust temperature to replicate DPF regeneration. After aging, the NOx performance and relevant chemistry of the SCR catalysts were evaluated in a bench flow reactor. The SCR in the DOC–SCR–DPF configuration was found to be severely affected by Na contamination, especially when NO was the only NOx species in the simulated exhaust gases. In the DOC–DPF–SCR configuration, no impact is observed in the SCR NOx reduction activity. Electron microprobe analysis (EPMA) reveals that Na contamination on the SCR samples in the DOC–SCR–DPF configuration is present throughout the length of the catalysts. 相似文献
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Fredrik Gunnarsson Jenny-Yue Zheng Hannes Kannisto Clément Cid Anna Lindholm Miroslawa Milh Magnus Skoglundh Hanna Härelind 《Topics in Catalysis》2013,56(1-8):416-420
The influence of ageing temperature, silver loading and type of reducing agent on the lean NO x reduction over silver–alumina catalysts was investigated with n-octane and bio-diesel (NExBTL) as reducing agent. The catalysts (2 and 6 wt% Ag–Al2O3) were prepared with a sol–gel method including freeze drying and the evaluation of NO x reduction and aging were performed using a synthetic gas-flow reactor. The results indicate a relatively high NO x reduction for both reducing agents. The hydrothermally treated 6 wt% Ag–Al2O3 sample displays a maximum NO x reduction of 78 % at 350 °C for n-octane as reductant and the corresponding value for NExBTL is 60 %. Furthermore, the catalysts show high durability and an increase in activity for NO x reduction after ageing at temperatures up to 650 °C, with n-octane as reducing agent. 相似文献
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Hongyan Zhang Ning Li Lin Li Aiqin Wang Xiaodong Wang Tao Zhang 《Catalysis Letters》2011,141(10):1491-1497
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In–Fe loaded sulfated zirconia (SZ) was firstly studied for the selective catalytic reduction (SCR) of NO with methane and exhibited higher activity than In/SZ and Fe/SZ. The addition of iron to the In/SZ increases its surface area and strong acid sites, which can be helpful for the SCR of NO. 相似文献12.
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Topics in Catalysis - The catalytic activity of M(Ag, Ru, Pt)–Ni/CeO2–SiO2 catalysts prepared by wet impregnation at different M loadings (0–3 wt%) for oxidative steam... 相似文献
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Yoshinori Sakamoto Mitsuru Kanno Toshio Okuhara Yuichi Kamiya 《Catalysis Letters》2008,125(3-4):392-395
Cu–Pd bimetallic clusters with a Cu/Pd atomic ratio of 2 supported on active carbon (AC) ([Cu2–Pd]cluster/AC) selectively hydrogenated nitrate ions in water to harmless compounds, including N2 and N2O (>99% selectivity), and the formation of NH3 was suppressed to tolerable levels (<.5 ppm). The activity and selectivity of [Cu2–Pd]cluster/AC were superior to that of conventionally prepared Cu–Pd/AC. [Cu2–Pd]cluster/AC showed stationary conversion and selectivity from the onset of the reaction and remained active for up to 110 h. 相似文献
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Aleksey A. Vedyagin Mikhail S. Gavrilov Alexander M. Volodin Vladimir O. Stoyanovskii Elena M. Slavinskaya Ilya V. Mishakov Yuri V. Shubin 《Topics in Catalysis》2013,56(11):1008-1014
Three-way catalysts with low content of Pd–Rh alloy particles used as active components were synthesized and studied. Monometallic and bimetallic mixed catalysts with corresponding precious metals loading were chosen as reference samples. The catalytic activity was tested in oxidation of carbon monoxide, hydrocarbons, and in nitrogen oxides reduction. The stability of the samples was estimated by prompt thermal aging in situ technique. Ethane hydrogenolysis testing reaction was used to determine the surface concentration of Pd and Rh, and to confirm the alloy formation. Photoluminescence and electron paramagnetic resonance spectroscopy were applied to clarify the possible reasons of deactivation and to elucidate the mechanism of stabilization. It was shown that Pd–Rh alloyed catalyst is characterized by comparable activity and enhanced stability. While the Pd and Rh particles of monometallic samples were found to interact with support at high temperatures resulting in sintering and bulk diffusion, the particles of alloy type kept their initial state of dispersion and catalytic activity. 相似文献