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jiachuo

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2. Experimental
2.1. Samples preparation
All the samples were prepared by impregnation from aqueous solutions, using two different supports: a graphitized carbon, referred to as GC, with BET speciﬁc surface area (SSA) = 280 m2/g, and a commercial active carbon, referred to as AC, with SSA = 1400 m2/g. Ru was deposited from Ru(NO)(NO3)3 as described in detail elsewhere [17], achieving a ﬁnal Ru/C loading of 3.8 wt%. The sample was reduced in ﬂowing hydrogen at 320 8C for 5 h. The Ru/GC sample was split into ﬁve portions, three of which were impregnated with only one single promoter (Cs, Ba or K) using an aqueous solution of nitrate, the fourth was impregnated with the three promoters altogether and the ﬁfth was left unpromoted. The promoters/Ru atomic ratios, optimised in a previous work [25] were Cs/Ru = 1, Ba/Ru = 0.6, K/Ru = 3.5 (mol/mol). A series of blank samples, i.e. without Ru, was also prepared (Table 1). A comparative sample was prepared by impregnation from RuCl3•3H2O, reduced under the same conditions and promoted with Ba + Cs + K in the same optimal amount.
SSA was measured by N2 adsorption at 77 K, using a Micromeritics ASAP 2010 apparatus. Temperature pro-grammed reduction (TPR) was carried out by means of a home-made apparatus described in detail elsewhere [31].The experiment was made on ca. 0.15 g of catalyst (0.15–0.25 mm particle size), in 5% H2/Ar gas mixture, by heating (10 8C/min) up to different temperatures and for different times, as detailed in Table 2. Samples reduction was followed by ﬂushing in He as reported in Table 2. The total gas ﬂow rate in both cases was 40 cm3 /min. The samples were then cooled to 0℃ and several pulses of 10% O2/He mixture were injected, until the peak area of the outcoming oxygen became constant (sample saturation). The outlet gas during both TPR and oxygen pulse chemisorp-tion analysis was monitored and quantiﬁed by means of a thermal conductivity detector (TCD), after careful calibration. A similar apparatus, equipped with a quadrupolar mass spectrometric detector (MKS, PPT Residual Gas Analyser) was used to identify the nature of the efﬂuent species. The total amount of oxygen adsorbed was expressed as chemisorbed oxygen volume per gram of sample (N cm3/gcat) or per gram of Ru. Metal dispersion and Ru surface area were calculated as described in [31].
2.3. Activity tests
Activity tests were performed by means of a bench scale, ﬁxed bed, down-ﬂow Incoloy 800 reactor. A detailed description of the apparatus and procedure is given elsewhere [2]. Brieﬂy, the catalyst in 0.15–0.25 mm particle size was loaded after dilution (1/22, v/v) with quartz particles of the same size, in order to minimise the hot-spot along the catalyst bed. The catalyst was activated in situ by ﬂowing a H2 +N2 mixture (H2/N2 = 1.5/1, v/v), at GHSV = 20,000 h-1, 30 bar, while increasing temperature following different activation programmes. Standard activation (Astd) was carried out by heating by 1℃/min up to 450℃, maintained for 5 h and then decreased down to 430℃. In order to check the effect of activation on catalytic activity, the following heating pro-grammes were also applied: heating by 1℃/min up to 450℃, kept for 120 h (A1), or up to 550 8C, kept for 5 h (A2). The reactant gas mixture was carefully puriﬁed from oxygenates by passing through a trap, packed with a proper amount of frequently regenerated, reduced Fe-based commercial ammo-nia synthesis catalyst.
Activity tests have been carried out under standard reaction conditions, i.e. 100 bar and 430℃, by varying the gas mixture space velocity from GHSV = 60,000 to 200,000 h-1. The efﬂuent gas was bubbled in a known amount of diluted H2SO4, followed by titration of the residual acid with NaOH solution.

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1樓 2011-05-30 16:24:42

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ringzhu(金幣+2): 不厚道哇~~ 2011-06-02 11:36:30
jiachuo(金幣+20, 翻譯EPI+1): 不完整 2011-06-09 13:25:25

2.實(shí)驗(yàn)部分
2.1 樣品的制備
所有的樣品都是使用兩種不同的載體在水溶液中制備：一種載體是石墨化碳，記為GC，BET比表面積（SSA）=280 m2/g,另一種是商業(yè)用的活性炭，記為AC，比表面積SSA=1400 m2/g. Ru參照文獻(xiàn)[17]由Ru(NO)(NO3)3沉積得到，最后得到的Ru/C，負(fù)載量為3.8 wt%.樣品在流動的H2氛圍中320℃放置5h，Ru/GC樣品分為5部分，其中的三種只由單一的促進(jìn)劑（Cs, Ba 或K）在硝酸溶液中制得，第四份是由三種促進(jìn)劑混合制得，第五份是不經(jīng)促進(jìn)劑處理。根據(jù)先前的文獻(xiàn)[25]報(bào)道，促進(jìn)劑與Ru原子比最優(yōu)化是Cs/Ru = 1, Ba/Ru = 0.6, K/Ru = 3.5（摩爾比）。還制備了一系列無Ru的空白樣品（表1）。在相同條件下還通過從RuCl3•3H2O制備了對比樣品，在相同優(yōu)化條件下，促進(jìn)劑為Ba + Cs + K。

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2樓2011-05-31 14:40:19