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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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ringzhu(金币+2): 不厚道哇~~ 2011-06-02 11:36:30
jiachuo(金币+20, 翻译EPI+1): 不完整 2011-06-09 13:25:25
ringzhu(金币+2): 不厚道哇~~ 2011-06-02 11:36:30
jiachuo(金币+20, 翻译EPI+1): 不完整 2011-06-09 13:25:25
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2.实验部分 2.1 样品的制备 所有的样品都是使用两种不同的载体在水溶液中制备：一种载体是石墨化碳，记为GC，BET比表面积（SSA）=280 m2/g,另一种是商业用的活性炭，记为AC，比表面积SSA=1400 m2/g. Ru参照文献[17]由Ru(NO)(NO3)3沉积得到，最后得到的Ru/C，负载量为3.8 wt%.样品在流动的H2氛围中320℃放置5h，Ru/GC样品分为5部分，其中的三种只由单一的促进剂（Cs, Ba 或K）在硝酸溶液中制得，第四份是由三种促进剂混合制得，第五份是不经促进剂处理。根据先前的文献[25]报道，促进剂与Ru原子比最优化是Cs/Ru = 1, Ba/Ru = 0.6, K/Ru = 3.5（摩尔比）。还制备了一系列无Ru的空白样品（表1）。在相同条件下还通过从RuCl3•3H2O制备了对比样品，在相同优化条件下，促进剂为Ba + Cs + K。 |
2楼2011-05-31 14:40:19