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| N2 isotopic exchange measurements were performed using the apparatus developed for oxygen isotopic exchange studies described previously [11] and [12]. A U-form reactor was placed in a closed recycle system which was connected on one side to a mass spectrometer (Pfeiffer Vacuum, QMS 200) for monitoring the gas phase composition and on the other side by a vacuum pump. The recycling pump placed in the system removes limitations due to gas-phase diffusion. Temperature programmed 15N2/14N2 homomolecular exchange (15N2(g) + 14N2(g) → 214N15N(g)) experiments were undertaken on 100 mg of CoRe4 as described below. Samples were subjected to either a 3:1 H2:N2 or 3:1 H2:Ar (80 ml min− 1) pre-treatment step at 600 °C for 1 h with a ramp rate of 10 °C min− 1 prior to cooling to 200 °C under the same gas mixture. Then, the system was purged using secondary vacuum at 200 °C for 1 h. 50 mbar of a mixture of 14N2 and 15N2 (98% + purity, supplied by Cambridge Isotope Laboratories, Inc.) was charged into the recycle system at 200 °C and the temperature was increased with a ramp rate of 2 °C min− 1 up to 600 °C. Another experiment of homomolecular exchange was undertaken with the addition of an activation step: After H2:N2 treatment, the catalyst was purged using N2 flow (20 ml min− 1) at 600 °C for 30 min prior to cooling down to 200 °C under N2. The masses 28, 29, 30 m/z were monitored as a function of time to follow the exchange and converted into 14N2, 14N15N and 15N2 partial pressures respectively. The m/z values of 2, 17 and 18 were also recorded to determine if H atoms remained at the surface of the nitride, thus yielding NH3 or H2 in the gas phase after decomposition. The absence of NOx and O2 was confirmed by monitoring the corresponding m/z values. The quantity of H2 (mbar) was also estimated after the calibration step. |
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gerryangel
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| 使用先前描述的用于氧同位素交换的装置进行N 2同位素交换测量。一U形反应器放入密闭循环系统，一侧连接到质谱仪（普发真空，QMS 200），另一侧连接到真空泵，用于监测气相组成。放置在系统中的循环泵可以去除由于气相扩散引起的限制。如下所示，我们进行了100毫克CoRe4的程序升温15N2 / 14N2 等分子交换（15N2（G）+ 14N2（G）→214N15N（G））的实验。在Ar（80毫升MIN- 1）下，600oC样品进行3:1 H 2：N 2或3：1 H 2：的前处理步骤持续1小时，以10°的斜坡率C MIN- 1 ，随后冷却到200℃。然后，该系统使用次级真空在200℃下净化1小时。 50毫巴14N2和15N2的混合物（98％+的纯度，由剑桥同位素实验室公司提供）在200℃下被加入到回收系统，并且将温度以2℃MIN- 1的升温速率升至600℃。等分子交换的另一个实验是通过加入活化步骤进行的：在H 2与N2处理后，将催化剂用N 2流在600℃下吹洗（20毫升MIN- 1）30分钟，然后冷却至200℃。监测分子量28，29，30 M / Z作为时间跟随交换函数，并且分别转换成14N2，14N15N和15N2分压。 分子量2，17和18的m / z值也被记录，以确定是否H原子保持在氮化物的表面上，从而在气相中分解后产生NH 3或H 2。相应的m / z值证实并未监测到NOx和O2。 在校准步骤后，H 2（毫巴）的量的也作了估计 |
2楼2016-04-16 15:57:42