Catalytic decomposition of ammonia gas with metal cations present naturally in low rank coals
Catalytic decomposition of ammonia gas with metal cations present naturally in low rank coals
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DOI：
10.1016/j.fuel.2005.03.019
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发表时间：
2005-10
期刊：
影响因子：
7.4
通讯作者：
C. Xu;N. Tsubouchi;H. Hashimoto;Y. Ohtsuka
中科院分区：
文献类型：
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作者：
C. Xu;N. Tsubouchi;H. Hashimoto;Y. Ohtsuka
在石英反应器上研究了一种新的热气净化方法，将低阶煤中固有的金属阳离子与低浓度的NH3分解为N2。在750~850℃，0.1 MPa，高空速−1的条件下，每种煤在900℃下热解制备半焦，再用氢气预处理2000ppm的NH3。所考察的五种焦都促进了NH3在惰性气体中的分解，但促进作用强烈地依赖于焦的种类，并且与铁含量的关系比与钙含量的关系更密切。这一结果可能表明，铁在反应中起着关键作用。含铁量为0.05wt%的工业用活性碳的NH3转化率低于5个焦炭。透射电子显微镜照片显示，在褐煤半焦上形成了纳米级的Fe和Ca组分，提供了最大的催化性能。在750℃的25h反应中，半焦保持了80%的高转化率，并在850℃实现了NH3的完全分解。在稳态下，H2、CO和CO2的混合物共进料对半焦的催化活性没有显著影响，而2000ppm的硫化氢的共存使其在整个投产时间范围内的催化活性降低。结合X射线衍射和TPD的观察结果，结合我们以前的研究结果，提出了惰性气体中NH3与低阶煤焦的催化分解是通过金属铁、氮化铁、CaO和CaCN2两种循环机理进行的。
A novel hot gas cleanup method to decompose a low concentration of NH3to N2with metal cations present inherently in low rank coals has been studied with a quartz reactor under the conditions of 750–850°C, 0.1MPa and high space velocity of 45,000h−1. Each coal is pyrolyzed at 900°C to prepare the char, which is subjected to the decomposition of 2000ppm NH3after pretreatment with H2. All of five chars examined promote NH3decomposition in inert gas, but the promotion effect depends strongly on the kind of char and can correlate more closely with the Fe content than with the Ca content. This result may indicate that the Fe plays a crucial role in the reaction. A commercial activated carbon with a very low Fe content of <0.05wt% exhibits lower conversion of NH3to N2than five chars. The TEM pictures reveal the formation of nanoscale particles of Fe and Ca components on a brown coal char that provides the largest catalytic performance. The char maintains the high conversion level of 80% during 25h reaction at 750°C and achieves the complete decomposition of NH3at 850°C. The co-feeding of a mixture of H2, CO, and CO2does not change significantly the catalytic activity of the char at a steady state, whereas the coexistence of 2000ppm H2S lowers it in the whole range of time on stream. It is proposed by combining the XRD and TPD observations with our previous results that the catalytic decomposition of NH3in inert gas with the chars derived from low rank coals proceeds through two cycle mechanisms involving iron metal, iron nitrides, CaO and CaCN2.