Effect of the addition of catalysts in solid state reactions : Akinetic study on the change of reaction pathways for its utilization

这项工作的目的是发现和研究固体静态反应，其途径可以通过添加催化剂转化为生产有用材料或有效地促进环境问题的解决。由于我们已经证实在没有催化剂的情况下，金属催化的CaCO_3加氢反应生成的是CH_4而不是CO，因此我们首先研究了CaCO_3-CaO固相转化反应中的逆反应。逆反应（CaO+2H_2O+CH_4 → CaCO_3+4H_2）是一个很有前途的制取纯氢的过程，本文首先通过实验证实了VIII族金属存在下的逆反应，然后对金属/CaO和金属/CaCO_3固体样品进行了详细的动力学研究。结果表明：（1）逆反应途径与还原反应途径不同， ...更多信息 正向反应生成CH_4。逆反应是由CH_4在金属表面上的水蒸气重整和CaO吸收CO_2的两步反应机理组成的，而正反应是由固体CaCO_3与金属表面解离的H原子直接作用的一步反应机理。(2)这种机理上的差异导致了氯离子中毒效应的巨大差异，这在正反应中是可以忽略的，但在反向反应中是严重的。(3)金属的催化活性依次为Rh、Ir> Pt、Pd> Ni。第一年年底，我们建立了一个配有QMS和GC的固定床流动反应器，以研究高温（600℃）下在Metal/CaO上CH_4水蒸气重整反应中CO_2的动力学行为。然而，上述常规装置不适合于此目的，因此转换成脉冲反应器。在此反应器中，除了对Ca（NO_3）_2在Pt存在下的程序升温分解反应进行了一些基础性的研究外，还没有进行过详细的研究。少

This work aims to find out and to investigate solid-stale reactions whose pathways can be converted by the addition of catalysts into those producing useful materials or effectively contributing towards the solution of environmental problems. We initiated a project to investigate at first the opposing reactions involving CaCO_3-CaO solid-state conversion, since we had already confirmed that metal-catalyzed hydrogenation of CaCO_3, gives CH_4, as a gaseous product, instead of CO without catalysts. It was the reverse reaction (CaO+2H_2O+CH_4 → CaCO_3+4H_2) that has been extensively studied here, because of the possibility as a promising process to give pure hydrogen.Preliminary experiments to confirm actual occurrence of the reverse reaction with Group VIII metals present were followed by a detailed kinetic study with solid samples in the form of Metal/CaO and Metal/CaCO_3. The results so far obtained are as follows : (1) Pathway for the reverse reaction is quite different from one for t … More he forward reaction to form CH_4. Namely, the reverse reaction proceeds via two-step mechanism consisting of steam-reforming of CH_4 on metal surfaces and subsequent process for absorbing CO_2 by CaO, while the forward reaction via one-step mechanism involving direct interaction of solid CaCO_3 with H atoms dissociated on metal surfaces. (2) Such a mechanistic difference results in large difference in a poisoning effect of Clions, which is negligible in the forward reaction but severe in the reverse one. (3) Catalytic activity of metals decreases in the order : Rh,Ir> Pt,Pd> Ni.Afixed-bed flow reactor equipped with QMS and GC were constructed in the end of the first year to carry out another project for elucidating dynamic behavior of C0_2 during the steam reforming of CH_4 on Metal/CaO at high temperatures (600℃), where CO_2 cannot be absorbed in the bulk of CaO at all. For this purpose, however, the above conventional apparatus was not suitable, and hence converted into a pulse-reactor. Detailed study have never been carried out yet, using this reactor, except for some fundamental results for the temperature-programmed decomposition of Ca(NO_3)_2 in the presence of Pt. Less