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

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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