Kinetic factors in steam reforming

The rate of formation of the products of steam reforming is extremely slow in the homogeneous reaction, and the reaction only proceeds at a useful rate in the presence of the catalyst. This indicates that adsorption of the reactant gases on the catalyst surface is a necessary step in the initiation of a useful reaction. The nature of the adsorption processes can be described by the equations  

Here n indicates an active surface site, and X— indicates die species X adsorbed on an active site. The first reaction allows for the possibility that methane may occupy more than one active site on adsorption. The dik d and fourth reactions show die observed retarding effects of steam and hydrogen 

The overall reaction kinetics conesponding to these stages of surface adsorption followed by reaction can be represented by die equation 

Similar expressions have been found to be applicable to the steam reforming of higher hydrocarbons. For example, it has been shown that if it is assumed that ethane, CaHg is adsorbed on two neighbouring sites, the overall reaction rate can be expressed by the equation 

The role of oxygen and hydrogen solutions in the metal catalyst does not appear to be that of impeding the major reactions, but merely to provide a source of these reactants which is uniformly distributed diroughout the catalyst particles, without decreasing die number of surface sites available to methane adsorption. It is drerefore quite possible that a significatit fraction of the reaction takes place by the formation of products between species adsorbed on the surface, and dissolved atoms just below the surface, but in adjacent sites to the active surface sites. 

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