Reduction of single particle catalyst

The proposal about the reduction of single particle catalysts by gas reductant is mature, but the theory and experimental work to clarify the of reduction process of catalyst bed by gas reductant are few. The following section will clarify the reduction of the single-particle catalysts by gas. 

The character of reduction process for single-particle catalyst is in its various stages which have certain orders. The reductant gas flows from the interspaces between the catalyst particles and large pores in the particles, and forms a border gas flow at around the particles and the surface of macro-pore. 

The mass transfer between the gas and oxide and the transfer of reactants (reducing agent and product) have to pass this boundary layer. Then, in order to contact with particle surface for the gas reductant, the gas has to diffuse through micropores in particle, and through layer of solid products formed by reduction to reach internal part of particles. 

The gas product derived from reduction should be expelled from the reaction region along the same path. Here, the reducing agent contacts with iron oxide, namely, it is adsorbed on the surface of the solid and starts surface reactions. The reduction reaction includes seizure of oxygen from oxides, the formation and growth of crystal nuclei of the product. The continuous growth of product layer is maintained by solid state reaction and the diffusion in solid state. 

It will be seen from this that the reduction of oxide is the sum of aU the processes, in which each process is its equilibrium and has own characteristics, where the deviation from these equilibriums in various stages is the driving force. For example, the driving force for diffusion is the difference of reactant concentration (or pressure) at the beginning and end of the process. 

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Generally, the reduction of single particle catalyst is composed of the following stages ... 

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