Catalyst deactivation carrier sintering

Carbon formation could be stopped in the presence of oxygen, while the catalyst deactivated under conditions of steam reforming (S/C =1.5), which was attributed to sintering of the carrier material [71]. 

Metal catalysts often consist of small metal crystallites deposited on a porous carrier. An important deactivation phenomenon is sintering of these small metal crystallites into larger ones. Of course, this leads to deactivation. Figure 3.36 shows a schematic representation of the phenomena occurring. 

Sintering is an important mode of deactivation in supported metals. The high surface area support (carrier or substrate) in these catalysts serves several functions (l) to increase the dispersion and utilization of the catalytic metal phase, (2) to physically separate metal crystallites and to bind them to its surface, thereby enhancing their thermal stability towards agglomeration, and (3) in some cases to modify the catalytic properties of the metal and/or provide separate catalytic functions. The second function is key to the prevention or inhibition of thermal degradation of the catalytically active metal phase. 

There aie indications fmm the relative small line width in both XRD patterns and Messbauer spectra that the imn(ir)sulfatc easily sinters, even at the relative low temperatures of the catalytic reaction. This is also indicated by the catalytic performance test of the catalyst B. Catalyst B containing iron oxide not interacting with the support shows a large deactivation. The time required for stabilization is much longer, and the remaining activity and selectivity is low. The effect of the dispersion, and the interaction with the carrier stresses the great importance of the preparation procedure [4]. 

Incorporation of Ce02 or Ti02 reduces the thermal sintering of both Cu and Cu-Cr catalysts. The structural stabilization of the Cu sites is probably due to a strong copper-dopant interaction.(14). In addition the dopants especially Ce02 can impart stability against the sintering of alumina carrier. However it can be seen that the thermal deactivation is much less pronounced for catalysts modified with cerium oxide. 

There are two problems connected with such operation. First sintering or deactivating of the catalyst may be done because of high temperature. The second one the carrier may be cracked because of temperature gradient. A simple remedy to these problems is to divide the bed in two parts and inject a cold reacting gas between them. 

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