Collapse of pores

In the paste with low hydration degree the capillary effect is of special importance. The capillary pressure leads to the collapse of pores with diameter in the range from 4 to 10 nm, associated with the specific surface decrease, as measured by nitrogen adsorption. 

This is another reason for loss of catalyst activity and it also is irreversible. This is also a result of high temperatures and particularly in connection with high water partial pressures. In this case the catalyst support material can lose surface area from a collapse of pores, or from an increase in the diameter of pores, with the pore volume remaining approximately constant. 

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