Partial-pressure gradients, gaseous diffusion

Maxwell,02) postulated that the partial pressure gradient in the direction of diffusion for a constituent of a two-component gaseous mixture was proportional to ... 

Changes in gas composition and other conditions have different impact on reduction rate of catalysts with different structures. When H2 content is increased, the exchange intensity of the diffusion in pores is increased. When a molecule moves, every component in the mixed gas independently diffuses in the speed of inverse square root proportion to the molecular weight. Therefore, under the same conditions, diffusion of H2 molecules in gas mixture (H2 and H2O) in the pores is faster than the diffusion of gaseous H2O in the opposite direction. As the result, the absolute pressure in pore rises continuously until the partial pressure gradient of H2 and H2O reaches the value of /Mh o/Mh = 300%). The diffusion equations for the two gas flows (H2 and H2O) can be established at this time, while the diffusion gradient in the pores is determined by the slowest step i.e., the diffusion of product H2O. 

The tlrermodynamic activity of nickel in the nickel oxide layer varies from unity in contact with tire metal phase, to 10 in contact with the gaseous atmosphere at 950 K. The sulphur partial pressure as S2(g) is of the order of 10 ° in the gas phase, and about 10 in nickel sulphide in contact with nickel. It therefore appears that the process involves tire uphill pumping of sulphur across this potential gradient. This cannot occur by the counter-migration of oxygen and sulphur since the mobile species in tire oxide is the nickel ion, and the diffusion coefficient aird solubility of sulphur in the oxide are both vety low. 

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