Restricted pore average density

Molecular dynamics results for restricted pore average density versus pore width. 

We will find it convenient to consider for the moment the special case of perfectly reflecting walls. In the long time-scale limit A a /D, the average propagator for fully restricted diffusion has a simple relationship to the pore geometry. This requirement on A, also known as the pore equilibration condition, implies that the time is sufficiently long that most molecules have collided with the walls. Under this condition the conditional probabilities are independent of starting position so that P(r, t I r, 0) reduces to p(r ), the pore molecular density function. 

Diffusion-limited removal of products from catalyst pellets leads to enhanced readsorption and chain initiation by reactive a-olefins. These secondary reactions reverse chain termination steps that form these olefins and lead to heavier products, higher chain growth probabilities, and more paraffinic products. Diffusion-enhanced readsorption of a-olefins accounts for the non-Flory carbon number distributions frequently observed during FT synthesis on Co and Ru catalysts. Diffusion-limited reactant (H2/CO) arrival leads instead to lower selectivity to higher hydrocarbons. Consequently, intermediate levels of transport restrictions lead to highest selectiv-ities to C5+ products. A structural parameter containing the pellet diameter, the average pore size, and the density of metal sites within pellets, determines the severity of transport restrictions and the FT synthesis selectivity on supported Ru and Co catalysts. 

Filling the pore. The basic idea to describe adsorption in restricted geometries is the following Let L(p) denote the average thickness of the adsorbed slab L(p) = N(p)/p, where p is the actual adsorbate density. Since p < po, a lower bound to L(p) is immediately obtained L(p) > N(p)/po. When L(p) becomes comparable with 8/2, each newly adsorbed molecule has a chance to belong to two or more piles, so that it behaves as pile terminator. This occurrence will also be expressed with the statement that the adsorbate is dense in the pore . 

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