Evolution of the pore structure-transport relationship during catalyst reduction and sintering studied by integrated multi-scale porosimetry and multi-modal imaging

Do Pores Exist?—Foundational Issues in Pore Structural Characterisation

“…It was found that the universal plot of the form in Figure 9 was able to predict a change from 1300 to 190 µm in the key length scale parameter w, and thus 'sift-out' the structural feature controlling mass transport in methanol catalyst pellets formed with RC feed particles. This prediction was confirmed by CXT images that showed that, following catalyst reduction and sintering, a new set of pores had, indeed, opened up in the pellet over the shorter length scale predicted by the plot of the gas sorption data to Equation (1) [87]. In principle, this procedure could also have been performed in reverse, whereupon this new information from the CXT could have been fed into the value of w for the plot of Equation (1) to predict the changes in mass transport rates resulting from changes to the pore structure.…”

“…The pores in the PNM do not correspond to individual pore elements of the type seen at the bottom of Figure 3. However, the CXT data (in Figure 8) suggest that the abstract, individual bonds in the model lattice have some correspondence with the physical void space within and/or surrounding individual pellet feed particles (such as the SD particles in Figure 7) [85,87]. Nevertheless, the representation of the void space is of a more statistical nature, where only the minimally necessary features have been 'sifted' out from the overall, background structural complexity.…”

“…This also causes the desorption knee to sharpen, as access to the interior of the pellet for the nitrogen becomes more restricted due to the partial mercury barrier. Hence, the apparent lattice size (from a percolation analysis of the gas sorption data) of the real pellet Despite the abstract nature of the underlying structure, as required for a successful scientific theory, the model implicit in Equation (1) was also found to be able to generate novel predictions for the evolution of fresh pellets following the reduction of the copper catalyst and the sintering of the catalyst due to use on-stream in the methanol synthesis process in a reactor [87]. It was found that the universal plot of the form in Figure 9 was able to predict a change from 1300 to 190 µm in the key length scale parameter w, and thus 'sift-out' the structural feature controlling mass transport in methanol catalyst pellets formed with RC feed particles.…”

“…The underlying PNM used in this previous work [85,87] is, as demonstrated by its unrealistic apparent 'growth', rather abstract (i.e., a 'mathematical fiction'). The pores in the PNM do not correspond to individual pore elements of the type seen at the bottom of Figure 3.…”