Pore volumes metal loading effects

NMR adsorption isotherms for Ru/SiOi catalysts have been obtained using explicit calibration (89). Although the pressure over the sample could be adjusted in situ, no volumetric data were taken simultaneously, probably because of the important spillover effects in this catalytic system (see Section III.A). The NMR study was performed at pressures between 10 and 760 Torr and at temperatures between 323 and 473 K (only the 323-K results are reviewed here). The dispersion of the catalyst was determined from the irreversible H NMR signal as 0.29. The metal loading was 8 wt% so that a monolayer coverage on 1 g of catalyst corresponds to 2.8 cm of H2 under standard conditions. It is typical for an NMR sample to contain 0.5 g of material in a 1-cm sample volume, and the pores in the powder make up about half the volume. If such a sample of this catalyst is under 760 Torr of hydrogen, the gas phase corresponds to one-third of a mono-layer, and it can make a detectable contribution to the NMR signal. 

Catalyst deactivation in hydrodemetallisation (HDM) is caused by the interaction of the metal deposits with the original active phase ( active site poisoning ) and the loss of pore volume due to the obstruction of catalyst pores i pore plugging) (1). However, metal deposits also have an auto-catalytic effect on the hydrodemetallisation reaction, thus active site generation may occur in low active phase loaded or bare support catalyst systems. 

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