Vanadium pore structure effect

In addition to catalyst pore structure, catalytic metals content can also influence the distribution of deposited metals. Vanadium radial profile comparisons of aged catalysts demonstrated that a high concentration of Co + Mo increases the reaction rate relative to diffusion, lowering the effectiveness factor and the distribution parameter (Pazos et al., 1983). While minimizing the content of Co and Mo on the catalyst is effective for increasing the effectiveness factor for HDM, it may also reduce the reaction rate for the HDS reactions. Lower space velocity or larger reactors would then be needed to attain the same desulfurization severity. 

Crystalline strontium titanate has no pore structure and its effectiveness as a vanadium trap is reliant vpoi maximizing its external surface area. This is achieved by reducing the average particle size of the tr, by milling and classlflcaticxi, to levels ccnparable with other catalyst ingredients. 

Sn-silicalites of MFI, MEL and MTW stmctures with Si/Sn > 30 have been synthesized hydrothemally under basic conditions. The unit cell volume eraansion in each case, though linear with respect to Sn content (upto 3 Sn per unit cell in MFI and MEL silicalites), does not correspond to theoretical T-atom substitution by Sn " ions. The well-dispersed SnOx units can be described as structural defects with octahedral coordination and are active in the oxidation of a number of organic substrates (phenol, toluene, m-cresol and m-xylene) with aqueous H2O2. These are similar to vanadium silicalites (VS-1 and VS-2), as both hydroxylation or the aromatic nucleus and the oxidation of the alkyl substituent are catalysed. Due to the presence of Sn + in large pores, Sn-ZSM-12 sample is able to oxidize bulkier naphthalene and 2-methylnaphthalene more effectively than the medium pore Sn-MFI and Sn-MEL silicalites. 

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