| 摘要 |
The invention relates to a multi-layered catalyst bed for producing phthalic anhydride by gas phase oxidation of o-xylol and/or naphtaline, which contains at least three differently composed catalyst layers, respectively an active mass, which are characterised as a first, second and/or third catalyst layer which leads from the gas inlet side to the gas outlet side. Said catalyst layers comprise an active mass containing TiO2 having a NA content of less that 0.3 wt. %, and the active mass content decreases from the first catalyst layer, which is placed in the direction of the gas inlet side, to the third catalyst layer, which is placed in the direction of the gas outlet side, under the proviso that (a) the first catalyst layer has an active mass content of between 7 and 12 wt. %, (b) the second catalyst layer has an active mass content in the region of between 6 and 11 wt %. The active mass content of the second catalyst layer is smaller or equal to the active mass content of the first catalyst layer, and (c) the third catalyst layer has an active mass content in the region of between 5 and 10 wt. %. The active mass content of the third catalyst layer is smaller or equal to the active mass content of the second catalyst layer. The invention also relates to a preferred method for producing said type of multi-layered catalyst bed, and to the preferred use of the titanium dioxide which is used according to the invention. ® KIPO & WIPO 2008
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