| 摘要 |
Reduced downgrading in xylene isomerization of ethylbenzene-depleted feeds is achieved by carrying the process out over gallosilicate or borosilicate zeolites, preferably in the form of compositions comprising a core of catalytically-inactive crystalline silica with an overlying zeolite layer. The composites are prepared by introducing preformed silica particles, preferably with a crystallite size greater than 0.1 mu , into a reaction mixture comprising a silicon source, a source of the modifying element, and preferably an organic template such as a tetraalkylammonium compound. The weight ratio of the silica core to SiO2 in the reaction mixture is preferably 0.5:1 to 25:1.
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