Preparation of selective ZnCl2/alumina catalysts for methyl chloride synthesis: Influence of pH, precursor and zinc loading

• Characterization of catalyst acid sites using FTIR depending on catalyst preparation.
• A shift in acid site type depending on zinc loading has been observed.
• Characterization of alumina surface OH vibrational modes depending on zinc loading.
• State of zinc has been investigated using XRD, TEM and electron diffraction.
• Correlation of catalyst characteristics with activity and selectivity.

Zinc-modified alumina catalysts for methyl chloride synthesis were prepared with varying zinc loadings: from 2.4 to 21.1 wt%. The influence of the zinc loading, zinc precursor and the pH of the impregnation on the physico-chemical properties of the catalyst, and on the catalyst activity and selectivity for methyl chloride (MeCl) synthesis was investigated. The prepared catalysts were thoroughly characterized by FTIR, TEM, physisorption and EDX. On the alumina surface, both molecular and bulk zinc species are created upon zinc loading. The surface area of the catalyst decreases steadily with zinc loading. Bulk zinc species dominate on the catalyst starting at a zinc loading of 9.4 wt% and the amount of Lewis acid sites (LAS) decreases. A shift in the acid site type takes place upon zinc modification. Sites assigned to stronger LAS are eliminated while zinc-based weaker acid sites started to predominate. The shift in acidity increases the selectivity and activity of methyl chloride synthesis, which was demonstrated in a series of experiments in a laboratory-scale fixed bed reactor.

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