Ozonized activated carbon as catalyst for MTBE-cleavage
The application of oxidized carbon materials for the cleavage of methyl-tert-butyl ether has been investigated under technical relevant conditions in a fully automated apparatus with paralleled tube reactors. The carbon spheres oxidized for 60 min (SAC60) are active for MTBE cleavage at 498 K and 6 bar(g). MTBE is selectively converted into isobutene (S > 99%) and MeOH (S > 99.9%) at 80% conversion. The catalytic activity of the oxidized activated carbon can be traced back to the surface groups generated by ozonization of the carbon as the untreated sample did not show any conversion of MTBE at all. Broensted acidic carboxylic acid and anhydride surface groups are responsible for the activity of oxidized carbon as was concluded from simulation of the ex situ DRIFT spectra of the applied materials. In contrast to commonly used amorphous alumosilicates, the modified carbon completely inhibited the production of the undesired by-product dimethylether. Therefore, as no Lewis-acid sites are present on SAC60 and none of the present surface groups (carboxylic acids, anhydrides, lactones and carbonyl groups) cause the dehydration of methanol into dimethylether, it can be concluded that DME formation most probably occurs purely on Lewis-acidic or on basic sites. The decrease in conversion over time-on-stream obtained for the oxidized carbon material is ascribed either to poisoning of present active sites or to a decarboxylation of the activated carbon.
Graphical abstractFigure optionsDownload full-size imageDownload high-quality image (106 K)Download as PowerPoint slideHighlights► The catalytic activity of the oxidized activated carbon can be traced back to the surface groups generated by ozonization. ► Carboxylic acid and anhydride groups are responsible for the activity of oxidized carbon. ► In contrast to commonly used amorphous alumosilicates, the modified carbon inhibited the production of the by-product dimethylether. ► MTBE cleavage is Broensted-acid catalyzed.
Journal: Applied Catalysis A: General - Volume 397, Issues 1–2, 30 April 2011, Pages 103–111