Silica gel-bound sulfobenzylsiloxane as a catalyst favors the scission of MeOCMe3 (I) to isobutene and MeOH. Increasing temp. (120-180 Deg) promotes the conversion of I and diminishes the selectivity for isobutene in favor of isobutene dimers. This behavior is also obsd. in dependence on the capacity (mmol H+/g) and the H+-concn. (mmol H+/m2) of the catalysts. At 180 Deg and whsv = 9,8 g I/g cat.h conversion of 96 mol% I and selectivity of 97 mol% of isobutene is obtained. The formation of di-Me ether is not obsd. under these conditions.