Novel solid superbases can be prepared by dispersing potassium salts such as K2CO3 and KHCO3 on alumina followed by thermal treatments. The resulting materials show an extremely high activity in the isomerization of cis-but-2-ene at 0°C and possess base strength of at least H− = + 26.5. X-Ray diffraction (XRD) and Raman spectra of K2CO3 or KHCO3 modified alumina reveal the formation of potassium hydroalumina carbonate, which is the precursor of active species. Decomposition of potassium salts on alumina has been studied by use of thermal gravimetric differential thermal analysis (TG-DTA) and temperature programmed decomposition-mass spectrometry (TPDE-MS). Two CO2 evolution processes were observed in the TPDE –MS profile, corresponding to the decomposition of potassium hydroalumina carbonate and bulk potassium salt.