Heterogeneous mesoporous stable basic catalysts have been prepared by wet or solid-state impregnation of MCM-41 with caesium acetate and lanthanum nitrate followed by thermal decomposition. 133 Cs MAS NMR data of CsLa/MCM-41 show an increase in the Cs–O bond length in the CsLa mixed oxides compared with that in Cs oxides supported on MCM- 41. A small difference in chemical shift between the hydrated and dehydrated materials is ...