Solid bases prepared by derivatisation of amorphous silica and hexagonal mesoporous silica with dimethylaminopropyl groups are good catalysts for Michael addition reactions. Of the prepared catalysts, those based on hexagonal mesoporous silica show particularly high activities. The sol-gel method used in preparing the catalysts based on hexagonal mesoporous silica enables loading to be increased to more than twice that of those based on amorphous silica which are prepared by the post-modification method.The Michael addition is a carbon -carbon bond forming reaction important in synthetic chemistry. Typically, the reaction involves a nucleophilic addition of carbanions to α,β-unsaturated carbonyl compounds. During the course of the reaction, electronic charge migrates from the carbon in the donor molecule to a better acceptor atom, usually oxygen, in the electrophile. A base is used to form the carbanion by abstracting a proton from an activated methylene precursor. The reaction is thus base catalysed and in addition to its synthetic utility, may serve as a useful test reaction for studying the catalytic activity of solid bases.Traditionally, the Michael reaction is catalysed by mild to moderately strong bases. Bases such as diisopropylamine, potassium t-butoxide 1 and tetramethylguanidine 2,3 have been used as homogeneous catalysts. However, production of significant amounts of multiple Michael adducts, other side reactions, difficult product separation and catalyst recovery, have always been problematic. These problems, plus the recent increase in the interest of developing environmentally friendly solid catalysts, has led to the development of heterogeneous catalytic systems for this reaction. Examples of such systems are those based on KF-and CsF-alumina, 4 potassium t-butoxide on xonotlite, 5 and Amberlyst A-27, 6 which have been used with different degrees of success. The number of genuinely useful systems however, remains low. As part of a programme aimed at developing heterogeneous base catalysts for use in reactions of synthetic value, we have prepared two catalysts by derivatising amorphous silica and hexagonal mesoporous silica (HMS) with N,N-dimethyl-3-aminopropyl groups. The catalysts were evaluated in the Michael additions of nitroalkanes and α,β-unsaturated carbonyl compounds.The first catalyst (N,N-dimethyl-3-aminopropyl-silica) 1, was prepared according to a known post-modification method 7 using N,N-dimethyl-3-aminopropyltrimethoxysilane (Fluorochem, Derbys, 95%) and silica gel (Kieselgel 100, Merck). Titration with dil. HCl showed a loading of about 0.85 mmol g -1 . Increasing the amount of N,N-dimethyl-3-aminopropylsilane did not increase the loading of the catalyst beyond 1 mmol g -1 , suggesting that this is the maximum loading with this type of preparation method. Thermogravimetric analysis revealed the material to be thermally stable and it does not lose the organic functions until temperatures above 350 o C. Surface area and pore size distribution were determined by N 2 physisorption. The ...