The heterogeneous catalysts are known to suppress side reactions, which include self-condensation and oligomerization, resulting in better selectivity and product yield. Also, heterogeneous catalysts are advantageous over conventional homogeneous catalysts as they can be easily recovered from the reaction mixture by simple filtration and can be reused after activation, thereby making the process economically viable. Recently, we prepared a series of silica-bonded sulfonic acids as solid acid and silica-bonded n-propyl-amines as solid base catalysts (Figure 1). In addition, their catalytic activitie were investigated in organic reactions [2-3]
.