## 6 Inorganic and Organic Mesoporous Composite Catalysts with Sulfonic Acid Functionality  
The diverse applications of mesoporous materials in the fields of separation, chromatography, large molecular release systems, and catalysis have stimulated the search for materials with new structures and framework compositions [183, 184, 185]. The recent discovery of the periodic mesoporous organosilacs (PMOs) derived from a number of bridged organosilane precursors represented by the general formula (R'O)\({}_{3}\)Si-R-Si(R'O)\({}_{3}\), where an organic group is an integral part of the mesoporous network, renewed interest in the applications of mesoporous materials [186, 187]. Depending on the organic species in the network, the chemical and physical properties of PMOs can be tuned for desirable end uses. Recent advances in this area have demonstrated that PMOs can be synthesized with improved hydrothermal and mechanical stability compared to the conventional MCM-41 type mesoporous silicas [188]. The approaches generally used to expand the possibilities for tailoring the physical/chemical properties of hybrid silica are the combination of organosilane precursors with organic groups either bridging in the framework or dangling into the channel pore. Such bifunctionalized periodic mesoporous organosilacs (BPMOs) have already been reported in the literature [189, 190]. Furthermore, due to the limited choice and unavailability of commercial bridged organosilane precursors, it is worth exploring the possible combinations of existing organosilane precursors with alkoxysilanes for the synthesis of PMOs and to study their structural relationship properties. In addition, the incorporation of transition metals into the framework of mesoporous organosilacs was also adopted in epoxidation and ammoximation reactions [192, 193]. In recent years, sulfonic acid functionalized mesoporous materials were reported to be efficient catalysts for acid catalyzed reactions [194]. For practical applications, the hydrothermal stability of the materials is very important because most of the industrially important acid catalyzed reactions such as esterification, hydration, and condensation always involve water. The previously reported sulfonic acid modified mesoporous materials are hydrothermally unstable, and the mesostructures tend to collapse when they are subjected to prolonged water contact. Incorporating the sulfonic acid functionality into mesoporous organosilacs improves the hydrothermal stability of the catalysts because the bridged organic groups in the mesoporous network make the materials hydrophobic. In this regard, we studied the synthesis of hydrophobic sulfonic acid functionalized benzene-, biphenylene-, and ethane-bridged mesoporous organosilicas for possible use as solid acid catalysts [195,196]. We used two methods to prepare such sulfonic acid functionalized mesoporous organosilic composites. One is direct synthesis [197] in which ethane- or benzene-bridged organosilane or tetramethylas (TMOS) was co-condensed with 3-mercaptoethanolpropyltrimethoxysilane [MPTMS: (MeO)\({}_{3}\)Si-CH\({}_{2}\)CH\({}_{2}\)CH\({}_{2}\)SH] in the presence of H\({}_{2}\)O\({}_{2}\) using a nonionic oligomeric polymer surfactant (Brij-76 or P123) in an acidic medium. During the condensation process, thiol (-SH) group was oxidized _in situ_ to a sulfonic acid (-SO\({}_{3}\)H) by hydrogen peroxide (30 wt % H\({}_{2}\)O\({}_{2}\)) (see Figure 10). The other method is a two-step route [198] in which periodic mesoporous organosilicas (PMOs) containing different fraction of 1,4-diethylenebenzene groups in the framework were first synthesized by co-condensation of 1,4-bis(trimethoxysilethyl)benzene with tetramethylasilane under acidic conditions using a triblock copolymer as a structural directing agent. Then the sulfonic acid sites were incorporated in the mesoporous framework by post-synthetic framework modification of 1,4-diethylenebenzene by sulfonation with chlorosulfonic acid (see Figure 11).