An overview on strategies towards clay-based designer catalysts for green and sustainable catalysis

Remarkable strategies for constructing clay-based catalysts are critically overviewed. Clay minerals provide distinct nanometer-scaled layers and interlayers for engineering them as active catalysts. As such, strategic design and preparation has led to a variety of catalysts, including ion exchanged catalysts, acidic activated clay catalysts, intercalated catalysts, pillared clay catalysts, clay-supported catalysts, inorganic and inorganic–organic composites and hybrids, and hierarchically structured solid catalysts. In many cases, the combination of several protocols was implemented so that the resultant materials functioned with synergetic effects. Electric, optical, photonic, and magnetic functionalities can also be endowed on the resulting clay-based catalysts. Synthetic clay minerals and their derivatives, including layered double hydroxides, have peculiar features in purity and composition to be designed and transformed to catalysts, showing a complementary relationship with their naturally-occurring counterparts. The clay-based heterogeneous catalysts have many practical and potential applications in green catalysis. A review of the literature indicates that precise determination of microstructure and in situ observation of reactions at the molecular and atomic levels remain essential tasks. Prospects for the preparation of clay-based catalysts and their catalytic applications are briefly discussed.