Amorphous porous mixed oxides: Sol-gel ways to a highly versatile class of materials and catalysts

This review discusses the preparation, characterization, and application of amorphous porous mixed oxides, a rapidly growing class of materials with wide applications and a huge potential for the tailoring of chemical composition, microstructure, porosity, and surface properties. In contrast to crystalline materials, these amorphous mixed oxides are prepared under mild reaction conditions in ambient atmosphere. An ever-increasing variety of precursors, additives, modifiers, solvents, catalysts, and posttreatment conditions provide ample fine-tuning options. These materials often display properties commonly associated with well-defined crystalline phases. The functional properties of such solids are largely unexplored and provide a tremendous opportunity for the development of new or alternative materials (solids with a function). Here, emphasis is paid to micro- and mesoporous mixed oxides and their catalytic properties. Easy access to these materials is offset by their much more problematic characterization. Microstructure, chemical structure, morphology, and pore sizes often show broad distributions, and materials description cannot compare with the precise data associated with crystalline phases. The facile preparation and accessibility of these materials make them ideally suited for the application of high-throughput technologies (HTT), which dramatically accelerate searches for new materials as well as fine tuning and optimization. HTT also allow investigators for the first time to access and optimize multinary mixed oxides on a realistic timescale.