AMORPHOUS POROUS MIXED OXIDES: Sol-Gel Ways to a Highly Versatile Class of Materials and Catalysts

Abstract

▪ Abstract 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.

Synthesis of Fe/Ti oxides from a single source alkoxide precursor under inert atmosphere

“…Above 700 o C, on the other hand, carbonaceous materials, generated by pyrolysis of organic residues, may have acted as reducing agents in the iron(III)→iron(II) conversion, leading to ilmenite. This finds support in the Raman spectrum recorded for IN700/ HNO 3 and IN1000/HNO 3 ( Figure S1, Supplementary Information), which show very broad bands in the 1200-1700 cm -1 range. The pattern of these Raman bands appears to be compatible with the presence of disordered (glassy or amorphous) carbon in the solid.…”

“…The EDS semi-quantitative results obtained for IN55/ HNO 3 and IN1000/HNO 3 (Tables 2 and 3) show that both solids contain variable and relatively high carbon contents, with ca. 17% as an average value (note the high standard deviations).…”

“…[1][2][3][4] Nowadays, the preparation of these oxides is often performed by chemical methods. 3,[5][6][7] In particular, the sol-gel process, either hydrolytic or non-hydrolytic, has been widely employed due to its advantages over conventional solid state methods. These advantages include lower processing temperatures and better control over microstructure, uniformity and stoichiometry of the final material.…”

“…The development of structural components, energy conversion devices, sensors and MRI contrast agents has also benefited from heterometal oxide research. [1][2][3][4] Nowadays, the preparation of these oxides is often performed by chemical methods. 3,[5][6][7] In particular, the sol-gel process, either hydrolytic or non-hydrolytic, has been widely employed due to its advantages over conventional solid state methods.…”

“…These advantages include lower processing temperatures and better control over microstructure, uniformity and stoichiometry of the final material. 3,8,9 The sol-gel synthesis of heterometal oxides is usually carried out from a mixture of homometal compounds, in which each precursor provides one of the desired metal elements to the final material. The molar ratio of these Synthesis of Fe/Ti Oxides from a Single Source Alkoxide Precursor under Inert Atmosphere J. Braz.…”