Micro-Macroporous Composite Materials – Preparation Techniques and Selected Applications: A Review Ulf Betke* and Alexandra Lieb Pores, on several orders of magnitude in size, control the properties of a solid material to a large extent. This is just as true for materials containing pores in the sub-nanometer range like zeolites as for cellular foam structures with pores of several millimeters in size. All these porous materials have their distinct potential application ranging from heterogeneous catalysis to metal melt filtration. In many cases, the (hierarchical) combination of pores with different size regimes can improve the performance of the respective porous material or can lead to entirely new properties and applications. This review addresses the preparation and properties of microporous-macroporous composite materials based on cellular foam supports (ceramic, metal, polymer) with a coating of a microporous compound (zeolite, zeotype framework, metal-organic framework). The manufacturing of these materials can either be performed by dispersion-based techniques, where the microporous coating is applied from a dispersion onto the cellular support (ex situ), or in situ by crystallization of the microporous compound directly onto the struts of the foam structure. In both cases, the general procedure can be modified by a pretreatment of the cellular support in order to improve the coating layer adherence, the overall amount of deposited material, or to control of the crystal morphology of the microporous compound. 1. Introduction The concept of “porosity” spans over a wide field of meaning, not only with respect to the order of magnitude in pore size, diverse pore morphologies or the type of materials pores are incorporated in, but also with regard to possible applications. Consequently, porous materials are addressed within several scientific disciplines and communities, always with very different approaches and demands. A classification of pores regarding their size has been proposed by the International Union of Pure and Applied Chemistry (IUPAC): Pores smaller than 2 nm are addressed as micropores and pores larger than 50 nm are classified as macropores. The range between 2 and 50 nm is called the mesoporous regime. [1,2] However, this classification is mainly based on typical analytical methods, such as gas adsorption and mercury intrusion, and characterizes porous materials being com- mon in chemistry and chemical engineer- ing, for example, zeolites as classical microporous compounds or mesoporous silica. In materials science, the term “porosity” is usually meant in a different way and commonly addresses cavities being incorporated in the micro- or even macrostructure of a solid material. Exam- ples are (sintered) ceramic materials or even cellular foam structures. With respect to the IUPAC convention, virtually all porosity found in these engineering mate- rials falls into the macroporous regime, which integrates several orders of magni- tude from the sub-micrometer scale up to the mm range. Consequently, a classifica- tion of pores in these solids complying with the IUPAC standard is not possible. In many cases this results in an obliteration of the terms “microporosity” and “macroporosity”, actually meaning smaller and larger cavities in engineering materials. This should be considered during the interpretation of publications in this field. Nevertheless, within this work the IUPAC convention is followed strictly in addressing the size of pores being present in a material. A current trend in the engineering of porous materials are hierarchical systems, which contain interconnected pores of several dimensions, sometimes with some extent of branching, being ordered from large cavities down to small (micro)pores. For zeolite materials used as microporous catalysts in chemical engineering, this concept has been thoroughly investigated and several approaches have been developed to include an additional level of porosity in these materials. Examples are templating methods which add macropores into zeolite crystals during their synthesis or the control of the crystallization process itself resulting in intercrystalline macroporosity. A good overview of such hierarchical materials and their preparation can be found in a recent review of Schwieger and co-workers. [3] The result are microporous zeolite materials containing additional macroporosity, which enhances the transportation Dr. U. Betke Otto-von-Guericke-University Magdeburg Institute for Materials and Joining Technology – Nonmetallic Inorganic Materials and Composites Große Steinernetischstraße 6, 39104 Magdeburg, Germany E-mail: ulf.betke@ovgu.de Dr. A. Lieb Otto-von-Guericke-University Magdeburg Chemical Institute – Industrial Chemistry Universitätsplatz 2, 39106 Magdeburg, Germany The ORCID identification number(s) for the author(s) of this article can be found under https://doi.org/10.1002/adem.201800252. DOI: 10.1002/adem.201800252 XXXX www.aem-journal.com REVIEW Adv. Eng. Mater. 2018, 1800252 © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim 1800252 (1 of 28)