German Edition: DOI: 10.1002/ange.201705042 Mesoporous Materials International Edition: DOI: 10.1002/anie.201705042 Surface-Casting Synthesis of Mesoporous Zirconia with a CMK-5-Like Structure and High Surface Area Dong Gu, Wolfgang Schmidt, ChristianM. Pichler, Hans-Josef Bongard, Bernd Spliethoff, Shunsuke Asahina, Zhengwen Cao, Osamu Terasaki, and Ferdi Schüth* Abstract: About 15 years ago, the Ryoo group described the synthesis of CMK-5, a material consisting of a hexagonal arrangement of carbon nanotubes. Extension of the surface casting synthesis to oxide compositions, however, was not possible so far, in spite of many attempts. Here it is demonstrated, that crystalline mesoporous hollow zirconia materials with very high surface areas up to 400 m 2 g À1 , and in selected cases in the form of CMK-5-like, are indeed accessible via such a surface casting process. The key for the successful synthesis is an increased interaction between the silica hard template surface and the zirconia precursor species by using silanol group-rich mesoporous silica as a hard template. The surface areas of the obtained zirconias exceed those of conventionally hard-templated ones by a factor of two to three. The surface casting process seems to be applicable also to other oxide materials. High surface area, nanostructured, crystalline metal oxides are a very interesting class of materials, due to their great potential in various applications. [1–8] Organic-inorganic assem- bly processes, using surfactants [9] or block co-polymers as soft templates, are one feasible pathway for the creation of ordered mesoporous metal oxides. [10–16] Nanocasting from ordered mesoporous silica or carbon as hard template [17] is an alternative, if soft templating fails or only yields ill-crystal- lized materials. However, especially the conditions for removal of the template from the pore system are problem- atic, since many oxides are reducible and/or thermally not stable, which can lead to collapse of the mesostructure. In addition, without special steps the atomic scale structure stays amorphous or is only ill crystallized. Numerous attempts have been reported to enhance the stability of the framework of mesoporous metal oxides, and many of them are successful for selected compositions. [18–22] In addition, often the surface areas of the nanocast metal oxides are rather low, due to structural shrinkage and sintering of primary particles during the thermal treatment. Moreover, since the complete pore system of the mold is filled, and thus the surface area of the cast oxide corresponds to the previously exposed surface of the mold, the achievable surface area is limited. The latter point also prevents the synthesis of some interesting struc- tures, such as hollow tubular arrays as in CMK-5 carbon, with very high surface areas (up to 2500 m 2 g À1 ) and large pore volumes (up to 2.0 cm 3 g À1 ). [23–27] While extension to other compositions has been attempted again and again over the last 15 years, this has not been successful so far. In the following, we describe a surface-casting method for the synthesis of crystalline zirconias with very high surface areas, and in selected cases in form of nanotube arrays (surface cast oxide, SCO), which can be extended also to other oxides. The process relies on a silanol group-rich mesoporous silica as hard template, with a surface function- alization step being crucial for the formation of the thin oxide coating. The resulting materials are interesting for a broad range of applications, including the synthesis of high perfor- mance catalysts and electrode materials. In order to promote surface templating instead of pore- filling templating, interaction of the material to be formed with the templating surface has to be highly favorable over interaction with its own surface. This appeared to be possible with a highly reactive silica surface very rich in silanol groups, which would provide numerous anchor points to form oxo- bridges. Our first attempts where directed to the synthesis of CMK-5 analogues with oxide composition, since for such structures it is most easy to prove the success of the strategy. The synthesis strategy therefore relies on a highly ordered mesoporous silica SBA-15 [28, 29] with such a surface rich in silanol groups as the hard template. It is prepared by a gentle oxidation method using HNO 3 and H 2 O 2 solution at low temperature (80 8C) to remove the block copolymer template, so that no calcination step is required. Compared to the traditional SBA-15, detemplated by calcination (SBA-15- Cal), the SBA-15-OH possesses much more non-crosslinked silanol groups (see Figures S1,S2 in the Supporting Informa- tion), and somewhat larger pore size and higher pore volume (Table 1). The impregnation process with the oxide precursor is thus well-controlled so that the precursor selectively only coats the surface of the pore walls (Scheme in Figure 1). The precursors are subsequently converted to a network of connected, very small metal oxide nanoparticles by high- [*] Dr. D. Gu, Dr. W. Schmidt, C. M. Pichler, H. J. Bongard, B. Spliethoff, Dr. Z. W. Cao, Prof. Dr. F. Schüth Max-Planck-Institut für Kohlenforschung Kaiser-Wilhelm-Platz 1, 45470 Mülheim an der Ruhr (Germany) E-mail: schueth@mpi-muelheim.mpg.de Prof. Dr. O. Terasaki School of Physical Science and Technology, ShanghaiTech Shanghai 200031 (P.R. China) and Department of Materials and Environmental Chemistry, Stockholm University 10691 Stockholm (Sweden) Dr. S. Asahina SM Application Group, JEOL Ltd. 1–2 Musashino 3-Chome Akisima Tokyo 196-8558 (Japan) Supporting information and the ORCID identification number(s) for the author(s) of this article can be found under: https://doi.org/10.1002/anie.201705042. A ngewandte Chemie Communications 11222  2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim Angew. Chem. Int. Ed. 2017, 56, 11222 –11225