We herein describe a novel use of spherical nanoparticle assemblies of TiO 2 with ultrafine surface concave-convex structure as a catalyst support to prevent the sintering of dispersed metal nanoparticles. Owing to the unique surface structure derived from their fine primary particles, the TiO 2 nanoparticle assemblies show excellent dispersion ability of Au nanoparticles on their rough surface. Extremely exothermic CO oxidation as a probe reaction confirmed the high catalytic activity and stability of Au nanoparticles on the TiO 2 support and sintering resistance even after several cycles of the heat stress reaction at high temperatures.Well-dispersed metal nanoparticles (NPs) have received much attention in many fields of chemistry, physics, materials science, and practical applications, including synthetic chemistry, energy conversion, and environmental issues. [1][2][3][4][5][6][7][8][9][10][11] To obtain good dispersibility of NPs, the surface of metal NPs are directly modified with organic materials or the NPs are mixed with dispersion media such as fatty acids and amines with long alkyl chains. [12][13][14] In the case of heterogeneous catalysts, the dispersion media are called "supports." [15][16][17][18][19][20][21] Metal oxides are the most commonly used supports, because they not only have high heat tolerance and mechanical strength required for very high temperatureÀhigh pressure reactions, but also provide a wide surface area for dilution effect to occur that releases reaction heat. It is also believed that the metal oxide surface affords electronic effect on their catalytic activity of supported metal NPs.In the case of exothermic catalytic reactions, the temperature of catalysts, especially that of the catalyst surface, becomes notably high. Under such high temperature condi-tions, one of the most serious problems is catalyst sintering, because of which several catalyst NPs agglomerate to form large particles. This reduces the activity of catalyst NPs because of the loss of the surface area. [22][23][24][25][26] Ablation of the NPs from the support surface, called leaching, is another common problem that shortens the catalyst life-time. Generally, once the catalyst NPs are sintered or leached, they do not reproduce the original size, morphology, surface area, and crystal structure. Thus, it is better to focus on the prevention of sintering and leaching rather than to regenerate the NPs.To prevent the sintering and leaching of metal NPs, several methods such as alloying, ligand-assisted pinning, fixing on defects, and encapsulating as core-shell/sheath structures by oxides or polymer have been reported. [27][28][29][30][31][32][33][34][35][36][37] These strategies mainly focus on the isolation of the individual nanocatalyst, resulting in low possibility of catalyst aggregation/growth. However, some of them reduce the accessibility of the reactant to the active sites of the catalyst NPs, which lead to a lowering in their reaction rate. Besides, most of their preparation methods are usually complicate...

The Cover Feature shows sintering‐resistant metal catalysts supported on concave‐convex surface of titania nanoparticle assemblies. In their Communication, F. Duriyasart et al. demonstrate that the nano concave‐convex surface of TiO2 support obstructs the movement of catalyst metal nanoparticles as compared to that of a smooth surface support which allows easy movement of the nanoparticles. It was shown that such nanoscale concave‐convex support surfaces effectively prevent sintering of metal nanoparticles, affording and maintaining small‐sized metal nanoparticles which resulted in high catalytic activity. More information can be found in the Communication by F. Duriyasart et al. on page 3392 in Issue 16, 2018 (DOI: 10.1002/cctc.201800624).