LETTERS PUBLISHED ONLINE: 11 NOVEMBER 2012 | DOI: 10.1038/NMAT3471 Towards stable catalysts by controlling collective properties of supported metal nanoparticles Gonzalo Prieto 1 , Jovana Zeˇ cevi´ c 1 , Heiner Friedrich 2 , Krijn P. de Jong 1 * and Petra E. de Jongh 1 * Supported metal nanoparticles play a pivotal role in areas such as nanoelectronics, energy storage/conversion 1 and as catalysts for the sustainable production of fuels and chemicals 2–4 . However, the tendency of nanoparticles to grow into larger crystallites is an impediment for stable performance 5,6 . Exemplarily, loss of active surface area by metal particle growth is a major cause of deactivation for supported catalysts 7 . In specific cases particle growth might be mitigated by tuning the properties of individual nanoparticles, such as size 8 , composition 9 and interaction with the support 10 . Here we present an alternative strategy based on control over collective properties, revealing the pronounced impact of the three-dimensional nanospatial distribution of metal particles on catalyst stability. We employ silica-supported copper nanoparticles as catalysts for methanol synthesis as a showcase. Achieving near-maximum interparticle spacings, as accessed quantitatively by electron tomography, slows down deactivation up to an order of magnitude compared with a catalyst with a non-uniform nanoparticle distribution, or a reference Cu/ZnO/Al 2 O 3 catalyst. Our approach paves the way towards the rational design of practically relevant catalysts and other nanomaterials with enhanced stability and functionality, for applications such as sensors, gas storage, batteries and solar fuel production. Metal nanoparticle growth can proceed through migration and coalescence of particles (sintering) or through transport of monoatomic or molecular species between individual particles (Ostwald ripening) 7 . Strategies to mitigate particle growth comprise alloying with a higher-melting point metal 9 and increasing the metal–support interaction energy by using specific oxides as carriers 10 . However, these approaches are not generally applicable because they restrict the catalyst chemical composition and therefore function. Recently, the encapsulation of individual colloidal nanoparticles in porous inorganic shells has received much attention 11,12 . Albeit conceptually elegant, bottom-up approaches at the single-nanoparticle level face challenges for large-scale production and usage. We present an alternative approach, using nanoparticle assembly tools to tune the stability-relevant collective properties of supported metal particles, that is, their spatial distribution at the nanoscale. Metal nanoparticles dispersed on a porous carrier are widely used as solid catalysts 13 . Irregular spatial distributions and ultra- short interparticle distances are quite common for technical cata- lysts. For instance, clustering of metal nanoparticles in high-density assemblies is known to occur for Ni–Mo/Al 2 O 3 and Co–Pt/Al 2 O 3 catalysts industrially employed in processes such as the sulphur removal from hydrocarbon feedstocks and the Fischer–Tropsch 1 Inorganic Chemistry and Catalysis, Debye Institute for Nanomaterials Science, NL-3584 CG Utrecht University, The Netherlands, 2 Laboratory of Materials and Interface Chemistry, Eindhoven University of Technology, NL-5600 MB Eindhoven, The Netherlands. *e-mail:k.p.deJong@uu.nl; p.e.deJongh@uu.nl. synthesis of fuels from synthesis gas, respectively 13,14 . Furthermore, commercial methanol synthesis catalysts typically consist of Cu particles (about 5–10 nm) spaced by smaller ZnO crystallites 15 . Nanoparticle spatial distributions might have a large significance for catalyst stability, given that metal particle growth is a rele- vant deactivation mechanism for commercial catalysts. Although on a micrometre scale metal distributions can be controlled to some extent (for instance egg-shell or egg-yolk distributions), the three-dimensional (3D) spatial distribution of metal particles on a nanometre scale is until now typically an uncontrollable outcome of the preparation process. In contrast, our work shows control over the size and location of active metal species while employing industrially relevant preparation tools, in this case impregnation of porous carriers with inexpensive metal precur- sors such as nitrates 16–18 . Quantitative information on the 3D nanospatial distribution of the metal particles is indispensable if we want to understand the stability of supported nanoparticles, and progress from 2D flat model substrates towards more realistic 3D support morphologies. This information is provided by electron tomography, which has emerged as a major tool in material science 19–21 . Electron tomography allows derivation of metal particle size distributions and nanospatial locations. In this work we also employ pore-specific analysis, which relates particle locations to the local support pore morphology. We combine these tools to demonstrate exceptional stability by control over the nanospatial distribution of supported metal particles, using Cu–Zn/SiO 2 catalysts for methanol synthesis as a case in point. The industrial production of methanol from synthesis gas (CO/CO 2 /H 2 ) amounts worldwide to more than 35 × 10 6 t yr −1 and uses Cu/ZnO/Al 2 O 3 as a catalyst. Growth of the Cu crystallites is the main deactivation pathway under standard plant conditions. In this study we employ as a support material ordered mesoporous silica (SBA-15; ref. 22) to facilitate quantitative image analysis. Samples based on industrial SiO 2 -gel supports with 3D interconnected pore networks were also investigated to validate the wider significance of our results. The CuZn/SiO 2 catalysts were prepared by impregnation using an aqueous solution of metal nitrates. Building on a recent mechanistic insight 17 , for the first time we succeeded in preparing exclusively <6 nm Cu nanoparticles at relatively high metal loadings. In particular, effective water removal at low temperatures was essential to avoid the large metal agglomerates and bimodal size distributions previously observed 17 (see Supplementary Methods). The dried impregnate was heated to 723 K (referred to as calcination hereafter) under either N 2 or 2% NO/N 2 flow. Samples are labelled as CuZn/x (y ), where x = S (SBA-15) or Sgel (SiO 2 -gel) and y = N 2 or NO according to the 34 NATURE MATERIALS | VOL 12 | JANUARY 2013 | www.nature.com/naturematerials