CO adsorption on neutral iridium clusters

The adsorption of carbon monoxide on neutral iridium clusters in the size range of n = 3 to 21 atoms is investigated with infrared multiple photon dissociation spectroscopy. For each cluster size only a single v(CO) band is present with frequencies in the range between 1962 cm-1 (n = 8) and 1985 cm-1 (n = 18) which can be attributed to an atop binding geometry. This behaviour is compared to the CO binding geometries on clusters of other group 9 and 10 transition metals as well as to that on extended surfaces. The preference of Ir for atop binding is rationalized by relativistic effects on the electronic structure of the later 5d metals

Generation of subnanometric platinum with high stability during transformation of a 2D zeolite into 3D

[EN] Single metal atoms and metal clusters have attracted much attention thanks to their advantageous capabilities as heterogeneous catalysts. However, the generation of stable single atoms and clusters on a solid support is still challenging. Herein, we report a new strategy for the generation of single Pt atoms and Pt clusters with exceptionally high thermal stability, formed within purely siliceous MCM-22 during the growth of a two-dimensional zeolite into three dimensions. These subnanometric Pt species are stabilized by MCM-22, even after treatment in air up to 540 degrees C. Furthermore, these stable Pt species confined within internal framework cavities show size-selective catalysis for the hydrogenation of alkenes. High-temperature oxidation-reduction treatments result in the growth of encapsulated Pt species to small nanoparticles in the approximate size range of 1 to 2 nm. The stability and catalytic activity of encapsulated Pt species is also reflected in the dehydrogenation of propane to propylene.This work was funded by the Spanish Government (Consolider Ingenio 2010-MULTICAT (CSD2009-00050) and MAT2014-52085-C2-1-P) and by the Generalitat Valenciana (Prometeo). The Severo Ochoa Program (SEV-2012-0267) is gratefully acknowledged. L.L. thanks ITQ for a contract. The authors also thank the Microscopy Service of UPV for the TEM and STEM measurements. The HAADF-HRSTEM works were conducted in the Laboratorio de Microscopias Avanzadas (LMA) at the Instituto de Nanociencia de Aragon (INA)-Universidad de Zaragoza (Spain), a Spanish ICTS National Facility. Some of the research leading to these results has received funding from the European Union Seventh Framework Program under Grant Agreement 312483-ESTEEM2 (Integrated Infrastructure Initiative-I3). R.A. also acknowledges funding from the Spanish Ministerio de Economia y Competitividad (FIS2013-46159-C3-3-P) and the European Union Horizon 2020 research and innovation programme under the Marie Sldodowska-Curie grant agreement No. 642742.Liu, L.; Díaz Morales, UM.; Arenal, R.; Agostini, G.; Concepción Heydorn, P.; Corma Canós, A. (2017). Generation of subnanometric platinum with high stability during transformation of a 2D zeolite into 3D. Nature Materials. 16(1):132-138. https://doi.org/10.1038/NMAT4757S132138161Boronat, M., Leyva-Perez, A. & Corma, A. Theoretical and experimental insights into the origin of the catalytic activity of subnanometric gold clusters: attempts to predict reactivity with clusters and nanoparticles of gold. Acc. Chem. Res. 47, 834–844 (2014).Flytzani-Stephanopoulos, M. & Gates, B. C. Atomically dispersed supported metal catalysts. Ann. Rev. Chem. Bio. Eng. 3, 545–574 (2012).Gates, B. C. Supported metal clusters: synthesis, structure, and catalysis. Chem. Rev. 95, 511–522 (1995).Corma, A. et al. Exceptional oxidation activity with size-controlled supported gold clusters of low atomicity. Nat. Chem. 5, 775–781 (2013).Yang, M. et al. Catalytically active Au-O(OH)x-species stabilized by alkali ions on zeolites and mesoporous oxides. Science 346, 1498–1501 (2014).Rivallan, M. et al. Platinum sintering on H-ZSM-5 followed by chemometrics of CO adsorption and 2D pressure-jump IR spectroscopy of adsorbed species. Angew. Chem. Int. Ed. 49, 785–789 (2010).Zecevic, J., van der Eerden, A. M., Friedrich, H., de Jongh, P. E. & de Jong, K. P. Heterogeneities of the nanostructure of platinum/zeolite Y catalysts revealed by electron tomography. ACS Nano 7, 3698–3705 (2013).Philippaerts, A. et al. Unprecedented shape selectivity in hydrogenation of triacylglycerol molecules with Pt/ZSM-5 zeolite. Angew. Chem. Int. Ed. 50, 3947–3949 (2011).Kim, J., Kim, W., Seo, Y., Kim, J.-C. & Ryoo, R. n-Heptane hydroisomerization over Pt/MFI zeolite nanosheets: effects of zeolite crystal thickness and platinum location. J. Catalys. 301, 187–197 (2013).Goel, S., Wu, Z., Zones, S. I. & Iglesia, E. Synthesis and catalytic properties of metal clusters encapsulated within small-pore (SOD, GIS, ANA) zeolites. J. Am. Chem. Soc. 134, 17688–17695 (2012).Choi, M., Wu, Z. & Iglesia, E. Mercaptosilane-assisted synthesis of metal clusters within zeolites and catalytic consequences of encapsulation. J. Am. Chem. Soc. 132, 9129–9137 (2010).Choi, M., Yook, S. & Kim, H. Hydrogen spillover in encapsulated metal catalysts: new opportunities for designing advanced hydroprocessing catalysts. ChemCatChem 7, 1048–1057 (2015).Kulkarni, A., Lobo-Lapidus, R. J. & Gates, B. C. Metal clusters on supports: synthesis, structure, reactivity, and catalytic properties. Chem. Commun. 46, 5997–6015 (2010).Guzman, J. & Gates, B. C. Supported molecular catalysts: metal complexes and clusters on oxides and zeolites. Dalton Trans. 1, 3303–3318 (2003).Leonowicz, M. E., Lawton, J. A., Lawton, S. L. & Rubin, M. K. MCM-22: a molecular sieve with two independent multidimensional channel systems. Science 264, 1910–1913 (1994).Camblor, M. A. et al. A new microporous polymorph of silica isomorphous to zeolite MCM-22. Chem. Mater. 8, 2415–2417 (1996).Hyotanishi, M., Isomura, Y., Yamamoto, H., Kawasaki, H. & Obora, Y. Surfactant-free synthesis of palladium nanoclusters for their use in catalytic cross-coupling reactions. Chem. Commun. 47, 5750–5752 (2011).Duchesne, P. N. & Zhang, P. Local structure of fluorescent platinum nanoclusters. Nanoscale 4, 4199–4205 (2012).Lu, J., Aydin, C., Browning, N. D. & Gates, B. C. Imaging isolated gold atom catalytic sites in zeolite NaY. Angew. Chem. Int. Ed. 51, 5842–5846 (2012).Yacamán, M. J., Santiago, U. & Mejía-Rosales, S. in Advanced Transmission Electron Microscopy: Applications to Nanomaterials (eds Francis, L., Mayoral, A. & Arenal, R.) 1–29 (Springer, 2015).Jena, P., Khanna, S. N. & Rao, B. K. Physics and Chemistry of Finite Systems: From Clusters to Crystals (Springer, 1992).Yamasaki, J. et al. Ultramicroscopy 151, 224–231 (2015).Sohlberg, K., Pennycook, T. J., Zhoud, W. & Pennycook, S. J. Insights into the physical chemistry of materials from advances in HAADF-STEM. Phys. Chem. Chem. Phys. 17, 3982–4006 (2015).Aydin, C., Lu, J., Browning, N. D. & Gates, B. C. A ‘smart’ catalyst: sinter-resistant supported iridium clusters visualized with electron microscopy. Angew. Chem. Int. Ed. 51, 5929–5934 (2012).Wei, H. et al. FeOx-supported platinum single-atom and pseudo-single-atom catalysts for chemoselective hydrogenation of functionalized nitroarenes. Nat. Commun. 5, 5634 (2014).Addou, R. et al. Influence of hydroxyls on Pd atom mobility and clustering on rutile TiO2(011)-2 × 1. ACS Nano 8, 6321–6333 (2014).Jung, U. et al. Comparative in operando studies in heterogeneous catalysis: atomic and electronic structural features in the hydrogenation of ethylene over supported Pd and Pt catalysts. ACS Catal. 5, 1539–1551 (2015).Agostini, G. et al. Effect of different face centered cubic nanoparticle distributions on particle size and surface area determination: a theoretical study. J. Phys. Chem. C 118, 4085–4094 (2014).Alexeev, O. & Gates, B. C. EXAFS characterization of supported metal-complex and metal-cluster catalysts made from organometallic precursors. Top. Catal. 10, 273–293 (2000).Chakraborty, I., Bhuin, R. G., Bhat, S. & Pradeep, T. Blue emitting undecaplatinum clusters. Nanoscale 6, 8561–8564 (2014).Zheng, J., Nicovich, P. R. & Dickson, R. M. Highly fluorescent noble-metal quantum dots. Ann. Rev. Phys. Chem. 58, 409–431 (2007).Okrut, A. et al. Selective molecular recognition by nanoscale environments in a supported iridium cluster catalyst. Nat. Nanotech. 9, 459–465 (2014).Zhou, C. et al. On the sequential hydrogen dissociative chemisorption on small platinum clusters: a density functional theory study. J. Phys. Chem. C 111, 12773–12778 (2007).De La Cruz, C. & Sheppard, N. An exploration of the surfaces of some Pt/SiO2 catalysts using CO as an infrared spectroscopic probe. Spectrochim. Acta A 50, 271–285 (1994).Klünker, C., Balden, M., Lehwald, S. & Daum, W. CO stretching vibrations on Pt(111) and Pt(110) studied by sum frequency generation. Surf. Sci. 360, 104–111 (1996).Stakheev, A. Y., Shpiro, E. S., Jaeger, N. I. & Schulz-Ekloff, G. Electronic state and location of Pt metal clusters in KL zeolite: FTIR study of CO chemisorption. Catal. Lett. 32, 147–158 (1995).Heiz, U., Sanchez, A., Abbet, S. & Schneider, W. D. Catalytic oxidation of carbon monoxide on monodispersed platinum clusters: each atom counts. J. Am. Chem. Soc. 121, 3214–3217 (1999).Levitas, V. I. & Samani, K. Size and mechanics effects in surface-induced melting of nanoparticles. Nat. Commun. 2, 284 (2011).Jiang, H., Moon, K.-s., Dong, H., Hua, F. & Wong, C. P. Size-dependent melting properties of tin nanoparticles. Chem. Phys. Lett. 429, 492–496 (2006).Nanda, K. K., Kruis, F. E. & Fissan, H. Evaporation of free PbS nanoparticles: evidence of the Kelvin effect. Phys. Rev. Lett. 89, 256103 (2002).Vajda, S. et al. Subnanometre platinum clusters as highly active and selective catalysts for the oxidative dehydrogenation of propane. Nat. Mater. 8, 213–216 (2009).Ortalan, V., Uzun, A., Gates, B. C. & Browning, N. D. Direct imaging of single metal atoms and clusters in the pores of dealuminated HY zeolite. Nat. Nanotech. 5, 506–510 (2010).Koch, C. Determination of Core Structure Periodicity and Point Defect Density along Dislocations PhD thesis, Univ. Arizona (2002).Mathon, O. et al. The time-resolved and extreme conditions XAS (TEXAS) facility at the European Synchrotron Radiation Facility: the general-purpose EXAFS bending-magnet beamline BM23. J. Synchrotron Radiat. 22, 1548–1554 (2015).Newville, M. IFEFFIT: interactive XAFS analysis and FEFF fitting. J. Synchrotron Radiat. 8, 322–324 (2001)

Modelling human choices: MADeM and decision‑making

Research supported by FAPESP 2015/50122-0 and DFG-GRTK 1740/2. RP and AR are also part of the Research, Innovation and Dissemination Center for Neuromathematics FAPESP grant (2013/07699-0). RP is supported by a FAPESP scholarship (2013/25667-8). ACR is partially supported by a CNPq fellowship (grant 306251/2014-0)