The impact of nanoscience on heterogeneous catalysis  Alexis T. Bell  From Science 2003,299,  Impact factor=27 Viewpoint

Basic knowledge Catalyst Performance Structure Characterization Reaction Structure and effect Material synthesis

Content Introduction Structure and effect Advance in characterization Advance in material synthesis Summary

Introduction Importance of catalysis Importance of dispersed nanoparticles Aim of the present review

Introduction  “one-third of material gross national product in the U.S. involves a catalytic process somewhere in the production chain”  Example: automotive converter  Aim : A. how the local size and composition of catalyst particles affect their performance (their activity and selectivity) B. how advances in nanoscience have contributed to a detailed understanding of the effects of particle composition, size, and structure on catalyst performance.

Structure and effect  Catalyst performance can be sensitive to particle size because the surface structure and electronic properties can change greatly in this size range. Example:  Fischer-Tropsch synthesis(Ni catalyat)  Oxidation of CO to CO 2 (Au/Titania, Fig.)  Oxidative dehydrogenation(ODH) of alkanes to olefins(Vanadia/ZrO 2,Al 2 O 3,MgO)

Structure and effect

 Local composition, as well as particle size, can affect the performance of catalysts. Example:  Remove S from petroleum and petroleum products(Co-MoS 2 /Alumina)  Fischer-Tropsch synthesis(Ru/titania Fig.)

Structure and effect

Advance in characterization  TEM : Information: A. Particle size and shape B. lattice structure and the chemical composition of individual particles  how the shape of metal particles is dictated by interactions of the particles with the support.  how portions of the support migrate to the surface of the metal particles.

Advance in characterization  STM :  Information: Promoter effects  Example:Steam reforming of methane(Au-Ni)

Advance in characterization  AFM (atomic force microscopy)  Example:  It has been possible to image growing polyethylene chains formed on individual Cr atoms supported on silica

Advance in characterization  EXAFS (extended x-ray absorption fine structure)  EXAFS has also been used to obtain evidence for the surface enhancement of one metal on the surface of another in bimetallic catalysts.

Advance in characterization  XPS (x-ray photoelectron spectroscopy)  Information: has been used as well to follow changes in the composition of oxide catalysts as they are placed under reaction conditions.  Example: methane oxidation over Cu 2 O

Advance in materials synthesis  Anchored by bridged agent ( Fig.)  Deposited using the tip of an STM as a molecular paintbrush  Carbon nanotubes hydrazine decomposition: Ir/CNTs

Advance in material synthesis

Summarize  This ongoing progress is rapidly enabling catalyst researchers in academe and industry to achieve the goal of catalysis by design.

 Thank you!