Neutron diffraction studies catalysis

The [M2(CX))io(p--H)] derivatives have been die subject of several recent structural studies. X-ray and infrared studies on its tetraethylammonium salt, (Cr2(CO)io(p.-H)], first indicated this to be die first example of a species containing a linear electron-deficient M-H-M system. Hiis was later found to be nonlinear by neutron diffraction studies. The chemical reactivity of these complex species is currendy being studied, because they are of interest both for their applications in catalysis and for the preparation of other metal carbonyls. The [Cr2(CO)io( J.-H)] complex, for example, is easily converted into [Cr2(CO),o(p.-X)] or into [Cr(CO)5X], thus providing a simple and rsqiid method for a high-yield synthesis of these species. ... 

The active site on the surface of selective propylene anmioxidation catalyst contains three critical functionalities associated with the specific metal components of the catalyst (37—39) an CC-H abstraction component such as Bi3+, Sb3+, or Te4+ an olefin chemisorption and oxygen or nitrogen insertion component such as Mo6+ or Sb5+ and a redox couple such as Fe2+/Fe3+ or Ce3+/ Ce4+ to enhance transfer of lattice oxygen between the bulk and surface of the catalyst. The surface and solid-state mechanisms of propylene ammoxidation catalysis have been determined using Raman spectroscopy (40,41), neutron diffraction (42—44), x-ray absorption spectroscopy (45,46), x-ray diffraction (47—49), pulse kinetic studies (36), and probe molecule investigations (50). 

H. Knozinger, Handbook of Heterogeneous Catalysis, vol. 2 (WUey/VCH, Weinheim, 1997) M. Armandi, B. Bonelli, I. Bottero, C.O. Arean, E. Garrone, Thermodynamic features of the reaction of ammonia with the acidic proton of H-ZSM-5 as studied by variable-temperature IR spectroscopy. J. Phys. Chem. C 114(14), 6658-6662 (2010). doi 10.1021/Jpl00799k G. Artioli, C. Lamberti, G.L. Marra, Neutron powder diffraction study of orthorhombic and monoclinic defective sUicaUte. Acta CrystaUogr. Sect. B Stmct. Sci. 56, 2-10 (2000)... 

Naturally, a fundamental requirement is the determination of the structure of the molecular sieves imder study (cf. Voliune 2) through techniques such as X-ray diffraction, neutron scattering, electron microscopy and so on. However, a remarkably broad variety of methods and tools are at our disposal for characterizing the physical and chemical properties of molecular sieves. Voliune 4 of the series Molecular Sieves - Science and Technology focuses on the most widely used spectroscopic techniques. Thereby, the contributions to this voliune not only review important applications of these techniques, but also comprise, to a greater or lesser extent, the basic principles of the methods, aspects of instrumentation, experimental handling, spectra evaluation and simulation, and, finally, employing spectroscopies in situ for the elucidation of processes with molecular sieves, e.g. synthesis, modification, adsorption, diffusion, and catalysis. 

By the 1980s most of the aluminosilicate zeolites currently used industrially were known, and the emphasis shifted to the study of these materials using a range of powerful new techniques that came of age at this time. These included, in particular, solid state NMR, X-ray and neutron powder diffraction analysis, high resolution electron microscopy and computational methods. All were ideal for the study of structural details of solids that were rarely available, and never used in industrial applications, other than as microcrystalline powders. All these techniques are applicable to the bulk of the solid - this in turn makes up the (internal) surface, which is accessible to adsorbed molecules. Since the techniques are able to operate under any conditions of gas pressure, they may be used to extract structural details in situ under the operating conditions of ion exchange, adsorption and catalysis. In particular, zeolitic systems have proved ideal for the study, understanding and subsequent improvement of solid acid catalysts. 

Understanding of the modification from bulk liquid water behavior when water is introduced into pores of porous media or confined in the vicinity of metallic surfaces is important in technological problems such as oil recovery from natural reservoirs, mining, heterogeneous catalysis, corrosion inhibition, and numerous other electrochemical processes. Water in porous materials such as Vycor glass, silica gel, and zeolites has been actively under investigation because of their relevance in catalytic and separation processes. In particular, the structure of water near layer-like clay minerals [11,12], condensed on hydroxylated oxide surface [13], confined in various types of porous silica [14-22] or in carbon powder [23] has been studied by neutron and/or x-ray diffraction. 

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