99Tc NMR of Technetium and Technetium - Ruthenium Metal Nanoparticles [chapter]

V. P. Tarasov, Yu. B. Muravlev, N. N. Popova, K. E. Guerman
2002 Magnetic Resonance in Colloid and Interface Science  
The properties of metals are related to their electronic structure and crystal structure. Small clusters of metal atoms exhibit extraordinary physical and electronic properties, caused by size effects, namely, by the surface-to-volume ratio and discreteness of electronic levels [1] . Bulk technetium metal has a hexagonal close-packed lattice with parameters a = 2.735 and c/a = 1.6047; technetium films less than 150 Å thick are characterized by a fcc lattice with a = 3.68 Å [2, 3] . Also, bulk
more » ... thenium metal has a hcp lattice with a = 2.704A and c/a = 1.5809. Tc-Ru alloys are infinite solid solutions [4] . One of the most important characteristics of the metal electronic structure is the density of states at the Fermi level N(E F ). For the two most probable states of technetium, (4d 6 5s 1 ) and (4d 5 5s 2 ), the calculated N(E F ) values are 12.25 and 11.87 states/(Ry atom), respectively [5] . The bulk densities of states in Tc and Ru metal are the same [6] . The experimental characteristics that reflect the metal electronic state and structure are NMR parameters, such as the Knight isotropic shift (K), its anisotropy (K an ), spin-lattice relaxation time (T 1 ), line width (∆ν), quadrupole coupling constant (C Q ), and asymmetry parameter η of the electric field gradient tensor. We have recently determined these parameters for a technetium metal powder with a grain size of 50-100 µm: K = 6872 ppm, K an = -400 ppm, (T 1 × T) -1 = 3.23 s -1 K -1 , C Q = 5.74 MHz, and η = 0 [7]. For the bulk ruthenium metal at 4.2 K, the Knight shift is 4900 ppm [8] . We are interested in comparing these characteristics with those for technetium nanoparticles. Here, we present the results of studying technetium and technetium-ruthenium of oxide-supported catalysts by 99 Tc NMR on supports with different crystal structures and specific surfaces. As is known, small technetium mono-and bimetallic particles on different supports are active catalysts [2] . Metallic active states at the inert oxide support surface are believed to be the cause of catalytic properties of the material formed. In the case of bimetallic catalysts, an increase in catalytic activity (synergism) is due to the formation of intermetallic compounds.
doi:10.1007/978-94-010-0534-0_40 fatcat:ezizq45d4veqpnxvfl2lm4tu4u