Periodic density functional study of Rh and Pd interaction with the (100)MgO surface

The adsorption geometry and electronic properties of palladium and rhodium atoms deposited on the regular (100)MgO surface were analyzed by means of periodic DFT calculations using local, gradient-corrected and hybrid (B3LYP) functionals. Spin-polarized computations revealed doublet spin state of Rh atom to be the most stable electronic state for the adsorbed rhodium atom on (100)MgO. The preferred adsorption site of the metal (Pd and Rh) atoms was found to be the site on top of the surface oxygen atoms. A relatively stable geometry for the adsorption of the Pd and Rh in a bridge position above the two surface oxygens was found as well. The electronic structures suggested partly covalent bonding with contribution from electrostatic attraction between the metal and the oxygen atoms for both optimized structures. Small charge transfer was obtained from the support to the Pd and Rh metal atoms. The calculations showed that rhodium was bound stronger to the substrate probably due to stronger polarization effects

A DFT study of the NO adsorption on Pdn (n = 1–4) clusters

We report a density-functional study of some properties of the adsorption process of the NO molecule on small palladium clusters (n = 1–4). The interaction between NO and the Pdn clusters is studied on various adsorption sites. Both, NO and Pdn geometrical relaxations are taken into account. The significant conformational reconstruction of the metallic cluster upon NO adsorption induces a large decrease of the NO adsorption energy. Nevertheless, the N–O binding energy is strongly weakened when the molecule is adsorbed on the small Pdn clusters due essentially to an electrostatic repulsion between both N and O atoms. The possible dissociation process of NO on Pd4 cluster is then investigated within two processes: the NO molecule does not dissociate on Pd4 with process (i) (dissociation of the isolated gas phase NO molecule followed by the adsorption of both nitrogen and oxygen atoms on the cluster). Process (ii)which presents three successive steps (adsorption of the NO molecule, dissociation of the NO molecule adsorbed on Pd4, adsorption of the O atom on the cluster) is studied in details and we propose a reaction pathway locating transition states and intermediate species. The activation energy for process (ii) is high and the dissociation of the NO molecule on the Pd4 cluster is thus highly improbable

Assessment of the Heat Capacity by Thermodynamic Approach Based on Density Functional Theory Calculations

The theoretical aspects of the thermodynamic calculation of the Gibbs energy and heat capacity of a crystalline system within the frame of the Density Functional Theory (DFT) are introduced in the present chapter. Various approximations of phonon motion (harmonic, quasiharmonic, and anharmonic) and their effects on the thermodynamic properties are discussed. The theoretical basis of the thermodynamic approach of the heat capacity of crystals for given thermodynamic conditions is presented, having as example six polymorphs of the magnesium hydrides

Studies on homogeneous and immobilized metal carbonyl clusters on inorganic oxide

A detailed investigation of the reaction between Os3(C))12 and Ru3(CO)12 with HOR (R &#61; CH3, SiPh3), HOOCR (R &#61; H, CH3) and 2,4-pentanedione was undertaken and the products of the form (&mu;-H)M_3(CO)_10(L) and [ M_3(CO)_10L^-] were characterized by i.r. and n.m.r. spectroscopies. The substitution of (&mu;-H)Os3(CO)10(O2CCH3) with phosphines is studied and the resulting cluster compounds(&mu;-H)Os_3(CO)_9(O_2CCH_3)(PPh_3) isolated and characterized by i.r. and n.m.r. spectroscopies. Infrared and raman spectroscopic studies of triosmium and triruthenium hydride carbonyl clusters were carried out to determine the hydrogen vibrational frequencies. The hydride modes of vibration in (&mu;-H)2M3(CO)10, (&mu;-H)_2M_3(CO)_9(E), (E &#61; S, PPh) and (&mu;-H) (&mu;-E')Os_3(CO)_10 (E' &#61; OR, O_2CR and acac) clusters were compared and the ability to identify particular co-ordination modes of hydrogen established. The immobilization of metal carbonyl clusters onto inorganic oxide and phosphine functionalized supports was investigated by i.r. and solid state magic angle spinning n.m.r. The triosmium and triruthenium carbonyls were shown to react with silica and alumina to form [(&mu;-H)M3(CO)_10-O O-silica/alumina] or [(&mu;-H)M3(CO)10-O-silica/alumina] in mild conditions. The reaction of Os3(CO)11(L) and H20s3(CO)10(L) (L &#61;PPh2(CH)2Si(OEt)3) with silica was shown to give intact supported species, while a surface attached cluster (&mu;-H)Os_3(CO)9(L)break (O O-silica) is proposed to result in the case of (&mu;-H)_2Os_3(CO)_9(L). The rhodium carbonyls Rh4(CO)_11(L) and Rh6(CO)_15(L) were found to form initially [ Rh_4(CO)_11(L')] and Rh_6(CO)_15(L') (L' = PPh_2(CH_2)_2Si-(OEt)_3-x(OSi&equiv;)x) which decompose on exposure to air to a common surface containing L'Rh(I)(O)2and Rh(I)(CO2)2. The direct interaction of Rh4(CO)12 and RH6(CO)16, at room temperature, with phosphinated silica was shown to result in initial formation of Rh (CO)12-x(L')x' x = 1,2 and complex surface, containing Rh6(CO)16-x(L')x x = 1, LRh(I)(CO)2, Rh(I)(CO)2fragments and CO covered metallic rhodium. (D74035/87)</p