ABSTRACT
Sulfides poisoning of metallic Ni is an important issue in catalyst deactivation. SO2, similar to H2S and other sulfides, is an impurity presented in reactants or during the regeneration steps. Herein, spin-polarized density functional theory calculations were used to study the adsorption and decomposition of SO2 on a pristine and metal-doped Ni(111) surface. The adsorption energy, transition state energy, and partial density of state (PDOS) were calculated. On the pristine Ni(111) surface, ten different configurations were considered, and three typical ones were selected for transition state searching. It was found that the reaction barrier of the first S-O bond dissociation was much higher than that of the second one. Doping the top layer with a second metal could strongly change the adsorption and decomposition behavior. Doping with 3/9ML Co slightly increases the adsorption energy of SO2 for most configurations and decreases the reaction barriers of the SO2-tht-2 decomposition, while the others decrease the adsorption ability and increase the barriers. The order of adsorption energy for the most stable configurations is Co > Ni > Cu > Rh > Pd. The order of the first S-O bond dissociation reaction barriers is Pd > Rh > Cu = Ni > Co, and the order of the second bond dissociation barrier is Rh > Pd > Cu > Ni > Co.
ABSTRACT
Temperature- and magnetic-field-dependent measurements of the loss tangent in Ba(Zn(1/3)Ta(2/3))O(3) doped with transition metals (Mn, Ni) are compared to those from samples doped with other impurities (Cd, Ga, Mg, and Zr). These results, combined with pulsed electron paramagnetic resonance measurements, show conclusively that microwave loss in transition-metal-doped Ba(Zn(1/3)Ta(2/3))O(3) at cryogenic temperatures is attributable to resonant spin excitations of unpaired transition-metal d electrons in isolated atoms (light doping) or exchange coupled clusters (moderate to high doping), a mechanism that differs from the usual suspects.
