Combining first-principles calculations with the particle swarm optimization （PSO） algorithm, we have explored the ground-state structure of Pd2N, whose structure is in debate although it is the first synthesized bi...Combining first-principles calculations with the particle swarm optimization （PSO） algorithm, we have explored the ground-state structure of Pd2N, whose structure is in debate although it is the first synthesized binary platinum group nitride. The ground-state structure is predicted to be tetragonal with space group P^-4m2, which is energetically more favorable than the previously proposed orthorhombic Co2N-type structure. The stability is confirmed by the subsequent calculations on the phonon dispersion curves and elastic constants. Furthermore, the calculated mechanical properties indicate that Pd2N has low incompressibility and is a common hard material.展开更多
N2O is a powerful greenhouse gas and plays an important role in destructing the ozone layer. This present work investigated the effects of Pd doping on N2O formation over Pt/BaO/Al2O3 catalyst. Three types of catalyst...N2O is a powerful greenhouse gas and plays an important role in destructing the ozone layer. This present work investigated the effects of Pd doping on N2O formation over Pt/BaO/Al2O3 catalyst. Three types of catalysts, Pt/BaO/Al2O3, Pt/Pd mechanical mixing catalyst （Pt/BaO/Al203 ＋ Pd/Al2O3） and Pt-Pd co-impregnation catalyst （Pt-Pd/BaO/Al2O3） were prepared by incipient wetness imoreenation method. These catalysts were first evaluated in NSR activity tests using H2/CO as reductants and then carefully characterized by BET, CO chemisorption, CO-DRIFTs and H2-TPR techniques. In addition, temperature programmed reactions of NO with H2/CO were conducted to obtain further information about NzO formation mechanism. Compared with Pt/BaO/Al2O3 （Pt/BaO/Al2O3 ＋ Pd/Al2O3） produced less N2O and more NH3 during NOx storage and reduction process, while an opposite trend was found over （Pt-Pd/BaO/Al2O3 ＋ Al2O3）. Temperature programmed reactions of NO with H2/CO results showed that Pd/Al2O3 component in （Pt/BaO/Al2O3 ＋ Pd/Al2O3） played an important role in NO reduction to NH3, and the formed NH3 could reduce NOx to N2 leading to a decrease in N2O formation. Most of N2O formed over （Pt-Pd/BaO/Al2O3 ＋ Al2O3） was originated from Pd/BaO/Al2O3 component. H2-TPR results indicated Pd-Ba interaction resulted in more difficult- to-reduce PdOx species over Pd/BaO/Al2O3, which inhibits the NO dissociation and thus drives the selectivity to N2O in NO reduction.展开更多
基金Project supported by the Science Foundation of Baoji University of Arts and Sciences,China(Grants Nos.ZK11061,ZK11135,and ZK12048)the Natural Science Foundation of the Education Committee of Shaanxi Province,China(Grant Nos.2013JK0637 and 2013JK0638)the Natural Science Basic Research Plan in Shaanxi Province,China(Grant No.2013JQ1007)
文摘Combining first-principles calculations with the particle swarm optimization （PSO） algorithm, we have explored the ground-state structure of Pd2N, whose structure is in debate although it is the first synthesized binary platinum group nitride. The ground-state structure is predicted to be tetragonal with space group P^-4m2, which is energetically more favorable than the previously proposed orthorhombic Co2N-type structure. The stability is confirmed by the subsequent calculations on the phonon dispersion curves and elastic constants. Furthermore, the calculated mechanical properties indicate that Pd2N has low incompressibility and is a common hard material.
基金Acknowledgements This work was financially supported by the National Key Research and Development Program （No. 2017YFC0211002） and the National Natural Science Foundation of China （Grant No. 21476170）.
文摘N2O is a powerful greenhouse gas and plays an important role in destructing the ozone layer. This present work investigated the effects of Pd doping on N2O formation over Pt/BaO/Al2O3 catalyst. Three types of catalysts, Pt/BaO/Al2O3, Pt/Pd mechanical mixing catalyst （Pt/BaO/Al203 ＋ Pd/Al2O3） and Pt-Pd co-impregnation catalyst （Pt-Pd/BaO/Al2O3） were prepared by incipient wetness imoreenation method. These catalysts were first evaluated in NSR activity tests using H2/CO as reductants and then carefully characterized by BET, CO chemisorption, CO-DRIFTs and H2-TPR techniques. In addition, temperature programmed reactions of NO with H2/CO were conducted to obtain further information about NzO formation mechanism. Compared with Pt/BaO/Al2O3 （Pt/BaO/Al2O3 ＋ Pd/Al2O3） produced less N2O and more NH3 during NOx storage and reduction process, while an opposite trend was found over （Pt-Pd/BaO/Al2O3 ＋ Al2O3）. Temperature programmed reactions of NO with H2/CO results showed that Pd/Al2O3 component in （Pt/BaO/Al2O3 ＋ Pd/Al2O3） played an important role in NO reduction to NH3, and the formed NH3 could reduce NOx to N2 leading to a decrease in N2O formation. Most of N2O formed over （Pt-Pd/BaO/Al2O3 ＋ Al2O3） was originated from Pd/BaO/Al2O3 component. H2-TPR results indicated Pd-Ba interaction resulted in more difficult- to-reduce PdOx species over Pd/BaO/Al2O3, which inhibits the NO dissociation and thus drives the selectivity to N2O in NO reduction.
