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NO dissociation on Cu(111) and Cu(2)O(111) surfaces is investigated using spin-polarized density functional theory. This is to verify the possibility of using Cu-based catalyst for NO dissociation which is the rate limiting step for the NO(x) reduction process. The dissociation of molecularly adsorbed NO on the surface is activated for both cases. However, from the reaction path of the NO-Cu(2)O(111) system, the calculated transition state lies below the reference energy which indicates the possibility of dissociation. For the NO-Cu(111) system, the reaction path shows that NO desorption is more likely to occur. The geometric and electronic structure of the Cu(2)O(111) surface indicates that the surface Cu atoms stabilize themselves with reference to the O atom in the subsurface. The interaction results in modification of the electronic structure of the surface Cu atoms of Cu(2)O(111) which greatly affects the adsorption and dissociation of NO. This phenomenon further explains the obtained differences in the dissociation pathways of NO on the surfaces.

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Self-regenerating automotive catalysts owe their remarkable performance to the repeated motion of the precious metal atoms in and out of the perovskite lattice under fluctuating oxidizing and reducing conditions, preventing coalescence of the metal nanoparticles. Here we use resonant inelastic X-ray scattering to characterize the occupied and unoccupied Pt 5d states in two self-regenerating Pt-perovskite catalysts, CaTi 0.95 Pt 0.05 O 3 and CaZr 0.95 Pt 0.05 O 3 . Upon reduction, the element and symmetry-specific charge excitation spectra reveal a sizable hybridization between the Pt 5d and the Ti 3d or Zr 4d states at the interface between the nanoparticles and the perovskite, which involves the occupied states and is thus invisible in X-ray absorption spectra. A correlation is found between the strength of this d-band hybridization and the proportion of Pt nanoparticles that remain buried below the surface during reduction, indicating that the motion of the Pt atoms toward the surface is hindered by this hybridization specifically, rather than by the Pt−O bonding. These results provide direct evidence that the strength of the metal−metal d-band hybridization plays a pivotal role in determining the efficiency of self-regeneration in perovskite catalysts. ■ INTRODUCTIONSelf-regeneration, a property of some perovskite catalysts to maintain a high activity during aging without requiring addition of excess precious metal, is a major discovery of modern-day automotive catalysis. The prospect of minimizing the amount of precious metal needed to satisfy stringent low-emission vehicle requirements has generated a large interest in the selfregeneration mechanism. A cornerstone of this research effort is the uncovering of the reversible motion of the precious-metal atoms into the perovskite lattice during oxidation, and out, forming nanoparticles on the surface, during reduction. 1 This motion was shown to prevent the agglomeration and growth of the metal particles during vehicle use. The proportion of precious metal cyclically moving in and out of the perovskite, called the self-regeneration ratio, has since then become the yardstick by which the self-regenerating performance is measured. 2 However, to date, little is known about the underlying physical mechanism of self-regeneration, and a unifying picture of self-regeneration and catalytic function is yet to emerge. Moreoever, there have been conflicting reports about the extent to which the precious atoms move out of the perovskite matrix during reduction. 1−4 Although much of the focus in the literature has been on the structural aspect of the self-regeneration mechanism, 1,2,5 we here report a study of the electronic structure of two selfregenerating Pt-doped catalysts, CaTi 0.95 Pt 0.05 O 3 (CTPO) and CaZr 0.95 Pt 0.05 O 3 (CZPO), before and after CO adsorption. We

This study introduces a new insight on the mechanism of selective electrooxidation of hydrazine in alkaline media. The catalytic process takes place on nickel oxide surface of a Ni oxide nano-particle decorated carbon support (NiO/C). The catalyst was synthesized by wet impregnation and a liquid reduction procedure followed by thermal annealing. In-situ X-ray absorption fine structure (XAFS) spectroscopy was used to investigate the reaction mechanism for hydrazine electrooxidation on NiO surface. The spectra of X-ray absorption near-edge structure (XANES) of Ni K-edge indicated that adsorption of OH − on Ni site during the hydrazine electrooxidation reaction. Density functional theory (DFT) calculations were used to elucidate and suggest the mechanism of the electrooxidation and specifically propose the localization of electron density from OH − to 3d orbital of Ni in NiO. It is found that the accessibility of Ni atomic sites in NiO structure is critical for hydrazine electrooxidation. Based on this study, we propose a possible reaction mechanism for selective hydrazine electrooxidation to water and nitrogen taking place on NiO surface as it is applicable to direct hydrazine alkaline membrane fuel cells. Diversification of fuel is important to enhance the versatility of fuel cells as viable power devices for the next generation. Liquid fuel such as methanol, ethanol, borohydride, formic acid, 2-propanol, dimethyl ether and hydrazine are liquid chemical substances that include hydrogen and are considered an energy source in which hydrogen is an electron carrier. The advantages of liquid fuels include, but are not limited to high energy density and ease of handling at both the energy supply and demand sides. In the case of liquid fuel, simple/existing infrastructure, such as conventional petrol stations, is sufficient as for fuel supply, and while the geographic and temporal gap between energy supply and receipt are being filled this would allow to concentrate and leveraging off energy contribution to the expansion of and market penetration of fuel cell technology.Direct hydrazine hydrate fuel cells (DHFCs) utilizing an anion exchange membrane have recently attracted attention as a clean power device. Hydrazine contains no carbon and excretes harmless nitrogen and water by theoretical electroreaction and non-platinum group metal (PGM) catalysts such as Fe, Co, and Ni. These catalysts have been demonstrated for both the anode and cathode electrodes as shown Fig. 1a. The fuel cell vehicle equipped with no PGM as catalysts was demonstrated at SPring-8 in 2013. We believe this demonstration of DHFCs as a power device contributes to the reduction of CO 2 emissions and begins to address the fossil fuel resource problem. If zero CO 2 emission fuel cell vehicles (FCVs), are to be deployed using carbon-free liquid fuel, the emissions of CO 2 would be associated only with the liquid fuel manufacturing facility side and the measures of reduction of CO 2 emission by the transportation sector are would be supported by the depl...