Vibrational mode-specific reaction of methane on a nickel surface

Laboratoire Chimie Physique Moléculaire, Ecole Polytechnique Fédérale de Lausanne, CH-1015 Lausanne, Switzerland.
Science (Impact Factor: 33.61). 11/2003; 302(5642):98-100. DOI: 10.1126/science.1088996
Source: PubMed


The dissociation of methane on a nickel catalyst is a key step in steam reforming of natural gas for hydrogen production. Despite substantial effort in both experiment and theory, there is still no atomic-scale description of this important gas-surface reaction. We report quantum state-resolved studies, using pulsed laser and molecular beam techniques, of vibrationally excited methane reacting on the nickel (100) surface. For doubly deuterated methane (CD2H2), we observed that the reaction probability with two quanta of excitation in one C-H bond was greater (by as much as a factor of 5) than with one quantum in each of two C-H bonds. These results clearly exclude the possibility of statistical models correctly describing the mechanism of this process and attest to the importance of full-dimensional calculations of the reaction dynamics.

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    ABSTRACT: The surface grating technologies enable to control the thermal radiation spectrum. We are applying this technique to promote the chemical reaction to produce hydrogen in the methane steam reforming process by spectrally resonant thermal radiation. The thermal radiation spectrum is adjusted to vibrational absorption bands of methane and water molecules near 3 µm by making a two-dimensional surface grating of period Λ=2.6 µm on the radiative surface. By matching the peak of thermal radiation to the absorption bands of gases, it is clearly observed that the hydrogen production is promoted five times as much as the case without spectrally resonant thermal radiation by the optical excitation of vibrational energy levels of molecules. From a series of experiments and analysis, it is suggested that radiative gas effectively excited the molecules up of high energy vibrational and rotational levels, and this lead to the high production rate of hydrogen in methane steam reforming process.
    Proceedings of SPIE - The International Society for Optical Engineering 08/2008; 7044. DOI:10.1117/12.794775 · 0.20 Impact Factor
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    ABSTRACT: Dielectric barrier discharge (DBD) and packed-bed reactor (PBR) are two of the commonly used nonthermal-plasma (NTP) reactors. In this paper, these two reactors are applied to remove two perfluorocompounds (PFCs), i.e., CF4 and SF6, which are extensively used in semiconductor- and liquid-crystal- display-manufacturing industries. Experimental results indicated that PBR constructed by packing dielectric pellets (chemical com- positions: CuO 64%, ZnO 24%, Al2O3 10%, and MgO 2% by weight) inside the DBD reactor achieved a higher CF4 removal efficiency and a lower SF6 removal efficiency than that of the DBD reactor. In other words, different behavior between CF4 and SF6 removal efficiencies achieved with two different types of NTP reactors was found in this paper. To elucidate this inter- esting finding, the influences of the discharge power, the reactor temperature, the catalytic effect, the nature of pollutants, and the plasma characteristics of DBD and PBR were investigated. It is found that the last two factors are mainly responsible for the interesting finding. At the same discharge gap, it is well known that PBR possesses higher mean electron energy than nonpacked plasma reactor (like DBD). Nevertheless, the dissociative attach- ment reaction of SF6 : SF6 + e → SF − 5 + F plays an important role for SF6 removal at low-electron-energy region. Therefore, a nonpacked plasma reactor is more suitable for SF6 removal; on the contrary, a PBR with higher mean electron energy is favorable for CF4 abatement. The finding provides useful information on selecting an appropriate NTP reactor for removing a specific PFC. Index Terms—Dielectric barrier discharge (DBD), greenhouse gases (GHGs), nonthermal plasma (NTP), packed-bed reactor (PBR), perfluorocompounds (PFCs), semiconductor-manufactur- ing industry.
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