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Ryotaro Kitagawa

Bio: Ryotaro Kitagawa is an academic researcher from Kyushu University. The author has co-authored 1 publications.


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TL;DR: In this article , the authors performed density functional theory (DFT) calculations to study the methane oxidation reaction on a pristine biphenylene network nanosheet to understand its catalytic property.

6 citations

Journal ArticleDOI
TL;DR: In this paper , a set of density functional theory (DFT) calculations on the H-CH3 bond cleavage over the Cu-O-Cu active site in the MOR zeolite with various Al-pair arrangements were performed to obtain molecular insight into the structure-activity relation and clarify key parameters that define the reactivity toward CH4.
Abstract: Understanding the factors that influence the activity of a catalyst toward CH4 activation is of high importance for tuning the catalyst performance or designing new, better catalysts. Here, we performed a set of density functional theory (DFT) calculations on the H-CH3 bond cleavage over the Cu-O-Cu active site in the MOR zeolite with various Al-pair arrangements to obtain molecular insight into the structure-activity relation and clarify key parameters that define the Cu-O-Cu reactivity toward CH4. We found that weakening of the Cu-O-Cu bond during CH4 activation is crucial for determining the O-H bond strength and thus the Cu-O-Cu reactivity. In this regard, the zeolite lattice constraints are found to play a significant role as, on the one hand, it strengthens the Cu⋯Cu interaction and consequently weakens the Cu-O-Cu bonds and, on the other hand, it forces the Cu-O-Cu bond elongation process to destabilize the active site structure. The non-planar Cu-O-Cu geometry, due to lattice constraints, is also found to make the CH4 adsorption site, whether positioned closer to the μ-O or the Cu atom, crucial in determining the C-H activation product, i.e., a ˙CH3 radical or a Cu2-CH3- ligand.

4 citations

Journal ArticleDOI
TL;DR: In this paper , an experimental and computational investigation of dry reforming of methane (DRM) was conducted in the presence of in situ sodium atoms in ZeoA, which increased the catalyst basicity and facilitated the CO 2 adsorption for activation.
Abstract: Experimental and computational investigations of dry reforming of methane (DRM) were conducted in this study. The experimented catalyst, NiOx/ZeoA, was synthesized via the functionalization of nickel salt with oxalate ligand to ensure the deposition of highly downsized Ni nanoparticles strongly interacting with the zeolite A support (ZeoA). The presence of in situ sodium atoms in ZeoA increased the catalyst basicity which facilitates the CO 2 adsorption for activation. The density of states computational result reveals the narrowing of the bandgap and the excitation of 3d electrons of Ni to the conduction band due to the isomorphic substitution of the Al and Si atoms with Ni atoms. The negative charges of the O atoms were found to decrease in intensity owing to the effect of Ni addition. This conferred high CO 2 and methane activation on the catalysts with high stability and resistance to carbon deposition during the DRM reaction. • Synthesis of oxalate ligand functionalized Ni catalysts. • Characterization and activity measurement of the synthesized catalyst. • Computational density of states investigation. • Correlation of the computational and experimental discoveries.

2 citations

Journal ArticleDOI
TL;DR: In this article , the authors performed density functional theory calculations on graphitic MN4G-BN and showed that the addition of B doping adjacent to the Fe and Co centers as well as P doing adjacent to Cu center facilitates a facile O═O bond dissociation with an activation barrier of less than 0.4 eV, resulting in active M-O and inactive B/P-O sites.
Abstract: Graphene-based single-atom catalysts have attracted increasing interest due to their potential to catalyze the direct conversion of CH4 to CH3OH. In particular, the porphyrin-like FeN4 complex has recently been reported to convert CH4 to CH3OH at low temperatures with high selectivity. However, only N2O and H2O2, which are high-cost and scarce compared to O2, can be used as the oxidant of the reaction. In this paper, we perform density functional theory calculations on graphitic MN4G-BN (M = Fe, Co, Cu) and CuN4G-PN systems to evaluate the CH4 oxidation to CH3OH using O2. We found that the addition of B doping adjacent to the Fe and Co centers as well as P doing adjacent to the Cu center facilitates a facile O═O bond dissociation with an activation barrier of less than 0.4 eV, resulting in active M–O and inactive B/P–O sites. This low barrier is due to the early O═O bond elongation at the O2 adsorption step and the stability of the atomically adsorbed O atoms. In the subsequent CH4 oxidation, the resultant OCuN4G-OPN is found to be significantly more CH4-reactive than the OFeN4G-OBN and OCoN4G-OBN with a H–CH3 activation barrier of only 0.66 eV. Such high reactivity is due to the proximity of the electron-acceptor orbital (i.e., the Cu–O lowest unoccupied molecular orbital) toward the Fermi level. Moreover, the CH4 oxidation on CuN4G-PN is predicted to form CH3OH with high exothermicity and high resistance to overoxidation. This study suggests a high possibility for CuN4G-PN as a potential catalyst for the stepwise conversion of CH4 to CH3OH using O2 at low temperatures.