Catalysis of Cu Cluster for NO Reduction by CO: Theoretical Insight into the Reaction Mechanism

Density functional theory calculations here elucidated that Cu₃₈-catalyzed NO reduction by CO occurred not through NO dissociative adsorption but through NO dimerization. NO is adsorbed to two Cu atoms in a bridging manner. NO adsorption energy is much larger than that of CO. N-O bond cleavage of the adsorbed NO molecule needs a very large activation energy (ΔG°^‡). On the other hand, dimerization of two NO molecules occurs on the Cu₃₈ surface with small ΔG°^‡ and very negative Gibbs reaction energy (ΔG°) to form ONNO species adsorbed to Cu₃₈. Then, a CO molecule is adsorbed at the neighboring position to the ONNO species and reacts with the ONNO to induce N-O bond cleavage with small ΔG°^‡ and very negative ΔG°, leading to the formation of N₂O adsorbed on Cu₃₈ and CO₂ molecule in the gas phase. N₂O dissociates from Cu₃₈, and then it is readsorbed to Cu₃₈ in the most stable adsorption structure. N-O bond cleavage of N₂O easily occurs with small ΔG°^‡ and significantly negative ΔG° to form the N₂ molecule and the O atom adsorbed on Cu₃₈. The O atom reacts with the CO molecule to afford CO₂ and regenerate Cu₃₈, which is rate-determining. N₂O species was experimentally observed in Cu/γ-Al₂O₃-catalyzed NO reduction by CO, which is consistent with this reaction mechanism. This mechanism differs from that proposed for the Rh catalyst, which occurs via N-O bond cleavage of the NO molecule. Electronic processes in the NO dimerization and the CO oxidation with the O atom adsorbed to Cu₃₈ are discussed in terms of the charge-transfer interaction with Cu₃₈ and Frontier orbital energy of Cu₃₈.

Quantitative Evaluation of the Effect of the Hydrophobicity of the Environment Surrounding Brønsted Acid Sites on Their Catalytic Activity for the Hydrolysis of Organic Molecules

Sulfo-functionalized siloxane gels with a variety of surface hydrophobicities were fabricated to elucidate the effect of the environment surrounding the Brønsted acid site on their catalytic activity for the hydrolysis of organic molecules. A detailed structural analysis of these siloxane gels by elemental analysis, X-ray photoelectron spectroscopy, Fourier-transformed infrared (FT-IR), and ²⁹Si MAS NMR revealed the formation of gel catalysts with a highly condensed siloxane network, which enabled us to quantitatively evaluate the hydrophobicity of the environment surrounding the catalytically active sulfo-functionality. A sulfo group in a highly hydrophobic environment exhibited excellent catalytic turnover frequency for the hydrolysis of acetate esters with a long alkyl chain, whereas not only conventional solid acid catalysts but also liquid acids showed quite low catalytic activity. Detailed kinetic studies corroborated that the adsorption of oleophilic esters at the Brønsted acid site was facilitated by the surrounding hydrophobic environment, thus significantly promoting hydrolysis under aqueous conditions. Furthermore, sulfo-functionalized siloxane gels with a highly hydrophobic surface showed excellent catalytic activity for the hydrolytic deprotection of silyl ethers.

The importance of direct reduction in the synthesis of highly active Pt–Sn/SBA-15 for n-butane dehydrogenation

Supported Pt–Sn bimetallic catalysts directly reduced by H₂ are highly active for the dehydrogenation of n-butane, while the catalysts calcined in air, followed by H₂ reduction are totally inactive.

Effect of perimeter interface length between 2D WO3 monolayer domain and γ-Al2O3 on selective hydrogenolysis of glycerol to 1,3-propanediol

The perimeter interface between WO₃ and γ-Al₂O₃ was found to play an important role in selective hydrogenolysis of glycerol to 1,3-propanediol.

Concerted Catalysis by Adjacent Palladium and Gold in Alloy Nanoparticles for the Versatile and Practical [2+2+2] Cycloaddition of Alkynes

A Pd-Au alloy efficiently catalyzed the [2+2+2] cycloaddition of substituted alkynes. Whereas monometallic Pd and Au catalysts were totally ineffective, Pd-Au alloy nanoparticle catalysts with a low Pd/Au molar ratio showed high activity to give the corresponding polysubstituted arenes in high yields. A variety of substituted alkynes participated in various modes of cycloaddition under Pd-Au alloy catalysis. The Pd-Au alloy catalysts exhibited high air tolerance and reusability.

Estimation of Arterial Mechanical Properties from Aortic and Tonometric Arterial Pressure Waveforms

Although arterial mechanical properties have been evaluated using arterial input impedance, the relative difficulty in accurate flow measurement made the value of impedance somewhat limited. To develop an alternative method to evaluate arterial mechanical properties, we analyzed the aortic pressure (AoP)-radial arterial pressure (RAP) relationship because of relative ease in obtaining peripheral pressure waveform by tonometry. In 8 patients we simultaneously recorded aortic root and radial arterial pressure waveforms. We calculated the transfer function from AoP to RAP. We then fitted the transfer function to a model of a lossless uniform elastic tube terminated with a modified Windkessel model. The fact that the model transfer function predicted AoP from RAP waveform with considerable accuracy indicated that the model represented the arterial mechanical properties well. We conclude that we can estimate the arterial mechanical properties by the pressure-pressure transfer function analysis.