Yuji Mahara

Enhanced activity for methane combustion over a Pd/Co/Al2O3 catalyst prepared by a galvanic deposition method

A Pd/Co/Al2O3 catalyst prepared by a galvanic deposition method exhibited notable catalytic activity for methane combustion, due to the higher reducibility of PdO nanoparticles on CoOx.

The Metal–Support Interaction Concerning the Particle Size Effect of Pd/Al2O3 on Methane Combustion

The particle size effect of Pd nanoparticles supported on alumina with various crystalline phases on methane combustion was investigated. Pd/θ, α-Al2 O3 with weak metal-support interaction showed a volcano-shaped dependence of the catalytic activity on the size of Pd particles, and the catalytic activity of the strongly interacted Pd/γ-Al2 O3 increased with the particle size. Based on a structural analysis of Pd nanoparticles using CO adsorption IR spectroscopy and spherical aberration-corrected scanning/transmission electron microscopy, the dependence of catalytic activity on Pd particle size and the alumina crystalline phase was due to the fraction of step sites on Pd particle surface. The difference in fraction of the step site is derived from the particle shape, which varies not only with Pd particle size but also with the strength of metal-support interaction. Therefore, this interaction perturbs the particle size effect of Pd/Al2 O3 for methane combustion.

Methane combustion over Pd/CoAl2O4/Al2O3 catalysts prepared by galvanic deposition

Pd/CoAl2O4/Al2O3 methane combustion catalysts were synthesized using a galvanic deposition (GD) method (PdCoAl-GD). This PdCoAl-GD catalyst showed higher activities and turnover frequencies (TOFs) than conventional Pd/Al2O3. According to X-ray diffraction (XRD), X-ray absorption fine structure (XAFS) and scanning transmission electron microscopy (STEM) measurements, PdCoAl-GD was composed of a CoAl2O4 phase supported on γ-Al2O3 and dispersed Pd nanoparticles of 2–7 nm in size on CoAl2O4. Operando Pd K-edge XAFS measurements indicated that the Pd in PdCoAl-GD was oxidized to highly active methane combustion PdO species at low temperatures. PdCoAl-GD also showed high activity (light-off tests) when PdO was initially present on the catalysts. Methane temperature-programmed reaction (CH4-TPR) measurements on PdCoAl-GD revealed that PdO was reduced by CH4 at low temperatures. The GD method used herein achieved PdO species that were effective for C–H activation.

Direct Synthesis of Lactams from Keto Acids, Nitriles, and H2 by Heterogeneous Pt Catalysts

We report herein the first general catalytic system for the direct synthesis of N‐substituted γ‐ and δ‐lactams by reductive amination/cyclization of keto acids (including levulinic acid) with nitriles and H2 under mild conditions (7 bar H2, 110 °C, solvent free). The most effective catalyst, Pt and MoOx co‐loaded TiO2 (Pt‐MoOx/TiO2), shows a wide substrate scope, high turnover number (TON), and good reusability.

Metal‐Support Interaction Concerning Particle Size Effect of Pd/Al₂O₃ on Methane Combustion

This paper investigated the particle size effect of Pd nanoparticles supported on alumina with various crystalline phases on methane combustion. Pd/θ, α-Al₂O₃ with weak metal-support interaction showed a volcano-shaped dependence of the catalytic activity on the size of Pd particles, and the catalytic activity of the strongly interacted Pd/γ-Al₂O₃ increased with the particle size. Based on a structural analysis of Pd nanoparticles using CO adsorption infrared spectroscopy and spherical aberration corrected scanning/transmission electron microscopy, the dependence of catalytic activity on Pd particle size and the alumina crystalline phase was due to the fraction of step sites on Pd particle surface. The difference in fraction of the step site is derived from the particle shape, which varies not only with Pd particle size but also with the strength of metal-support interaction. Therefore, the metal-support interaction perturbs the particle size effect of Pd/Al₂O₃ for methane combustion.

Synthesis of Supported Bimetal Catalysts using Galvanic Deposition Method

Supported bimetallic catalysts have been studied because of their enhanced catalytic properties due to metal-metal interactions compared with monometallic catalysts. We focused on galvanic deposition (GD) as a bimetallization method, which achieves well-defined metal-metal interfaces by exchanging heterogeneous metals with different ionisation tendencies. We have developed Ni@Ag/SiO2 catalysts for CO oxidation, Co@Ru/Al2 O3 catalysts for automotive three-way reactions and Pd-Co/Al2 O3 catalysts for methane combustion by using the GD method. In all cases, the catalysts prepared by the GD method showed higher catalytic activity than the corresponding monometallic and bimetallic catalysts prepared by the conventional co-impregnation method. The GD method provides contact between noble and base metals to improve the electronic state, surface structure and reducibility of noble metals.

Time Resolved in situ DXAFS Revealing Highly Active Species of PdO Nanoparticle Catalyst for CH4 Oxidation

The highly active species of Pd/Al2O3 catalysts for methane combustion was revealed by in situ time‐resolved dispersive X‐ray absorption fine structure (DXAFS) spectroscopy. By using CH4 as a reduction agent, PdO in Pd/Al2O3 is reduced in a 2‐step model involving Pd0 nucleation and growth of Pd0 domain in a PdO particle. Kinetic analysis of the 2‐step model reduction of PdO nanoparticles leads to a suggestion that partial formation of Pd0 in a PdO particle accelerates methane combustion.