Ja Hun Kwak

Bonding Oxides and Metals The binding of noble metals that can act as catalysts to metal oxides that are reducible is assumed to occur at the exposed cation of the oxide. For nonreducable oxides such as aluminum oxide, it is not so obvious how the metal can bind strongly. Kwak et al. (p. 1670 ) used a combination of high-resolution transmission electron microscopy and solid-state magic-angle spinning nuclear magnetic resonance to study the anchoring of platinum at high and low loadings on alumin

The catalytic performance of a series of Ru/Al2O3 catalysts with Ru content in the 0.1–5% range was examined in the reduction of CO2 with H2. At low Ru loadings (≤0.5%) where the active metal phase is highly dispersed (mostly atomically) on the alumina support, CO is formed with high selectivity. With increasing metal loading, the selectivity toward CH4 formation increases, while that for CO production decreases. In the 0.1% Ru/Al2O3 catalyst, Ru is mostly present in atomic dispersion, as scanni

H(2)-TPR and FTIR were used to characterize the nature of the Cu ions present in the Cu-SSZ-13 zeolite at different ion exchange levels. The results obtained are consistent with the presence of Cu ions at two distinct cationic positions in the SSZ-13 framework.

Because of their heterogeneous nature, supported metal catalysts always contain metal centers in a rather broad dispersion range, and the presence of even atomically dispersed metals has been reported on oxide supports. The role of the atomically dispersed metal centers in the overall catalytic performances of these supported metal catalysts, however, has not been addressed to date. In this study, temperature programmed reaction and scanning transmission electron microscopy experiments were appl

In this work, the structural stability of γ-alumina (γ-Al2O3) was investigated by a combination of XRD and high-resolution solid-state 27Al MAS NMR at an ultrahigh magnetic field of 21.1 T. XRD measurements show that γ-Al2O3 undergoes a phase transition to θ-Al2O3 during calcination at 1000 °C for 10 h. The formation of the θ-Al2O3 phase is further confirmed by 27Al MAS NMR; additional 27Al peaks centered at 10.5 and ∼78 ppm were observed in samples calcined at this high temperature. Both the XR

Side on! Combined FTIR and NMR studies revealed the presence of a side-on nitrosyl species in the zeolite Cu-SSZ-13. This intermediate is very similar to those found in nitrite reductase enzyme systems. The identification of this intermediate led to the proposal of a reaction mechanism that is fully consistent with the results of both kinetic and spectroscopic studies.

Self-assembly has proven to be a widely successful synthetic strategy for functional materials, especially for metal-organic materials (MOMs), an emerging class of porous materials consisting of metal-organic frameworks (MOFs) and metal-organic polyhedra (MOPs). However, there are areas in MOM synthesis in which such self-assembly has not been fully utilized, such as controlling the interior of MOM crystals. Here we demonstrate sequential self-assembly strategy for synthesizing various forms of

Ex situ natural abundance magic angle spinning (MAS) NMR was used for the first time to study fundamental mineral carbonation processes and reaction extent relevant to geologic carbon sequestration (GCS) using a model silicate mineral forsterite (Mg2SiO4)+supercritical CO2 with and without H2O. Run conditions were 80 °C and 96 atm. With H2O but without CO2, 29Si MAS NMR reveals that the reaction products contain only two peaks of similar intensities located at about −84.8 and −91.8 ppm, which ca

For Pd-based catalysts, facile and fast interconversion between Pd and PdO occurs continuously during the CH4 oxidation reaction, which makes it challenging to determine active sites. Herein, we report that the amount of partially oxidized palladium (PdOx) on the catalyst surface shows a linear correlation with the CH4 oxidation activity in a series of Pd/Al2O3 and Pt–Pd/Al2O3 catalysts hydrothermally aged under commercially relevant conditions. We characterized the amount of surface PdOx throug