Ja Hun Kwak

In many heterogeneous catalysts, the interaction of metal particles with their oxide support can alter the electronic properties of the metal and can play a critical role in determining particle morphology and maintaining dispersion. We used a combination of ultrahigh magnetic field, solid-state magic-angle spinning nuclear magnetic resonance spectroscopy, and high-angle annular dark-field scanning transmission electron microscopy coupled with density functional theory calculations to reveal the

The catalytic performance of a series of Ru/Al 2 O 3 catalysts with Ru content in the 0.1–5% range was examined in the reduction of CO 2 with H 2 . 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 CH 4 formation increases, while that for CO production decreases. In the 0.1% Ru/Al 2 O 3 catalyst, Ru is mostly present in atomic dispersion,

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

γ-Al 2 O 3 -supported Pt group catalysts are widely used in many industrially important catalytic processes. However, γ-Al 2 O 3 -supported Pt catalysts are prone to deactivation via metal sintering at high temperatures, in oxidative reaction environments, or both. Using a combination of experimental HRTEM and EXAFS measurements and theoretical DFT calculations, we find that pentacoordinated Al 3+ sites (Al p ) on the γ-Al 2 O 3 (100) surface can inhibit Pt sintering both thermodynamically and k

In this work, the structural stability of γ-alumina (γ-Al 2 O 3 ) was investigated by a combination of XRD and high-resolution solid-state 27 Al MAS NMR at an ultrahigh magnetic field of 21.1 T. XRD measurements show that γ-Al 2 O 3 undergoes a phase transition to θ-Al 2 O 3 during calcination at 1000 °C for 10 h. The formation of the θ-Al 2 O 3 phase is further confirmed by 27 Al MAS NMR; additional 27 Al peaks centered at 10.5 and ∼78 ppm were observed in samples calcined at this high temperat

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 (Mg 2 SiO 4 )+supercritical CO 2 with and without H 2 O. Run conditions were 80 °C and 96 atm. With H 2 O but without CO 2, 29 Si MAS NMR reveals that the reaction products contain only two peaks of similar intensities located at about −84.8 and −91.8 pp