Gia Hung Pham

Adsorption of CH4 and CO2 on Zr-metal organic frameworks.

Zirconium-metal organic frameworks (Zr-MOFs) were synthesized with or without ammonium hydroxide as an additive in the synthesis process. It was found that addition of ammonium hydroxide would change the textural structure of Zr-MOF. The BET surface area, pore volume, and crystal size of Zr-MOF were reduced after addition of ammonium hydroxide. However, the crystalline structure and thermal stability were maintained and no functional groups were formed. Adsorption tests showed that Zr-MOF presented much higher CO(2) adsorption than CH(4). Zr-MOF exhibited CO(2) and CH(4) adsorption of 8.1 and 3.6 mmol/g, respectively, at 273 K, 988 kPa. The addition of ammonium hydroxide resulted in the Zr-MOF with a slight lower adsorption of CO(2) and CH(4), however, the selectivity of CO(2)/CH(4) is significantly enhanced.

Ce0.9Gd0.1O2−δ membranes coated with porous Ba0.5Sr0.5Co0.8Fe0.2O3−δ for oxygen separation

Robust oxygen ion conducting membranes based on doped ceria oxides can be used as oxygen permeation membranes with a short circuit to provide the required electronic conduction. Previous methods have coated both surfaces of the ion conducting electrolyte membrane with expensive noble metals as the electronic conducting phase to allow the electron shuttling required for oxygen reduction and oxidation to take place between the two membrane surfaces. During operation of the membrane, the atmosphere on the two sides of the membrane is different. The feed side is exposed to air, whereas the permeated side may be exposed to CO2 or reducing gases such as CH4 or H2. At high operating temperatures, such exposure to different gases requires the use of different materials to prepare the membranes, giving opportunities for further optimisation and the reduction of costs. In this work, a novel Ce0.9Gd0.1O2−δ membrane coated on the surface exposed to air with a cost-effective mixed conductive layer of Ba0.5Sr0.5Co0.8Fe0.2O3−δ was developed to deliver a highly stable oxygen flux for use in clean energy applications or as a membrane reactor for chemical synthesis. The membrane coated with Ba0.5Sr0.5Co0.8Fe0.2O3−δ improved the flux of oxygen compared with membranes coated with pure Ag. A triple phase boundary theory is put forward to explain the observed improvement in the oxygen flux.

The Relationship Between Structural and Catalytic Activity of α and γ-Bismuth-Molybdate Catalysts for Partial Oxidation of Propylene to Acrolein

Bismuth-molybdate catalysts are known to be effective for catalytic partial oxidation of propylene to acrolein. Their properties and the kinetics and reaction mechanisms for acrolein production have been extensively studied, especially in their basic forms, such as α, β, and γ-bismuth-molybdate. Although the reaction mechanisms have been reported widely in the literature, a general agreement has not been reached, especially from a catalyst-structure point of view. The present contribution reports an effort to understand the structural changes of α and γ-bismuth-molybdate catalysts at varying temperatures as examined using high temperature XRD and to relate the catalyst performance (activity and selectivity) for propylene partial oxidation to acrolein. The XRD analysis was performed at temperature between 250 and 450°C in ambient atmosphere and the Rietveld refinement method was used to extract unit cell parameters. The results showed a distinct similarity between the shapes of the thermal expansion of the catalysts and their activity and selectivity curves, indicating a significant role that the catalyst interatomic structure plays in the overall reaction mechanism.

Dry reforming of methane over Co–Mo/Al2O3 catalyst under low microwave power irradiation

In this work, microwave (MW) irradiation was used to activate Co/Al2O3, Mo/Al2O3, and Co–Mo/Al2O3 catalysts for dry reforming of methane (DRM) reactions. Experimental results indicate that single metallic catalysts of either Co or Mo are inactive for DRM under all the tested conditions due to their limited MW-absorbing ability. In contrast, Co–Mo bimetallic catalysts supported by Al2O3 exhibit high catalytic activity due to the formation of a magnetodielectric Co0.82Mo0.18 alloy, which plays the dual role of a good MW acceptor and the provider of active centers for the DRM reaction. The MW power level required to activate such bimetallic catalysts for DRM is significantly dependent on the molar ratio between Co and Mo. The CoMo2 catalyst (with a molar ratio of 2.0 Co to 1.0 Mo) supported on Al2O3 exhibits the best catalytic performance, converting 80% CH4 and 93% CO2 to syngas at a ratio of H2/CO of 0.80 at the total volumetric hourly space velocity (VHSV) of 10 L g−1 h−1 and MW power of 200 W. As compared to the reported C-based catalysts, the Co–Mo/Al2O3 catalyst delivers more favorable stability over 16 time-on-stream (TOS) by virtue of its intrinsic ability to absorb MW without the inclusion of auxiliary MW acceptors.