Ken Chiang

Synthesis and facile size control of well-dispersed cobalt nanoparticles supported on ordered mesoporous carbon

Ordered mesoporous carbons, as potential catalyst supports, have attracted great attention in the catalysis field in recent years. Researchers have attempted to introduce guest particles into these carbons by versatile methods. Great success has been achieved with noble metal particles because of their lower sintering tendency. However, challenges occurred with more active metals such as cobalt because of their much higher sintering tendency, the hydrophobic nature of the carbon surface and channel confinement effects, which were believed to have prevented the wetness of the surface. Most researchers found that the carbon surface had to be specially treated to achieve good metal dispersion. In our current work, cobalt@carbon composites were synthesized using CMK-3 as the carbon support and cobalt nitrate hexahydrate as the metal precursor. We demonstrated the facile control of the metal particle size and dispersion by carefully controlling the impregnation conditions according to the physical chemistry of the precursor. Our results suggested that not only the acid pre-treatment of the carbon surface and the ammonia post-treatment of the cobalt nitrate precursor improved the metal dispersion but also simple impregnation itself could achieve good metal dispersion if the preparation conditions were controlled as suggested. Highly thermal stable cobalt@carbon composites with very well-controlled cobalt dispersion (15 wt%) and particle size (∼4–20 nm) were produced.

Mesoporous carbon-supported Cu/ZnO for methanol synthesis from carbon dioxide

Catalysts based on Cu/CuO–ZnO supported on mesoporous carbon (FDU-15) were synthesised and tested for methanol production from CO2 and H2. The catalytic activity was strongly dependent on the method by which the Cu and Zn components were loaded onto the carbon support. Three synthetic methods were trialled and the materials produced were characterised by various techniques. The materials with better contact between the Cu/CuO and ZnO particles were catalytically more active towards methanol production (CZC-3 > CZC-2 > CZC-1). The methanol production rate for CZC-3 (7.3 mmol g–1 h–1) was higher, on a catalyst weight basis, than that of a commercial catalyst (5.6 mmol g–1 h–1). Also, CZC-3 had a higher turnover frequency (1.8 × 10–2 s–1) than the commercial catalyst (0.2 × 10–2 s–1). This work demonstrates that Cu/CuO and ZnO particles supported on mesoporous carbon, prepared by an appropriate method, are promising catalysts for methanol synthesis from carbon dioxide.

Nanoporous carbon supported metal particles: their synthesis and characterisation

In the current work, a simplified hard templating approach is used to synthesise metal (Ag, Rh, Ir and Pt) containing structured carbon. The target metals are first introduced into the NaY zeolite template by wetness impregnation. The metals are carried in the super cages of the zeolite and subsequently embedded in the final structures after the steps of carbonisation and the template removal. Scanning electron microscopy images have confirmed that the carbon structures produced by this method retain the morphology of the original template. Transmission electron microscopy reveals the presence of dispersed metal particles in all the carbon structures produced. The metal loadings in these templated structures can reach 35 wt% without significant losses of surface areas and pore volumes. Selected carbon supported metals are tested for their catalytic activity for the methanation of carbon monoxide. The finding suggested that this method is effective in preparing metal nanoparticles for use as catalysts.

Small Scale Hydrogen Production from Metal-Metal Oxide Redox Cycles

The industrial production of hydrogen by reforming natural gas is well established. However, this process is energy intensive and process economics are adversely affected as scale is decreased. There are many situations where a smaller supply of hydrogen, sometimes in remote locations, is required. To this end, the steam-iron process, an originally coal-based process, has been re-considered as an alternative. Many recent investigations have shown that hydrogen (H2) can be produced when methane (CH4) is used as the feedstock under carefully controlled process conditions. The chemistry driving this chemical looping (CL) process involves the reduction of metal oxides by methane and the oxidation of lower oxidation state metal oxides with steam. This process utilises oxygen from oxide materials that are able to transfer oxygen and eliminates the need of purified oxygen for combustion. Such a system has the potential advantage of being less energy intensive than reforming processes and of being flexible enough for decentralised hydrogen production from stranded reserves of natural gas. This chapter first reviews the existing hydrogen production technologies then highlights the recent progress made on hydrogen production from small scale CL processes. The development of oxygen carrier materials will also be discussed. Finally, a preliminary economic appraisal of the CL process will be presented.