Nick Burke

Methane storage in metal organic frameworks

In this applications article (116 references), the use and viability of metal organic frameworks (MOFs) for natural gas storage is critically examined through an overview of the current state of the field. These smart materials can be tuned to deliver best performance according to demand, as a function of temperature, desired storage pressure and mandated fill/release rates. Whilst the chemistry behind optimising natural gas storage performance in MOFs is highlighted, it is contextualised to the specific application in vehicular transport, and the best means of testing performance parameters are canvassed. Future applications of MOFs with natural gas are also discussed.

Production of p-cymene and hydrogen from a bio-renewable feedstock–1,8-cineole (eucalyptus oil)

The catalytic transformation of pure 1,8-cineole was performed in a custom-built down-flow fixed bed pyrolysis rig over various metal-doped alumina pellets controlled at temperatures between 523 K (250 °C) and 873 K (500 °C). Varying amounts of oxygen were added to the feed. Hydrophilic, hydrophobic and gaseous products were analysed separately. The hydrophilic phase was predominantly water, while the composition of the hydrophobic phase varied with catalyst type and contained mainly mixtures of both aromatic and non-aromatic C10 hydrocarbons. The main gases produced were hydrogen, carbon monoxide and carbon dioxide. As the reaction temperature increased, yields of gas phase components increased for all catalysts. The palladium-doped γ-Al2O3 catalyst at ∼250 °C showed excellent yields and selectivity for the continuous production of p-cymene together with hydrogen gas. For the best catalysts and reaction conditions, the process is very atom and carbon efficient, with all ten carbon atoms from the cineole molecule being used in the p-cymene product in an oxygen-free environment. The process uses no solvents and the high yields achieved ensure there is no waste clean-up required.

Influence of charge compensating cations on propane adsorption in X zeolites: experimental measurement and mathematical modeling

Separation of minor components is necessary prior to natural gas liquefaction. There are many methods to achieve this but one that has not been studied in great detail is adsorption of hydrocarbon gases on zeolite materials. A more comprehensive understanding of the fundamentals of hydrocarbon adsorption on zeolites is required in order to determine the efficacy of these materials in natural gas processing. This study investigates the influence of the charge compensating (non-framework) cation on the adsorption of propane on X zeolite by both dynamic experiments and mathematical modeling. This work presents a systematic experimental study examining the effects of the 5 typical types of charge compensating cations (Li+, Na+, K+, Ca2+, La3+) in X zeolites for saturated hydrocarbon adsorption. The dynamic experimental results reveal that for the X zeolites examined, all exhibited an affinity for propane, with LiX being the best, having a propane adsorption capacity of 15.5 wt%. Interestingly, unlike many non-zeolite solid sorbent materials, such as carbons, surface area and pore size alone do not necessarily determine propane adsorption capacity in these X zeolites. It has been shown that the charge compensating cation of the X zeolites of interest, in particular its valence, number of ions and size are the major factors affecting the propane adsorption capacity. Mathematical modeling equations are established by using mass balance in the adsorbent column, macroporous pellets and microporous crystals. The model-predicted results show a good match with our experimental results. The prediction results show that in our current experimental conditions, LiX has a slower adsorption rate than the other zeolites. The obtained adsorption equilibrium constants for all the X zeolites follow the same trend as their propane adsorption capacity, with LiX having the largest constant, suggesting a stronger binding energy between LiX and propane compared to the other zeolites.

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.

Experimental studies of hydrocarbon separation on zeolites, activated carbons and MOFs for applications in natural gas processing

Separation of minor hydrocarbon components in natural gas is necessary prior to liquefaction to avoid operational (plugging of equipment) and product specification issues. While there have been many studies describing adsorption of gases on solid materials there have been relatively few focused on decreasing concentrations of light hydrocarbons in methane in non-equilibrium experimental configurations. In order to best understand the chemistry of competitive adsorption of saturated hydrocarbons for gas processing applications we investigated light hydrocarbon dynamic adsorption properties on 16 solid adsorbents of different structures and chemistries. The best adsorbents, as determined by adsorption capacity, were tested for their ability to separate higher molecular weight hydrocarbons from methane. It is found that for charged frameworks, the induced dipole moment between the adsorbent and adsorbate plays the most important role in adsorption capacity. For uncharged frameworks, pore size plays the critical role in adsorption: micropores are more effective than mesopores. For separation of mixtures of methane, ethane, propane and butane, the kinetics of adsorption must also be considered. Of the materials tested, a carbon derived from coal and activated with steam (carbon #5 (37771)), zeolite KX and zeolite 5A were the best in terms of adsorption and separation capability. These materials show promise for separating light hydrocarbons of similar chemical nature.

Synthesis and Electrochemical Properties of Mesoporous Carbon Supported Well-Dispersed Cobalt Oxides Nanoparticles

In this article, well–dispersed cobalt oxide nanoparticles supported on mesoporous carbon (CMK–3) have been successfully synthesized. The composites were characterized by field emission scanning electron microscopy, transmission electron microscopy, X–ray diffraction and nitrogen adsorption–desorption analysis. The results have confirmed that, at a cobalt loading of 15 wt%, the composites have not only retained mesoporous structure of the support but also shown a good control of dispersed cobalt oxide nanoparticles with size of ~4 nm. The electrochemical property tests for the synthesized samples have shown significant improvement compared to the blank carbon (CMK–3) without cobalt oxide incorporation.