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The chemical looping hydrogen production (CLHP) process is a new approach for hydrogen ( H 2 ) fuel production. The proposed process consists of three reactors which are air reactor (AR), fuel reactor (FR) and steam reactor (SR). In this study, the gas solid flow behaviour in a cold model of the proposed CLHP process was simulated using computational fluid dynamics (CFD) with kinetic theory of granular flow. The effect of drag coefficient models on the pressure profile of each reactor was investigated and the results from the modified Syamlal–O’Brien drag model agreed well with the experimental data. The model was further used to investigate effects of the operating parameters on the hydrodynamics profiles of each reactor. The solid flux increased with the increasing of inlet velocity of AR and FR but decreased with the increasing of the inlet velocity of SR. At the same time, the solid flux increased with the increasing of the solid inventory.

The methane–steam redox process is an alternative methane conversion route to high-purity hydrogen production. Using natural ilmenite as an oxygen carrier, we investigated the effect of three different pre-oxidation temperatures (800, 1000 and 1200 °C) on redox performance and stability. We found that the pre-oxidation temperature significantly altered the crystalline properties of the ilmenite sample, which subsequently affected its morphology, reducibility and redox performance. Pre-oxidation above 1000 °C caused the formation of pseudo-brookite (Fe2TiO5), while hematite (Fe2O3) was formed at 800 °C. The presence of Fe2TiO5 lowered the reduction kinetics, but improved the oxygen-transfer capacity. This resulted in the highest redox activity for the sample pre-oxidised at 1000 °C, which had a three to fourfold increase in hydrogen yield compared with samples pre-oxidised at the other temperatures. Redox activity progressively increased during the cyclic redox operation, due to an increase in surface area caused by continual pore and crack development. Hydrogen yield was sustained at double the level of the initial yield, with a purity of more than 98% over 40 redox cycles.

Chemical looping combustion (CLC) offers a low emission route for fossil fuel-based power generation. In this study, a compact fully looped chemical looping reactor was developed in-house, and operated continuously with a Victorian brown coal as fuel and an Australian ilmenite as oxygen carrier at 940–980 °C and atmospheric pressure for 36 h. The study found that the CLC performance increased with increasing operation time. The CO2/CO molar ratio, used to evaluate the CLC reaction degree, increased from 2.3 to 8.9 over the 36 h of operation. Specifically, this paper provides a comprehensive study and evaluation of the ilmenite characteristics on morphology changes and ash interaction, due to the continuous operation. No noticeable effect by ash interaction on the CLC performance or operation was observed during the continuous operation. The characterisation results revealed a clear segregation of iron species from the iron‑titanium matrix, its migration to and enrichment over the particle surfaces. Hematite (Fe2O3) formation became more pronounced while pores developed internal and external of the ilmenite particles. These changes are believed to improve the carrier reactivity, and so the CLC performance, but also to weaken the mechanical strength of the carrier, promoting particle attrition and leading to its loss by elutriation.

This study reports the conversion of carbon dioxide (CO2) by ceria (CeO2)-zirconia (ZrO2) composites with various ZrO2 contents (0, 20, 50, 80 and 100 %). The modification introduced by ZrO2 altered the structural properties of the ceria samples, affecting their reducibility and subsequent activity to convert CO2. The characterisation results showed a clear relationship between the structural properties of the materials and the activity for CO2 conversion. The addition of ZrO2 was effective to improve a close interaction between CeO2 and ZrO2 and induced the formation of structural defects that further promoted oxygen transport and facilitated the creation of oxygen vacancies that were critical for CO2 conversion. All samples investigated were found to be effective in converting CO2 into carbon monoxide (CO) at 450 °C, and the addition of ZrO2 was also found to be effective in improving the thermal resistance and stabilising the crystalline structure of the samples especially when the ZrO2 content was > 50 %. When the content of ZrO2 controlled between 50 % and 80 %, the onset temperature for CO2 conversion was found to be 285 °C, which was about 80 °C lower than that required for the sample without ZrO2 modification. Thus, modifying CeO2 by ZrO2 was effective to prevent both the textural and structural alteration of the samples under a high temperature environment as well as cyclic redox operations, resulting in a constant and high degree of CO2 conversion into CO.

This study reports the effects of oxidative-reductive (OR) treatment on 10 wt% Co/Al 2 O 3 and 0.25 wt% Ru-10 wt% Co/Al 2 O 3 catalysts. Temperature-programmed analysis revealed that the cobalt in both catalysts became more reducible with increase number of OR treatment. A reduction–oxidation–reduction treatment increased Co surface area and dispersion of the Ru-Co/Al 2 O 3 catalyst from 7.6 to 10.1 m 2 /g and from 14.9% to 17.3%, respectively. The treatment also increased the CO conversion from 21% to 36% and accompanied a small increase in CH 4 selectivity in Fischer–Tropsch synthesis experiments. However, the effect of OR treatment on the Co/Al 2 O 3 catalysts was insignificant.

The effects of ceria loading (0.1–6.0 wt%) on the properties of Li/MgO catalysts and on their activities for oxidative coupling of methane (OCM) were studied. The catalysts were characterised by surface area measurement, XRD, XPS, SEM and CO 2 temperature programmed desorption. The catalyst activity study suggested that the addition of 0.5–1.0 wt% ceria improved the methane conversion of Li/MgO catalyst significantly at reaction temperatures below 800 °C with little change in C 2 selectivity compared to un-promoted Li/MgO. Further increases in ceria loading resulted in lower methane conversion and C 2 selectivity. The CH 4 conversion was related to the surface distribution of O − and O 2− on the catalysts. An increase in reaction temperature beyond 800 °C or a decrease in CH 4 :O 2 ratio from 7:1 to 3:1 imparted negative effects on the methane conversion and C 2 selectivity of the ceria (0.5 wt%) doped Li/MgO catalyst. All ceria doped catalysts did not show any methane coupling activity in the absence of gaseous oxygen, suggesting that they were ineffective to work with alternate feeds of CH 4 and O 2 (redox) mode. Based on the OCM activity and characterisation results, a new pathway that describes the formation of active sites through the electron transfer between Ce 4+ /Ce 3+ and Li/MgO was proposed to help explain the improved OCM activity by using ceria doped Li/MgO catalysts.

The redox performance of pure iron oxide (Fe2O3) and iron oxide modified with ceria (CeO2) and/or zirconia (ZrO2) as an oxygen carrier was investigated for hydrogen (H2) production through a methane–steam redox process. The addition of both CeO2 and ZrO2 were found to be a more effective modification of Fe2O3 than the addition CeO2 or ZrO2 alone. It was found that the reducibility of Fe2O3 was enhanced by CeO2 and the thermal stability of Fe2O3 was improved by ZrO2. These results, therefore, led to the conclusion of the synergistic effect in the Fe2O3-CeO2-ZrO2 mixed oxide. As a result, both the redox activity and the thermal stability were significantly improved, and increases in H2 yield and purity could be maintained by the modification. The redox temperature was found to have a significant effect on redox performance. The production of H2 was considerably improved when the redox temperature was increased from 650 to 750 °C. The ZrO2 concentration in Fe2O3-CeO2-ZrO2 mixed oxide samples was also found to influence performance with the highest H2 yield observed at a ZrO2 concentration of 75 wt.%. Although all materials tested showed a reduction in surface area in the first redox cycle, the change in surface area in subsequent cycles was found to be smaller and the yield of H2 could be maintained at a constant level over a longer period for the mixed oxide containing 75 wt.% ZrO2.

The catalytic behaviour of ceria supported iron catalysts (Fe–CeO2) was investigated for methane decomposition. The Fe–CeO2 catalysts were found to be more active than catalysts based on iron alone. A catalyst composed of 60 wt.% Fe2O3 and 40 wt.% CeO2 gave optimal catalytic activity, and the highest iron metal surface area. The well-dispersed Fe state helped to maintain the active surface area for the reaction. Methane conversion increased when the reaction temperature was increased from 600 to 650 °C. Continuous formation of trace amounts of carbon monoxide was observed during the reaction due to the oxidation of carbonaceous species by high mobility lattice oxygen in the solid solution formed within the catalyst. This could minimise catalyst deactivation caused by carbon deposits and maintain catalyst activity over a longer period of time. The catalyst also produced filamentous carbon that helped to extend the catalyst life.

Supercritical water gasification is an innovative thermochemical conversion method for converting wet feedstocks into hydrogen-rich gaseous products. The non-catalytic gasification characteristics of Victorian brown coal were investigated in supercritical water by using a novel immersion technique with quartz batch reactors. Various operating parameters such as temperature, feed concentration and reaction time were varied to investigate their effect on the gasification behaviour. Gas yields, carbon gasification efficiency and the total gasification efficiency increased with increasing temperature and reaction time, and decreasing feed concentration. The mole fraction of hydrogen in the product gases was lowest at 600 °C, and increased to over 30 % at a temperature of 800 °C. Varying parameters, especially reaction time, did not improve the coal utilisation for gas production significantly and the measured data showed a large deviation from the equilibrium level.

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.