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Tuning methane conversion at emergent Fe–Ni alloy nanoparticles through control of perovskite composition.

A series of composite CaO-Ca 3 Al 2 O 6 mixed oxides were investigated as potential catalysts for biodiesel synthesis from waste fish oil. Different Ca/Al ratios, in the range of 1.5 to 6 were studied, alongside pure CaO. The catalysts were characterised by X-ray diffraction (XRD), scanning electron microscopy (SEM) and CO 2-Temperature Program Desorption (TPD). The catalytic activity of the materials was studied for the transesterification reaction of cod liver oil with methanol at 65 °C, with 1:12 oil to methanol molar ratio and 10 wt% of catalyst. Over 97% conversion of the triglycerides to methyl esters was achieved for the 6Ca/Al catalyst after 2 h reaction time. This was similar to the performance of CaO. However, 6Ca/Al catalyst was reused successfully for seven consecutive tests, in contrast to CaO that was reused for only five tests, before it deactivated. Therefore, by incorporating the Ca 3 Al 2 O 6 , it was possible to enhance the stability of the catalytically active species and improve the lifetime of the catalyst. Post-test catalyst characterisation showed the formation of an intermediate phase (calcium diglyceroxide) that enhanced the catalyst's performance and tolerance to air exposure and humidity. Finally, the catalyst deactivation, after seven cycles, took place due to the formation of Ca(OH) 2 and CaCO 3 species.

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Alternative and sustainable waste sources are receiving increasing attention as they can be used to produce biofuels with a low carbon footprint. Waste fish oil is one such example and can be considered an abundant and sustainable waste source to produce biodiesel. Ultimately this could lead to fishing communities having their own ‘off-grid’ source of fuel for boats and vehicles. At the industrial level, biodiesel is currently produced by homogeneous catalysis because of the high catalyst activity and selectivity. In contrast, heterogeneous catalysis offers several advantages such as improved reusability, reduced waste and lower processing costs. Here we investigate the phase evolution of two heterogeneous catalysts, CaO and a Ca3Al2O6:CaO (‘C3A:CaO’) composite, under in-situ conditions for biodiesel production from fish oil. A new reactor was designed to monitor the evolution of the crystalline catalyst during the reaction using synchrotron powder x-ray diffraction. The amount of calcium diglyceroxide (CaDG) began to increase rapidly after approximately 30 min, for both catalysts. This rapid increase in CaDG could be linked to ex-situ nuclear magnetic resonance studies which showed that the conversion of fish oil to biodiesel rapidly increased after 30 min. The key to the difference in activity of the two catalysts appears to be that the Ca3Al2O6:CaO composite maintains a high rate of CaDG formation for longer than CaO, although the initial formation rates and reaction kinetics are similar. The Ca for the CaDG mainly comes from the CaO phase. In addition, towards the end of the second test utilising the CaO catalyst (after 120 min), there is a rapid decrease in CaDG and a rapid increase in Ca(OH)2. This was not observed for the Ca3Al2O6:CaO catalyst and this is due to Ca3Al2O6 stabilising the CaO in the composite material. No additional calcium containing intermediate crystalline phases were observed during our in-situ experiment. Overall this specialised in-situ set-up has been shown to be suitable to monitor the phase evolution of heterogeneous crystalline catalysts during the triglycerides transesterification reaction, offering the opportunity to correlate the crystalline phases to activity, deactivation and stability.