Amonyaktan COx açığa çıkartmadan hidrojen üretimi için yüksek ve stabil performanslı, çevre dostu ve maliyetsiz katalizör: Basit metodlarla modifiye edilmiş kırmızı çamur

Hydrogen, considered as one of the most promising alternative energy carriers, faces storage and transportation problems due to its very low boiling point, extremely low density in gaseous phase and very high density in liquid phase. Therefore, the utilization of ammonia as a storage medium for hydrogen can be a solution to the safe and effective storage problem of hydrogen. Because, it is carbon free, has a high hydrogen density (17.7 wt.%), and has an already existing infrastructure. Best performing catalysts for hydrogen production by ammonia decomposition are Ru-based catalysts suffering from high costs, whereas Ni- and Fe-based counterparts have significantly lower costs. Red mud is a by-product formed during the alumina production process, produced approximately two tons for each ton of aluminum produced. It is considered as a hazardous industrial waste due to its high alkalinity and toxic content, which makes it harmful to the environment. It contains compounds which are the oxides of mainly Fe, Al, Si, and Ti. These elements makes red mud attractive in utilizing it in application areas such as ceramics, construction, and catalysis. In this thesis, Turkish red mud, from Seydişehir, with an iron oxide content of more than 35%, was converted into a cost-free catalyst for hydrogen production by ammonia decomposition with record high stable performance. Firstly, as received red mud was subjected to simple treatment methods including acid digestion followed by ammonia precipitation to enhance the physical and chemical properties. While performing these modifications, treatment parameters were systematically varied and resulting samples were deeply characterized by XRD, XRF, and FTIR spectroscopy, SEM, TGA, and ICP-MS before and after modification. The parameters which were investigated were the type of acid used for digestion (HCl and H2SO4), molarity of the acid (2M-6M), digestion temperature (85 and 220 °C), and calcination temperature (300 - 500 °C). In general, in the modified samples, iron oxide amount was enhanced and surface area values were increased. After performing the catalytic activity measurements of these modified red mud samples at 500 °C, it was revealed that the sample with the highest surface area value of 232 m2/g (that was digested at 220 °C in 6M HCl, MRM-2) has an exceptionally high activation energy indicating a high temperature dependency. Thus, this modified red mud sample was further investigated for hydrogen production by ammonia decomposition at a higher temperature, at 700°C. MRM-700R@700 provided stable 97  0.5 % conversion for a space velocity of 72 000 cm3 NH3 h-1 gcat-1 at 700 °C, which is a record high value among all non-noble metal catalyst reported in the literature. It was elucidated that an activation period of 10 h under NH3 flow prior to the reaction forms the nitrided iron specie -Fe2N in MRM-700R@700, which is responsible for this high and stable performance. Detailed feasibility study was also performed on the economics of hydrogen production on such a cost-free catalyst based on these performance values. Utilization of red mud as a catalyst for hydrogen production by ammonia decomposition provides opportunities for i) the utilization of such a hazardous waste produced in vast amounts; ii) having a cost-free, highly active and stable catalyst for COx-free hydrogen production by ammonia.