New insights on Pt promotion of Co/γ-Al2O3 catalysts for Fischer Tropsch synthesis

In the last decade until the oil crisis of 2014, industries’ interest in Gas-to-Liquids (GTL), Coal-to-Liquids (CTL) and Biomass-to-Liquids (BTL), capable of converting natural gas, coal and biomass into liquid fuels had grown considerably in a scenario which, due to a constant growth in energy demand, was experiencing a reduction in the availability of low price crude oil. At that time, XTL (X-to-Liquids, general acronym for these processes) technologies represented valid economic alternatives for fuels production, as they could exploit relatively cheap and widely available resources. The significant advantage offered by such processes is the manufacture of higher added value and performance products, with lower environmental impact compared to equivalent standards. XTL technologies obey on the following fundamental steps: 1. Production of the syngas mixture, consisting of CO and H2, from the raw materials by consolidated processes such as gasification and Steam Methane Reforming (SMR). 2. Syngas conversion into liquid hydrocarbons at high molecular weight using Fischer-Tropsch synthesis (FTS). 3. Product upgrading, via standard refining processes, to obtain gasoline and diesel. Conventional GTL plants are designed on a large scale, as they run Fischer-Tropsch synthesis within large fixed bed or slurry reactors. Therefore, these solutions are only suitable for processing huge quantities of raw materials. Industries’ interest in exploiting smaller and remote reservoirs, continuously growing in number in the recent years, has led to researching for reduced size of equipment, which can easily be transported on-site (CompactGTL technologies). In the last three years, the LCCP (Laboratory of Catalysis and Catalytic Processes) group at Politecnico di Milano has studied these technologies, focusing on the development of innovative cobalt-based catalysts, capable of reaching high CO conversion and high selectivity towards desired Fischer-Tropsch products. In this thesis attention has been given principally to performance improvement of such catalysts. To achieve this goal, the effect of a small addition of platinum, acknowledged promoter in the FT research, although very expensive, was thoroughly studied. Also, with the same objective unconventional catalysts were investigated: the latter are different from the conventional due to the addition of an organic compound, namely diethylene glycol (DEG), in the usual impregnating solution of cobalt-nitrate salts which contain the active phase. Further target was to demonstrate the validity of catalyst testing run at atmospheric pressure against that run at industrially relevant Fischer-Tropsch conditions (high pressure). While low pressure testing on conventional catalysts was valid, for the unconventional, discrepancies were observed between the results of the two tests.