Fischer–Tropsch synthesis over various Fe/Al2O3–Cr2O3 catalysts

Reac Kinet Mech Cat https://doi.org/10.1007/s11144-018-1372-6 Fischer–Tropsch synthesis over various Fe/Al2O3– Cr2O3 catalysts Pawel Mierczynski1 • Bartosz Dawid1 • Waldemar Maniukiewicz1 • Magdalena Mosinska1 • Mateusz Zakrzewski1 • Radoslaw Ciesielski1 • Adam Kedziora1 • Sergey Dubkov2 • Dmitry Gromov2 • Jacek Rogowski1 • Izabela Witonska1 • Malgorzata I. Szynkowska1 • Tomasz Maniecki1 Received: 20 November 2017 / Accepted: 10 February 2018 Ó The Author(s) 2018. This article is an open access publication Abstract Monometallic iron supported catalysts were prepared by the impregnation method and tested in Fischer–Tropsch (F–T) synthesis. The activity tests performed in the studied reaction showed that the composition of the catalyst strongly influences the reactivity of the catalytic systems in the F–T reaction. It was also found that the system which showed the highest content of iron species on the catalyst surface exhibited the highest yield in F–T reaction. In addition, the most active catalyst also showed high specific surface area, high total acidity value and the highest amount of iron species on the catalyst surface. The analysis of the liquid product of F–T synthesis confirmed the occurrence of aliphatic, branched and unsaturated linear hydrocarbons. Keywords Fischer–Tropsch  Iron catalyst  CO hydrogenation  Binary oxide  Monometallic catalysts Introduction Currently, Fischer–Tropsch synthesis is considered to be the main alternative to fossil fuels. Undoubtedly, the advantage of this process is a possibility to the pure types of fuel production without any sulfur and nitrogen compounds [1, 2]. F–T synthesis is a well known process starting from 1920s and today increasing interest of usage is observed to obtain alternative feedstock of hydrocarbons such us fuels and waxes [3–6]. The composition of the final product obtained in F–T synthesis & Pawel Mierczynski ; 1 Lodz University of Technology, Lodz, Poland 2 National Research University of Electronic Technology, Zelenograd, Russia 123 Reac Kinet Mech Cat depends on the process conditions and the type of the catalyst used in the studied process. Besides the aliphatic, branched and unsaturated linear hydrocarbons, oxygen containing hydrocarbons like alcohols, aldehydes, ketones and acids can also be formed during this process. In addition, except the remaining hydrocarbons, which can be formed during the synthesis also the paraffin waxes can be produced via hydrogenation of CO [7]. The most commonly used catalysts in F–T synthesis are cobalt [8–10], nickel and iron [3, 5, 11–13].The typical composition of the syngas used during the FT synthesis realized on the catalytic system correspond to the molar ratio between H2 and CO equal to 2. The wide distribution of organic compounds formed during the F–T process leads to the conclusion that it is needed to select appropriate catalytic systems in order to increase the selectivity to the desired products, such as petrol or diesel fractions. Generally, it is well known that iron catalysts are active systems in the F–T process [14]. Many researchers try to improve the catalytic properties by the addition of various promotors. Noble metal addition is one of the possibilities to improve selectivity, activity and stability of Fe system in F–T reaction. The typical supports used for the preparation of the catalytic systems are Al2O3, SiO2, CeO2, TiO2, ZrO2 and binary oxides, mixtures of previously mentioned oxides systems and zeolites. It should also be noted that catalysts supported on binary oxide systems showed higher specific surface area, mechanical strength and exhibited higher catalytic activity in various processes [15–19]. The selection of the specific composition of the binary system generates the change of their physicochemical properties in a certain direction. In summary, all of these facts suggest that it is important to produce hydrocarbons via Fischer–Tropsch synthesis on Fe catalyst supported on binary oxide systems. In order to achieve the intended goal, we decided to synthesize monometallic iron supported catalysts by impregnation method and we studied their surface composition and the reactivity properties in the F–T process. Furthermore, the physicochemical properties of the prepared catalytic systems were also studied in this work using BET, TPR–H2, SEM–EDS, TPD–NH3 and TOF–SIMS methods. Experimental part Catalysts preparation Monometallic iron supported catalysts supported on various Al2O3–Cr2O3 binary oxides system (Al:Cr = 2, 1, 0.5) were prepared by impregnation method using Fe(NO3)39H2O as an active phase precursor. The supports which were used during the preparation step of the catalytic systems were prepared by co-precipitation method from appropriate aqueous solution of Al(NO3)39H2O and Cr(NO3)39H2O. Ammonia was used as a precipitating agent during the co-precipitation process. The obtained supports were calcined for 4 h in air atmosphere at 400 °C. Whereas, the monometallic supported iron catalysts were calcined for 4 h in air atmosphere at 500 °C. 123 Reac Kinet Mech Cat Specific surface area measurements The BET surface area and porosity of the prepared supports and monometallic supported iron catalysts were determined in a sorptometer Sorptomatic 1900 apparatus. FTIR measurements The analysis of the liquid products formed during the F–T process were performed on an IRTracer-100 FTIR (Shimadzu) spectrometer equipped with liquid nitrogen cooled MCT detector. During all experiments, a resolution of 4.0 cm-1 was used and 128 scans were taken to achieve a satisfactory signal to noise ratio. For all measurements, the ‘‘Specac’’ ATR accessory was used. SEM–EDS measurements The morphology of the monometallic iron catalyst supported on Al2O3–Cr2O3 binary oxide system (Al:Cr = 2, 1, 0.5) were studied by S-4700 scanning electron microscope HITACHI (Japan), equipped with an energy dispersive spectrometer EDS (ThermoNoran, USA). TPR–H2 measurements TPR–H2 measurements were performed for both binary supports and the prepared monometallic iron supported catalysts using an automatic AMI-1 instrument in the temperature range 25–900 °C. The heating rates applying during the reduction process were 10 and 1 °C min-1 for supports and monometallic catalysts, respectively. The mass of the investigated catalyst was about 0.1 g in each test. During the reduction process the mixture of 5%H2–95%Ar was used with a thermal conductivity detector. Acidity measurements The total acidity and the distributions of the acids centers for all the prepared catalysts which were previously reduced at 500 °C in a mixture of 5%H2–95%Ar were studied by TPD–NH3 technique. Before all experiments, each sample (about 0.2 g in each test) was reduced in situ in a mixture of 5%H2–95%Ar at 500 °C for 1 h and then purified in situ in flowing He at 600 °C for 30 min-1. Then the sample was cooled down to ambient temperature in a helium stream. In the next step, the phys (...truncated)