The kinetics and the effect of indigenous and externally added water on methane formation during Fischer–Tropsch synthesis (FTS) was studied over Co based catalysts using a 1 L continuously stirred tank reactor (CSTR). The water cofeeding study (10% water) was conducted over a 0.27%Ru–25%Co/Al2O3 catalyst at a low CO conversion level of 19% at 220 °C in order to lessen the effect of catalyst aging during the addition of water, while the kinetic experiment was conducted over 25%Co/γ-Al2O3 at the conditions of 205–230 °C, 1.4–2.5 MPa, H2/CO = 1.0–2.5, and 3–16 (NL/gcat)/h (X CO < 60%). Indigenous and externally added water decreases methane formation by a kinetic effect. The addition of 10% water led to a decrease in the CH4 rate by 12% (3.5 → 3.0 (mmol/gcat)/h), while little catalyst deactivation was observed during water addition. Increases in indigenous water partial pressure also lowered the CH4 rate and its selectivity. Kinetic analysis was performed using a group of 220 °C data collected between 365 and 918 h when the deactivation rate was very low. An empirical CH4 kinetic model, with a water effect term (P H2O/P H2 ), (r CH4 = kP CO a P H2 b /(1 + mP H2O/P H2 )) was used to fit kinetic data. The CH4 kinetic results suggest a negative water effect on CH4 formation during FTS on the unpromoted cobalt catalyst, consistent with the water effect results. The final methane kinetics (r CH4 ) equation obtained at 220 °C over 25%Co/γ-Al2O3 is as follows: r CH4 /[(mol/gcat)/h] = 0.001053{P CO –0.86 P H2 1.32/[1 + 0.46(P H2O/P H2 )]}. Meanwhile, a methane selectivity model at 220 °C for the 25%Co/Al2O3 catalyst was also developed: S CH4 = 0.0792P CO –0.55 P H2 0.44[(1 – 0.24P H2O/P H2 )/(1 + 0.46P H2O/P H2 )]. The CH4 selectivity model provided a good prediction of CH4 selectivities under the experimental conditions used. Furthermore, our empirical CH4 kinetic results on the cobalt catalyst are consistent with literature kinetic models that were derived from carbide mechanisms; high CH4 selectivity from the cobalt catalyst is found to be mainly due to a high CH4 reaction rate constant.

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The effect of water on the performance of potassium-promoted precipitated iron catalyst was investigated during Fischer-Tropsch synthesis (FTS) using a continuously stirred tank reactor (CSTR) at two different reaction temperatures. Water was added in such a manner as to replace an equivalent amount of inert gas so that all other reaction conditions (e.g., reactant partial pressure, space velocity) remained the same before, during, and after water addition. The externally added water had a positive effect on CO conversion at 270°C whereas, for the reaction carried out at 230°C, the added water decreased CO conversion and deactivated the catalyst. From these findings, the addition of water at 230°C oxidized the catalyst, transforming the iron carbide to the Fe 3 O 4 phase. When the reaction was carried out at 270°C, severe oxidization did not take place and a carbide phase was retained. The loss in activity and the rate of deactivation were more pronounced at 230°C compared to the 270°C condition for the same catalyst. Mössbauer spectroscopic measurements revealed that for the reaction carried out at 230°C, the catalyst had 85% of the iron present as Fe 3 O 4 and the remaining as Hägg carbide (v-Fe 5 C 2 ), whereas at the higher temperature reaction condition the catalyst had about 66% of the iron present as e 9-Fe 2.2 C, with the remaining as Fe 3 O 4 . These findings were also supported by XANES analysis, where a high white line intensity was observed for the sealed used catalyst sample for the low temperature reaction condition, indicating a higher extent of oxidation. A low white line intensity was recorded for the used sample for the high temperature reaction condition, indicative of a higher extent of reduction.

The morphological, phase transformations and carbon‐layer growth for unpromoted and K‐promoted iron catalysts were investigated over time during Fischer–Tropsch synthesis. Catalysts were activated in CO for 24 h, which transformed hematite into a mixture containing 93 % iron carbide and 7 % magnetite for the unpromoted catalyst and 81 % iron carbide and 19 % magnetite for the K‐promoted catalyst. Initially, the activated catalysts had high CO conversions (≈85 %); however, the conversions decreased to approximately 30 % after approximately 280 h of synthesis time. For the unpromoted catalyst, the amount of iron carbide gradually decreased over time while the corresponding magnetite phase increased. However, for the K‐promoted one, only one iron carbide phase (χ‐Fe5C2) gradually decreased, while the other ($\acute \epsilon $‐Fe2.2C) phase steadily increased and magnetite remained unchanged. TEM analyses revealed that for the K‐promoted catalyst, carbon deposition increased over time, unlike that of the unpromoted catalyst.

The effect of potassium promoter loading (0, 0.5, 1.0 and 2.0 atomic ratio) on the performance of precipitated iron catalysts was investigated during FischerTropsch synthesis using a continuously stirred tank reactor. Characterization by temperature-programmed reduction with CO, Mössbauer effect spectroscopy, and transmission/ scanning transmission electron microscopy were used to study the effect of potassium promoter interactions on the carburization, phase transformation and carbon layer formation behavior of the catalysts. Under similar reaction conditions, all four catalysts exhibited similar initial CO conversions (*85 %), whereas stability was found to increase with potassium loading up to 0.5 % (atomic ratio related to the iron), and further increases in potassium led to decreased activity. Unpromoted and excessively K loaded (2.0K/100Fe) catalysts exhibited similar deactivation trends with time and followed essentially similar conversion levels with time-on-stream. The selectivity of various potassium promoted catalysts was found to increase the average molecular weight of hydrocarbon products with increasing potassium loading. The deactivation rate was related to carbon deposition which could embed the iron carbide particles. If not enough K is present, Fe carbides tend to oxidize with TOS; with excessive K-loading, carbon deposition/site blocking become problematic.

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The successful adaptation of conventional cobalt and iron-based Fischer-Tropsch synthesis catalysts for use in converting biomass-derived syngas hinges in part on understanding their susceptibility to byproducts produced during the biomass gasification process. With the possibility that oil production will peak in the near future, and due to concerns in maintaining energy security, the conversion of biomass-derived syngas and syngas derived from coal/biomass blends to Fischer-Tropsch synthesis products to liquid fuels may provide a sustainable path forward, especially considering if carbon sequestration can be successfully demonstrated.However, one current drawback is that it is unknown whether conventional catalysts based on iron and cobalt will be suitable without proper development because, while ash, sulfur compounds, traces of metals, halide compounds, and nitrogen-containing chemicals will likely be lower in concentration in syngas derived from mixtures of coal and biomass (i.e., using an entrained-flow oxygen-blown gasifier) than solely from coal, other byproducts may be present in higher concentrations. The current project examines the impact of a number of potential byproducts of concern from the gasification of biomass process, including compounds containing alkali chemicals like the chlorides of sodium and potassium.In the second year, researchers from the University of Kentucky Center for Applied Energy Research (UK-CAER) continued the project by evaluating the sensitivity of a commercial iron-chromia high temperature water-gas shift catalyst (WGS) to a number of different compounds, including KHCO 3 , NaHCO 3 , HCl, HBr, HF, H 2 S, NH 3 , and a combination of H 2 S and NH 3 . Cobalt and iron-based Fischer-Tropsch synthesis (FT) catalysts were also subjected to a number of the same compounds in order to evaluate their sensitivities.