Fischer–Tropsch Synthesis: Deactivation as a Function of Potassium Promoter Loading for Precipitated Iron Catalyst

Abstract

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.

Hydrogenation of Carbon Dioxide over K‐Promoted FeCo Bimetallic Catalysts Prepared from Mixed Metal Oxalates

“…In the used catalyst, the amount of ϵ‐Fe carbide increased with increasing K content, whereas the ϵ‐Fe 2.2 C content for the freshly activated catalysts remained more or less the same; this indicates that potassium enhanced the transformation of highly active χ‐Fe 5 C 2 carbide into less active ϵ‐Fe 2.2 C carbide. A similar result was reported by our group with CO hydrogenation over precipitated Fe catalysts . The origin of this transformation is not well understood.…”

Effect of Support Pretreatment Temperature on the Performance of an Iron Fischer–Tropsch Catalyst Supported on Silica-Stabilized Alumina

“…The positive correlation between catalyst activity and ε′-Fe2.2C content is shown in Figure 9. It has been reported that the formation of χ-Fe2.5C is favored over unsupported Fe catalysts under typical FT conditions and identified as an active iron carbide phase [36,37]. Nevertheless, the catalysts used in most of those studies are unsupported, whereas the catalyst in the present study is supported with pretreated silica-stabilized alumina.…”

Sodium-promoted iron catalysts prepared on different supports for high temperature Fischer–Tropsch synthesis

“…The catalytic performance of iron catalysts in high temperature FT synthesis is usually attributed to iron carbides [3][4][5]7,8,[37][38][39]. The presence of sodium affects iron carbidization.…”