Journal of Natural Gas Chemistry 17(2008)242–248 Deactivation studies of bifunctional Fe-HZSM5 catalyst in Fischer-Tropsch process Ali Nakhaei Pour ∗ , Seyed Mehdi Kamali Shahri, Yahya Zamani, Mohammad Irani, Shohreh Tehrani Research Institute of Petroleum Industry, National Iranian Oil Company, P. O. Box 18745-4163, Tehran, Iran [ Manuscript received March 10, 2008; revised April 30, 2008 ] Abstract: A physical mixture of alkali-promoted iron catalyst with binder based on Fischer-Tropsch synthesis and an acidic co-catalyst (HZSM5) for syngas conversion to hydrocarbons was studied in a fixed bed micro reactor. Deactivation data were obtained during the synthesis over a 1400 h period. The deactivation studies on iron catalyst showed that this trend followed the phase transformation Fe 2.2 C(´ ε) → Fe 5 C 2 (χ) → Fe 3 C(θ), and the final predominant phase of the catalyst was Fe 3 C(θ). Deactivation of zeolite component in bifunctional catalyst may be caused by coking over the zeolitic component, dealumination of zeolite crystals, and migration of alkali promoters from iron catalyst under synthesis conditions. The deactivation rate of iron catalyst was also obtained. Key words: catalyst deactivation; Fischer-Tropsch synthesis; iron catalyst; HZSM5 zeolite 1. Introduction The Fischer-Tropsch synthesis (FTS) offers the possibil- ity of converting a mixture of hydrogen and carbon monox- ide (synthesis gas) into clean hydrocarbons, free from sulfur [1-3]. Considerable progress has been made in the past two decades in the development of more active, selective cobalt and iron catalysts and more effective reactor/process tech- nologies [3,4]. The FTS product contains large amounts of normal paraffins with high cetane number and low octane number near 0. Thus, the FTS product is suitable to apply as diesel fuel, but not for gasoline. The addition of HZSM5 to the FT process was seen to improve both selectivity and quality of gasoline range products. It was possible to minimize the formation of hydrocarbons beyond the gasoline range product with these catalysts and obtain appreciable amount of aromat- ics in the liquid product simultaneously. The pore structure of zeolite and its catalytic cracking operation can limit the size of produced molecules [5-9]. In the past two decades, several researches have been fo- cused on catalyst activity-structure relationships. Studies on the reaction mechanisms and kinetics [1-4] have led to a rea- sonably good understanding of these issues. At the same time, some researches have been focused relatively on the kinetics and mechanisms of catalyst deactivation. Yet, the most sig- nificant opportunities for the FTS process improvement lie in the development of more stable and regenerable catalysts. The main reason of iron FTS catalysts deactivation is the transfor- mation of active surface carbon species and/or active iron car- bide phases to inactive carbon or carbide forms, which will cause fouling or poisoning of the catalyst surface [10-17]. The present study evaluates the change of the catalyst ac- tivity, product selectivity, and deactivation manner of iron- zeolite catalyst with time on stream. Also, the phase changes for each phase change stage were described by deactivation rate equations on the iron catalyst. In addition, the zeolite de- activation process was investigated and the relation between decreasing zeolite acidity and carbon deposition on acidic sites was obtained. 2. Experimental 2.1. Catalyst preparation Fe-Cu-La-SiO 2 catalysts were prepared by co- precipitation of Fe and Cu nitrates at constant pH to form porous Fe-Cu oxyhydroxide powders, which were promoted by impregnation with La(NO 3 ) 3 precursor and silica sol so- lution after treatment in air. A solution containing both Fe(NO 3 ) 3 (Aldrich, >99.9%), Cu(NO 3 ) 2 (Aldrich, >99.9%) and a separate solution of Na 2 CO 3 (Aldrich, >99.9%) was used in the precipitation process. These two feed solutions were held at 75-80 ◦ C before being charged to bring about the precipitation. The salt solution and sodium carbonate so- lution were pumped to the reactor at equal rates to maintain outlet pH of 7.0±0.3. The mixture was stirred for several ∗ Corresponding author. E-mail: nakhaeipoura@ripi.ir