Mo−Fe Catalysts Supported on Activated Carbon for Synthesis of Liquid Fuels by the Fischer−Tropsch Process:  Effect of Mo Addition on Reducibility, Activity, and Hydrocarbon Selectivity

Abstract

The effects of Mo loading (0−12 wt %) on the properties of activated-carbon- (AC-) supported Fe−Cu−K catalysts and their performance for Fischer−Tropsch synthesis are studied. Physicochemical properties studied include particle size, reducibility, and dispersion, and catalytic properties include activity, selectivity, and stability. Catalysts were characterized by N2 adsorption, energy-dispersive spectroscopy, X-ray diffraction (XRD), H2 temperature-programmed reduction (TPR), and CO chemisorption. Catalyst performance was studied at 310−320 °C, 2.2 MPa, 3 Nl/g-cat/h, and H2/CO = 0.9. Reaction results in a fixed-bed reactor show that addition of 6% Mo into the Fe−Cu−K/AC catalyst improves catalyst stability without sacrificing activity, but activity is suppressed dramatically on a 12% Mo-loaded catalyst. Detectable hydrocarbons of C1 to C34 are produced on the Fe−Cu−K/AC catalysts with or without Mo. However, the addition of Mo results in the production of more CH4 and less C5+ hydrocarbons. The Mo promoter greatly enhances secondary reactions of olefins, leading to a large amount of internal olefins (i.e., other than 1-olefins) in the product. TPR shows that a strong interaction between Fe and Mo oxides is present, and the extent of reduction of Fe is suppressed after addition of Mo to the Fe−Cu−K catalyst. CO-chemisorption and XRD studies show increased iron dispersion and decreased particle size of the iron carbide and iron oxide after the addition of Mo. Segregation of iron active sites, thereby preventing them from agglomerating, and a larger number of active sites on the 6% Mo catalyst are possible reasons for the improved stability and higher activity of Mo-promoted catalysts.

Synthesis of thin-multiwalled carbon nanotubes by Fe-Mo/MgO catalyst using sol-gel method

“…However, Ar and H 2 decomposed Fe-Mo/MgO catalysts (SG-2 and SG-3) showed decreased pore diameter, pore volume, and surface area compared to the case of the MgO support material. This behavior can be explained as being due to pore filling and the blocking phenomenon of metal precursors [26]; this behavior supports our hypothesis that Fe-Mo systems form in a well-dispersed manner within MgO support. The product yields of carbon materials were found to be correlated with the BET surface area of the starting Fe-Mo/MgO catalysts.…”

Fe-Mo Catalysts with High Resistance to Carbon Deposition During Fischer–Tropsch Synthesis

“…Ma et al [16] conducted experiments at high reaction temperature (300-320°C) with activated carbon supported FeCuMoK catalysts and observed that 6% Mo (weight ratio) addition improved catalyst stability without sacrificing activity. However, in our previous work [19], it was demonstrated that 5% (weight ratio) Mo addition sharply decreased the activity of FeK/SiO 2 catalyst.…”

“…Although Mo has been excluded from ideal catalysts for FTS because it is much less active than iron and cobalt, it is still worthy to be considered as a potential promoter with additive functions. Ma et al [16] investigated the Mo loading Fe catalysts supported on activated carbon and found that Mo addition significantly improved the catalytic stability for FTS. The recent quantum chemistry calculation results [17] have proved that using Mo as promoter could increase the sulfur poisoning tolerance of Co and Fe catalysts.…”

Carbon nanotubes prepared by anodic aluminum oxide template method

“…Carbon nanotubes (CNTs) with unique structure and properties such as well-defined hollow interiors, inert surface properties, and resistance to acid and base environment have been proven to be excellent candidates as support in catalytic reactions [1][2][3][4][5][6][7] and energy storage and conversion medium [8][9][10][11]. Structural parameters of CNTs such as inner diameter, wall thickness, length, crystallinity, and electronic structure have a great influence on the performance of the supported particles or loaded matters [12][13][14][15].…”