CO Conversion Of Catalyst Research Articles

Active Fischer-Tropsch synthesis Fe-Cu-K/SiO2 catalysts prepared by autocombustion method without a reduction step

ABSTRACT The purpose of this study was to prepare iron-based catalysts supported on silica by autocombustion method for directly using for Fischer–Tropsch synthesis (FTS) without a reduction step. The effect of different citric acid (CA):iron nitrate (N) molar ratios and acid types on the FTS performance of catalysts were investigated. The CA:N molar ratios had an important influence on the formation of iron active phases and FTS activity. The iron carbide (FexC), which is known to be one of the iron active phases, was demonstrated by the X-ray diffraction and X-ray photoelectron spectroscopy. Increasing the CA:N molar ratios up to 0.1 increased CO conversion of catalyst to 86.5%, which was then decreased markedly at higher CA:N molar ratios. An excess of CA resulted in carbon residues covering the catalyst surface and declined FTS activity. The optimal catalyst (CA:N molar ratio = 0.1) achieved the highest CO conversion when compared with other autocombustion catalysts as well as reference catalyst prepared by impregnation method, followed by a reduction step. The autocombustion method had the advantage to synthesize more efficient catalysts without a reduction step. More interestingly, iron-based FTS catalysts need induction duration at the initial stage of FTS reaction even after reduction, because metallic iron species need time to be transformed to FexC. But here, even if without reduction, FexC was formed directly by autocombustion and induction period was eliminated during FTS reaction.

Effects of alkaline-earth metals on the structure, adsorption and catalytic behavior of iron-based Fischer–Tropsch synthesis catalysts

Effects of alkaline-earth metals (magnesium, calcium, strontium and barium) on the physico-chemical properties and Fischer–Tropsch synthesis (FTS) performances of precipitated Fe/SiO2 catalysts were investigated by N2 physisorption, laser Raman spectroscopy, FT-IR spectroscopy, in situ X-ray diffraction, Mössbauer effect spectroscopy, temperature programmed reduction or desorption and fixed-bed reactions. The characterization results indicated that alkaline-earth metals strengthened FeO bonds of Fe2O3 in as-prepared catalysts, which consequently inhibited the reduction of catalysts under H2 atmosphere. Mg and Ca suppress the carbonization of catalysts while Sr and Ba enhance the carbonization. The H2 adsorption was suppressed while the CO adsorption was enhanced by alkaline-earth metals. In the FTS reaction, alkaline-earth metals had no apparent influence on the CO conversion of catalysts, whereas they suppressed the formation of methane and enhanced the selectivities to olefin and higher molecular weight products. Among these alkaline-earth metals, Sr has the most pronounced influence on inhibiting the light hydrocarbon production. Furthermore, the increased Sr content can further restrain the formation of light hydrocarbons.