Effect of Drying Temperature on Iron Fischer-Tropsch Catalysts Prepared by Solvent Deficient Precipitation

Abstract

A novel solvent deficient precipitation (SDP) method to produce nanoparticles was studied for its potential in Fischer-Tropsch synthesis (FTS) catalysis. Using Fe(NO 3 ) 3 ⋅9H 2 O as the iron-containing precursor, this method produces ferrihydrite particles which are then dried, calcined, reduced, and carbidized to form the active catalytic phase for FTS. Six different drying profiles, including final drying temperatures ranging between 80 and 150 ∘ C, were used to investigate the effect of ammonium nitrate (AN), a major by-product of reaction between Fe(NO 3 ) 3 ⋅9H 2 O and NH 4 HCO 3 in the SDP method. Since AN has two phase-transitions within this range of drying temperatures, three different AN phases can exist during the drying of the catalyst precursors. These AN phases, along with physical changes occurring during the phase transitions, may affect the pore structure and the agglomeration of ferrihydrite crystallites, suggesting possible reasons for the observed differences in catalytic performance. Catalysts dried at 130 ∘ C showed the highest FTS rate and the lowest methane selectivity. In general, better catalytic performance is related to the AN phase present during drying as follows: phase III > phase II > phase I. However, within each AN phase, lower drying temperatures led to better catalytic properties.

Synthesis of Dimethyl Ether via CO2 Hydrogenation: Effect of the Drying Technique of Alumina on Properties and Performance of Alumina-Supported Copper Catalysts

“…During catalyst preparation, drying and calcination are known to be the important steps that strongly affect the textural properties of a catalyst (in such terms as surface area, pore size, and pore volume); distribution of the active metal on a support , and interaction between active sites and a support are also known to be affected by these two preparation steps . While hot air drying has traditionally been used for catalyst preparation, alternative drying techniques such as freeze drying and microwave drying have also been studied. ,− Different drying techniques and conditions have noted to differently affect the pore size, Brunauer–Emmett–Teller (BET) surface area, dispersion of metal on a support, and hence the performance of a catalyst. , Albretsen et al, for example, reported that an iron-based catalyst dried at 130 °C had larger pore volume, surface area, extent of reduction, and Fischer–Tropsch synthesis rate but lower methane selectivity compared to identical catalysts dried at higher or lower temperatures. Villegas et al found that metal dispersions, especially in the case of Ni, were strongly influenced by the applied drying method; Ni dispersion was more homogenous upon microwave drying or ambient-temperature drying than in the case of oven drying.…”