Preparation and characterization of Co–Fe nano catalyst for Fischer–Tropsch synthesis: Optimization using response surface methodology

Abstract

A Co–Fe–resol/SiO2 nano catalyst was prepared by a simple and cheap co-precipitation method for the Fischer–Tropsch synthesis (FTS) and characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), temperature programmed reduction (TPR), Fourier transform infrared (FT-IR), energy dispersive X-ray (EDX), and N2 adsorption–desorption. The effect of calcination conditions was investigated and it was found that the catalyst calcined at 650 °C for 6 h is almost free of resol. The TPR spectrum showed lower reduction temperatures respect to similar Co–Fe catalysts. After the Fischer–Tropsch reaction, a sintered irregular surface with lower surface area, pore volume, and pore diameter was obtained which may be due to diffusion of reactants and products into the pores. Analysis of variance (ANOVA) for FTS was carried out by the central composite design (CCD) using response surface methodology (RSM). Four operational factors namely; pressure, H2/CO molar ratio, gas hourly space velocity (GHSV), and temperature were selected for design of experiments. As GHSV increases, the CO conversion and selectivity toward light hydrocarbons (LHCs) decrease while selectivity toward heavy hydrocabons (HHCs) and alcohols (ROH) increases because the contact time between the feed and catalyst surface decreases.