Insights into promoter-enhanced aqueous phase CO hydrogenation over Co@TiO2 mesoporous nanocomposites

Abstract

The particle sizes and metal support interactions play a pivotal role in Fischer Tropsch synthesis. Herein, promoter-embedded Co/TiO2 mesoporous nanocomposites with a high surface area were synthesized through a templated assisted solvothermal method comprising highly dispersed spherical shaped Co nanoparticles on titania nanoparticles of less than 10 nm. Moreover, Fischer Tropsch synthesis in aqueous media, rather than wax-slurry, is a new and relatively attractive approach to improve product selectivity and catalyst isolation. The Aqueous phase Fischer-Tropsch (AFTS) is a unified catalytic process to improve CO conversion and enhance selectivity towards higher hydrocarbon (C5+) at low temperatures. The performance under aqueous phase CO hydrogenation was investigated with varying cobalt, platinum, and manganese promoter concentrations to obtain an optimized catalyst recipe for AFTS. The metal support interaction has been studied with the help of temperature-programmed reduction (TPR) couple with XPS and HRTEM analysis. Moreover, the dispersibility of the active species was demonstrated through H2 chemisorption coupled with pulse reoxidation experiments. The CO-TPD and STEM analysis have been performed to understand the role of manganese during the reaction. The reaction parameters have been optimized thoroughly by varying temperature and pressure conditions. The catalyst with the optimized recipe (3 M0.5P25C) and parameters performed the exceptional CO conversion at a rate of 1.75 molCO.molCo−1.h−1 (excluding CO2) with 73% selectivity towards C5+ hydrocarbons with less than 5% methane. Additionally, despite the aqueous phase, CO conversion rates for 3M1P25C were kinetically modeled well by standard Fischer-Tropsch empirical rate expressions, with little H2O term dependence.