Catalysts Development For The Conversion of Syngas to Higher Alcohols Using Alkali-promoted MoS2-based Catalysts Over Carbon Supports

Abstract

Conversion of syngas to mixed (C1-C5) and higher (C2+) alcohols over alkali-doped MoS2 (ADM) catalysts, promoted with cobalt (Co) and rhodium (Rh), has exhibited great potential for commercial higher alcohols synthesis (HAS) reaction. Carbon-based supports with attractive physico-chemical and mechanical properties have immense potential to be explored for the HAS catalyst development. Due to their characteristic properties such as high surface area, thermal stability, and chemical inertness, this Ph.D study sought to explore three main carbon-based supports namely; multi-walled carbon nanotubes (MWCNTs), ordered mesoporous carbon (OMC) and carbon nanohorns (CNHs) for HAS catalyst formulation. The overall research objective was to explore options to develop novel carbon-supported ADM catalyst systems to effectively convert syngas to higher alcohols. The novelty of the work is in two folds: 1) to investigate the influence of binders incorporation, pelletization, and particle size on the HAS reactions using carbon (MWCNT, OMC and CNH)-supported KCoRhMoS2 catalyst systems; and 2) to explore OMCs and CNHs as new support systems for the HAS reactions. The influence of binders (bentonite clay, coal tar, and humic acid) addition, catalyst pelletization as well as the comparison of MWCNT and large-pore OMC-supported KCoRhMo catalyst systems were investigated in phases 1 and 2, respectively. Extensive studies in phases 3, 4 and 5 are enumerated as: 3) the comparative study of chemical pre-treatments (acid and base) of OMC-supported KCoRhMoS2 catalysts; 4) the optimization of binder (BC) loadings on OMC-supported KCoRhMoS2 catalysts and their catalytic performance study; and 5) the synthesis, characterization and application of novel K-promoted CoRhMo catalysts supported over CNH and its by-products (OCPf & OCP) for the HAS reactions. Finally, the impacts of process parameters (temperature, pressure, and gas-hourly-space-velocity) were evaluated using the optimum KCoRhMo/CNH catalyst. The power law model was then used to fix the experimental data in the kinetic study to ascertain the activation energies (Ea) of ethanol and propanol. Low values of Ea (54.4 and 92.2 kJ/mol, respectively) were obtained compared to those reported by other researchers. Long-term deactivation study of the sulfided KCoRhMo/CNH catalyst corroborated its durability over 500 h of continuous HAS reaction in a fixed bed reactor.