Synthesis of higher alcohols from syngas over alkali promoted MoS 2 catalysts supported on multi-walled carbon nanotubes

Abstract

An extensive study of higher alcohol synthesis from synthesis gas using potassium (K) promoted molybdenum sulfide supported on multi-wall carbon nanotubes (MWCNT) catalysts is reported. Up to 20 wt.% of Mo and 9 wt.% of K are added to the MWCNT by incipient wetness impregnation method. The catalysts are extensively characterized by different methods and the activity and selectivity of the catalysts are assessed in a fixed-bed micro-reactor. Increasing the amount of K from 3 to 9 wt.% increased K–Mo–O interactions, decreased the Mo particle sizes from 20.6 to 12.2 nm and increased the percentage dispersion from 20.2% to 30.9%. Most of the metal particles (∼80%) were homogeneously distributed inside the tubes and the rest on the outer surface of the MWCNT. Temperature programmed reduction (TPR) tests showed that increasing the amount of Mo increased the first and second TPR peak temperatures from 516 and 765 to 530 and 835 °C, respectively. However, addition of K decreased the peak temperatures from 534 and 825 to 519 and 787 °C, respectively. DRIFT spectroscopy of absorbed CO was used to study the nature of active species in the sulfided form of catalysts. Addition of K increased the formation of alcohols and suppressed the formation of hydrocarbons. Catalyst 15 wt.% Mo and 9 wt.% K supported on MWCNT showed the highest yield (0.11 g of total alcohol/g catalyst/h) and selectivity (25.6%) towards alcohols. The optimum conditions for producing the higher alcohols from synthesis gas (mole ratio of H 2 and CO is equal to 2) using gas hourly space velocity (GHSV) of 3.6 m 3 (STP)/h/kg of catalyst are determined to be 320 °C and 9.65 MPa (1400 psig).