Syngas conversion to higher alcohols: A comparative study of acid and base-treated mesoporous carbon-supported KCoRhMoS2 catalysts

Abstract

Ordered mesoporous carbons (OMC) of desirable textural properties have been synthesized by the novel one-pot soft-templating synthesis approach. Prior to catalyst metals loading, the OMC supports were functionalized using the wet chemical oxidation technique to introduce surface oxygen-containing functional groups for metals anchorage. In this regard, the crucial role functionalizing agents (acidic and basic) on the morphology & structural integrity of the parent OMC support was also investigated. It was observed that the structural integrity of the parent OMC material remained intact as confirmed by the TEM analyses. Moreover, less defective sites were generated as evidenced from the Raman spectroscopic analysis; suggesting that non-acidic oxidative treatment could be a mild way of introducing oxygen functionalities as metal anchoring sites on the surface of pristine OMC support. Based on the defective sites generated on the OMC supports, the severity of chemical oxidative treatment was observed to follow the trend: HNO3>NH4OH/H2O2>KOH. The HNO3, NH4OH/H2O2 and KOH treated-OMC supports were used to prepare a series of KCoRhMoS2 catalysts with nominal compositions of 9%K, 4.5%Co, 15%Mo, & 1.5wt.%Rh, respectively. Catalytic performance evaluations of these catalysts for syngas conversion to higher alcohols were also studied at similar reaction conditions: T=300–340°C, P=8.3MPa, GHSV=3600mL (STP)/h.gcat, and H2/CO=1.25. The HNO3-treated OMC-supported KCoRhMoS2 catalyst showed superior total alcohol productivity as compared to its NH4OH/H2O2 and KOH counterparts; probably due to the greater number of surface oxygen-containing functional groups, thereby, enhancing its metal-oxygen anchorage properties in the catalyst formulation. All catalysts showed an increase in CO conversion with incremental temperature with a maximum of 40.2% recorded for the KCoRhMo/OMC-HNO3 catalyst at T=330°C as opposed to 26.1 and 19.6% for the catalysts with KOH and NH4OH/H2O2 treatment, respectively.