Correlating the degree of metal–promoter interaction to ethanol selectivity over MnRh/CNTs CO hydrogenation catalysts

• CNT supported rhodium catalysts with variable amounts of Mn promoter were synthesized and evaluated for CO hydrogenation.
• The active phase of the promoter is identified by XANES and EELS as MnO.
• The enhancement in the degree of metal–promoter interaction leads to an increase in the ethanol selectivity.

Multi-walled carbon nanotubes (MCNTs) were used as a support for Rh-based catalysts for high pressure (20 bar) CO hydrogenation. 3 wt% Rh/CNTs catalysts were loaded with 1 wt% and 2 wt% Mn promoter, respectively, in order to study the effect of metal–promoter interactions for ethanol synthesis. Both STEM and EXAFS results showed ∼1 nm Rh particles in promoted as well as the unpromoted catalysts, STEM and EELS results verified the enhanced metal–promoter interaction when the amount of Mn promoter increased from 1 wt% to 2 wt%. The enhancement in the degree of metal–promoter interaction leads to an increase in the ethanol selectivity. Moreover, due to the nature of CNTs (low Z number), the Mn–Rh interactions could be observed at atomic resolution during the STEM–EELS characterization, and the promoter phase is confirmed as Mn(II) oxide by XANES and EELS.

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