Insight on mechanism of Sn modification in alumina supported RhSn catalysts for acetic acid hydrogenation to fuel-grade ethanol

- RhSn/Al2O3 with high Sn/Rh ratio was suitable for acetic acid hydrogenation.
- Coexistence of metallic Rh and Sn oxides enhanced hydrogen spillover.
- Tin(II) species can stabilize top adsorption of acetyl species.

Acetic acid hydrogenation has been carried out over Rh/Al2O3 and RhSn/Al2O3 with various Sn/Rh ratios and different loadings. Metallic Rh, Rh oxides and Sn oxides were detected after reduction of RhSn/Al2O3 at 623 K. Spillover of hydrogen was observed in H2 desorption process due to the coexistence of metallic Rh and Sn oxides. The addition of Sn improved dissociation of COH bond and stabilized top adsorption of acetyl species during the adsorption of acetic acid at 548 K. With the introduction of hydrogen, high Sn/Rh ratio suppressed methane production and generated more ethoxy species. High loadings of Sn and Rh can also improve catalytic performance of acetic acid hydrogenation to ethanol. In our experiments, 3Rh5Sn/Al2O3 achieved the selectivity to ethanol of 74% with the corresponding conversion value of about 98%.

73