Low temperature ethanol steam reforming: Selectivity control with lithium doping of Pt/m-ZrO2

Lithium promoted 2%Pt/m-ZrO2 catalysts previously observed to exhibit higher rates for the low temperature water-gas shift (LTS) were tested for the ethanol steam reforming with the aim of exploring the potential tuning of the selectivity. Characterization of catalysts having optimized Li content (0.5-0.75%Li) for LTS exhibited (a) weakened C-H bonding of formate, a proposed intermediate in the LTS mechanism, as shown by a shift in the nu(CH) band to lower wavenumbers, (b) a relatively low extent of blocking of Pt, as measured by the nu(CO) band intensity of Pt-CO, (c) increased basicity as measured by CO(2 )temperature-programmed desorption with mass spectrometry, but not so high as to strongly inhibit CO2 product removal, and finally (d) no evidence of electron transfer from Li to Pt. Here, the same catalysts were tested for ethanol steam reforming (ESR). Results show that Li could likewise weaken the C-C bond of the acetate intermediate, the analog of formate in LTS, and facilitate decarboxylation over decarbonylation altering the selectivity in favor of methanation. This trend was confirmed by fixed bed reaction testing, in-situ infrared spectroscopy experiments of transient ESR, and temperature -programmed ESR using MS. The Li-doped catalysts may be used to pre-reform ethanol prior to feeding to a methane steam reformer to increase the overall H2 selectivity of the process. DRIFTS of steady state ESR revealed that deactivation occurs through losses in the Pt-support interface, thereby hindering the turnover of the acetate intermediate.

Automated summary

The study found that lithium-promoted Pt/m-ZrO2 catalysts not only exhibit higher reaction rates in the low temperature water-gas shift (LTS) reaction, but also have the potential to tune the selectivity in ethanol steam reforming, promoting methanation. This suggests that lithium-doped catalysts can increase methane production by improving the selectivity of hydrogen in ethanol reforming.