Steam reforming of methanol over oxide decorated nanoporous gold catalysts: a combined in situ FTIR and flow reactor study

Abstract

Methanol as a green and renewable resource can be used to generate hydrogen by reforming, i.e., its catalytic oxidation with water. In combination with a fuel cell this hydrogen can be converted into electrical energy, a favorable concept, in particular for mobile applications. Its realization requires the development of novel types of structured catalysts, applicable in small scale reactor designs. Here, three different types of such catalysts were investigated for the steam reforming of methanol (SRM). Oxides such as TiO₂ and CeO₂ and mixtures thereof (Ce₁Ti₂O_x) were deposited inside a bulk nanoporous gold (npAu) material using wet chemical impregnation procedures. Transmission electron and scanning electron microscopy reveal oxide nanoparticles (1–2 nm in size) abundantly covering the strongly curved surface of the nanoporous gold host (ligaments and pores on the order of 40 nm in size). These catalysts were investigated in a laboratory scaled flow reactor. First conversion of methanol was detected at 200 °C. The measured turn over frequency at 300 °C of the CeO_x/npAu catalyst was 0.06 s⁻¹. Parallel investigation by in situ infrared spectroscopy (DRIFTS) reveals that the activation of water and the formation of OH_ads are the key to the activity/selectivity of the catalysts. While all catalysts generate sufficient OH_ads to prevent complete dehydrogenation of methanol to CO, only the most active catalysts (e.g., CeO_x/npAu) show direct reaction with formic acid and its decomposition to CO₂ and H₂. The combination of flow reactor studies and in operando DRIFTS, thus, opens the door to further development of this type of catalyst.