Methanol steam reforming on LaCo1−x−yPdxZnyO3±δ

Abstract

Perovskite-type oxides LaCo1−x−yPdxZnyO3±δ are studied for the methanol steam reforming (MSR) reaction. LaCo1−x−yPdxZnyO3±δ with and without Co substitution by Pd and/or Zn are synthesized by the amorphous citrate method. The effect of substitution on the reducibility of the materials is investigated by in situ XRD and differential thermal/thermogravimetric analysis (DTA/TG) during temperature programmed reduction (TPR) with hydrogen. From this, the phase composition evolving as a function of temperature is determined. The TPR data indicate that the reducibility of the materials strongly depends on the substituent, i.e., Pd or Zn. The former increases the reducibility, while substitution by Zn decreases the reducibility. Materials containing both Pd and Zn exhibit intermediate reducibility as compared to the un-substituted LaCoO3±δ (LCO) and mono-metal substituted LaCo0.873Pd0.127O3±δ (LCPO) and LaCo0.89Zn0.11O3±δ (LCZO). In general, the metal ions in the materials are completely reduced at 590°C, except La2O3. After reductive pre-treatment at 590°C for 2h, the MSR performance of the materials is evaluated between 150 and 400°C while keeping comparable CH3OH conversion to assess the product-concentration-dependent CO2 selectivity. These results confirm that the CO2 selectivity is strongly dependent on the material composition. For example, the un-substituted LCO, LCPO and LCZO show a CO2 selectivity of around 13% at 300°C, while it is improved to 80% on both Pd and Zn containing LaCo0.85Pd0.075Zn0.075O3±δ (LCPZO-15).