Chromium based catalyst for low-CO hydrogen production by methanol steam reforming.

摘要

Methanol steam reforming (MSR) is used to produce hydrogen for fuel cells. A commercial Cu based catalyst, Cu/Zn/Al, is active for both MSR and water gas shift (WGS) reactions. Adding Zr into a Cu based catalyst reduces CO production in MSR, but CO concentration is still governed by the reverse WGS reaction at long contact times. Cr is used as the main component in a sol-gel catalyst, instead of Cu. This catalyst produces less CO even at high temperatures and also is not active for WGS. The temperature programmed reduction (TPR) profile indicates that the new catalyst is not reduced within the operation conditions, which means it is not pyrophoric. The mechanism is explored by using various spectroscopic analyses. Methanol dissociates to methoxide which converts to bidentated carbonate or formate species. Formate species could transform to bidentated bicarbonate which might convert to carbonate species. The presence of double bonded oxygen in Cr2O3 or CuO may be preferably for the formation of carbonate species. Carbonate species further decompose to CO2. A small amount of formate might contribute to CO formation by its decomposition. During MSR on the sol-gel catalyst Cr mainly provides the site to adsorb carbon containing intermediates, Zr supplies hydroxyl to react with all the intermediates, Cu serves as a hydrogen sink to accelerate the reaction. Excess Cu or Zr causes unexpected side reactions. A new MSR catalyst is developed based on our understanding of the mechanism, and it generates CO about 5000 ppm with the full conversion of methanol although it is not optimized.