Oxygen-Enhanced Water Gas Shift over Bimetallic Catalysts for More Efficient Hydrogen Production

Water gas shift (WGS) and deep CO removal are critical for hydrogen production and low-temperature fuel cell applications. Our recent work demonstrates the significant advantage of oxygen-enhanced water gas shift (OWGS) for more efficient H₂ production over bimetallic catalysts, wherein a small amount of O₂ is added to reformate gas to enhance CO shift.  Pd-Cu and Pt-Cu bimetallic catalysts supported on CeO₂ show strong synergetic promoting effect in OWGS, which leads to much higher CO conversion and higher H₂ yield than WGS at low temperature around 250 ^oC. TPR showed strong interaction between Pd and Cu in Pd-Cu/CeO₂ by a single reduction peak in contrast to multiple peaks on monometallic Cu/CeO₂. EXAFS analysis revealed that such bimetallic Pd-Cu and Pt-Cu form alloy nanoparticles, where noble metal is mainly surrounded by Cu atoms. OSC measurements point to higher resistance of Pd-Cu to oxidation indicating that Pd keeps Cu in reduced state in air pulse condition. From kinetic study, Pd in Pd-Cu was found to promote CO shift, rather than CO oxidation, and Cu in Pd-Cu suppress H₂ activation (that is inherent to monometallic Pd), which minimizes both the inhibition effect of H₂ and the loss of H₂ by oxidation in OWGS. Transient response technique revealed that Cu in Pd-Cu enhances desorption of strongly chemisorbed CO₂ on catalyst surface in contrast to very slow CO₂ desorption from surface of monometallic Pd. The role of CeO₂ support will also be discussed.