Researchers from China and the US have synthesized gold layered clusters on an α-MoC substrate to create an interfacial catalyst system for the ultra-low-temperature water-gas shift (WGS) reaction for the production of high-purity hydrogen and concomitant utilization of carbon monoxide (CO). The discovery, described in a paper in the journal Science, could improve the performance of fuel cells that run on hydrogen fuel but can be poisoned by CO.
In the work described in the paper, water was activated over α-MoC at 303 K (30 ˚C), while the CO adsorbed on adjacent Au sites reacted with surface hydroxyl groups formed from water splitting, leading to a high WGS activity at low-temperatures.
Low-temperature efficient catalysts for the WGS reaction, especially those operating under 423 K, are of interest for applications in fuel cells, especially those use H2 generated by hydrocarbon reforming processes that are contaminated with CO, which deactivates the catalysts. For the heterogeneous catalysis, besides Cu based catalysts which display low activity at low temperature, Pt group noble metals and Au supported on reducible metal oxides, like ceria or FeOx which contain oxygen vacancies, are commonly used. Flytzani-Stephanopoulos and co-workers demonstrated that noble metal catalysts dispersed on alkali promoted inert supports can also be active for WGS, making a reducible oxide support no longer a requirement.
… In order to achieve high WGS activity at low temperature, we searched for catalysts that could dissociate water efficiently and reform the generated oxygen-containing species (reaction of surface oxygen or hydroxyl with CO*) at low temperature. We report that Au confined over face centered cubic (fcc) structured α-MoC is at least one order of magnitude more active than previous reports for the WGS reaction below 423 K. The α-MoC substrate facilitates epitaxially-grown atomic Au layers with altered electronic structure for favorable bonding with CO. Its synergy with adjacent Mo sites in α-MoC can effectively activate water at low temperature.—Yao et al.
As a result of the catalyst operating at low temperature and low pressure to convert water and carbon monoxide to hydrogen gas and carbon dioxide, it could also lower the cost of running the WGS reaction.
With low temperature and pressure, energy consumption will be lower, making the process less expensive and easier to use in small settings, such as in fuel cells for cars.
Siyu Yao, Xiao Zhang, Wu Zhou, Rui Gao, Wenqian Xu, Yifan Ye, Lili Lin, Xiaodong Wen, Ping Liu, Bingbing Chen, Ethan Crumlin, Jinghua Guo, Zhijun Zuo, Weizhen Li, Jinglin Xie, Li Lu, Christopher J. Kiely, Lin Gu, Chuan Shi, José A. Rodriguez, Ding Ma (2017) “Atomic-layered Au clusters on α-MoC as catalysts for the low-temperature water-gas shift reaction” Science doi: 10.1126/science.aah4321