Selective Formic Acid Dehydrogenation on Pt-Cu Single-Atom Alloys

详细信息    查看全文

• 作者：Matthew D. Marcinkowski ; Jilei Liu ; Colin J. Murphy ; Melissa L. Liriano ; Natalie A. Wasio ; Felicia R. Lucci ; Maria Flytzani-Stephanopoulos ; E. Charles H. Sykes
• 刊名：ACS Catalysis
• 出版年：2017
• 出版时间：January 6, 2017
• 年：2017
• 卷：7
• 期：1
• 页码：413-420
• 全文大小：466K
• ISSN：2155-5435

文摘

Formic acid is a potential hydrogen storage molecule which dehydrogenates to form CO₂ and H₂ on metal surfaces. However, it can also decompose via a competing dehydration reaction that forms CO and H₂O, reducing the amount of H₂ produced and poisoning the catalyst with CO. Formic acid re-formation to hydrogen is typically performed by Pt and Pd catalysts, which while highly active for dehydrogenation also catalyze dehydration. Cu is typically not utilized, as it requires prohibitively high temperatures, although Cu surfaces are very selective toward dehydrogenation. We studied the reaction of formic acid on single-atom alloys (SAAs), consisting of single Pt atoms substituted into a Cu lattice. Surface science studies allowed us to relate alloy structure to reactivity and selectivity and visualize reaction intermediates. These experiments revealed that SAAs are able to selectively dehydrogenate formic acid with a 6-fold increase in yield in comparison to Cu. This increase in conversion is due to a more facile dehydrogenation of formic acid to formate on the SAA surface (120 K vs 160 K on Cu(111)). We acquired quantitative desorption and molecular scale imaging data showing spillover of formate from Pt sites to Cu. Increasing the Pt concentration beyond the SAA regime resulted in loss of selectivity. These results prompted us to test SAA nanoparticle (NP) catalysts under realistic conditions. However, only a slight increase in conversion was observed between pure Cu and Pt-Cu SAA NPs. In our surface science studies, dehydrogenation of formate to CO₂ and H₂ did not occur until above 400 K on both the SAA and pure Cu surfaces, indicating that Pt sites do not catalyze this rate-limiting step. While SAAs do not offer increased reactivity for formic acid dehydrogenation, they do offer significantly lower barriers for O–H bond breaking, which holds promise for other dehydrogenation reactions.