| Autor: |
Karatok M; Department of Chemistry and Chemical Biology, Harvard University, Cambridge, Massachusetts 02138, United States., Ngan HT; Department of Chemistry and Biochemistry, University of California, Los Angeles, California 90095, United States., Jia X; Department of Chemistry and Chemical Biology, Harvard University, Cambridge, Massachusetts 02138, United States., O'Connor CR; Department of Chemistry and Chemical Biology, Harvard University, Cambridge, Massachusetts 02138, United States., Boscoboinik JA; Center for Functional Nanomaterials, Brookhaven National Laboratory, Upton, New York 11973, United States., Stacchiola DJ; Center for Functional Nanomaterials, Brookhaven National Laboratory, Upton, New York 11973, United States., Sautet P; Department of Chemistry and Biochemistry, University of California, Los Angeles, California 90095, United States.; Department of Chemical and Biomolecular Engineering, University of California, Los Angeles, California 90095, United States., Madix RJ; School of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts 02138, United States. |
| Abstrakt: |
Palladium-silver-based alloy catalysts have a great potential for CO-free hydrogen production from formic acid for fuel cell applications. However, the structural factors affecting the selectivity of formic acid decomposition are still debated. Herein, the decomposition pathways of formic acid on Pd-Ag alloys with different atomic configurations have been investigated to identify the alloy structures yielding high H 2 selectively. Several Pd x Ag 1- x surface alloys with various compositions were generated on a Pd(111) single crystal; their atomic distribution and electronic structure were determined by a combination of infrared reflection absorption spectroscopy (IRAS), X-ray photoelectron spectroscopy (XPS), and density functional theory (DFT). It was established that the Ag atoms with Pd neighbors are electronically altered, and the degree of alteration correlates with the number of nearest Pd. Temperature-programmed reaction spectroscopy (TPRS) and DFT demonstrated that the electronically altered Ag domains create a new reaction pathway that selectively dehydrogenates formic acid. In contrast, Pd monomers surrounded by Ag are demonstrated to have a similar reactivity compared to pristine Pd(111), yielding CO and H 2 O in addition to the dehydrogenation products. However, they bind to the produced CO weaker than pristine Pd, demonstrating an enhancement in resistance to CO poisoning. This work therefore shows that surface Ag domains modified by interaction with subsurface Pd are the key active sites for selective decomposition of formic acid, while surface Pd atoms are detrimental to selectivity. Hence, the decomposition pathways can be tailored for CO-free H 2 production on Pd-Ag alloy systems. |
