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Single‐atom alloy (SAA) catalysis research often reports that a SAA catalyst, in the general formulation of a single‐atom metal M1 alloyed on the surface of the host metal M2, facilitates a probe reaction. However, for catalytic reactions that present decoupled rate‐ and selectivity‐limiting steps, the alloying site density may significantly manipulate these independent steps, but it has rarely been explicitly examined for any SAA systems. Herein, using the electrocatalytic CO reduction as a probe reaction, we report that the nominal Pd1Cu cube SAA catalysts exhibit distinctive high reactivity toward ethylene or ethanol, respectively, depending on whether the Pd atoms are in dilute or crowded forms. Although the presence of single‐atom Pd embedded on Cu uniformly promotes CHO* formation and C─C coupling, the dilute‐Pd1Cu favors ethylene formation by enabling low‐barrier C─O cleavage from a flat CH2CH2OH* intermediate, whereas the crowded‐Pd1Cu promotes ethanol formation by stabilizing an upright hydrogenation transition state of the same intermediate. Furthermore, we present evidence that the catalytic chemistry of crowded Pd1 species differs from that of the Pd2‐dimer; the latter, albeit unstable, steers reaction selectivity to acetate instead. These results uncovered the underappreciated importance of controlling SAA catalytic chemistry from the perspective of single‐atom site densities.
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“Single Pd Atom–In2O3 Catalyzes Production of CH3CH2OH from Atom-Economic C–C Coupling of HCHO and CH4.”,
Using methane as a reagent to synthesize high-value chemicals and high-energy density fuels through C−C coupling has attracted intense attention in recent decades, as it avoids completely breaking all C−H bonds in CH4. In the present study, we demonstrated that the coupling of HCHO with the CH3 species from CH4 activation to produce ethanol can be accomplished on the single Pd atom−In2O3 catalyst based on the results of density functional theory (DFT) calculations. The results show that the supported single Pd atom stabilizes the CH3 species following the activation of one C−H bond of CH4, while HCHO adsorbs on the neighboring In site. Facile C−C coupling of HCHO with the methyl species is achieved with an activation barrier of 0.56 eV. We further examined the C−C coupling on other single metal atoms, including Ni, Rh, Pt, and Ag, supported on In2O3 by following a similar pathway and found that a balance of the three key steps for ethanol formation, i.e., CH4 activation, C−C coupling, and ethoxy hydrogenation, was achieved on Pd/In2O3. Taking the production of acetaldehyde and ethylene on the Pd/In2O3 catalyst into consideration, the DFT-based microkinetic analysis indicates that ethanol is the dominant product on the Pd/In2O3 catalyst. The facile C−C coupling between HCHO and dissociated CH4 makes formaldehyde a potential C1 source in the conversion and utilization of methane through an energy- and atom-efficient process.
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- Award ID(s):
- 2150489
- PAR ID:
- 10584197
- Publisher / Repository:
- NSF-PAR
- Date Published:
- Journal Name:
- ACS catalysis
- ISSN:
- 2155-5435
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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