Abstract

Ketene, a versatile reagent in production of fine and specialty chemicals, is produced from acetic acid. We investigate the synthesis of ketene from acetic acid over the (3,0;1,1) surface of Cu2O(100) through analysis of the adsorption and desorption characteristics of formic and acetic acids. The results allow us to establish a reaction mechanism for ketene formation. Observations from x-ray photoelectron spectroscopy (XPS), scanning tunneling microscopy, and temperature programmed desorption (TPD), supported by a comparison with formic acid results, suggest that acetic acid reacts with Cu2O through deprotonation to form acetate species coordinated to copper sites and hydroxylation of nearby surface oxygen sites. For formic acid the decomposition of adsorbed formate species results in desorption of CO2 and CO while, for acetic acid, high yields of ketene are observed at temperature >500 K. Modeling by density functional theory (DFT) confirms the strong interaction of acetic acid with the (3,0;1,1) surface and the spontaneous dissociation into adsorbed acetate and hydrogen atom species, the latter forming an OH-group. In an identified reaction intermediate ketene binds via all C and O atoms to Cu surface sites, in agreement with interpretations from XPS. In the vicinity of the adsorbate the surface experiences a local reorganization into a c(2 × 2) reconstruction. The total computed energy barrier for ketene formation is 1.81 eV in good agreement with the 1.74 eV obtained from TPD analysis. Our experimental observations and mechanistic DFT studies suggests that Cu2O can operate as an efficient catalyst for the green generation of ketene from acetic acid.

Highlights

  • The chemical flexibility of Cu2O, that allows for facile storage or release of oxygen atoms, has rendered reactions over its surface a topic of great interest for heterogeneous catalysis

  • The clean Cu2O(1 0 0) surface was first exposed to 1 Â 10À8 mbar of formic acid for 5 min at 120 K in the preparation chamber and, after transfer to the analysis chamber, analyzed by x-ray photoelectron spectroscopy (XPS)

  • XPS and temperature programmed desorption (TPD) observations suggest that low temperature adsorption of both formic and acetic acid results in formation of thick layers of physisorbed acid molecules

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Summary

Introduction

The chemical flexibility of Cu2O, that allows for facile storage or release of oxygen atoms, has rendered reactions over its surface a topic of great interest for heterogeneous catalysis (e.g. watersplitting [1,2], oxidation [3,4], dehydrogenation [5], photochemical CO2 reduction reactions [6]). Ketene has been identified as a reaction product in the temperature range from 500 K to 700 K with yields dependent on chemical nature, composition, and structure of the surface [13,14,15,16,17,18,19] Among these surfaces, acetic acid adsorption and decomposition have been investigated on TiO2 surfaces, both from an experimental and theoretical point of view, and can be compared to the results obtained from Cu2O surfaces [17,20,21,22,23,24]. Acids were stored in glass vials and purified by several freeze-pumpthaw cycles before introduction to the analysis chamber via a leak valve

XPS details
Experimental section
TPD details
Computational details
Results
Discussion
Author information
Conclusions
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