Abstract
The relative stability of carboxylates on Au(110) was investigated as part of a comprehensive study of adsorbate binding on Group IB metals that can be used to predict and understand how to control reactivity in heterogeneous catalysis. The binding efficacy of carboxylates is only weakly dependent on alkyl chain length for relatively short-chain molecules, as demonstrated using quantitative temperature-programmed reaction spectroscopy. Corresponding density functional theory (DFT) calculations demonstrated that the bidentate anchoring geometry is rigid and restricts the amount of additional stabilization through adsorbate-surface van der Waals (vdW) interactions which control stability for alkoxides. A combination of scanning tunneling microscopy (STM) and low-energy electron diffraction (LEED) shows that carboxylates form dense local islands on Au(110). Complementary DFT calculations demonstrate that adsorbate-adsorbate interactions provide additional stabilization that increases as a function of alkyl chain length for C2 and C3 carboxylates. Hence, overall stability is generally a function of the anchoring group to the surface and the inter-adsorbate interaction. This study demonstrates the importance of these two important factors in describing binding of key catalytic intermediates.
Highlights
Heterogeneous catalysis is key to ensuring sustainability in chemical transformations.[1]
One approach to establishing such principles is the creation of a database of key properties (“descriptors”) that can be related to catalytic performance;[2,3,4,5,6] for example, binding energies of key intermediates to speci c materials
Experimental work determined that carboxylate species, while strongly bound to the surface, have a much weaker dependence of stability on alkyl chain length compared to alkoxides
Summary
Heterogeneous catalysis is key to ensuring sustainability in chemical transformations.[1]. Carboxylates are intermediates in the oxidation of alcohols and ole ns, yielding both carboxylic acids and CO2, and electrochemical reduction of CO2.10–27 Carboxylate intermediates strongly bind to surfaces so as to block sites.[17,22,23,24] For example, carboxylates formed in over-oxidation of alcohols block subsequent formation of the key alkoxide intermediates; suppressing activity.[17] Because of the broad importance of carboxylates in oxidation catalysis, we have systematically investigated them to develop a hierarchy of binding strength and to provide a more detailed understanding of the factors that dictate their stability This investigation is part of the development of a database for key intermediates on Group IB metals (Cu, Ag and Au), following on our prior studies of alkoxides.[28,29,30,31,32,33] binding of carboxylates to Au(110) is investigated because of the broad interest in it as a selective oxidation catalyst.[34,35,36,37,38,39,40]
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