Density functional theory adsorption modes

This range of possible adsorption modes for acetone prompted us to study the alternative adsorption possibilities for formaldehyde, as an example where the eno/ form is not possible, and acetone on Pt and Pd surfaces using periodic density functional theory. A previous theoretical study in this area has been published by Dumesic e al. however they have concentrated on the reaction pathway for hydrogenation of acetone over Pt(lll) assuming the r (0)-acetone is the only adsorbed state present. In this contribution we compare adsorption of acetone in the enol and keto isomers on both Pt(l 11) and Pd(l 11). 

Ruthenium has long been known to be an effective catalyst for ammonia synthesis. However, compared to the traditional iron-based catalysts, studies on ruthenium-based catalysts are limited. The rate determining step of ammonia synthesis, the dissociative adsorption of dinitrogen, has been shown to extremely structure sensitive on both iron and mthenium catalysts. To study this structure sensitivity on ruthenium, density functional theory calculations were performed on Ru(OOl) and Ru(llO) clusters. End-on, side-on, and dissociated adsorption states were investigated on both surfaces. While the Ru(llO) cluster could stabilize aJl three adsorption modes, a minimum energy structure for the side-on adsorption on Ru(OOl) could not be found. It is likely that this side-on mode can provide a low energy pathway to the dissociated state, thereby resulting in faster dissociative adsorption on Ru(llO). 

TERS on DNA bases was demonstrated for the hrst time in 2004 by Watanabe et al. In that work, experiments and density-functional theory (DFT) calculations on adenine molecules in a nanocrystal were presented. From the acquired spectra, which differed from standard Raman spectra, it was concluded that those crystals were mechanically deformed in contact-mode TERS [74]. Consequently, band shifts were observed and attributed to interactions of molecule and metal tip. Comparing SER and TER spectra, a band shift could be observed, too, mainly caused by more specihc interactions of adenine and metal. In SERS of adenine on silver island hims, molecules were evenly attached to the rough surface by the amino group and its adjacent nitrogen atoms (N1 and N7). In contrast, in contact-mode TERS experiments (i.e., tip always touches the sample), the silver tip was constantly moved over the molecules with a force of - 5 pN per molecule. Based on theoretical calculations, the authors concluded that the TERS probe was selectively pressed to one nitrogen atom (namely N3). Later it was shown that in contact-mode TERS, an adsorption-desorption process of the molecule at the tip could be responsible for the band shift [62]. 

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