Article pubs.acs.org/JPCC
NH3−NO Coadsorption System on Pt(111). I. Structure of the Mixed Layer Angelo Peronio,†,‡,§,# Andrea Cepellotti,†,▲ Stefano Marchini,†,§,¶ Nasiba Abdurakhmanova,§,○ Carlo Dri,†,§ Cristina Africh,§ Friedrich Esch,§,◊ Maria Peressi,†,∥,⊥ and Giovanni Comelli*,†,‡,§ †
Department of Physics, Università degli Studi di Trieste, via Alfonso Valerio 2, 34127 Trieste, Italy Center of Excellence for Nanostructured Materials (CENMAT), Università degli Studi di Trieste, via Alfonso Valerio 2, 34127 Trieste, Italy § IOM-CNR Laboratorio TASC, Area Science Park, s.s. 14 km 163.5, Basovizza, 34149 Trieste, Italy ∥ IOM-CNR DEMOCRITOS Theory@Elettra Group, Sincrotrone Trieste, Area Science Park, s.s. 14 km 163.5, Basovizza, 34149 Trieste, Italy ⊥ Consorzio Interuniversitario Nazionale per la Scienza e la Tecnologia dei Materiali (INSTM), Unità di ricerca di Trieste, piazzale Europa 1, 34128 Trieste, Italy ‡
ABSTRACT: In the selective catalytic reduction (SCR) process, nitrogen oxides are selectively transformed to N2 by reductants such as ammonia. The specificity of this reaction on platinum-based catalysts was tentatively attributed to the formation of NH3−NO coadsorption complexes, as indicated by several surface science techniques. Here we combine scanning tunneling microscopy (STM) and density functional theory (DFT) calculations to characterize the NH3−NO complex at the atomic scale on the (111) surface of platinum, investigating the intermolecular interactions that tune the selectivity. In this first article, we analyze the structures that arise upon coadsorption of NH3 and NO in terms of adsorption sites, geometry, energetics, and charge rearrangement. An ordered 2 × 2 adlayer forms, where the two molecules are arranged in a configuration that maximizes mutual interactions. In this structure, NH3 adsorbs on-top and NO on fcc-hollow sites, leading to a cohesional stabilization of the extended layer, calculated to be 0.29 eV/unit cell. The calculated vibrational energies of the coadsorption structure agree with the experimental values found in the literature.
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INTRODUCTION The reduction of nitric oxide by ammonia to form N2 and water has a prominent role in the control of NOx emission from industrial and automotive processes. Ammonia (NH3) is added to the exhaust gases flowing on a catalyst that promotes selective NO reduction without favoring other undesired, concurrent reactions such as O2 reduction.1 The most common catalysts for this selective catalytic reduction (SCR) process are based on metal oxides or zeolites, whereas for low-temperature applications (
