Octahedral Ni-nanocluster (Ni85) for Efficient and Selective Reduction of Nitric Oxide (NO) to Nitrogen (N2)

Arup Mahata,Kuber Singh Rawat,Biswarup Pathak,Indrani Choudhuri

doi:10.1038/srep25590

Arup Mahata, Kuber Singh Rawat + Show 2 more

Open Access

https://doi.org/10.1038/srep25590

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Journal: Scientific Reports	Publication Date: May 9, 2016
Citations: 16	License type: CC BY 4.0

Affiliation: Indian Institute of Technology Indore

Abstract

Nitric oxide (NO) reduction pathways are systematically studied on a (111) facet of the octahedral nickel (Ni85) nanocluster in the presence/absence of hydrogen. Thermodynamic (reaction free energies) and kinetic (free energy barriers, and temperature dependent reaction rates) parameters are investigated to find out the most favoured reduction pathway for NO reduction. The catalytic activity of the Ni-nanocluster is investigated in greater detail toward the product selectivity (N2 vs. N2O vs. NH3). The previous theoretical (catalyzed by Pt, Pd, Rh and Ir) and experimental reports (catalyzed by Pt, Ag, Pd) show that direct N-O bond dissociation is very much unlikely due to the high-energy barrier but our study shows that the reaction is thermodynamically and kinetically favourable when catalysed by the octahedral Ni-nanocluster. The catalytic activity of the Ni-nanocluster toward NO reduction reaction is very much efficient and selective toward N2 formation even in the presence of hydrogen. However, N2O (one of the major by-products) formation is very much unlikely due to the high activation barrier. Our microkinetic analysis shows that even at high hydrogen partial pressures, the catalyst is very much selective toward N2 formation over NH3.

Highlights

Nitric oxide (NO) reduction pathways are systematically studied on a (111) facet of the octahedral nickel (Ni85) nanocluster in the presence/absence of hydrogen
Experimental and theoretical studies have been carried out for NO reduction reactions catalysed by Ni-catalysts[31,32,33,34,35,36,37], and it is reported that NO undergoes dissociative adsorption over Ni-catalyst[38], resulting in the formation of N2 as a major product
The binding energies are in very much agreement with previous studies[6,7,35,36,37] though some of our calculated binding energies are higher than the previous reported values

Summary

Introduction

Nitric oxide (NO) reduction pathways are systematically studied on a (111) facet of the octahedral nickel (Ni85) nanocluster in the presence/absence of hydrogen. The previous theoretical (catalyzed by Pt, Pd, Rh and Ir) and experimental reports (catalyzed by Pt, Ag, Pd) show that direct N-O bond dissociation is very much unlikely due to the high-energy barrier but our study shows that the reaction is thermodynamically and kinetically favourable when catalysed by the octahedral Ni-nanocluster. Experimental and theoretical studies have been carried out for NO reduction reactions catalysed by Ni-catalysts[31,32,33,34,35,36,37], and it is reported that NO undergoes dissociative adsorption over Ni-catalyst[38], resulting in the formation of N2 as a major product. Apart from different metal based catalysts, the surface morphology and size of the metal catalyst play important roles in the bond scission process, which in turn control the catalytic activity of a metal catalyst. We have modelled a ~1 nm size of octahedral nickel nanocluster (Ni85) enclosed by well-defined low index facets [eight (111) facets] to understand the NO reduction activity (Fig. 1)

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Results