A microkinetic model of ammonia decomposition on a Pt overlayer on Au(1 1 1)

• Published in: Journal of molecular catalysis. A, Chemical Chemical, 2010-06, Vol.325 (1), p.15-24
• Main Authors: Rasim, Karsten, Bobeth, Manfred, Pompe, Wolfgang, Seriani, Nicola
• Format: Article
• Language: English
• Subjects: Ab initio simulation; Ammonia decomposition; Catalysis; Chemistry; Condensed Matter; Exact sciences and technology; General and physical chemistry; Gold; Kinetic model; Materials Science; Physics; Platinum; Theory of reactions, general kinetics. Catalysis. Nomenclature, chemical documentation, computer chemistry
• ISSN: 1381-1169; 1873-314X
• DOI: 10.1016/j.molcata.2010.03.021

Ammonia decomposition on the surfaces Pt(1 1 1), Pt(1 0 0), and a Pt overlayer on Au(1 1 1) has been studied by DFT calculations. Steady-state surface coverages and ammonia decomposition rates have been obtained by microkinetic modeling. Interestingly the Pt overlayer on Au(1 1 1) has been found to be significantly more active with respect to ammonia decomposition compared to the pure Pt surfaces. Ammonia decomposition is important for a series of technological applications. For developing efficient catalysts for this reaction, basic understanding of underlying mechanisms is fundamental. We have investigated ammonia decomposition on platinum (1 1 1) and (1 0 0) surfaces, and on a platinum overlayer on a (1 1 1) gold substrate within a microkinetic model. The kinetic parameters in the corresponding rate equations have been estimated on the basis of ab initio calculations of reaction and activation energies for the adsorption and dehydrogenation processes on the catalyst surface. Steady-state coverages of species participating in the decomposition have been determined as solution of the rate equations in the limiting case of small ammonia concentrations of an N 2–NH 3 model gas mixture under flow conditions. Calculated turnover frequencies of ammonia decomposition as a function of the temperature reproduce characteristic features reported for platinum wires. The highest turnover frequency and hydrogen coverage have been obtained for the platinum overlayer on gold. Potential application of this system as ammonia-sensing device is discussed.