Repositori URV

Identifier: TDX:891

Handle: https://hdl.handle.net/20.500.11797/TDX891

Authors:
Gómez Díaz, Jaime

Abstract:
In this dissertation, the mechanisms that govern four essential industrial processes have been studied by means of Density Functional Theory (DFT). The processes are the following: Ostwald (HNO3 production), Degussa and Andrussow (HCN production) and MacArthurForrest (gold recovery). In these processes, ammonia is the main raw material or a precursor of it.The KohnSham equations that describe the model systems have been solved by means of VASP and GPAW using the RPBE functional. These packages make use of periodic boundary conditions to simulate an infinite solid as model of the real metal surface.Ostwald Process: The first step of this process, NO formation, has been studied on the (111) and (211) surfaces of Au, Cu, Ir, Pd, Pt and Rh metals. The reactions involved have been analyzed as well in the PtRh alloy (the one used in industry). The thermodynamic stability of Pt and Rh oxides as a function of the temperature and the pressure of oxygen has been described. Finally, the volatility of these oxides has been calculated to determine catalyst loses in form of PtO2 and RhO2 gases.Good selectivity towards NO formation has been found for Pt metal. The desorption of NO has been found determinant for several metals that produce NO on the surface but hardly leaves it. The addition of Rh impurities to Pt does not increase its reactivity, but Rh oxides are more stable than Pt ones and Rh is less prone to form volatile oxides.Degussa and Andrussow Processes: The formation of CN bonds from individual atoms and hydrogenated moieties on a series of transition and noble metals has been studied there.A comprehensive study on all the possible couplings between partially hydrogenated species, CHx and NHy, on Pt(111) surface is shown. The differences between the mechanism under the dis