Kleine moleculen in een wereld van twee dimensies

De uitlaatgaskatalysator onder de auto rnaakt koolrnonoxide, stikstofoxide en onverbrande benzine onsehadelijk. Dit gebeurt op het oppervlak van de in de katalysator aanwezige platina- en rhodiurndeeltjes. In dit artikel bekijken we wat kleine rnoleeulen zoals CO en NO zoal kunnen beleven als ze zich op een rnetaaloppervlak bevinden

Reaction between NO and CO on Rh(100): how lateral interactions lead to auto-accelerating kinetics

The reactions between NO and CO adsorbed on Rh(100) were studied with temperature programmed reaction spectrometry and static secondary ion mass spectrometry and compared with similar reactions on Rh(111). Elementary steps in the overall reactions, such as dissociation of NO, and reaction between CO and O atoms were studied as well. Dissociation of NO is faster on the more open Rh(100) surface, while formation of N2 is slower. Desorption of either CO or NO occurs at comparable rates on Rh(100) and Rh(111). The oxidation of CO to CO2 proceeds much faster on Rh(100) than on Rh(111). When the Rh(100) surface is saturated with NO and CO, explosive formation of CO2 is observed, which can be explained by an autocatalytic mechanism, in which the availability of empty sites plays a crucial role

NO dissociatie op Rh(100) : het modelleren van de NO dissociatie op Rh(100) met dynamische Monte Carlo simulaties

No Abstrac

Formation of NH3 and N-2 from Atomic Nitrogen and Hydrogen on Rhodium(111)

Reactions of adsorbed N atoms on Rh(111) to N2 and NH3 were studied with temp. programmed desorption, temp. programmed reaction spectroscopy, and static secondary ion mass spectrometry. For N-atom coverages below ~0.15 monolayers, desorption of N2 follows simple second-order kinetics, but at higher coverages the desorption traces broaden to higher temps. Hydrogenation to NH3 can be described by a stepwise addn. of H atoms to Nads in which the reaction from NH2,ads+Hads to NH3,ads dets. the rate. The activation energy for the rate detg. step is 76 kJ/mol. The desorption of NH3 from Rb(111) was studied sep. The kinetic parameters for desorption at low NH3 coverage are 81 kJ/mol and 1013 s-1, but the rate of desorption increases rapidly with increasing NH3 coverage. It is argued that the remarkable coverage dependence of the desorption rate is unlikely to be caused by lateral repulsive interactions but may be due to a coverage of the pre-exponential facto