A Generalized Approach for Predicting Coverage-Dependent Reaction Parameters of Complex Surface Reactions:  Application to H₂Oxidation over Platinum

Abstract

A new methodology is presented for calculating parameters of complex surface reaction mechanisms. This approach takes into consideration adsorbate−adsorbate interactions along with their influence on the activation energies of surface reactions as a function of operating conditions. It combines an extension of the unity bond index−quadratic exponential potential theory, reactor scale modeling, important feature identification, and model validation. The H2 oxidation over platinum has been chosen as a model system to test this methodology. Comparison with a variety of available experimental data in the literature, such as catalytic ignition temperature, laser-induced fluorescence OH desorption measurements, catalytic autotherms, and species profiles, shows that the proposed surface mechanism is capable of quantitatively capturing all the important features of the published experiments. Our approach offers the potential of quantitative modeling of catalytic reactors exhibiting complex surface reaction processes under realistic operating conditions.

Microkinetic Study of CO Oxidation and PROX on Ir−Fe Catalyst

“…In the absence of H 2 (i.e., CO oxidation only), only steps 1-3 are involved in the reaction model. 30,39 The first step involves the adsorption of CO, whose initial heat was measured to be 120 kJ/mol. Because the adsorption energy decreases rapidly with the CO coverage, 12 we used an average value of 70 kJ/mol as an estimation of the activation energy for the desorption of CO.…”

Kinetics of ammonia oxidation over Pt foil studied in a micro-structured quartz-reactor

“…The reaction has been described as non-activated process with either constant initial sticking probability [16,[48][49][50], or an initial sticking coefficient that decreased with increasing temperature, resulting in slightly negative apparent activation energies (Pt(1 1 1): E A= − 2.6 kJ/mol [51]; Pt(4 4 3): E A = −7.5 kJ/mol [10]). Maximum coverage of adsorbed oxygen atoms and initial sticking coefficients vary with Pt crystal plane [51][52][53].…”

“…Water can be formed on the Pt surface via reaction OH + H [48,70], via OH + OH [48,70], and via NH x + OH [18,59]. The subsequent desorption is fast, leading to a negligible surface coverage of water under reaction conditions [10,16,70].…”

“…Moreover, non-activated reversible dissociative O 2 adsorption [16,[48][49][50]71] is supposed (E O 2 ads A ≡ 0). Furthermore, the simplifying assumption is made that the kinetics of oxygen desorption are coverage independent.…”

Microkinetic Modeling of the Oxygen Reduction Reaction at the Pt(111)/Gas Interface

“…Unlike several previous studies [21][22][23], which included fitting parameters to empirical data to bring the model into agreement with experimental results, their model is entirely first-principles-based, and allows the exploration of the influence of the cell voltage on the reaction rate and thus on the current density. Based on their mean-field kinetic model, they were able to distinguish between two electrode potential regimes, in which the ORR primarily proceeds by means of two different reaction pathways, as is manifest in the change in the Tafel slope.…”