A microscopic model for catalyst surfaces—II: Supported catalysts
Abstract A new “pebbly surface” model of supported metal catalysts is presented which can explain observed multiplicity and oscillatory behaviour of catalyst particles. This model combines the dynamic behavior of the individual metal crystallites on the surface of the support with diffusion and heat transfer processes in the porous particle. The bifurcation of oscillations is analyzed in terms of relaxation oscillations as well as by Hopf's theorem and it is shown how the bifurcation phenomena depend on the system parameters. The parameter study may be used to suggest operating conditions and catalyst design parameters such that sintering effects may be reduced. Qualitative comparisons with data for carbon monoxide oxidation at various temperatures show very good agreement; however, this present simple form of the pebbly surface model seems unable to predict the long period oscillations observed in hydrogen oxidation.
Corrosion and protection of the underwater steel structures for W114A platform were investigated.The offshore platform has been in service in the South China Sea for 15 years.It was found that the bio-fouling was serious and the maximum attachment thickness was 20cm,while,the cathodic protection system was normal and the protective effect was favorable.After analyzing the detective methods and their results,some problems were found.The program of potential detection was inappropriate,the detection method for physical size of the sacrificial anodes was inaccurate,and the base surface of the thickness measurement points was not clean;therefore,the cathodic protective effect could not be accuraely evaluated.To solve these problems,some valuable suggestions are put forward accordingly.