Process of SCR Catalyst Deactivation by Dimethylsiloxanes Present in Marine Fuels

Abstract

AbstractIn recent years, there have been reports of the deactivation of selective catalytic reduction (SCR) exhaust gas catalysts after a short period of operation in marine applications. The trigger and the processes of this catalyst damage have now been investigated experimentally using a fuel burner test bench and various analysis techniques. It was found that organic silicon compounds (OSCs), which are present in marine fuels after use in mineral oil extraction and processing, cause the catalyst deactivation. In practice, these are predominantly dimethylsiloxanes. By the burner experiments, it was found that the OSCs were completely converted into combustion products, in particular SiO2. Measurements of particle size distributions and particle number concentrations up- and downstream of the catalyst showed that SiO2 particles < 20 nm in particular were retained in the catalyst. This filtration effect decreased until no further reduction was observed for particles > 50 nm. Other inorganic, particulate, SiO2-containing fuel impurities (catalyst fines) had no poisoning effect here, as these particles are mostly > 50 nm. The small particles formed a closed SiO2 layer with a thickness of approx. 5 µm on the catalyst surface which grew from the catalyst inlet to the outlet and blocked the catalyst as a diffusion barrier. As the SiO2 layer increased, the NO conversion rate decreased. The poisoning effects were observed experimentally at OSC concentrations of 5 to 60 mg Si kg−1 fuel. A field-aged catalyst that had been operated on board of a merchant ship revealed the same findings.