Poisoning of automotive methane oxidation catalysts by silicon compounds

Biomethane production offers a viable option to meet the growing demands of renewable energy sources in the transportation sector. However, biomethane contains trace amounts of impurities, such as siloxanes, that can potentially hinder the methane oxidation catalyst performance and lead to excessive greenhouse gas emissions. To investigate this potential problem, the commercial methane oxidation catalysts were poisoned in a laboratory setup with two common siloxanes found in biomethane and with their combustion product, silica. The performances of the clean and poisoned methane oxidation catalysts were measured under realistic lean-burn conditions, after which the catalyst structural changes were determined using XRD, BET and CO chemisorption. The results revealed two different possible poisoning mechanisms. First, both tested siloxanes poisoned the catalysts by migrating selectively on top of the active metal sites and became combusted to form amorphous silica. This caused the methane oxidation performance to drop rapidly with relatively small amounts of siloxane used. In contrast, a significantly higher dose of silica was required to produce a similar poisoning effect because its poisoning mechanism is based on nonselective deposition and physical blocking of the catalyst surface.