Development of Pre-Turbo Catalyst for Natural Gas Engines

Distributed power generation is an efficient method for reducing CO2 emissions through the elimination of transmission losses. Co-generation has similar benefits with higher thermal efficiency. Natural gas engines are very popular for these applications. Unfortunately, these engines emit significant levels of methane, which is a greenhouse gas. Reduction of methane emissions would greatly improve the environment and provide greenhouse gas emissions credits. The exhaust temperature downstream of the turbocharger in a natural gas engine is typically below 500°C. At these temperatures, methane is difficult to oxidize with current oxidation catalysts. It would be a much better option to install the oxidation catalyst before the turbocharger where temperatures are 100–150°C higher. Pressures upstream of the turbocharger are higher than downstream and also affect catalyst conversion efficiencies. Misfiring events are common in natural gas engines. During misfiring events, the catalyst will see a sudden increase in hydrocarbon (methane). When this pulse of hydrocarbon hits the catalyst, it will be oxidized and generate a large exotherm which could lead to catalyst failure (mechanical and/or chemical). This issue is critical for a pre-turbo catalyst: 1) Mechanical failure of the catalyst could lead to catastrophic turbocharger failure, a result of the turbine blades being damaged. 2) Misfiring with catalyst installed before the turbocharger is more likely to ignite the methane pulse because of the higher temperatures in this location. High exotherms from ignition could negatively affect catalyst performance. Through careful catalyst design, one can minimize this risk and this paper will address these issues.