Performance Degradation and Poison Build-Up of an Oxidation Catalyst in Two-Stroke Natural Gas Engine Exhaust

Abstract

Due to current and future exhaust emissions regulations, oxidation catalysts are increasingly being added to the exhaust streams of large-bore, two-stroke, natural gas engines. Such catalysts have a limited operational lifetime, primarily due to chemical (i.e., catalyst poisoning) and mechanical fouling resulting from the carry-over of lubrication oil from the cylinders. It is critical for users and catalyst developers to understand the nature and rate of catalyst deactivation under these circumstances. This study examines the degradation of an exhaust oxidation catalyst on a large-bore, two-stroke, lean-burn, natural gas field engine over the course of 2 years. Specifically, this work examines the process by which the catalyst was aged and tested and presents a timeline of catalyst degradation under commercially relevant circumstances. The catalyst was aged in the field for 2-month intervals in the exhaust slipstream of a GMVH-12 engine and intermittently brought back to Colorado State University for both engine testing and catalyst surface analysis. Engine testing consisted of measuring catalyst reduction efficiency as a function of temperature as well as the determination of the light-off temperature for several exhaust components. The catalyst surface was analyzed via scanning electron microscope (SEM)/energy dispersive X-ray spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS) techniques to examine the location and rate of poison deposition. After 2 years online, the catalyst light-off temperature had increased ∼55 °F (31 °C) and ∼34 wt % poisons (S, P, Zn) were built up on the catalyst surface, both of which represent significant catalyst deactivation.