Compressed natural gas combustion and exhaust system

A compressed natural gas combustion and exhaust system comprising:

• (i) a natural gas combustion engine and
• (ii) an exhaust treatment system comprising an intake for receiving an exhaust gas from the combustion engine and a catalyst article arranged to receive and treat the exhaust gas, wherein the catalyst article comprises:
• a substrate having at least first and second coatings, the first coating comprising a palladium-containing alumina and/or a base-metal containing alumina and the second coating comprising a palladium-containing zeolite,
• wherein the first coating is arranged to contact the exhaust gas before the second coating;
• and, wherein the system is configured to selectively operate in:
• (a) a lean first mode in which sulphur is trapped on the first coating;
• and
• (b) a rich second mode whereby sulphur is released from the first coating;
• the system further comprising
• (iii) a sulphur trap downstream of the catalyst article for receiving sulphur released from the first coating during the rich second mode.