Method of removing ash from particulate filter

A method of removing ash from a wall flow type particulate filter which is arranged in an exhaust passage of an internal combustion engine in which combustion is performed in an excess of oxygen for trapping particulate matter in exhaust gas, using a solid acid which is carried on the particulate filter, the method wherein

• the method renders the state of the particulate filter a state where the exhaust gas which flows into the particulate filter is lowered in concentration of oxygen and the particulate filter is raised in temperature to thereby atomize the ash and hold the atomized ash in the solid acid in a dispersed state,
• then renders the state of the particulate filter a state where the exhaust gas which flows into the particulate filter in an oxidizing atmosphere contains SOx to thereby release the atomized ash which is held at the solid acid from the solid acid and make it be released from the particulate filter.