Activation of ilmenite as an oxygen carrier for solid-fueled chemical looping combustion

•Improving ilmenite OC’s performance by adding a small amount of foreign elements.•Gasification and combustion efficiency are correlated to OC reactivity and selectivity.•Strong catalyzed WGSR from K-added OCs play vital role in improving gasification.•Cu-coating hinders Fe-element segregation on the ilmenite surface during redox cycle.•Ca-, Ni- and Mn-added ilmenite OCs did not show promising prospects.