In this study, phase changes, catalytic active species that appeared at the phase change, and the corresponding water tolerance of samples obtained upon thermal treatment from K2CO3-supported microsized and nanosized sodalite as diesel-soot combustion catalyst are examined. We have shown the successful preparation of nepheline with water tolerance from sodalite as starting material. It is confirmed that the interaction between alkali metal carbonate and crystalline aluminosilicate is prerequisite for enhancing water tolerance of the catalytically active component, Na/K carbonate, located on the nepheline.