Al + KNO3 + 2 H2O → NO + K[Al(OH)4]
This is a complexation reaction: K[Al(OH)4] is the formed complex.
This is an oxidation-reduction (redox) reaction:
Al0 - 3 e- → AlIII (oxidation)
NV + 3 e- → NII (reduction)
Al is a reducing agent, KNO3 is an oxidizing agent.