What is an simple way to burn glucose for visible effect?
You could combine the demonstration that glucose can be burned with the principle of catalysis: a sugar cube won't burn by itself if you hold a match at it. Using a bit of MnO2 or even simple ash on the cube will make it inflammable through catalysis: the MnO2 acts as catalysator (is not used up).

MnO2 (manganese(IV) oxide), a dark powder, is a safe chemical that only reacts with acids, and is insoluble in water.