A mixture of products does not necessarily involve a chemical reaction! How do you recognize a reaction? By looking for atomic transformations in the matter! Basically, were bonds between atoms broken or made?
A mixture is simple contact between two compounds. A chemical reaction gives birth to new molecules with different properties than those of the original compounds.

A catalyst helps speed up very slow reactions. This is done through a catalyzer.
Notice how a car without a catalytic converter in its exhaust system emits a great deal of noxious molecules produced by the motor.
On the other hand, catalyzed vehicles have a catalytic converter (cerium or platinum oxide) in the exhaust system that facilitates oxygen exchanges between the pollutants, thus transforming them into less harmful products.