Acatalyst is

the product of a combustion reaction

a solid product of a reaction

not used up in a reaction

one of the reactants in a single-replacement reaction

It is a mixture. simply put, a compound must be pure, that is, of only one chemical structure and composition. a mixture is made of different chemical substances (i.e. elements, molecules, compounds) that are not chemically bonded to each other, but instead physically grouped together, as in the case of gasoline (a homogeneous solution).