In presence of acetanilide, the rate of decomposition of H2O2 reduced. Acetanilide is called a positive catalyst.
There are few reactions in which catalyst can slow down the chemical reaction. These types of catalyst are called as negative catalyst.
Example: Decomposition of hydrogen peroxide can be slowed down if some substances like glycerin, urea, acetanilide, sodium pyrophosphate etc are added to H2O2