Is it possible to make an anticatalyst?
Some substances do exist that slow down reactions and they're different from catalytic inhibitors/poisons. Such substances are called negative catalysts. Here is one example I can think of right now:
$$\ce{2H2O2 \xrightarrow{\large\mathrm{glycerol}} 2H2O + O2}$$

Glycerol, in this case behaves as a negative catalyst and slows down the reaction.

Another notable example you might have heard is tetraethyllead (TEL) which was used in petrol to prevent knocking.

It may be tempting to think that a negative catalyst will raise the energy of activation for a given reaction, however this isn't true. It takes away the internal energy of reactants and deactivates them to reduce the rate of a reaction.