Subject: Catalysts with the reaction of Zn and HCl to form H2 gas.

I am running an investigation looking at the effects of different 
catalysts on the rate of the above reaction. I used standard electrode 
potentials to predict several likely catalysts, and these were correct. 
However, I also tried Copper (II) ions (below the electrode potential of 
H+ system) and this nearly blew the gas syringe out! The answer to this 
phenomenon cannot be due to electrode potentials. Is it something to do 
with the reactivity series and displacement reactions?

Re: Catalysts with the reaction of Zn and HCl to form H2 gas.