Why is more of a catalyst added, when it is not consumed?
In short, a catalyst does participate in a chemical reaction the rate of which it increases, it just do so in a somewhat tricky way so that it does not appear in the overall reaction equation.

Wikipedia article on catalysis provides a concise explanation of why this is the case:


  Catalysts generally react with one or more reactants to form
  intermediates that subsequently give the final reaction product, in
  the process regenerating the catalyst. The following is a typical
  reaction scheme, where $\ce{C}$ represents the catalyst, $\ce{X}$ and $\ce{Y}$ are
  reactants, and $\ce{Z}$ is the product of the reaction of $\ce{X}$ and $\ce{Y}$:
  $$
     \ce{X + C → XC} \tag{1}
$$
  $$
     \ce{Y + XC → XYC} \tag{2}
$$
  $$
     \ce{XYC → CZ} \tag{3}
$$
  $$
     \ce{CZ → C + Z} \tag{4}
$$
  Although the catalyst is consumed by reaction 1, it is subsequently
  produced by reaction 4, so it does not occur in the overall reaction
  equation:
  $$
    \ce{X + Y → Z} \, .
$$
  As a catalyst is regenerated in a reaction, often only small amounts
  are needed to increase the rate of the reaction. In practice, however,
  catalysts are sometimes consumed in secondary processes.