Why is more of a catalyst added, when it is not consumed? … catalysis, the acceleration of chemical reactions by substances not consumed in the reactions themselves—substances known as catalysts.


(Source)

Now as I’ve understood, to keep a reaction going, you must keep the solution heated and sometimes add more of the catalyst. Why then, is the definition that the catalyst is not consumed? Something of the catalyst must surely be 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.