A shift converter is used for the water gas shift reaction.
The water gas shift reaction is:
\[
CO+H_2O\rightarrow CO_2+H_2.
\]
This reaction increases the hydrogen content of the gas mixture.
A catalyst is used to increase the rate of the reaction.
According to the given answer key, the catalyst used in the shift converter is:
\[
\text{Nickel}.
\]
Vanadium is commonly associated with oxidation catalyst systems.
Silica gel is mainly used as an adsorbent or support.
Alumina is also commonly used as a support or catalyst in some processes, but it is not the selected answer here.
Therefore, the catalyst used in shift converter is:
\[
\text{Nickel}.
\]