Why transition metals show catalytic properties?

Explanation

Many transition metal and their compound are found to acts as catalyst. Because of the presence of the incompletely d-subshell. They can form unstable intermediate give reaction path of lower activation energy and therefore increase the rate of reaction.
For Example : 1. Iron and molybdenum are used as catalyst in the manufacture of ammonia from `N_2` (g) and `H_2` (g) in Habber.s process.
`N_2(g)+3H_2(g) overset("Fe or Mo")harr 2NH_3(g)`