The pair of metals refined by "vapour phase refining" is

Vapour phase refining process involves conversion of a metal into a volatile compound and then it is decomposed to obtain pure metal.

Nickel is purified by Mond process: Impure nickel is heated in a stream of carbon monoxide to form a volatile complex which is further decomposed to obtain pure nickel.

$\mathrm{Ni} + 4\mathrm{CO} \stackrel{350 \mathrm{K}}{\to }\mathrm{Ni}{\left(\mathrm{CO}\right)}_4\stackrel{470 \mathrm{K}}{\to }\mathrm{Ni}\left(\mathrm{pure}\right) + 4\mathrm{CO}$

Van Arkel method: Zirconium or titanium is purified by this method. Zirconium is heated in iodine vapours to form a volatile complex at $870\mathrm{K}$ which is further decomposed to obtain pure metal.

$\mathrm{Zr} + 2{\mathrm{I}}_2\stackrel{870 \mathrm{K}}{\to }{\mathrm{ZrI}}_4\stackrel{1800\mathrm{K}}{\to }\mathrm{Zr}\left(\mathrm{pure}\right) + 2{\mathrm{I}}_2$