Surface Chemistry

Observe the following reactions

I. $\mathrm{N}_2(g)+3 \mathrm{H}_2(g) \xrightarrow[773 \mathrm{~K}, 200 \mathrm{~atm}]{x} 2 \mathrm{NH}_3(g)$

II. $\mathrm{CO}(\mathrm{g})+\mathrm{H}_2 \mathrm{O}(\mathrm{g}) \xrightarrow[673 \mathrm{~K}]{Y} \mathrm{CO}_2(\mathrm{~g})+\mathrm{H}_2(\mathrm{~g})$

III. $\mathrm{CH}_4(g)+\mathrm{H}_2 \mathrm{O}(g) \xrightarrow[1270 \mathrm{~K}]{\mathrm{z}} \mathrm{CO}(g)+3 \mathrm{H}_2(g)$

Catalysts $X, Y, Z$ respectively are