$AP\frac{d}{}-A{l}_2{O}_3$ supported catalyst is characterized for specific surface area based on the

nitrogen adsorption isotherm in which adsorption volume, $V_{\text{a}\text{d}\text{s}}(c{m}^{3}STP)$ and nitrogen

partial pressure $\frac{p}{p_0}$ data are collected. When the obtained data are plotted according to

the usual Brunauer$-$Emmet$-$Teller, $($BET$)$ method between the value of

$y-$intercept is found to be $3\mathrm{.}96{10}^{-4}$ and the gradient for the linear line is $0\mathrm{.}0122.$

Taking the surface area covered by a single $N_2$ molecule is $0\mathrm{.}162n{m}^2,$ calculate the

specific area of $0\mathrm{.}55g$ catalyst sample.

$(12$ marks$)$

After being used for catalytic combustion of organic pollutants in air at $550C$ in

a packed bed reactor, the surface area is found to drop by $30\%.$ Suggest reasons

leading to the observation $($at least $3).$

$(3$ marks$)$