I have focused on important issues in the field of catalysis research, namely, the development of generic tools for the in silico screening of new catalysts. I studied two environmental catalysis processes of immense importance: NH3 oxidation and hydrogen assisted selective catalytic reduction of NOx using NH3. I have developed models for including the adsorbate-adsorbate interactions for both single site and multi-site surfaces to study the effect of incorporating adsorbate-adsorbate interactions in prediction of catalytic rates. I also have worked on the method for obtaining the shape of the nanoparticles under reaction condition by combining the microkinetic modeling with the Wulff construction. The developed methods and mechanisms in this thesis give a better understanding of current catalysts and give guidence in the development of highly reactive, selective and stable future industrial and environmental catalysts.