Principle of Catalysts [closed]








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How exactly do Catalysts work? In the cracking of Alkanes, Aluminum Oxide is used as a catalyst. However how does Aluminum Oxide decrease the conditions required to undergo cracking. At the molecular level, what is actually happening? How can a catalyst increase the rate of a reaction without being used itself?




Here is how a metallic surface catalyzes the reaction of $\ce{H2}$ + $\ce{O2}$. First $\ce{H2}$ reacts with the metal $\ce{M}$, making weak $\ce{M-H}$ bonds at its surface. As a consequence, the covalent bond between the two $\ce{H}$ atoms is extended, and weakened. Seen from outside, it looks as if the surface of the metal $\ce{M}$ is covered by nearly free $\ce{H}$ atoms. If $\ce{O2}$ molecules are touching one of these $\ce{H}$ atoms, it can make a O-H hydrogen bond in O-O-H-M. If this hydrogen bond is weaker than the $\ce{H-M}$, the reactive molecule $\ce{HO2}$ will quit the metallic surface and reacts later with other atoms, molecules or radical to produce $\ce{H2O}$ at the end.


The catalytic effect of $\ce{Al2O3}$ on alkanes may be similar to this mechanism.


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