FT-IR spectroscopy has been utilized to study the adsorption of acetaldehyde over Al-MCM 41 using a specially designed ultrahigh vacuum IR cell. At 233 K the surface –OH groups involves in H-bonding with carbonyl oxygen of acetaldehyde, however, as the temperature is raised, a fraction of acetaldehyde undergoes condensation and dehydration reaction forming crotonaldehye surface species. The oxidation reaction of adsorbed aldehyde was carefully monitored both in the dark and in presence of UV-Visible light to explore the effect of light including the mechanism of photodecomposition. Mass spectral studies were utilized to monitor the products of photooxidation.