Chemoselective hydrogenation of aromatic ketones plays an important role in producing fine chemicals and pharmaceuticals. One of the simplest model reactions is acetophenone (AP) hydrogenation to corresponding alcohol 1-phenylethanol (PE). We studied the role of dominant product 1-phenylethanol (PE) on a Pt/Al2O3 catalyst. In situ attenuated total reflection infrared spectroscopy (ATR-IR) in combination with modulation excitation spectroscopy (MES) and phase sensitive detection (PSD) revealed that PE was more strongly adsorbed on Al2O3 than on Pt. PE was hardly hydrogenated to 1-cyclohexylethanol (CE) on the support. CO from AP decomposition didn’t inhibit PE adsorption on the support. The strong adsorption and accumulation of PE on the support allows active sites on Pt always accessible to AP, achieving efficient Pt-catalyzed catalysis.