Irradiation at 266 nm of Ti silicalite (TS-1) molecular sieve loaded with CO and CH3OH gas at 173 K gave methyl formate as the main product. The photoreaction was monitored in situ by FT-IR spectroscopy and was attributed to reduction of CO at LMCT-excited framework Ti centers under concurrent oxidation of methanol. Infrared product analysis based on experiments with (CO)-O-18, (CO)-C-13, and (CH3OH)-C-13 revealed that carbon monoxide is incorporated into the eater as a carbonyl moiety. It is proposed that CO is photoreduced by transient Ti3+ to HCO radical in the primary redox step. This finding opens up the possibility for synthetic chemistry of carbon monoxide in transition metal materials by photoactivation of framework metal centers.