CONVERSION OF METHYL RADICALS TO METHANOL AND FORMALDEHYDE OVER MOLYBDENUM OXIDE CATALYSTS

Methyl radicals, formed by the thermal decomposition of azomethane, were allowed to react over both MoO3 and MoO3/SiO2 catalysts. In the continuous flow mode, the dominant reaction was the homogeneous coupling of CH3. radicals to form C2H6; however, significant amounts of HCHO and CH3OH were also observed. Over MoO3 at 300 degrees C, CH3OH was the principal oxygenate, but at 500 degrees C the CH3OH was converted mainly to HCHO. At both temperatures, HCHO was the favored product over MoO3/SiO2. The addition of H2O to the reactants enhanced the formation of CH3OH at 300 degrees C. During temperature-programmed reaction studies, CH3. radicals were first allowed to react with MoO3/SiO2 at 150 degrees C, Methanol began to appear in the gas phase at about 170 degrees C and was the main product up to 400 degrees C. As a result of adding H2O continuously during the TPR experiment, CH3OH was produced at 80 degrees C, and the integral amount of CH3OH formed over the temperature range from 80 to 500 degrees C increased. These results are consistent with the view that CH3. radicals react with MoO3 to form surface methoxide ions. The methoxide ions may either decompose to form HCHO or they may react with surface protons or water to form CH3OH.