beta-silicomolybdic acid (SMA)/SiO2 was successfully prepared and its catalytic activity in methanol partial oxidation was studied. After catalytic study, beta-SMA was transformed into two other types of alpha-MoO3 that had different Raman relative peaks ratios upon the pre-treatment prior to the reaction. On the other hand, alpha-SMA/SiO2 was also prepared for comparison. alpha-SMA was decomposed into surface oxomolybdates species which favored the formation of COx while MoO3 was formed from beta-SMA and promoted HCHO formation.