In the present work, circulating fluidized bed boiler (CFB) fly ash and pulverized coal boiler (PC) fly ash were selected as raw material to prepare silica sulfuric acid by sulfuric acid activation. Physical and chemical properties of CFB and PC fly ash after sulfuric acid activation were comprehensively compared by using different techniques. In addition, the effects of acid activation temperature, acid activation time, and calcination temperature on silica sulfuric acid prepared from CFB fly ash were also investigated. Finally, NO removal efficiencies of the silica-supported sulfuric acid with gas-phase H2O2 were tested on a fixed bed reactor, and the possible reaction pathways, stability test and the effects of simulated flue gas temperature, H2O2 concentration, and SO2 concentration on NO removal were discussed.