Hydrogen-bonded clusters in transformed Lewis acid to new Bronsted acid over WOx/SiO2 catalyst

The behavior of hydrogen species on the surface of the catalyst during the Lewis acid transformation to form Bronsted acid sites over the spherical silica-supported WOx catalyst was investigated. To understand the structure-activity relationship of Lewis acid transformation and hydrogen bonding interactions, we explore the potential of using the in situ diffuse reflection infrared Fourier transform spectroscopy (DRIFTS) with adsorbed ammonia and hydrogen exposure. From the results of in situ DRIFTS measurements, Lewis acid sites on surface catalysts were transformed into new Bronsted acid sites upon hydrogen exposure. The adsorbed NH3 on Lewis acid sites migrated to Bronsted acid sites forming NH4+. The results show that the dissociated H atoms present on the catalyst surface formed new Si-OH hydroxyl species - the new Bronsted acid site. Besides, the isolated Si-O-W species is the key towards H-bond and Si-OH formation. Additionally, the H atoms adsorbed surrounding the Si-O-W species of mono-oxo O=WO4 and di-oxo (O=)(2)WO2 species, where the Si-O-W species are the main species presented on the Inc-SSP catalysts than that of the IWI-SSP catalysts.