Surface structure and metathesis activity of photoreduced allyl-based Mo/SiO2 catalysts

XPS and metathesis activity studies were performed on oxidic allyl-based Mo /SiO2 catalysts (0.5 wt% Mo) and the oxidic catalyst following photoreducti on to various extents. XPS results and average oxidation state measurements from the amount of CO2 formed during photoreduction, indicated that contro lled photoreduction of the oxidic catalyst, in CO atmosphere, produces a mi xture of Mo6+ and Mo4+ oxidation states with Mo4+ in abundances ranging fro m 0 to 100%. Propene metathesis activity studies were performed on the oxid ic and photoreduced allyl-based Mo/SiO2 catalysts. The results indicated th at metathesis activity appears on photoreduction and increases linearly wit h increasing abundance of Mo4+ present on the catalyst. The linear relation ship between the % propene conversion and the % Mo4+ present on the catalys t is consistent with the proposed uniformity of the Mo species and with the hypothesis that the active site (or active site precursor) is associated w ith Mo4+.