Comparison of MoO₃ and WO₃ on arsenic poisoning V₂O₅/TiO₂ catalyst: DRIFTS and DFT study

The mechanisms of arsenic poisoning on MoO₃- and WO₃-doped V₂O₅/TiO₂ catalysts are studied and the poisoning resistance effect of MoO₃ are revealed. The arsenic at certain amount (above 10% of arsenic from XPS) decreases the surface area and the number of active sites where reduction takes place. From the results of DRIFTS and DFT, arsenic lowers the surface acidity by decreasing the quantity of Lewis acid sites and the stability of Brønsted acid sites. We also found newly formed As-OH groups of poisoned catalysts (at 1440cm^-1) have quite low activity at high temperature. MoO₃ provides better activity on poisoned catalysts than WO₃ does on V₂O₅/TiO₂ catalysts. This may be due to the good dispersion of MoO₃ on the support. The reactivity of surface W-O-W and W=O groups is considerably lower than the corresponding Mo-O-Mo and Mo=O groups from the DFT calculations models. This could be one of the explanations on the decrease of surface acidity of poisoned catalysts.