Gas-phase oxygen oxidation of alkylaromatics over CVD Fe/Mo/DBH: VIII. Alteration of the oxidation mechanism of xylenes by Ag-doping Original Research Article

The Ag-doped Fe/Mo/deboronated borosilicate molecular sieve, Ag/Fe/Mo/partially deboronated borosilicate molecular sieve (DBH), was prepared by impregnating an aqueous solution of AgNO3 solution onto the calcined CVD Fe/Mo/DBH catalyst by the incipient wetness technique. The Ag-doped catalyst had surface area significantly lower than that of CVD Fe/Mo/DBH, and the Ag2+ ions were enriched on the surface, and associated with Fe2(MoO4)3 and MoO3 phases. This brought about a dramatic change in the para-selective oxidation mechanism of xylenes exhibited by the undoped CVD Fe/Mo/DBH counterpart. Para-selective oxidation path as well as the side reactions were almost completely suppressed. The “pair” site responsible for the formation of terephthaldehyde in the p-xylene oxidation and acidic site of the DBH matrix causing the side reactions were almost completely poisoned by the Ag-doping. Consequently, p-tolualdehyde produced on the remaining “single” site became a predominant product at the expense of terephthaldehyde over Ag/Fe/Mo/DBH.