Discerning the Metal Doping Effect on Surface Redox and Acidic Properties in a MoVTeNbOx for Propa(e)ne Oxidation

Abstract

[EN] Adding a small quantity of K or Bi to a MoVTeNbOx via impregnation with inorganic solutions modifies its surface acid and redox properties and its catalytic performance in propa(e)ne partial oxidation to acrylic acid (AA) without detriment to its pristine crystalline structure. Bidoping encourages propane oxydehydrogenation to propene, thus enlarging the net production rate of AA up to 35% more. The easier propane activation/higher AA production over the Bi-doped catalyst is ascribed to its higher content of surface V leading to a larger amount of total V5+ species, the isolation site effect of NbOx species on V, and its higher Lewis acidity. K-doping does not affect propane oxydehydrogenation to propene but mainly acts over propene once formed, also increasing AA to a similar extent as Bidoping. Although K-doping lowers propene conversion, it is converted more selectively to acrylic acid owing to its reduced Brønsted acidity and the presence of more Mo6+ species, thereby favoring propene transformation via the ¿-allylic species route producing acrylic acid over that forming acetic acid and COx via acetone oxidation and that yielding directly COx.