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

Abstract

Adding a small quantity of K or Bi to a MoVTeNbO x 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. Bi-doping 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 V 5+ species, the isolation site effect of NbO x 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 Bi-doping. 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 Mo 6+ species, thereby favoring propene transformation via the π-allylic species route producing acrylic acid over that forming acetic acid and CO x via acetone oxidation and that yielding directly CO x .

Tuning catalysis by surface-deposition of elements on oxidation catalystsviaatomic layer deposition

“…Recently, a doping study on MoVTeNbO x with Bi showed a similar effect of increased AA selectivity, which was correlated to a more oxidized surface state and also an increased Lewis acidity. 104 In contrast, the MnO x -modified sample shows an even more reduced oxidation state of V compared to the base catalyst, which is maintained after reaction. Thus, the low AA selectivity measured on this catalyst is consistent with the discussion above.…”

Decarbonizing Petrochemical Processes: Contribution and Perspectives of the Selective Oxidation of C1–C3 Paraffins

“…48%, despite the decrease in the quantity of phase M1. 274 In a recent publication by our group, 259 the impregnation of MoVTeNbOx with inorganic solutions of K or Bi led to changes in the acid and RedOx surface properties that improved the catalytic behavior in propane oxidation to acrylic acid reaching yields of ca. 45% at 380 °C, with Bidoping participating earlier in propane's pathway compared to K-doping.…”

“…The main pathway to acrylic acid is accompanied by a set of side reactions yielding not only other oxygenate species (acetone, acetic acid, propanol, propanoic acid, etc.) but also the total oxidation product (Figure ); all these reactions are exothermic reactions, which is an important additional challenge in the catalyst design and the reactor configuration . The diverse formulations historically designed for catalyzing the direct oxidation of propane to acrylic acid have been classified into three general groups, namely, vanadium pyrophosphates (e.g., V–P–O, Fe–P–O, Mn–P–O, Cu–P–O, etc.…”

“…ration 259. The diverse formulations historically designed for catalyzing the direct oxidation of propane to acrylic acid have been classified into three general groups, namely, vanadium pyrophosphates (e.g., V−P−O, Fe−P−O, Mn−P−O, Cu−P− O, etc.…”

Cr-doped Mesoporous M1 Phase MoVTeNbOx Catalyze Selective Oxidation of Propane to Acrylic Acid

“…It is reported that breaking the C-H bond is the limiting step in the oxidative dehydrogenation of propane and that this step occurs at the active site consisting of V ions on the surface of the M1 phase. Therefore, V 5+ ions are considered the active site for alkane activation [48,49]. In Fig.…”