Acrolein Oxidation to Acrylic Acid on Mo/V/W‐Mixed Oxide Catalysts

Abstract

Oxidation of acrolein to acrylic acid on Mo/V/W-mixed oxide catalysts has been studied by means of the isotopic exchange method steady-state isotopic transient kinetic analysis (SSITKA). As a result of these isotopic exchanges performed with 16 O 2 and 18 O 2 , some new mechanistic details could be obtained. Acrolein exchanges its oxygen with oxygen of the mixed oxide catalyst. Additionally, the kinetics of the different isotopologues is significantly influenced by oxygen exchange reactions between the surface and the bulk sites. From the SSITKA results, an extended reaction model has been deduced. Thus, the experimentally gained data of the individual isotopologue kinetics could be verified by modeling.

Kinetic Modeling of Acrolein Oxidation Over a Promoted Mo−V Oxide Catalyst

“…Aldehydic and aromatic byproducts of acrolein oxidation observed at carbon selectivities below 0.1 % mar the downstream purification and polymerization of acrylic acid . Past studies have noted production of CO and CO 2 as well as acetic acid,, during selective acrolein oxidation over MoVO x and similar materials, while we reported production of other C 2 and C 4 −C 7 products in a recent publication . In this work, we report a kinetic model based off of the mechanisms for acrolein oxidation recently formulated by Miller and Bhan…”

Activity Hysteresis during Cyclic Temperature‐Programmed Reactions in the Partial Oxidation of Acrolein to Acrylic Acid

“…The role of bulk oxygen in the catalytic mechanism has already been discussed in previous works [14,26,28,30,48,50,[52][53][54]. This participation is considered by a reversible reaction between bulk and surface and, thus, is directly related to the concentration of reduced bulk and surface sites or to the bulk and surface degree of reduction, respectively.…”

“…D ax is the axial dispersion coefficient, u is the flow velocity, both in direction of the spatial coordinate x , and ν i,j are the stoichiometric coefficients of the component i in the reaction j. D ax was estimated from residence time experiments to a constant value of 2 × 10 −5 m 2 s −1 , , . Thus, an independency of D ax from temperature and gas composition is approximated.…”

“…From X‐ray absorption (XAS) measurements it is known that Mo +VI and V +V can be reduced under reaction‐relevant conditions to Mo +IV and V +IV , respectively. Tungsten as W +VI does not change its oxidation state , , , . Hence, 0.27 mmol of oxygen atoms could be removed from 50 mg mixed oxide.…”

Mechanistic Study on the Selective Oxidation of Acrolein to Acrylic Acid: Identification of the Rate‐Limiting Step via Perdeuterated Acrolein

“…As mentioned above, isotopic labeling is particularly suitable in order to gain a deeper understanding of the individual reaction steps. SSITKA‐experiments involving an exchange of the oxygen isotopologue 16 O 2 to 18 O 2 or of the water isotopologue H 2 16 O to H 2 18 O are examples from previous works. By combining SSITKA with other transient response methods and DRIFTS (diffuse‐reflectance‐infrared‐fourier‐transform‐spectroscopy), we developed an extended reaction mechanism (Figure ), as described in our previous work …”