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

Abstract

Dedicated to Professor Rüdiger Lange on the occasion of his 65th birthdayOxidation of acrolein to acrylic acid on a Mo/V/W mixed oxide catalyst was studied by transient (cyclic temperature-programmed (TP)) as well as steady-state methods. TP reactions (TPReactions) exhibit an activity hysteresis of the catalyst with respect to temperature. As a result of the steady-state measurements, the activity hysteresis is not related to multiple steady states and is exclusively a transient phenomenon. Generally, the dynamics of bulk oxygen plays a key role leading to a reversible oxidation/reduction of the catalyst surface which influences the activity. This means the bulk acts as oxygen buffer. In this context, a reaction model, which involves the participation of bulk oxygen, was deduced and 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…”

“…The 36 irreversible and seven equilibrated reactions postulated to quantitatively describe the mechanisms illustrated in Scheme are listed in Table 1. Reducibility of MoVO x ‐based materials during acrolein oxidation, in accord with the Mars‐van Krevelen (MvK) mechanism, has been confirmed by anaerobic oxidation,, 18 O isotopic labeling, temperature‐programmed reaction, high‐resolution microscopy of catalysts before and after reaction,, and in situ X‐ray absorption spectroscopy . We model reoxidation of vacancy sites (V) by gas phase O 2 to form lattice oxygen sites (O L ) as first order in O 2 pressure and second order in , as did Bui and Bhan in a recent publication detailing a kinetic model for propylene oxidation on promoted BiMoO x (Reaction 1).…”

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

“…The stoichiometry of the mixed oxide determined via XPS (Mo 8 V 1.8 W 1.1 ) and ICP‐OES (Mo 8 V 1.5 W 0.6 ) shows a slight deviation from the target stoichiometry Mo 8 V 2 W 0.5 (the stoichiometric composition of the precursor mixture). XRD measurements after preparation, oxidative and reductive treatments verified the redox stability of the catalyst …”

“…Mo 8 V 2 W 0.5 O x was prepared by hydrothermal synthesis. Details of the synthesis and characterizations are described in previous works . According to the preparation route, non‐porous needle‐like particles with a BET surface area of 34 m 2 g −1 can be obtained.…”

“…By calibrating all components, the volume fractions ( ) are calculated from the ion signals. Details of the setup are described in previous works …”