Selective Oxidation Of Methacrolein Research Articles

Dendritic polyamide-amine modified phosphomolybdovanadic hybrid microspheres as a catalyst for methacrolein to methacrylic acid

The selective oxidation of methacrolein (MAL) to high value-added methacrylic acid (MAA) using green chemical technology is of high research value.

The role of steam in selective oxidation of methacrolein over H3PMo12O40

Role of steam in selective oxidation of methacrolein with molecular oxygen over H3PMo12O40 catalyst was investigated. Addition of steam to feed gas significantly enhanced both catalytic activity and selectivity to methacrylic acid, which were fivefold and twice increases, respectively, under the optimal steam pressure (PH2O = 0.13 atm). Kinetic analysis demonstrated that the addition of steam caused 200-fold increase in the pre-exponential factor for the formation of methacrylic acid, leading to the significant increase in the activity. The steam in the feed gas varied hydrous state of H3PMo12O40 under the reaction conditions, while did not alter redox property, molecular and crystalline structures, and surface area of the catalyst. In the presence of steam at 573 K, three H2O per one H3PMo12O40 were absorbed and hydrated protons like [H3O]+ were formed in the bulk of H3PMo12O40. Methacrolein was adsorbed on the surface of the hydrous catalyst, but not on anhydrous one at all. Based on the results, it was concluded that activation of methacrolein readily occurred on the catalyst in the presence of steam, leading to the significant increase in the pre–exponential factor. Quantum chemical calculation supported the smooth activation of methacrolein by the reaction with [H3O]+ without any transition state.

New crystalline complex metal oxides created by unit-synthesis and their catalysis based on porous and redox properties.

The development of new complex metal oxides having structural complexity suitable for solid-state catalysis is of great importance in fundamental catalysis research and practical applications. However, examples of these materials are rare. Herein, we report two types of crystalline complex metal oxides with new structures and their catalytic properties. The first one is an all-inorganic ε-Keggin polyoxometalate-based material with intrinsic microporosity. The framework of the material is formed by the assembly of ε-Keggin polyoxomolybdate units with metal ion linkers in a diamondoid topology. The micropores of the material can be opened without change of the structures, and the material adsorbs small molecules. This material has both redox properties and acidity and can be applied to O2 adsorption, selective oxidation of methacrolein, and hydrolysis of cellobiose. The other material is a crystalline metal oxide based on molecular nanowires. The hexagonal POM units stack along the c axis to form prismatic clusters as molecular wires. The molecular wires further assemble in a hexagonal fashion to form the crystals, and NH4(+) and water are present in between the molecular wires. The material is active as an acid catalyst for cellobiose conversion.

Selective Oxidation of Methacrolein towards Methacrylic Acid on Mixed Oxide (Mo, V, W) Catalysts. Part 1. Studies on Kinetics

Comprehensive kinetic studies of the oxidation of methacrolein on mixed oxide (Mo, V, W) catalysts have been undertaken in order to find ways of catalyst improvement to achieve a high selectivity toward methacrylic acid. Steady-state kinetic experiments were carried out in a differential recycle reactor that behaves like an ideal continuous stirred tank reactor (CSTR). A kinetic model based on the scheme of Mars−van Krevelen was developed for a fair representation of the reaction rates of methacrolein conversion, methacrylic acid formation, byproduct formation, and selectivity toward methacrylic acid. For a better understanding of the kinetics, transient experiments were carried out in an apparatus to render possible sorption studies as well as transient kinetic experiments, which are powerful tools to study independently both the oxidation of the aldehydes on the catalyst in the absence of oxygen and the reoxidation of the catalyst. Steady-state kinetic data and transient experiments agree well. It could be clearly shown that the conversion of methacrolein is mainly determined by the reoxidation of the catalyst and that the selective oxidation of the aldehydes and the consecutive oxidation of the acids occur on different domains of the catalyst.

Selective Oxidation of Methacrolein towards Methacrylic Acid on Mixed Oxide (Mo, V, W) Catalysts. Part 2. Variation of Catalyst Composition and Comparison with Acrolein Oxidation

While the oxidation of acrolein on mixed oxide (Mo, V, W) catalysts shows an exceptionally high selectivity with respect to acrylic acid, the selectivity of the analogous oxidation of methacrolein is only moderate. This is due to a considerably lower oxidation rate of methacrolein compared to that of acrolein, while the undesired subsequent oxidation of methacrylic acid is of the same order of magnitude as the oxidation of acrylic acid. Comprehensive kinetic studies in particular by transient experiments have led to a sound hypothesis to explain this difference and to show ways of catalyst improvement for the conversion of methacrolein to methacrylic acid. A moderate increase of methacrylic acid selectivity could be reached by variation of the Mo/V ratio of the mixed oxide. Surprisingly the addition of phosphoric acid and Cs-acetate effected a reduction of the subsequent oxidation of methacrylic acid without affecting the methacrolein oxidation, leading to a marked increase of the selectivity toward methacrylic acid. Furthermore, the comparison of methacrolein and acrolein oxidation results in a confirmation of the hypothesis that aldehyde oxidation and subsequent oxidation of acid occur on different domains of the mixed oxide catalyst.