Nina Blickhan

The Effect of Water on the Heterogeneously Catalyzed Selective Oxidation of Acrolein: An Isotope Study

The effect of water on the selective gas phase oxidation of acrolein to acrylic acid on a Mo/V/W mixed oxide catalyst was studied by performing steady‐state isotopic transient kinetic analysis experiments with H218O. Experiments were performed in the temperature range of 90–345 °C at ambient pressure. It could be shown that acrolein exchanges its carbonylic oxygen with oxygen from water even at low temperatures (<200 °C), at which no acrolein oxidation occurs. At higher temperatures (>200 °C), the oxygen atoms of the water molecules incorporate into all oxidation products such as acrylic acid, carbon monoxide, and carbon dioxide.

Valeronitrile Hydrolysis in Supercritical Water

Nitriles act as important intermediates for the chemical industry and are accessible on a large scale through hydrocyanation or ammonoxidation. Nitrile hydrolysis yields amides and acids used in various applications. The conventional nitrile hydrolysis process relies on stoichiometric amounts of mineral acid or base which inherently deliver great amounts of waste brine. Improving this process towards green chemistry would require reaction conditions which can provide technically significant results without the use of catalysts. Under these conditions, the hydrolysis of valeronitrile in pure supercritical water was investigated. The experiments were performed in a continuous high pressure laboratory-scale apparatus at a temperature between 400 and 500 degrees C, 30 MPa pressure and maximal residence time of 100 s. Nitrile conversion and valeric acid selectivity greater than 90% were achieved.

Interplay between Defect Structure and Catalytic Activity in the Mo10−xVxOy Mixed‐Oxide System

The Mo(10-x)V(x)O(y) solid-solution systems (0≤x≤10) were studied by electron paramagnetic resonance spectroscopy. The results show the existence of paramagnetic vanadyl VO(2+) species, whose concentration becomes maximal for Mo(5)V(5)O(y·). A quantitative analysis of the [VO(2+)] concentration as a function of the Mo/V ratio allows it to characterize the prevailing defect chemistry in the Mo(10-x)V(x)O(y) system. In this respect, the semi-conducting properties of Mo(10-x)V(x)O(y) are p-type in an interval of Mo(9)V(1)O(y)-Mo(5)V(5)O(y) and switch into n-type because of the conduction electrons in a composition range of Mo(5)V(5)O(y)-Mo(1)V(9)O(y). Highest catalytic activity is obtained when vanadium acts as an acceptor center and oxygen vacancies ν(··)(O) are formed for reasons of charge compensation. In addition to the surface, ν(··)(O) and VO(2+) centers in the bulk have to be considered too for heterogeneous catalysis.

Homogeneous catalysis of valeronitrile hydrolysis under supercritical conditions.

Supercritical nitrile hydrolysis can be used for both, amide and acid production as well as waste water treatment, as the hydrolysis products show good biodegradability. The conventional process at ambient conditions requires large amounts of mineral acid or base. Approaches that use supercritical water as a green solvent without a catalyst have been investigated over recent years. Findings for valeronitrile hydrolysis presented recently showed promising reaction rates and valeric acid yields. In an attempt to further maximize product yield and to better understand the impact of the pH, reactions in dilute sulfuric acid (0.01 mol L(-1)) were performed in a continuous high-pressure laboratory-scale apparatus at 400-500 °C, 30 MPa, and a maximum residence time of 100 s. Results from both reaction media were compared with regard to productivity and sustainability.