We have developed a noncontact method to probe the electrical conductivity and complex permittivity of single and polycrystalline samples in a flow-through reactor in the temperature range of 20-500 1C and in various gas atmospheres. The method is based on the microwave cavity perturbation technique and allows the simultaneous measurement of microwave conductivity, permittivity and of the catalytic performance of heterogeneous catalysts without any need for contacting the sample with electrodes. The sensitivity of the method towards changes in bulk properties was proven by the investigation of characteristic first-order phase transitions of the ionic conductor rubidium nitrate in the temperature range between 20 and 320 1C, and by studying the temperature dependence of the complex permittivity and conductivity of a niobium(V)-doped vanadium-phosphorous-oxide catalyst for the selective oxidation of n-butane to maleic anhydride. Simultaneously, the catalytic performance was probed by on line GC analysis of evolving product gases making the technique a real in situ method enabling the noninvasive investigation of electronic structure-function relationships.

Don’t touch! Without electrode contacts, but contact-free with microwaves in a resonant cavity the electronic conductivity of a VPO powder catalyst could be measured under the reaction conditions of the selective oxidation of n-butane to maleic anhydride. As a result, a linear correlation between conductivity and formation rate of maleic anhydride was observed

Based on our newly developed microwave cavity perturbation technique, the microwave conductivity of diverse vanadium(III), (IV), and (V) phosphate catalysts was measured under reaction conditions for the selective oxidation of n‐butane. The conductivity response on the gas phase was identified as a very sensitive measure for the redox kinetics, reversibility, and stability of the samples, which are important prerequisites for highly selective and active catalysts. The sensitivity achieved by our method was comparable to surface‐sensitive methods such as X‐ray photoelectron spectroscopy, whereas more conventional analytic techniques such as X‐ray diffractometry or Raman spectroscopy only indicated the stability of the bulk crystal phase under the same reaction conditions.

A total of 29 hitherto unknown vanadyl(IV)-, vanadyl(V)-, and vanadate(V) phosphates were synthesized, structurally characterized, and tested in terms of their behavior as catalysts in the selective oxidation of n-butane to maleic anhydride. The new materials did not surpass the performance of commercially used (VIVO)2P2O7-based catalysts, but a silver vanadium phosphate of approximate composition Ag2VIV,VP1.6O7+δ (0 ≤ δ ≤ 0.5), supposedly having a vanadyl(IV, V) phosphate pyrophosphate layer structure, shows promising activity and selectivity with potential for further improvements. With the aim to study the charge carrier dynamics a new method for in situ non-contact measurement of the electric conductivity of catalysts was developed. The analysis of conductivity changes in response to the chemical potential of oxygen in the gas phase offers valuable clues to understand structure-reactivity relationships in selective oxidation catalysis

MoVing on up: AgMoVO6, a new crystalline catalyst for the gas‐phase oxidation of o‐xylene, with a remarkably high selectivity to value products, has been developed by high‐throughput experimentation. Doping of the catalyst with elements such as P results in further enhancement of the catalytic properties.

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Nicht anfassen! Nicht über Elektrodenkontakte, sondern kontaktlos mit Mikrowellen in einem Resonator konnte die elektronische Leitfähigkeit eines VPO‐Pulverkatalysators unter den Reaktionsbedingungen der selektiven Oxidation von n‐Butan zu Maleinsäureanhydrid gemessen werden. Dabei wurde ein linearer Zusammenhang zwischen der Leitfähigkeit und der Bildungsrate von Maleinsäureanhydrid beobachtet.