Thermal Oxidation of Carbonaceous Nanomaterials Revisited: Evidence of Mechanism Changes

Abstract

Kinetic data, for example,a ctivation energy and reaction order,a re crucial for the understanding of chemical reactions and processes.Here,wedescribe anovel method for obtaining kinetic data based on thermogravimetric measurements (TGA) that exploits in each measurement multiple successive isothermal steps (SIS). We applied this method to the notoriously challenging carbon combustion process for vastly different carbons for oxygen molar fractions between 1.4 %a nd 90 %. Our obtained apparent E A values are within the wide range of results in the literature and vary in as ystematic way with the oxygen partial pressure.T he improved accuracy and large amount of obtainable data allowed us to show that the majority of experimentally obtained apparent data for apparent E A are neither in akinetic regime nor in ad iffusion-controlled one but rather in atransition regime.

Thermal Defect Engineering of Precious Group Metal–Organic Frameworks: A Case Study on Ru/Rh-HKUST-1 Analogues

“…This allowed accessibility of both predefined weight losses and the protection of the obtained highly reactive samples from undesired deactivation in air (e.g., uncontrolled guest sorption or oxidation). TDE-MOF sample homogeneity is ensured through a multistep temperature program design (Figure ) utilizing successive isothermal steps as a combination of isothermal parts and ramps with constant heating rates . Weight loss monitoring allowed for a controlled TDE between 150 °C (423 K) and 300 °C (573 K) to reproducibly yield samples of specified (Y%) defectiveness.…”

“…utilizing successive isothermal steps as a combination of isothermal parts and ramps with constant heating rates. 45 Weight loss monitoring allowed for a controlled TDE between 150 °C (423 K) and 300 °C (573 K) to reproducibly yield samples of specified (Y%) defectiveness. Specifically, predefined analytical mass losses of 5.5, 10, and 15% (due to small molecular mass species C x H y O z , e.g., H 2 O, CO, CO 2 , H 2 CCO) were targeted to yield three series of samples for each pristine MOF of the study.…”

An Introduction to the Combustion of Carbon Materials

“…However, in recent years a change of the order of reaction was observed by a few authors including us, which can not be explained by the commonly used models. [9,79,202,203] The observed order of reaction is also influenced by diffusion and thus by no means a fixation or assumption of 0 or 1 ought to be done a priori.…”

“…[7,8] As simple as it may appear, carbon combustion or the reaction of carbon and oxygen to yield carbon monoxide and dioxide, is known for its complexity. [9] The following is a brief tentative to review the state of the art of carbon combustion and the challenges it still encompasses.…”

“…However, it is clear that especially for nanosized carbon materials, the application of those methods and the interpretation of the derived data become challenging. With such a variety of carbon materials, all possessing different properties as a result of different structures, it is not surprising that very different kinetic behavior has been reported for the carbon combustion reaction [9] . This is even more pronounced with materials which are sorted rather by synthesis condition than structural parameters, for example pitch tars, coals and coke.…”