Experimental Method for Kinetic Studies of Gas–Solid Reactions: Oxidation of Carbonaceous Matter

Abstract

A methodology comprising careful consideration of sample preparation, reactor design, experimental procedures and data evaluation routines for precise analysis of the kinetics of gas-solid reactions, specifically the oxidation of carbonaceous materials, has been developed and validated. The well-controlled solvent-free deposition of the carbonaceous material onto cordierite monolith substrates ensures experimental studies in the absence of diffusion limitations, temperature gradients and hot zones. These critical aspects are supported also by theoretical considerations. Temperature-programmed oxidation and isothermal oxygen stepresponse experiments in continuous gas-flow reactor using a homogeneous synthetic carbonblack material demonstrate excellent reproducibility and the conversion profiles agree well with previously reported data. An independent set of global kinetic parameters was estimated ⇤ To whom correspondence should be addressed 1 for each 5% sub-conversion interval using linear regression such that the conversion dependence of each parameter could be analyzed separately and compared to previously published data. The results show that the evolution of reactive carbons cannot be described with a single global reaction order. This is supported by intermittent ex situ measurements of the specific surface area of the carbon-black material during the course of isothermal oxidation, which reveals a developing microporous structure at high conversions. Physically the changes in carbon reaction order are interpreted as changes in fraction of accessible reactive carbon atoms during progressing oxidation. Moreover, at high conversions, the carbon reaction order approaches 0.7 implying that the evolution of the concentration of reactive carbon atoms is not only proportional to the external surface area of shrinking spheres but also that these spheres have approximately the same size.

Surface Species and Metal Oxidation State during H2-Assisted NH3-SCR of NOx over Alumina-Supported Silver and Indium

“…Briefly, the reactor consisted of a horizontal quarts tube (L = 80 cm, Ø i = 22 mm) heated by a metal coil. The catalyst sample was positioned close to the tube outlet, surrounded by bare monoliths for shielding of heat radiation to the thermocouples [68], which were placed inside and just before the coated monolith. Prior to each measurement, the sample was pretreated in 10% O 2 (Ar-balance) at 500 • C for 30 min.…”

Hydrogen-assisted SCR of NO over alumina-supported silver and indium catalysts using C2-hydrocarbons and oxygenates

“…The catalyst temperature is measured inside the sample and the reactor temperature is controlled 15 mm before the catalyst sample by K-type thermocouples. Uncoated monoliths (L = 80 cm, Ø i = 22 mm) were placed before and after the coated monolith to shield the thermocouple from heat radiation emitted by the heating coil as well as reduce axial radiation heat losses from the coated monolith sample [36]. The hydrocarbons and oxygenates used as reducing agents in this study were ethane (H 3 C-CH 3 ), ethene (H 2 C=CH 2 ), ethanol (H 3 C-CH 2 OH), acetic acid (H 3 C-CHOOH) and DME (H 3 C-O-CH 3 ), respectively.…”

Structure and Oxidation Activity Correlations for Carbon Blacks and Diesel Soot

“…Printex-U (see Figure S1c of the Supporting Information) and diesel soot-1 (see Figure S1d of the Supporting Information) had almost the same average particle sizes (68.5 and 68.6 nm, respectively), supporting the idea of morphological similarity between the two materials. 27 Because the samples selected in our work had a broad distribution of average particle sizes, the oxidation activity data obtained from TGA were correlated with the average particle size, as shown in Figure 1. The data did not follow a clear correlation (low R ∼ 0.4 with all points).…”