In Situ Generation of Radical Coke and the Role of Coke-Catalyst Contact on Coke Oxidation

Abstract

A thermogravimetric analyzer (TGA) equipped for flowing hydrocarbon gases allowed in situ deposition of coke on catalyst and support samples with excellent coke-catalyst contact. The coke deposition on the catalysts and supports, which occurs via a gas phase radical mechanism, depends on the reaction time, temperature, hydrocarbon concentration, and sample external surface area but not on the chemical composition of the support under the conditions used. The coke samples, including in situ generated samples and an industrial coke sample, are characterized quantitatively by both deconvolution of Raman spectra and temperature-programmed oxidation (TPO) analyses. Thermal aging of coke is shown to be effective in increasing the hardness of the coke samples. Ceria dispersed on α-alumina, used as a model catalyst for coke oxidation, allows coke oxidation at lower temperatures. Using these catalysts, coke deposited in situ is shown to oxidize similarly to ground (tight contact conditions) coked catalyst samples, suggesting that in situ coke deposition in the TGA can be used to generate samples with realistic coke-catalyst contacting, as might be found in an industrial reactor or catalyst bed. In situ coking is also observed to be reproducible and reliable as compared to loose and tight contact methodologies