High-Temperature Carbon Deposition on Oxide Surfaces by CO Disproportionation

Abstract

Carbon deposition due to the inverse Boudouard reaction (2CO → CO2 + C) has been studied on yttria-stabilized zirconia (YSZ), Y2O3, and ZrO2 in comparison to CH4 by a variety of different chemical, structural, and spectroscopic characterization techniques, including electrochemical impedance spectroscopy (EIS), Fourier-transform infrared (FT-IR) spectroscopy and imaging, Raman spectroscopy, and electron microscopy. Consentaneously, all experimental methods prove the formation of a more or less conducting carbon layer (depending on the used oxide) of disordered nanocrystalline graphite covering the individual grains of the respective pure oxides after treatment in flowing CO at temperatures above ∼1023 K. All measurements show that during carbon deposition, a more or less substantial surface reduction of the oxides takes place. These results, therefore, reveal that the studied pure oxides can act as efficient nonmetallic substrates for CO-induced growth of highly distorted graphitic carbon with possible important technological implications especially with respect to treatment in pure CO or CO-rich syngas mixtures. Compared to CH4, more carbon is generally deposited in CO under otherwise similar experimental conditions. Although Raman and electron microscopy measurements do not show substantial differences in the structure of the deposited carbon layers, in particular, electrochemical impedance measurements reveal major differences in the dynamic growth process of the carbon layer, eventually leading to less percolated islands and suppressed metallic conductivity in comparison to CH4-induced graphite.

Threshold catalytic onset of carbon formation on CeO2during CO2electrolysis: mechanism and inhibition

“…Carbon deposition has been found more favorable near defect sites. 18 Therefore, carbon atoms deposited on the surface with a higher defect concentration are more likely to be located closer to each other, promoting the "clustering" process. In this scenario, the observed threshold [Ce 3+ ]-carbon relation should be associated with a threshold surface defect density to ensure that the deposited carbon forms clusters.…”

“…7,8 This coking process can lead to irreversible catalyst deactivation and cause mechanical degradation. 9 One major type of carbon poisoning is from CO, [10][11][12][13][14] which has been reported as either CO dissociation 15,16 (CO / C + O) or the Boudouard disproportionation [17][18][19] (2CO / CO 2 + C). At operating temperatures below 700 C, carbon deposition is thermodynamically more favorable and occurs mainly via the Boudouard reaction.…”

Fast and easy preparation of few-layered-graphene/magnesia powders for strong, hard and electrically conducting composites

“…It is analogous to a route reported earlier for the direct synthesis of carbon nanotubes within a ceramic powder [45e52], only simpler because it does not involve any transition metal catalyst. Aside from the field of catalysis where accumulation of carbon on the surface of solid catalysts is a well-known poison, the deposition of carbon onto metal and oxide powders has already been reported, as FLG [53,54], heavily distorted graphene layers [55] or ultra-thin (1e5 nm) graphitic carbon layers [56] but to the best of our knowledge it has not been reported specifically for the production of graphene/ceramic composites. The present sintered FLG/MgO samples show strengthening and hardening compared to pure MgO as well as a very low electrical percolation threshold.…”

Simulation of Cotton Stalks for Syngas Generation Using CO2 and Air as Gasifying Agents

“…As mentioned earlier the cotton stalk feeding rate was maintained 61kg/hr, the increase in CO2/cotton stalks ratio intended that additional CO2 was introduced to the entrained flow reactor, increased percentage of air or oxygen, due to that temperature inside the reactor increased. With the increase in reactor temperature, the BR (Boudouard Reaction) became more activated [16]. As well as because of the high operating temperature of the reactor RWGSR also became more rigorous.…”