Ethanol and Acetaldehyde Decomposition on Co(0001): The Effect of Hydrogen Atom on C–O Bond Scission

Abstract

Fischer−Tropsch synthesis (FTS) with Co-based catalysts has attracted renewed interest in recent years due to its potential applications to produce transportation fuels. However, experimental investigations about the FT mechanism at the atomic level, especially for the essential C−O bond scission step, are rarely carried out. Using the temperature-programmed desorption method, we have investigated the mechanism of C−O bond scission in the decomposition of ethanol (C 2 H 5 OH) and acetaldehyde (CH 3 CHO). We have clearly found that the H atom attached to the C-end of the CO molecule is significant for C−O bond scission accompanied by CH 3 at the C-end. Otherwise, C−C bond scission will occur facilely if only a CH 3 group is attached to the C-end of the CO molecule. These results indicate that CH 3 CHO may be an important intermediate in FTS for C−O bond scission to produce C 2 H x or for C 2 + oxygenate production. Moreover, the H atoms on the Co(0001) surface could largely inhibit the dehydrogenation of the H atom at the C-end of CO, leading to an enhancement of C−O bond scission. The results for the first time demonstrate that, except the CH 3 radical at the C-end of the CO molecule, an additional H atom at the C-end of the CO molecule and the surface H atoms play vital roles in promoting the C−O bond scission in the FT process as well.

Evaluation of Strengthening Mechanisms in Novel Fully Ferritic Advanced High‐Strength Steels

“…It is interesting to notice that, despite the fact that the same estimated dislocation density of 5 × 10 13 was used in a few earlier studies, its contribution was reported to vary from 62 to 168 MPa. [ 15,34–36 ] The latter value was strictly consistent with the value of 169 MPa, which was based on the TEM studies reported by Singh et al [ 19 ] However, Kim et al [ 20 ] suggested that the dislocation strengthening could be neglected due to its minor contribution to the YS of their steels. The present results indicated that the contribution of the different strengthening mechanisms depended strongly on the CT and steel chemistry.…”

“…However, some exceptions were found in the literature; fine (<3 μm) ferrite grains were formed in Ti–Mo–Cr–(V) steels during continuous cooling after the 50% and 30% hot deformation at temperatures of 1050 and 900 °C, respectively, whereas 20% hot deformation at the temperature 900 °C, followed by the subsequent isothermal dwell at the temperature of 650 °C for 1 h, resulted in the relatively large ferrite grain size of 30 μm in a 0.1Ti–0.2Mo steel. [ 26,35 ] In the former case, the enhanced hardenability of the steels due to the extra Cr alloying might cause rapid nucleation and growth of allotriomorphic ferrite grains at the intermediate temperatures during the slow cooling (cooling rate ≦1 °C s −1 ). In the latter case, it was reported that the 0.1Ti–0.2Mo steel contained nearly 50% austenite after 5 min at the isothermal temperature of 650 °C.…”

“…This phenomenon has also been reported in the earlier studies. [ 35,54,55 ] Therefore, the effect of precipitation hardening on the YS was calculated using Equation (11), which was based on the assumption that the increment of precipitation hardening can be calculated by subtracting friction stress of pure iron, solid solution strengthening, grain boundaries strengthening, and dislocation strengthening from total YS. [ 31 ] …”

Atomic-Scale Observation of Sequential Oxidation Process on Co(0001)

“…However, up to date, only limited numbers of studies are involved with Co single crystals because of the difficulty of getting a well-defined surface. − As the most stable surface of low-index cobalt single crystal, Co(0001) has usually been chosen as a model FTS catalyst for fundamental mechanism study. , Moreover, this surface is a structural analog of the fcc-Co(111) surface present on real Co catalyst particles. Earlier works ,− have investigated the oxygen interaction with Co(0001) by means of surface science techniques.…”