Surface Chemistry of C₂H₄, CO, and H₂ on Clean and Graphite Carbon-Modified Co(0001) Surfaces

Abstract

Chemisorption and surface reactions of C2H4, CO, and H2 on clean and graphite carbon-modified Co(0001) surfaces have been investigated by thermal desorption spectroscopy, X-ray photoelectron spectroscopy, and low-energy electron diffraction. The chemisorption and decomposition behaviors of C2H4 depend largely on the vacant sites available on clean Co(0001) at 130 K. C2H4 chemisorbs dissociatively to produce C2H2(a) and H(a) at low exposures but both dissociatively and molecularly to produce C2H4(a), C2H2(a), and H(a) at large exposures. Upon heating, some C2H4(a) desorbs and vacates surface sites, which results in the simultaneous decomposition of C2H4(a) into C2H3(a) and H(a). At 350 K, C2H3(a) either undergoes further dehydrogenation into C2H2(a) and H(a) or hydrogenates to produce C2H4. C2H2(a) then completely dehydrogenates to graphite carbon and H2 at 424 K. Graphite carbon modified Co(0001) surfaces were prepared by the thermal decomposition of C2H4 on clean Co(0001). The graphite carbon exerts both site-blocking effect and electronic effect on the reactivity of Co(0001) surface, suppressing the decomposition of C2H4(a) and weakening the interaction between the Co surface and CO(a) and H2(a). These results provide fundamental understandings of elementary steps of relevant heterogeneous catalytic reactions catalyzed by Co-based catalysts.

Rediscovering cobalt's surface chemistry

“…On Co(0001) the adsorption of H 2 has been shown to occur dissociatively at temperatures as low as 130 K, producing typical second-order-kinetics desorption peaks between 300-450 K in TPD spectra. 60,61 A similar behaviour is also observed on the same low index plane when D 2 is used instead of H 2 . 46,62 DFT calculations for all surface coverages indicate that the most stable site for H on Co(0001) is the three-fold hollows, with fcc hollows slightly favoured over hcp hollows.…”

Reflections on the Fischer-Tropsch synthesis: Mechanistic issues from a surface science perspective

“…limit the discussion to the main findings, thereby highlighting the crucial role of co-adsorbed CO on the surface chemistry of FTS surface intermediates. In brief, ethylene was dosed onto the Co(0001) surface held at 100 K and heated to 200 K afterwards to produce 0.12 ML acetylene + 0.24 ML H ad [24,66,68]. The infrared absorption spectrum after heating to 250 K, plotted in Fig.…”

Self‐Anticoking of a Cobalt Surface by Subsurface Oxygen in the Fischer–Tropsch Synthesis

“…Great efforts have been devoted to understanding the CO activation and carbon chain propagation mechanisms, but the results are of ongoing debate . Only a few experimental studies have been reported on the reactivity of carbidic carbon, atomic oxygen, and atomic hydrogen on Co surfaces …”

“…Therefore, it is crucial to understand the fundamental processest aking place on Co surfaces during FT synthesis, in order to optimize the design of Co FT catalysts essential for the efficient use of the metal. [13][14][15][16][17][18][19][20] We previously reported that the carbidic carbon species on aC o(0001)s urfacetransformsi nto the graphitic carbon species at elevated temperatures. [10][11][12] Only af ew experimental studies have been reported on the reactivity of carbidic carbon, atomic oxygen, and atomic hydrogen on Co surfaces.…”

“…[10][11][12] Only af ew experimental studies have been reported on the reactivity of carbidic carbon, atomic oxygen, and atomic hydrogen on Co surfaces. [13][14][15][16][17][18][19][20] We previously reported that the carbidic carbon species on aC o(0001)s urfacetransformsi nto the graphitic carbon species at elevated temperatures. [16] Using this approach we prepared 0.3 monolayer( ML) carbon-covered Co(0001)s urfaces with various carbidic carbon/graphitic carbon ratios ( Figure 1A).…”