Unraveling the Chemical State of Cobalt in Co-Based Catalysts during Ethanol Steam Reforming: an in Situ Study by Near Ambient Pressure XPS and XANES

Abstract

The steam reforming of ethanol (ESR) has been studied by Near Ambient Pressure XPS (NAP-XPS), Extended X-ray Absorption Fine Structure (EXAFS) and X-ray Absorption Near Edge Structure (XANES) under in situ conditions in the ALBA synchrotron facility at 200-580ºC and S/C=3 over different cobalt-based catalysts that showed different catalytic performance: Co 3 [Si 2 O 5 ] 2 (OH) 2 (Co-talc), [Co 2 Mg 4 Al 2 (OH) 16 ]CO 3 •4H 2 O (Co-hydrotalcite shortened as Co-HT) calcined at 550ºC, and Co 3 O 4 (Co-spinel). Both, Co-spinel and Cotalc yield to a greater or lesser degree metallic cobalt under ESR conditions. While the Cospinel shows a complete reduction to metallic cobalt under the conditions used for the XANES measurements, more bulk-sensitive, the Co-talc sample exhibits only a partial reduction. On the other hand under the ESR conditions used with the NAP-XPS, a more surface sensitive technique, the results indicate a higher reduction degree for the Co-talc sample as compared to the Co-spinel. In contrast, the catalyst prepared from the Co-HT does not show metallic cobalt traces under the experimental conditions used with both techniques. Comparing these three cobalt-based catalysts, the stable operation exhibited by Co-HT under ESR reaction conditions is justified by the absence of metallic cobalt formation under in situ conditions, which is identified as responsible for the carbon deposition phenomena that triggers the deactivation suffered by most cobalt-based catalysts during ESR.

Effect of Metal Content on Ethanol Decomposition over Ni-Co Catalysts Supported on La-Ce Oxides

“…Signals obtained are consistent with Co metallic and Co in Co 2+ and Co 3+ oxidation states, as has been reported [34][35][36][37]. A peak detected around 777.6 eV could be assigned to metallic Co but shifted approximately 0.6 eV from the reported value [34][35][36][37], which confirms the results found for Ni XPS. Co 2* and/or Co 3+ species were identified by the presence of peaks around 780 eV and the characteristic strong satellite peak at around 786 eV ascribed to CoO.…”

“…XPS results confirmed the presence of metallic particles of Ni and Co and may suggest an interaction between them. Signals obtained are consistent with Co metallic and Co in Co 2+ and Co 3+ oxidation states, as has been reported [34][35][36][37]. A peak detected around 777.6 eV could be assigned to metallic Co but shifted approximately 0.6 eV from the reported value [34][35][36][37], which confirms the results found for Ni XPS.…”

Cooperative Co0/CoII Sites Stabilized by a Perovskite Matrix Enable Selective C−O and C−C bond Hydrogenolysis of Oxygenated Arenes

“…[1d, 10] In the context of renewable transportation fuels and chemicals, metal-metal oxide interfaces have been tailoredt ou pgrade biomass-derived oxygenates through hydrogenolysis. [12,13] Surprisingly,d espite their tremendousp otential to generate tunable metal-metal oxidesi nterfaces, [1d, 9, 14] perovskites have not been extensively studied as catalysts for CÀOa nd CÀCb ond cleavage in biomass-derived oxygenates. [1a, 12] For ethanol steam reforming (ESR) on cobalt oxide, Co 0 sites catalyzed CÀCb ond cleavage, whereas the lattice oxide maintained catalysts tabilityt hrough the removal of dehydrogenated fragments.…”

“…[1a, 12] For ethanol steam reforming (ESR) on cobalt oxide, Co 0 sites catalyzed CÀCb ond cleavage, whereas the lattice oxide maintained catalysts tabilityt hrough the removal of dehydrogenated fragments. [12,13] Surprisingly,d espite their tremendousp otential to generate tunable metal-metal oxidesi nterfaces, [1d, 9, 14] perovskites have not been extensively studied as catalysts for CÀOa nd CÀCb ond cleavage in biomass-derived oxygenates.…”

Ru–Ni bimetallic catalysts for steam reforming of xylene: effects of active metals and calcination temperature of the support

“…The catalytic activity and stability are dependent on the metal type, metal dispersion, properties and structures of supports, and interactions between metals and supports. 8,9 Both noble metal-supported catalysts (Pt, Ru, Pd, etc.) and transition metal-supported catalysts 10,11 (Ni, Co, Cu, etc.)…”