Steam Reforming of Ethanol on Ni/CeO₂: Reaction Pathway and Interaction between Ni and the CeO₂ Support

Abstract

The steam reforming of ethanol on a Ni-based CeO2-supported catalyst was studied using in situ X-ray diffraction (XRD), operando diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), and mass spectroscopy (MS) with a focus on the structural characterization of the catalysts, chemical identification of the reaction pathway, and understanding of the interaction between Ni and the CeO2 support. Ethoxy, acetate, carbonate, and hydroxyl species are identified by DRIFTS as surface intermediates that appear during the reaction process. The oxidation of ethoxy to acetate and the decomposition of acetate are two key steps in the steam reforming process. The CeO2 support facilitates the oxidation of ethoxy to acetate below 350 °C. Above 350 °C, the Ni metal catalyzes dissociation of the C–C bond in acetate to form carbonate and methyl, something that the CeO2 support is not able to do. The Ce(III) sites produced by the reduction of ceria in ethanol help to dissociate water forming the surface hydroxyl groups, which react with the methyl groups to produce CO2 and inhibited the methyl groups’ progress to CH4. Post-reaction transmission electron microscopy (TEM) images of the Ni/CeO2 catalyst reveal two types of carbon configurations: encapsulating carbon and filamentous carbon. A water-rich atmosphere favors formation of carbon filaments, which do not deactivate the catalyst.

Ambient pressure XPS and IRRAS investigation of ethanol steam reforming on Ni–CeO2(111) catalysts: an in situ study of C–C and O–H bond scission

“…47 Compared with previous Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS) study of powder Ni-CeO2, 8 the formation of acetates species at room temperature and its subsequent transformation to carbonates species at higher temperature are evident in both cases, but the all the features on the powder system are more pronounced and could be retained at higher temperature, probably due to the multiple crystal facets of powder ceria affect the adsorption/desorption selectivity. In addition, a small peak at 2680 cm -1 corresponding to the ν(OD) derived from the dissociation of D2O, is resolved at 700 K. 48 Correlating this with the Ce(OH)x demonstrated in the AP-XPS results above, the observation of hydroxyls (-OD) verifies the participation of water in the formation of ceria hydroxides while water can be the hydroxyl feed stock for the reforming reaction.…”

“…8,26 However, ethanol does react with ceria to produce hydrocarbon oxygenates such as acetaldehyde, and ceria can be strongly reduced by ethanol to give rise to Ce 3+ and its associated O vacancies. The creation of Ce 3+ and O vacancies will in turn dissociate H2O to -OH groups and even give rise to the formation of ceria hydroxide compounds.…”

Catalytic steam reforming of ethanol over W-, V-, or Nb–modified Ni-Al-O hydrotalcite-type precursors

“…Under steadystate reaction conditions Ni is mainly in the metallic state and Ni 0 sites are responsible for the rupture of C-C and C-H bonds in ethanol and intermediates/surface complexes (acetaldehyde, ethoxy species, etc.) [5][6][7][8][9][10]. Partially reduced VO x surface clusters are apparently involved in H 2 O activation yielding H 2 and reactive surface oxygen species.…”

“…The following reactions are possible routes for hydrogen production from ethanol: steam reforming (1), partial oxidation (2), and decomposition (3 and 4): (4) Although steam reforming provides the highest hydrogen yield, it is highly endothermic; high conversions require high operation temperatures [8,[12][13][14][15]. The pathways for hydrogen production [11] …”

Catalytic activity of cobalt and cerium catalysts supported on calcium hydroxyapatite in ethanol steam reforming

“…The incorporation of cobalt ions into ceria crystal lattice was benefi cial for resistance to carbon deposition. It is also known that the presence of ceria ions favour the water activation-decomposition of water with the subsequent generation of OH groups, which are essential to CO 2 and H 2 formation during SRE process 40 . Results of the TPR-H 2 measurements (Fig.…”