Operando NAP-XPS and XAS of Cobalt Catalyst during the steam reforming of etanol

LLUIS SOLER; ALBERT CASANOVAS; CRISTIÁN HUCK IRIART; CARLOS ESCUDERO; JORDI LLORCA PIQUÉ

Málaga

Congreso; 6th International Congress on Operando Spectroscopy; 2018

The steamreforming of ethanol (ESR) has been studied by near-ambient pressure XPS(NAP-XPS) and XAS under operando conditions at the ALBA synchrotron facility at473-853 K and S/C=3 over Co3[Si2O5]2(OH)2(cobalt talc, prepared as [1]), [Co2Mg4Al2(OH)16]CO3·4H2O(cobalt hydrotalcite, prepared as in [2]) and Co3O4(cobalt spinel). Two different photon energies have been used for NAP-XPS, 965and 1250 eV, to provide variable surface sensitivity.Thecatalytic steam reforming of ethanol (ESR) is a well-known process used forgenerating hydrogen: C2H5OH + 3H2O à 6 H2 + 2 CO2. Cobalt-basedcatalysts can operate at much lower temperature when compared with noble metal-and nickel-based catalysts, typically at 673-823 K, since they do not yieldmethane as an intermediate species, which can only be reformed at hightemperature. An important advantage of conducting the ESR at lower temperatureis that the WGS equilibrium favours the formation of hydrogen and CO2at the expense of CO and water, thus maximizing the production of H2.However, most cobalt catalysts suffer from severe deactivation during ESR dueto extensive carbon deposition, particularly under realistic loads of ethanol.Essential for this matter is the understanding of the role of cobalt oxidationstate. The redox pair Co0-Cod+ isresponsible for the activity of cobalt in ESR, which depends on the catalyststructure, particle size, support material, and gas phase composition, amongothers. Over Co-talc and Co-spinel, we have found that metallic Conanoparticles are formed easily at the surface under ESR conditions, whichoriginate carbon deposition. At the same time, selectivity to methane andhigher hydrocarbons increases at the expense of the reforming products. Incontrast, the catalyst derived from Co-hydrotalcite shows an excellentperformance for ESR and no metallic cobalt is formed. This interesting resultallows designing cobalt-based catalysts for ESR without coke deposition byplacing in appropriate environments Cod+ activespecies.