Interplay between particle size, composition, and structure of MgAl2O4-supported Co-Cu catalysts and their influence on carbon accumulation during steam reforming of ethanol

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)The effect of Cu/Co ratio on the structure of MgAl2O4-supported Cu-Co nanoparticles, and on their catalytic properties during steam reforming of ethanol (SRE), was studied using a series of ex situ and in situ techniques. X-ray photoelectron spectroscopy (XPS) analyses showed that Cu atoms migrated to the surfaces of reduced nanoparticles. Extended X-ray absorption fine structure (EXAFS) data revealed the formation of Cu-Co alloy. The size and structure of the nanoparticles were estimated by development of a model based on the EXAFS and XPS data, considering the nanoparticles to be spherical with reduced cores and oxidized shells. It was found that both the reduced core and nanoparticles size were dependent on the Cu/Co ratio. The observed apparent dependence of carbon accumulation rate during SRE (r(carbon,SRE)) on Co-Cu crystallite size was mainly associated with the presence of the element in an oxidized state and with the nature of the metal on the nanoparticle surface. (C) 2013 Elsevier Inc. All rights reserved.307222237Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Brazilian Synchrotron Light Laboratory (LNLS) for the XAS beamline experiments [D06A-DXAS 10156, D04B-XAFS1]Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)CNPq [proc. 472050/2011-7]FAPESP [proc. 2011/50727-9]Brazilian Synchrotron Light Laboratory (LNLS) for the XAS beamline experiments [D06A-DXAS 10156, D04B-XAFS1

Understanding the stability of Co-supported catalysts during ethanol reforming as addressed by in situ temperature and spatial resolved XAFS analysis

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Co catalysts, based on alumina supports modified with La2O3 and CeO2, have been explored in the steam reforming of ethanol (SRE). The addition of oxygen in the reactants, process called oxy-reforming of ethanol (ORE), and the effect of adding Pt as a promoter were also addressed. One of the main challenges of this system is to hinder carbon deposition that leads to catalyst deactivation. In this work, the stability against carbon deposition was correlated to the control of the Co2+/Co-0 ratio, which was addressed by in situ temperature-resolved X-ray absorption near edge spectroscopy (XANES). Temperature- and spatial resolved XANES indicated that the nature of supports, the presence/absence of Pt promoter and the composition of oxidants (water and oxygen) in the feed stream determine the degree of reduction of Co under reaction conditions. The control of the Co2+/Co-0 ratio can equilibrate the steps of ethanol activation and carbon oxidation, resulting in stable catalysts. (C) 2011 Elsevier Inc. All rights reserved.287124137VALEFundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)FINEP (Financiadora de Estudos e Projetos)Brazilian Synchrotron Light Laboratory (LNLS)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP