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ng and Lifang Chen ESIQIE, Instituto Politécnico Nacional, 07738 México D. F., México

Xim Bokhimi Universidad Nacional Autónoma de México (U.N.A.M.), 01000 México City, México

Alejandro Pérez-Larios and Ricardo Gómez Department of Chemistry, Universidad Autónoma Metropolitana-Iztapalapa, Mexico City, D.F. 09340, México (Received 7 June 2013; accepted 23 October 2013)

A series of Ni/C catalysts with different Ni content (15, 20, and 30 wt% Ni) were prepared by the wet incipient impregnation method. Their textural properties were studied by surface fractal dimension (Ds) and nonlocal density functional theory using nitrogen sorption data. Their structural properties were studied by x-ray diffraction, Rietveld refinement, radial distribution functions (RDFs), and electron density maps of Fourier. Surface areas of Ni/C catalysts decreases slightly from 614 to 533 m2/g as Ni content increases from 15 to 30 wt%; however, the Ni crystallite size (5.1–31.4 nm) increases as the nickel content increases. Many point defects were found by Rietveld refinement in nickel nanostructures of Ni/C catalysts with 20 and 30 wt% Ni. This was confirmed by RDFs and electronic density maps. On the other hand, the hydrogen production via the photodehydrogenation of ethanol is very sensitive to the nickel crystallite size and the number Ni atoms in nickel nanostructures. The maximum reaction rate (363.64 lmol/h) is achieved on Ni/C catalyst with 15 Wt% Ni content which has the smallest crystallite size (5.1 nm) and less point defects in its nickel nanostructures. Ab initio calculations were performed to propose a reaction mechanism in the photodehydrogenation of ethanol.

I. INTRODUCTION

Many investigations of new materials with catalytic properties have been focused on the hydrogen production by means of water, methane, methanol, and ethanol among others as hydrogen precursors.1–7 A number of Ni-based catalysts with different supports, for example, Ni/CeO2–ZrO2,1 Ni/CeO2,2 Ni/c-Al2O3,3 Ni–Cu–Fe/c-Al2O3,4 Cu–Ni/SiO2,5 Ni/SiO2,6 and Ni/ZnO7 have been successfully applied in the hydrogen production. Nickel is chosen and widely used as the active phase in steam-reforming reactions because of its high activity and low cost. However, the nanostructural properties of Ni supported on activated carbon in the hydrogen production have not been extensively studied. For this, in the present research work, a series of Ni/C catalysts with various nickel loadings were prepared by a)

Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2013.337 J. Mater. Res., Vol. 28, No. 23, Dec 14, 2013

http://journals.cambridge.org

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the wet incipient impregnation method using nickel nitrate as the nickel precursor and activated carbon as the support. In oxidative dehydrogenation reactions at 623 K, Pereira et al.8 reported catalytic photoactivity of carbon. In this research, the photodehydrogenation of ethanol is performed under mild conditions (pH
7, 298 K). Although nickel immobilized on activated carbo