2.1.3. Catalyst Pre-Reduction

The catalysts were used either as synthesized or after a pre-reduction treatment. In the latter case, the solids were treated at room temperature under N2 flow (20 mL·min−1) for 15 min and then submitted to hydrogen (10mL·min−1), the temperature being ramped up to 400 ◦C (rate, 10 ◦C·min−1) and the final temperature being maintained for 1 h. The nomenclature of pre-reduced solids includes the "Red" su ffix.

#### *2.2. Characterization of the Solids*

The determination of the metallic content in the samples was carried out by by inductively coupled plasma mass spectrometry (ICP-MS) using a Perkin Elmer NexionX instrument. Digestion of the samples consisted in dissolution of the sample in an acid solution of 1:1 H2O/H2SO4/HF solution at 80 ◦C and and after in 1:3 HNO3/HCl mixture. The measurements were carried out by the sta ff at the Central Service for Research Support (SCAI) of the University of Córdoba.

Transmission electron microscopy (TEM) images were obtained with a JEOL JEM 1400 transmission electron microscope. For the measurements were used a 3 mm holey carbon copper grids. Particle sizes were obtained using using the software ImageJ (a public domain Java image processing and analysis program). TEM was carried out at the Central Service for Research Support (SCAI) of the University of Córdoba.

X-ray di ffraction (XRD) analysis was performed on a D8 Discover instrument (Bruker Corporation, Billerica, USA) using CuK α radiation over the range 5–80◦.

A Cary 1E (Varian) instrument was used for determination of Band Gap values by Di ffuse reflectance UV–vis spectra, using as reference material the polytetraethylene (density = 1 <sup>g</sup>·cm-3 and thickness = 6 mm). The plot of the modified Kubelka–Munk function [F(R)·E]<sup>1</sup>/<sup>2</sup> versus the energy of the absorbed light E was use to obtain the value of band gap, extrapolating to y = 0 of the linear regression range.

X-ray photoelectron spectroscopy (XPS) data were recorded by a Leibold–Heraeus LHS10 spectrometer capable of operating down to less than 2 × 10−<sup>9</sup> Torr, was equipped with an EA-200MCD hemispherical electron analyzer with a dual X-ray source using AlKα(*h*ν = 1486.6 eV) at 120 W, at 30 mA, with C (1s) as energy reference (284.6 eV). The sample was prepared in a on 4 mm × 4 mm pellets 0.5 mm thick, and outgassing to a pressure below about 2 × 10−<sup>8</sup> Torr at 150 ◦C in the instrument pre-chamber. XPS experiments were carried out at the Central Service for Research Support (SCAI) of the University of Córdoba.

In an Autochem 2920 analyser (Micromeritics Instrument Corp., Norcross, GA, USA) was carried out the Temperature-programmed reduction (TPR) measurements, 200 mg of the solids was used to carried out the experiment with a flow of 40 mL·min−<sup>1</sup> of a 5% H2/Ar stream. The temperature was ramped from room temperature to 500 ◦C at 10 ◦C·min−1.
