We demonstrated recently that CuPd/TiO 2 –Na bimetallic catalysts synthesized by sequential wet impregnation are active, selective, and stable for the hydrodeoxygenation (HDO) of glycerol into propylene glycol at low H 2 pressure. The present study reports on the nature and distribution of Cu and Pd surface species in CuPd/TiO 2 –Na bimetallic catalysts using different scanning transmission electron microscopy techniques that supply cluster-specific alloying details. In particular, we used atomic-resolution Z -contrast imaging, X-ray energy-dispersive spectroscopy, and electron energy-loss spectroscopy. We also include X-ray photoelectron spectroscopy results. Our analysis shows that the metallic nanoparticles adopt mainly five different structures according to how the Cu and Pd atoms coordinate among themselves: a homogeneous CuPd alloy structure (45–61%), a Cu shell/CuPd core (15–23%), a smaller number of particles formed by Cu on the surface and Pd in the nucleus (10–17%), and there are also nanoparticles formed only by Pd (4–7%) or by Cu (8–13%). We determined that there is a inhomogeneous distribution of Cu and Pd in the bimetallic nanoparticles, with Cu being predominant on the surface (between 76 and 90% of the total area analyzed for each particle). Most bimetallic nanoparticles have sizes below 6 nm, the Pd monometallic nanoparticles are in the 2–4 nm range, whereas the monometallic Cu nanoparticles are larger than 8 nm. Bimetallic nanoparticles with sizes smaller than 6–7 nm are fundamentally made up of Cu 0 –Pd 0 and Cu 1+ –Pd 0 . The nanoparticles with sizes greater than 7 nm consist of Cu 2+ and Cu 2+ –Pd 2+ . Our obtained results also help describe reports about the activation of HDO by Pd–Cu in the absence of H 2 , an effect apparently not observed with other bimetallic systems.

Palabras clave: agua residual de la industria de pinturas, ion ferroso, peróxido de hidrógeno, ion oxálico RESUMEN Se evaluó la efectividad del proceso foto-Fenton asistido con ferrioxalato para la mineralización de 1000 mg/L de etilenglicol presente en agua destilada y en agua residual proveniente de una planta de producción de pinturas. Se observó que la eficiencia de mineralización del etilenglicol es función de las concentraciones iniciales de ion ferroso, oxalato y peróxido de hidrógeno. Los mayores niveles de degradación del etilenglicol (90 y 85 %, para el agua destilada y el agua residual, respectivamente), se obtuvieron con 10 mg/L de Fe 2+ , 150 mg/L de C 2 O 4 2-y 500 mg/L de H 2 O 2 , después de 3 h de irradiación artificial con lámparas UV a una longitud de onda máxima de 365 nm. La descomposición del etilenglicol produjo cantidades traza (< 136 mg/L) de ácido acético y ácido fórmico, por lo que la disminución en la demanda química de oxígeno debida a este contaminante fue prácticamente total, ya que no se detectó ningún otro producto intermediario. El hierro no actuó directamente de manera catalítica en el sistema.Key words: wastewater from the paint industry, hydrogen peroxide, ferrous ion, oxalic ion ABSTRACTThe effectiveness of the ethylene glycol mineralization using ferrioxalate-induced photo-Fenton was evaluated. The efficiency of 1000 mg/L ethylene degradation was a function of the initial concentrations of ferrous ion, oxalate and hydrogen peroxide. The highest levels of degradation (90 and 85 % for distilled water and wastewater from the paint industry, respectively) were obtained using 10 mg/L of Fe 2+ , 150 mg/L of C 2 O 4 2-and 500 mg/L of H 2 O 2 after 3 hours of UV artificial irradiation (wavelength ~ 365 nm). Ethylene glycol was converted to acetic acid and formic acid in trace amounts (< 136 mg/L) resulting in a decrease of chemical oxygen demand due this contaminant. No other intermediate products were detected.

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