Ni-Cu alloy nanoparticles loaded on various metal oxides acting as efficient catalysts for photocatalytic H-2 evolution

Abstract

Catalysis of Al2O3-SiO2, TiO2, SiO2 and CeO2 (MOx) impregnated with pre-formed Ni-Cu alloy nanoparticles (Ni-CuNPs/MOx) for photocatalytic hydrogen (H-2) evolution was compared with that of MOx impregnated with Ni2+ and Cu2+ ions followed by calcination and reduction (Ni-Cu/MOx). The photocatalytic H-2 evolution was conducted by photoirradiation (lambda > 340 nm) of a deaerated mixed solution of a phthalate buffer (pH 4.5) and acetonitrile [1 : 1 (v/v)] containing beta-dihydronicotinamide adenine dinucleotide (NADH), 2-phenyl-4-(1-naphthyl)quinolinium ion (QuPh(+)-NA), and Ni-CuNPs/MOx or Ni-Cu/MOx as an electron donor, a photosensitiser and an H-2-evolution catalyst, respectively. Ni-CuNPs/Al2O3-SiO2 exhibited activity for the photocatalytic H-2 evolution, whereas Ni-Cu/Al2O3-SiO2 showed no activity. Such precursor dependent catalysis can be elucidated by the ion-exchangeable nature and high surface area of Al2O3-SiO2, on which Ni-Cu alloy particles hardly form from metal salts. On the other hand, Ni-Cu/TiO2 and Ni-Cu/SiO2 exhibited higher activity than Ni-CuNPs/TiO2 and Ni-CuNPs/SiO2, respectively, resulting from formation of smaller Ni-Cu alloy nanoparticles on TiO2 and SiO2 by reducing Ni2+ and Cu2+ on the surfaces. When CeO2 was used as the support, no catalytic activity was observed for either Ni-CuNPs/CeO2 or Ni-Cu/CeO2. Kinetic study for thermal H-2 evolution suggested that Ni-CuNPs were severely deactivated for H-2 evolution by being loaded on CeO2.