An effective preparation method of composite photocatalysts for hydrogen evolution using an organic photosensitizer and metal particles assembled on alumina-silica

• Published in: Catalysis today 2016-12, Vol.278, p.303-311
• Main Authors: Yamada, Yusuke, Tadokoro, Hideyuki, Fukuzumi, Shunichi
• Format: Article
• Language: English
• Subjects: Hydrogen production; Organic photosensitizer; Photocatalyst; Preparation method
• ISSN: 0920-5861; 1873-4308
• DOI: 10.1016/j.cattod.2016.01.018

[Display omitted] •Photosensitizers and metal particles were functionally combined on silica-alumina.•Deposition of metal particles in the vicinity of photosensitizers was achieved.•Selection of precursors of Pt particles is important for efficient H2 evolution.•Selection of precursors of Cu particles is less important for H2 evolution. Composite catalysts for photocatalytic hydrogen (H2) evolution were prepared by loading an organic electron donor–acceptor linked dyad [2-phenyl-4-(1-naphthyl)quinolinium ion, QuPh+–NA] as an organic photosensitizer and Pt or Cu particles as H2-evolution catalysts on alumina-silica. The composite catalysts loading Pt particles were prepared by two different methods; first, Pt particles were deposited by reduction of PtCl62− owing to photocatalysis of QuPh+–NA supported on alumina-silica (PD method), and second, alumina-silica was impregnated with the PtCl62− and calcined, and then QuPh+–NA was loaded on the Pt/alumina-silica by a cation exchange method (IMP method). When a composite catalyst was prepared by the IMP method, a high Pt-loading amount of 4.2wt% was necessary to achieve the highest H2-evolution rate of 0.27μmolh−1. On the other hand, a composite catalyst prepared by the PD method exhibited three times faster H2 evolution (0.83μmolh−1) even though the loading amount of Pt was as low as 0.4wt%. The activity of composite catalysts prepared by the PD method highly depends on the electric charges of precursors for Pt particles. A composite catalyst prepared with positively charged Pt(NH3)42+ as a precursor of Pt particles exhibited low catalytic activity with the H2-evolution rate of 0.10μmolh−1, which is significantly lower than the rate (0.27μmolh−1) for the composite catalyst prepared with PtCl62−. However, such precursor-dependence was not observed for composite catalysts employing Cu particles as an H2-evolution catalyst, because the Cu precursors are more labile than the Pt precursors in a reaction solution. The electrostatic interaction between the precursors of metal particles and negatively charged surfaces of alumina-silica should be taken into account to construct efficient H2-evolution catalysts.