In near-future hydrogen society, the electricity can be stored as chemical energy and readily utilized. Planned power down is not needed until damaged big infrastructure is recovered. Hydrogen is produced derived from oil and it is necessary to highly purify in order to use as energy source. Carbon monoxide (CO) is included as impurity inevitably derived from oil. It is removed via the reaction CO + H2O -> CO2 + H2, but the reverse reaction to reform CO also proceeds (chemical equilibrium).

In this context, preferential photo-oxidation catalysts have been investigated utilizing sunlight. The direction of zinc oxide crystalline growth was controlled and metal ions were adsorbed to trap photo-generated electrons. The photo-catalyst removed 10000 ppm (1%) of CO to be less than 10 ppm via selective photo-oxidation 2CO + O2 -> 2CO2. By the control of photo-catalytic mechanism, the reaction of 2H2 + O2 -> 2H2O never proceeded. This method is sustainable to use only cheap materials, e.g. zinc oxide (the original paper in preparation).

As mentioned in section 1 and 2, photo-catalysts and homogeneous nanoparticle catalysts significantly contribute to protect/improve the environment and energy problem. These new technologies can be used and further improved based on clear understanding of the principle.

Vanadium or sulfur doped titanium oxide photo-catalysts were developed activated under visible light (400 - 800 nanometers) (2007). The dynamic steps to receive photo-generated electrons and to donate them to reactants were investigated for doped V and S in/on TiO2 were investigated by selective X-ray spectroscopy. Based on the spectroscopy developed in our research group, the structure and the valence state are analyzed as a set and thus the detailed photo-catalytic mechanism was clarified (2007, 2007, 2008, 2009, 2009).

Though it is expensive in comparison with our preferential photo-oxidation catalysts, the intermediate formed by the electron donation to O2 molecules over the gold nanoparticles of 3 nanometers was detected to dissociate the O-O bond in the preferential CO oxidation mechanism (2008).

Polymer electrolyte fuel cells have the advantages to work at low temperature and compact. The obstacle for practical use is the catalyst that requires expensive and not sustainable platinum. Our research group reduced the size of Pt particles to 1 nanometer using ordered mesoporous silicon oxide as template and carbon nanotubes were grown as anchored on the Pt nanoparticles (2010). Owing to the replica synthesis, O2 gas diffusion paths were generated by the removal of SiO2 with hydrofluoric acid and the electron-conducting property of formed carbon nanotubes was excellent. Hence, the Pt-carbon nanotube composite exhibited nice catalytic performance as cathode catalyst. Further, new cathode catalysts those do not include Pt are investigated.

In-situ monitoring of amino acids and DNA with ferrite surface with respect to drug delivery (2006), the monitoring of self-assembly mechanism polyoxomolybdenum ring potentially used as single molecule magnet and photo-catalyst (2010), the investigation of operation mechanisms of sorbents to remove trace amount of poisonous elements (lead, arsenic) in environment (2006, 2005, 2002, 2002), and the investigation of catalytic mechanism of nano-catalysts to remove NOx (2003, 2002) were done as collaborations.