Photocatalytic hydrogen production from methanol over Nd/TiO₂
Reli^a M., Edelmannová M.^a,Troppová I.^a, Čapek L.^b, Kočí K.^a

^aInstitute of Environmental Technology, VŠB-Technical University of Ostrava, 17. listopadu 15/2172, Ostrava, 70833, Czech republic,
^bFaculty of Chemical Technology, University of Pardubice, Studentská 95, 532 10 Pardubice, Czech Republic.
e-mail: martin.reli@vsb.cz

Abstract

The question of renewable energy is becoming more and more frequent these days. Not only because the fossil fuels are becoming to be scarce but also due to increasing environment pollution caused by combustion of fossil fuels. Besides utilizing the elements like wind, sun or water, a new more reliable way of clean energy production is being seek out. One of such possibility is the photocatalytic oxidation of low alcohols, for example methanol. Not only, this reaction is environmentally friendly, but also is a promising way, how to replace obsolete fossil fuel combustion. Unfortunately, there is a very long way to achieve this goal and a further research is required. This work is focused on a modification of titanium dioxide by neodymium. Lanthanides possess 4f electron configuration, which can significantly improve photocatalytic activity of TiO₂. The partly filled 4f electrons in rare earth ions can form a new energy level between the TiO₂ valence and conduction bands resulting in narrowed band gap. However, before Nd/TiO₂ photocatalysts can be prepared an optimal preparation conditions have to be find. Therefore, three different TiO₂ photocatalysts prepared by various methods have been tested for the photocatalytic oxidation of methanol and compared to commercial TiO₂ Evonik P25. At first, TiO₂ was prepared by sol-gel method followed by either calcination or processing by pressurized water at high temperature. The temperature at high pressure processing is very important, therefore two samples at two different temperatures (200°C and 225°C) were prepared. These different prepared pure TiO₂ photocatalysts were tested for photocatalytic oxidation of methanol. Based on the yields of generated hydrogen and methane, the optimal preparation condition was used for the preparation of series of Nd/TiO₂ photocatalysts with various amounts of neodymium. All prepared photocatalysts were characterized by X-ray powder diffraction, N₂ physisorption, Raman spectroscopy, transmission electron microscopy, UV–vis diffuse reflectance spectroscopy and photoelectrochemical measurements, respectively. The doping of TiO₂ with neodymium can influence the particle size, the specific surface area, the value of band gap energy, the recombination of electron and hole and also the position of valence and conduction bands. Thus, the photocatalytic activity of the TiO₂ photocatalyst for H₂ evolution can be increased by optimum doping amount of neodymium. The presented and even more the future work is introducing not very common modification of TiO₂ by neodymium prepared by unconventional method; the high pressure processing by hot water.