Several metals in the form of nanoparticles loaded on metal oxides exhibit activity for photocatalytic production of hydrogen from water (1-4). Among them, gold has received attention recently in pollution control and fuel cell applications (5,6), but has received very little attention with regard to photocatalysis.The activity of gold loaded on metal oxides depends on many factors such the type of support material, the preparation method and the calcination temperature. This group has carried out a number of investigations concerning the activity of Pd/TiO 2 (7-13) and Au/TiO 2 to produce hydrogen gas (11)(12)(13)(14). We have found that Au/TiO 2 was slightly more reactive than Pd/TiO 2 and mixed metal catalysts of gold and palladium on titania have greater activity than sums of the reaction using the single metal catalysts (14).In this paper, we show the activity of Au/TiO 2 in the liquid phase and, for the first time, in the gas phase, and a mechanism for the photocatalytic reforming of methanol is presented.
ExperimentalExperiments were carried out in a Pyrex reaction flask which contains two arms, one for purging the reaction by argon and the other for sampling through a rubber septum. For liquid phase reactions, the reaction mixture is 0.2 g of the catalyst, 100 ml of deionized water and 100 l methanol. Note that we have previously found that the reaction is close to zero order in the concentration of methanol in solution (7,8). For gas phase reactions, 0.05 g of the catalyst was mounted on a slide which is supported in a modified reactor without direct contact with the reaction mixture (15 ml of deionized water and 100 l methanol). There is no forced circulation of the gas phase.In both cases, the mixture was stirred with a magnetic stirrer and was illuminated with light from a 400 W xenon arc lamp (Oriel model) from the side. Every 30 minutes, 0.2 ml samples were taken from the gas phase and analysed by GC (Varian 3900).The catalyst was prepared by the incipient wetness method as follows. The appropriate mass of metal salt (HAuCl 4 ) was dissolved in water and a volume of this solution was added to P25 titania (Degussa) which was just sufficient to fill the pores of the support. The sample was then dried in an oven at 110°C for 2 h, ground in a pestle and mortar, calcined at 500°C for 2 h and finally sieved to less than 53 m aggregate size.
Results and discussion a) Liquid phaseIt was found that the gold was active for photocatalysis, as shown in Figure 1, and had very good activity compared with
AbstractMethanol can be reformed with water, at ambient temperature, using photocatalysis, and this reaction represents a possible low energy, more sustainable pathway to hydrogen production than (for instance) steam reforming. The requirements for the catalysts are rather strict since titania itself is almost inactive for anaerobic photocatalysis, whereas the addition of a very limited range of metals to the surface renders it active. Surprisingly, this includes gold, which shows one of the highest reactivitie...
