Photocatalytic methanol reforming on Au/TiO2 for hydrogen production

Abstract

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...

Hydrogen Production by Photoreforming of Renewable Substrates

“…They reported ca. 135 μL/g cat min H 2 productivity, more than three times higher value than in liquid phase photoreforming [161].…”

The Photocatalytic Window: Photo-Reforming of Organics and Water Splitting for Sustainable Hydrogen Production

“…However, if operating as a window, obviously it would not be achieving its maximum potential since it needs to transmit a large proportion of the light. Further, in separate experiments we have found that maximum hydrogen production is only achieved when a layer *0.2 mm thick [34] is applied to the glass, which then absorbs/scatters most of the light. The gas produced from the panel passes through to a storage device which could either be batch storage or could be directly connected to the cooker.…”

Novel Au/TiO2 photocatalysts for hydrogen production in alcohol–water mixtures based on hydrogen titanate nanotube precursors

“…10(a)) and 80:20 ( Fig. 10(b) [26][27][28][29][30][31][32]35]. At both ethanol concentrations, the 0.5 wt.% Au/TiNTx photocatalysts displayed excellent stability during the tests, as evidenced by the linearity of the H 2 production plots with UV irradiation time.…”

“…We are currently conducting detailed GC analyses of the other reaction products formed during Au/TiO 2 photo-excitation in the different alcoholwater mixtures, with the aim of better understanding the alcohol photo-oxidation pathway and role in promoting H 2 production. This will also allow the relative contributions of alcohol photoreforming and water-splitting to the observed H 2 yields to be determined, and meaningful comparisons to be drawn with prior related studies on the Pd/TiO 2 system [26][27][28][29][30][31][32]. Further photocatalytic tests are also being conducted under visible and full solar excitation, to determine the extent to which the plasmonic effect [35,[46][47][48] can enhance H 2 production rates.…”

“…It is not clear at all from current literature what the optimum alcohol concentration is for H 2 production in the different M/TiO 2 systems, and whether the optimum concentration varies from alcohol to alcohol (alcohols typically used as sacrificial agents are methanol and ethanol, and to a lesser extent ethylene glycol and glycerol). Bowker and co-workers have made the most important contributions in this area to date [10,[26][27][28][29][30][31][32], reporting hydrogen production rates for the photoreforming of a variety of bio-derivable feedstocks over Pd/P25 and Au/P25 under UV excitation. In the Pd/P25 system, H 2 production rates at an alcohol concentration of 1 vol.% were observed to follow the order triols > diols > 2°alcohols > 1°alcohols > 3°alcohols [26,[28][29][30].…”