hydrogen is the preferred fuel for fuel cell vehicles. Due to these reasons, the hydrogenproduction is <strong>in</strong> high dem<strong>and</strong> <strong>and</strong> <strong>in</strong>novative <strong>and</strong> alternate methods are be<strong>in</strong>g <strong>in</strong>vestigated forproduction of hydrogen.Recently, the research activities have been focused on the development of noveltechniques for the generation of hydrogen <strong>and</strong> oxygen by splitt<strong>in</strong>g of water [5-10] as water ismost abundant <strong>in</strong> nature. Heterogeneous photo-catalysis is one of the techniques applied forthe generation of H 2 <strong>and</strong> O 2 <strong>in</strong> aqueous solution us<strong>in</strong>g semiconductor catalysts. This photocatalytictechnique is considered to be feasible <strong>and</strong> attractive for practical purposes s<strong>in</strong>ce onecan possibly use natural sun light as an irradiation source <strong>in</strong> the future. Most of the previouswork <strong>in</strong> this doma<strong>in</strong> has been carried out with broadb<strong>and</strong> UV lamps us<strong>in</strong>g pure TiO 2 or TiO 2based semiconductor powders as photo-catalysts [11-13].Recent studies on photocatalysis us<strong>in</strong>g laser, carried out at our laboratory suggestedthat an important parameter which plays a crucial role <strong>in</strong> the enhancement of the activity ofthe catalyst is the irradiation source. Most of the research work reported on photocatalysis isbased on use of conventional lamps [13-18]. Very little work has been carried out onphotocatalysis with lasers [19]. S<strong>in</strong>ce laser light has special properties like monochromaticity,high <strong>in</strong>tensity, <strong>and</strong> low beam divergence, it is of great <strong>in</strong>terest to use laser radiation as anexcitation source to study the activity of photocatalysts. We <strong>in</strong>vestigated the photocatalyticactivity of α-Fe 2 O 3 , WO 3 , TiO 2 <strong>and</strong> NiO as semiconductor catalysts for splitt<strong>in</strong>g of water <strong>in</strong>tohydrogen <strong>and</strong> oxygen <strong>and</strong> for conversion of methanol <strong>in</strong>to hydrogen.2. Experimental Setup DetailsThe setup used to study the photocatalytic conversion of methane <strong>in</strong>to methanol,splitt<strong>in</strong>g of water, conversion of methanol <strong>in</strong>to hydrogen <strong>and</strong> degradation of phenol for wastewater treatment is discussed <strong>in</strong> detail <strong>in</strong> our earlier publications [20-28]. To study thephotocatalytic cativity for these applications over α-Fe 2 O 3 , WO 3 , TiO 2 <strong>and</strong> NiO, all thecatalysts were subjected to identical experimental conditions. While us<strong>in</strong>g laser as a lightsource, it was observed that the important parameters which significantly affects the productyield are: laser energy, amount of catalyst (particle density), stirr<strong>in</strong>g rate <strong>and</strong> laser beamdiameter. The two parameters i.e. stirr<strong>in</strong>g rate <strong>and</strong> laser beam diameter were kept constant forall the studies reported <strong>in</strong> this paper. However, the dependence of products yield on laserenergy <strong>and</strong> amount of catalyst, to identify the maximum yield of Hydrogen <strong>and</strong> Oxygen wasstudied carefully for WO 3 catalyst <strong>in</strong>itially. Once the laser energy <strong>and</strong> amount of catalyst wasidentified for optimum product yield, these two parameters (laser energy & catalystconcentration) were then kept constant for other catalysts for the sake of activity comparison.The destructive effect of focused laser beam was m<strong>in</strong>imized by exp<strong>and</strong><strong>in</strong>g the diameter of thebeam to 1 cm by us<strong>in</strong>g lenses <strong>and</strong> mirrors.The photo-catalytic <strong>in</strong>duced reactions over α-Fe 2 O 3 , WO 3 , TiO 2 <strong>and</strong> NiO were studiedby suspend<strong>in</strong>g an optimized amount (400 mg) of above-mentioned semiconductor powders <strong>in</strong>60 ml of deionized water. This amount (400 mg) was kept constant for all catalysts. Argonwas used as purge gas to remove dissolved gases <strong>and</strong> the progress of the purg<strong>in</strong>g process wasmonitored by analyz<strong>in</strong>g the gas samples from the dead volume of the reaction cell. All theexperiments were performed <strong>in</strong> batches <strong>and</strong> the quantity of evolved gases was estimated byanalyz<strong>in</strong>g the gas samples at regular <strong>in</strong>terval of ten m<strong>in</strong>utes by us<strong>in</strong>g a SHIMADZU GC-17Agas chromatograph equipped with a 30 m, 0.53 mm <strong>in</strong>ner diameter, molecular sieve 5APLOT column <strong>and</strong> a TCD detector. Argon was used as carrier gas. All the catalysts wereexposed to an optimized laser energy of 100 mJ as higher energies were found detrimental.
43211516814567991310121. Nd:YAG <strong>Laser</strong> (1060nm)2. Third harmonic generator (355 nm)3. Beam splitter4. <strong>Laser</strong> energy meter5. Mirror6. Beam diameter controller7. Quartz w<strong>in</strong>dow8. Dead volume of cell9. Effective volume of cell10. Megnatic stirrer11. Megnatic plate12. Gas <strong>in</strong>let13. Liquid sampl<strong>in</strong>g valve14. Gas sampl<strong>in</strong>g valve15. Gas outlet16. Pyrex cellFigure 3.111Experimental Setup for measur<strong>in</strong>g evolvedgases <strong>and</strong> liquid products dur<strong>in</strong>gphotocatalytic process.
Change language