Laser-Induced Photocatalysis and its Applications in Petrochemicals ...

3. Results and DiscussionThe important applications of laser induced photocatalytic process undertaken at ourlaboratory are the photocatalytic conversion of methane into methanol and hydrogen, splittingof water into Hydrogen and oxygen, conversion of methanol into hydrogen and phenoldegradation for cleaning of waste water.3.1 Photocatalytic conversion of methane into methanolMethane is considered to be a cheap source of energy and its worldwide reserves arelarge. Global research efforts are under way in industrial as well as academic institutionsfunded by both private and government sectors for the development of methods to convertmethane to useful, more readily transportable and storable products such as methanol.Methanol is a desirable product of conversion because it retains much of the original energyof methane while satisfying transportation and storage requirements. Methanol is liquid atroom temperature and can be transported to market using the existing petroleum pipeline andtanker network. It can be used as a fuel or may be converted to other valuable products. Theexisting techniques to convert methane to methanol are not cost effective and efficient due topoor selectivity and require extreme conditions such as high temperature and sophisticatedequipment.The main aim of this study was to explore and develop novel pathways for conversion ofmethane into methanol under mild experimental conditions using laser light, water and asemiconductor photocatalysts such as α-Fe 2 O 3 , WO 3 , TiO 2 and NiO.To study the photocatalytic conversion of methane into methanol, the optimized amount ofthe catalyst under study (determined by the procedure mentioned earlier), was suspended in60 ml of water. Instead of purging the catalyst suspension with argon, methane was bubbledthrough the suspension for a fixed period of 15 minutes at a fixed flow rate of 100 ml/minand the cell was sealed at atmospheric pressure. The suspension was illuminated with 355 nmlaser having a beam diameter of 10 mm. The progress of the reaction was studied bymeasuring the amount of hydrogen produced and change in methanol concentration withtime. Separate batch experiments were performed to measure the production of hydrogen andmethanol.To measure the produced hydrogen, the sample from the dead volume of reaction cell, wasanalyzed at a regular interval of 15 minutes by using a Shmimadzu gas chromatograph (GC-17A) equipped with a thermal conductivity detector and a 30m molecular sieve 5A “PLOT”column. Argon gas was used as carrier at a flow rate of 10 ml/min. To estimate the amount ofmethanol during the reaction, liquid samples were drawn from the reaction cell at a regularinterval of 10 minutes, centrifuged and analyzed by using a gas chromatograph (supplied byAgilent Technologies) equipped with an FID detector and a 2m Chromosorb-101 packedcolumn. Helium gas was used as carrier at a flow rate of 25 ml/min. The injector, column anddetector temperatures were set at 250 o C, 200 o C and 250 o C respectively. Both the gaschromatographs were calibrated by using self prepared external standards prior to sampleanalysis. The reproducibility of the process was checked by repeating the experiments atregular intervals while the reproducibility of the analysis was estimated by running thestandards time to time.The progress of methanol formation was monitored by analyzing the liquid samples at regularintervals. The methanol yield as a function of time are plotted in Figures 2 & 3 for WO 3 and