Research Journal of Chemical Sciences ______________________________________________ ISSN 2231-606X   Vol. 2(6), 50-54, June (2012) Res.J.Chem.Sci. International Science Congress Association        
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Preparation and activity of Pt (Pd)/WP catalysts for H Oxidation Lisnyak V.V., Safonova V.V.Ischenko E.V., Stratiichuk D.A., Boldyrieva O.Yu. and Yatsymyrskyi A.V.Kyiv National Taras Shevchenko University, 01601 Kyiv, UKRAINE V.N. Bakul Institute for Superhard Materials, 04074 Kyiv, UKRAINEAvailable online at: 
www.isca.in
(Received 21st March 2012, revised 26th March 2012, accepted 27th March 2012)Abstract WP7 prepared by convenient technique was used as a support for platinum group metals. WP, Pt/WP and Pd/WP7 were characterized by powder X-ray diffraction, Ar physisorption, SEM-EDX, and were tested in the H oxidation reaction. The activity of Pt/WP and Pd/WP catalysts was compared with that of Pt/Al and Pd/Al3 catalysts containing the same amount of supported platinum metals. It was shown that the Pt/WP and Pd/WP7 catalysts exhibit enhanced activity attributed to synergistic effect realizes between Pt(Pd) metal and WP phase. Key words: hydrogen oxidation, WP, catalytic activity, supported platinum group metals, SEM-EDXIntroduction Biodegradation, biofiltration and chemical reactions catalyzed by solids of different nature3-5 are among known routs used to prevent polluting the environment with different toxic chemical substances. It is known that oxidation of hydrogen (H), the later yields the water as only the one product, is the most prominent environmentally benign way for an energy production. However, the H2 emissions at the fuel operations can cause accumulation of high concentrations of flammable gas mixtures in the containment vessel. The same scenario can realize in reactor blocks of nuclear power plants at accidents caused the failure of the reactor pressure container. The catalytic recombination (oxidation) is one of the ways can be used to prevent accumulation of H. The catalysts for this process should characterize by a very high activity, functioned at low temperatures and at low H concentrations and cannot be affected by the presence of water. Pt or cheaper Pd metals supported over various oxide carriers are known catalysts can be used for catalytic oxidation of H. However, phosphates resistant to different reaction media (e.g. reducing agents, solvents, acids and alkali) can be utilized instead of oxides as supports. The latter could allow achieving desired characteristics and ensuring a reasonable stability of catalytic properties. Among series of different phosphates, the tungsten (IV) diphosphate can be considered as a promising support for platinum group metal catalysts due to its proton exchange properties and a certain catalytic activity in the oxidation reactions10. So, in the present communication we report the preparation, characterization and catalytic activity towards Hoxidation of Pt and Pd metals supported over WP. Material and MethodsPreparation of catalysts: The starting materials was a mixture of WO and (NHHPO, taken with the molar ratio of 1:4. The mixture was grounded and put into a porcelain crucible. The mixture was heated using an electric furnace at two sequential temperatures. At first temperature, about 873 K, the mixture was held for 2 h until (NHHPO4 decomposed and reacted with WO. The resulted product was cooled to r.t. and bi-distilled water was added. This mixture was heated up to 673 K and held with stirring for 2 h. The dark solid obtained was dissolved in hot water to recover microcrystalline powder. The microcrystals were filtered and dried in thermo-programmed desiccator at 373 K for 6 h. For preparation of Pt or Pd metal supported catalysts, the microcrystalline powder (0.5 g) was impregnated with the preset quantity of 8 mM aqueous solution of HPtCl or PdCl in order to reach 0.5 wt. % load of Pt or Pd. The solutions were evaporated from the samples and obtained powder was dried in thermo-programmed desiccator at 373 K for 1 h. The powders impregnated with Pt or Pd were packed within quartz wool layers inside a flow reactor and were reduced in a gas mixture :Ar = 10:90 vol. % (GSV = 10–4 m/min) at 673 K for 1 h. The reduced samples, denoted further as 0.5% Pt/WP and 0.5% Pd/WP, were cooled and stored under ambient conditions. To compare these samples with traditional Pt(Pd)-catalysts, 0.5 wt. % load of Pt or Pd metals were supported over -Al3 sp = 3.6 m/g) in the same way as reported above. These catalysts are denoted further as 0.5% Pt/Al and 0.5% Pd/Al. Characterization of catalysts: The specific surface area (sp) was determined by means of Ar physisorption at 77 K. W and P content in the microcrystalline powder obtained was determined by X-rays fluorescence (Philips X’Unique II 1480). The powder X-ray diffraction (PXRD) patterns of grounded samples were collected using a Philips PW 3710 diffractometer (filtered 1, 2-radiation,  = 1.7903 Å). The phase identification was performed by matching experimental PXRD patterns to the powder diffraction file (PDF) 11. The morphology and elemental analysis of the catalysts were determined using a Jeol XA 88002 
Research Journal of Chemical Sciences __________________________________________________________ ISSN 2231-606X  Vol. 2(6), 50-54, June (2012)   Res.J.Chem.SciInternational Science Congress Association 
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scanning electron microscope (SEM) equipped with a Oxford Inca 350 energy dispersive X-ray (EDX) spectrometer. Catalytic activities: The catalytic activity in H oxidation was examined in a flow U-type reactor at atmospheric pressure. 0.5 g of the sample powder (fraction 0.2–0.5 mm) was packed between layers of quartz wool and formed a uniform catalyst bed inside a glass tube of the reactor. The reactor with the sample within was immersed into a bath of a thermostat. The thermostat was programmed to heat and to cool the bath according to a defined procedure in the temperature range 273–380 K. A tube furnace was used to heat the reactor up to 800 K. The temperature of the catalyst bed is measured by a thermopile situated in the center of the bed and connected to a digital displayer. The composition of the reaction gases mixture was monitored in the reactor inlet to a mixture H:O:Ar = 1:20:79 vol.%, GSV = 10–4 m/min. At the catalytic tests, the reaction temperature was increased from 273 K to whatever temperature was necessary to achieve complete H conversion ((H)) to O. The first temperature increase refers to the pretreatment stage. This procedure was then repeated for at least two times in order to reach a steady temperature at 100% H conversion 100%(H)), which was used as a measure of the catalytic activity. The reactor outlet was sampled sequentially and gas chromatography analysis of the composition of the effluent gas mixture was achieved in a molecular sieve 5A packed column of a Shimadzu GC-2014 chromatograph (Ar carrier gas). Results and DiscussionThe X-rays fluorescence results for the microcrystalline powder obtained were as follow; found: W, 48.8%; P, 16.3%; theoretical: W, 51.4%; P, 17.3% for WP. The PXRD patterns of the powder of WP, 0.5% Pt/WP7 and 0.5% Pd/WP, the latter is depicted on figure-1, are similar and typical for cubic diphosphates MP11, 12.  No crystalline phases of metallic Pt or Pd11 were found from the PXRD patterns due to the metals low concentration in the catalysts, which is below the instrument detection limit. The spvalues of the samples 0.5% Pt/Al3 and  0.5% Pd/Al3 are the same as for the initial -Al. spreaches the value of 2.0 m/g for 0.5% Pt/WP and for 0.5% Pd/WP. Pure WP with sp = 1.0 m/g shows no prominent activity in the H oxidation at low temperature as it is shown in figure-2. The full symbols in the figure-2 correspond to X(H) obtained from the measurements on heating, the open ones on cooling.  The (H) of 5 and 25% reach over WP at 520 K and 725 K, correspondingly. Figure-3 show that the temperature of a certain  conversion () over 0.5% Pd/WP7 is about on 40 lower than that over 0.5% Pt/Al. The temperature hysteresis of (H), can be seen on the figure-3, is typical for Pt or Pd metals supported on oxides13.  Figure-4 shows that over 0.5% Pd/WP7 is 40–50 lower than over 0.5% Pd/Al.  It is clearly seen from these figures that 0.5% Pt/WP7 and 0.5% Pd/WP7 catalysts show excellent H conversion with 100% = 335–338 K, their activity in H oxidation is close. The temperature hysteresis loop becomes wider if compare its width for the platinum metals supported on WP and on Al. The platinum group metals supported over WP are more active in  oxidation than supported over inert carrier Al. So, it could be conclude that enhanced activity is attributed to synergistic effect between Pt (Pd) metal and WP. The impregnation method14 used for the platinum metals (Pt, Pd) supporting onWP and-Al gives a wide spectrum of supported metals particles from nanosized to micrometric. Pt metal particles of different dimensions were registered by EDX Pt L1 mapping, typical mapping of a part of catalyst surface can be seen on figure-5.  Non-uniform distribution of Pt or Pd confirms by EDX data registered from selected surface area. For example EDX spectra from areas 1 to 6, depicted on the figure-5, show from 0.15 to 0.65 at. % Pt. The same observation is clear also for Pt or Pd supported on -Al. So, the effect of the platinum metals dimension on the catalytic activity could not be clearly estimated from the data. ConclusionWP was prepared by convenient technique was used as support for platinum group metals. The supported catalysts were characterized by PXRD, SEM-EDX, Ar physisorption, and tested in the H oxidation. The Pt/WP and Pd/WP7 catalysts show higher activity than traditional Pt and Pd catalysts supported over inert carrier -Al. Enhanced activity of the Pt/WP and Pd/WP catalysts is attributed to the synergistic effect between platinum metal (Pt or Pd) and WP. References1. Rahul, Mathur A.K. and Balomajumder Ch., Biodegradation of Waste Gas containing Mixture of BTEX by B. Sphaericus, Res. J. Chem. Sci.1(5), 52-60 (2011) 2. Thakur P.K., Rahul, Mathur A.K. and Balomajumder Ch., Biofiltration of Volatile Organic Compounds (VOCs) – An Overview, Res. J. Chem. Sci.1(8), 83-92 (2011) 3. Sonawane V.Y., Mechanistic study of chromium (VI) catalyzed oxidation of benzyl alcohol by polymer supported chromic acid, Res. . Chem. Sci., 1(1), 25-30 (2011) 
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4. Pandey B. and Fulekar M.H., Nanotechnology: Remediation Technologies to clean up the Environmental pollutants, Res. . Chem. Sci., 2(2), 90-96 (2012) 5. Pandey Bh. and Fulekar M.H.,Environmental Management - strategies for chemical disaster, Res. J. Chem. Sci., 1(1), 111-117 (2011) 6. Kotz J.C., Treichel P. and Townsend J.R., Chemistry and chemical reactivity, Interchapter: The chemistry of Fuels and Energy Recourses, Brooks/Cole, Belmont (2011) 7. Hewitt G.F. and Collier J.G., Introduction to nuclear power, Taylor Francis, London (2000) 8. Chakraborty A.K., Klatt K.-H., Konrad R., Rohde J. and Wenzl H., Catalyst for the removal of hydrogen from an atmosphere containing hydrogen, oxygen and steam, US Patent 5198405, March, (1993)9. Jin Y.C., Yang L., Nishid M., Kanematsu W. and Hibino T., Partially proton-exchanged WP with high conductivity at intermediate temperatures, Electrochem. Solid-State Lett.13(11), B123-B126 (2010)10. Lesnyak V.V., Slobodyanik N.S., Yatsimirsky V.K. and Boldyreva N.A., Catalytic activity of tungsten phosphate (IV), (V), (VI) at carbon monoxide oxidation, Stud. Surf. Sci. Catal., 130, 3807-3812 (2000)11. PDF-2 Data Base JCPDS-ICDD 2007. JCPDS International Centre for Diffraction Data: Newtown Square, PA, USA (2007) 12. Lisnyak V.V., Stoos N.V., Slobodyanik N.S., Belyavina N.M. and Markiv V.Ya., Crystal structure of a novel cubic pyrophosphate WP, J. Alloys Compd.309(1),83-87 (2000) 13. Yatsimirskii V.K., Lesnyak V.V., Gut I.N. and Boldyreva O.Yu., Effect of Pt, Pd, and Cs Additives on the Surface State and Catalytic Activity of WO in Oxidation of Hydrogen, Theor. Exper. Chem.41(2), 135-138 (2005) 14. Strizhak P.E., Trypolskyi A.I., Kosmambetova G.R., Didenko O.Z. and Gurnyk T.N., Geometric and electronic approaches to size effects in heterogeneous catalysis, Kin. Catal.52(1), 128-138 (2011) Figure-1 PXRD patterns of the 0.5% Pd/WP7 catalyst, the insert shows the perspective view of WP unit cell directed on [010] 
Research Journal of Chemical Sciences __________________________________________________________ ISSN 2231-606X  Vol. 2(6), 50-54, June (2012)   Res.J.Chem.SciInternational Science Congress Association 
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Figure-2  conversion over WP against the temperature Figure-3  conversion against the temperature over catalysts: 1) 0.5% Pt/WP, 2) 0.5% Pt/Al3 
Research Journal of Chemical Sciences __________________________________________________________ ISSN 2231-606X  Vol. 2(6), 50-54, June (2012)   Res.J.Chem.SciInternational Science Congress Association 
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Figure-4  conversion against the temperature over catalysts: 1) 0.5% Pd/WP, 2) 0.5% Pd/AlFigure-5 SEM-EDX microphotos of catalyst 0.5% Pt/WP, the insert shows EDX Pt Laa1 mapping of surface 
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