Carbon supported Gold Catalysts for Catalytic Applications By : S.DHIVYA th May 2010

1/11/  Introduction  Synthesis of Au/carbon catalyst by sol - immobilization method  Physico – Chemical Characterisation of Au/C catalyst XRD – Composition, Crystallographic phase, Crystallite size ICP analysis of the filtrate – Estimation of Au on carbon support UV Vis analysis – Surface plasmon resonance – approximate idea of particle size TGA – Thermal stability and also the amount of gold loading on carbon BET sorptometry – Specific surface area and pore size distribution SEM analysis - Surface Morphology of Au nano structures on the cabron support TEM analysis – Surface Morphology of Au nano structures  Use of Au/C catalysts for Oxygen Reduction Reaction (ORR)  Work status Contents

1/11/ Why Au ?  Electrochemical potential of gold is lowest of any metal  Gold is the most electronegative of all metals (in the Pauling or absolute scale)  Ability to catalyze (in nano state) the reduction of oxygen  Good resistance to corrosion and dissolution Hiroko Okatsu et.al., Applied Catalysis A : General 369 (2009) 8-14

1/11/ Why Carbon Support ?  Inert support - only slightly affects the catalytic properties of Au nanoparticles (NPs)  Stable in both acidic and basic environments  Combustible to allow the recovery of catalytic metals  Presence of acidic function group on the carbon surfaces enhances the deposition and dispersion of Au NPs  Electrically conductive, leading to applications to electrodes for fuel cells, batteries, and chemical sensors Hiroko Okatsu.et.al., Applied Catalysis A : General 369 (2009) 8-14

1/11/ Catalysis by Gold : Some Glittering Facts  Catalysis by Gold – a ‘rags to riches’ story  It has been overlooked for many years as a key component in catalysis  Two key observations of 1980’s that revolutionized the field: i.Finding of G. J. Hutchings that gold would be the best catalyst for ethylene hydro chlorination ii.Finding of Haruta et al. that supported Au nanoparticles possess exceptionally high CO oxidation activity  2.0 nm appears to be a crutial diameter for noble metals (gold) to lose intrinsic metallic nature  Gold clusters with diamters below 2.0 nm or with atoms less than 300 will lead to many interesting and useful scientific discoveries G. J. Hutchings, J. Catal. 96 (1985) 292 M. Haruta, T. Kobayashi, H. Sano, N. Yamada, Chem. Lett. 1987, 405

1/11/  Sol immobilization method  Deposition precipitation method  Impregnation method  Solid grinding method Au/C catalyst - Methods of preparation

1/11/ mL of H 2 O M NaOH (7.5 mL) 5mL dil. aq. THPC (1.2 mL,78 wt.% THPC solution made upto 100 mL) Stirring for 2 minutes 0.03 g Au (15 mL, M HAuCl 4 Stirring for 1 h 0.97 g Carbon (Carbon support) Stirring for 3 h Filtering, washing, drying and mortaring Inert gas, Ar, treatment (3 h/350 °C/ N 2 ) Reduction (3 h/350 °C/ H 2 )  3 wt.% Au/C (1.0 g) Demirel Gulen and Lucas Claus, Catalysis Today, (2005) Gold-Sol Immobilization Method

1/11/ Images of the process of Catalyst preparation Stirring of 15 mL, M HAuCl 4 in the presence of NaOH and THPC solutions (reddish brown colour solution of Au is seen)

1/11/ Filtering of Au - C suspension The colour of the filtrate is reddish brown, almost similar to the colour of the solution before C addition

1/11/ Synthesis of Au/Nuchar Activated Carbon Au sol solvent rich adsorption layer Carbon support Filtration and drying Stirring Au Carbon support Au Carbon support Schematic representation of the catalyst synthesis process

1/11/ The filtrate turns purple colour after 2 weeks indicating the agglomeration of gold NPs

1/11/  X - ray Diffraction (XRD)  ICP Analysis  UV-Vis Analysis  Scanning Electron Microscopy (SEM)  Transmission Electron Microscopy (TEM)  BET sorptometry Physico-Chemical Characterization

1/11/ Analysis of the filtrate for Au content: 1.To know the amount of Au loaded o the carbon support, 10 mL of the filtrate is diluted to 500 mL and 25 mL of this dilute solution of the filtrate is given for ICP analysis Presence and state of Au on Carbon support: The presence as well as the cystallographic structure of Au particles on C support in the Au/C catalyst is be evaluated by XRD analysis ICP Analysis XRD Analysis

1/11/ Au/Nuclar activated carbon – XRD Analysis XRD pattern of Au/C (Nuchar) o The broad and intense diffraction peak at the 2  value of 24.7 is attributed to the (002) plane of Nuchar activated carbon o The diffraction peaks at the 2  values of 38.8, 44.8, 64.7 and 78.4 were indexed to the (111), (200), (220) and (311) Diffraction planes of Au metal particles in fcc lattice o The crystallite size of Au Nano structures on gold was Calculated by considering (111) peak Using Debye Scherrer’s equation o The crystallite size of Au nanoparticles on carbon support is 3.4 nm

Au/Vulcan XC 72 R – XRD Analysis XRD pattern of Au/C (Vulcan XC 72 R)

Au/Black Pearl 2000 – XRD Analysis XRD pattern of Au/C (Black Pearl 2000)

Au/CDX 975 – XRD Analysis XRD pattern of Au/C (CDX 975)

Au/C catalysts – BET sorptometry CatalystSpecific surface area (m 2 /g) Total pore volume (cm 3 /g) Au/Nuchar Au/Vulcan Au/Black Pearl Au/CDX

1/11/ Oxygen reduction reaction (ORR) is a four electron process: O H e - → 2 H 2 O E o = V vs. NHE Oxygen Reduction Mechanism Importance of electrochemical reduction of oxygen  Fuel Cells  Metal-Air batteries  Industrial electrolytic processes H+H+ H+H+ H+H+ H+H+ H+H+ Cathode Water Air/O 2 Electrons H+H+ Fuel Cells - Principles and Applications; Viswanathan, B., Aulice Scibioh, M., Eds.; Universities Press (India) Private Limited, 2006.

1/11/ Reaction pathways for oxygen reduction reaction Path A – direct pathway, involves four-electron reduction O H e -  2 H 2 O ; E o = V Path B – indirect pathway, involves two-electron reduction followed by further two-electron reduction O H e -  H 2 O 2 ; E o = V H 2 O H e -  2 H 2 O ; E o = 1.77 V Halina S. Wroblowa, et,al., J. Electroanal. Chem., 69 (1979) 195

1/11/  Reversible  Oxygen adsorption capacity  Structural stability during oxygen adsorption and reduction  Stability in electrolyte medium and also in suitable potential window  Ability to decompose H 2 O 2  Good conductivity  Low cost Essential criteria for choosing an electro catalyst for oxygen reduction

1/11/ S.NoCatalystMetal loading ( Wt %) ORR activity 1 Au/MWCNT mA/cm 2 2 Au/Vulcan XC- 72R & BP 52.5 (mA/cm 2 3 AuPt/C4 (Pt:Au=3:2)793.2 mW/cm 2 4 AuPt/C (I E =mA/cm 2 /mg AuPt) M KOH0.5 M H 2 SO V at 400 C I E -0.1v at 500C I E 0.55V at 400C I E 0.55V at 500C I E Au 72 Pt 28 /C Au 56 Pt 44 /C Au based catalysts for ORR Nadezda Alexeyeva.et.al., Journal of Electroanalytical Chemistry (2010) Michael Bron.et.al., Journal of Electroanalytical Chemistry 624 (2008) Yuanwei Ma.et.al., catalysis Communications 11 (2010) Jin Luo.et.al., Electrochemistry Communication 8 (2006)

1/11/  The ORR activity of Au/Vulcan XC 72 is evaluated  The ORR activity of Au/Nuchar, Au/Black Pearl and Au/CDX 975 is being tested Work in progress

1/11/