Toshihiko Fujimori, Katsumi Kaneko Research Center for Exotic - PowerPoint PPT Presentation

March 5 th , 2013 SJ-NANO 2013 “Nanotechnologies and New Materials for Environmental Challenges” Epochal Tsukuba International Congress Center, Tsukuba, JAPAN Toshihiko Fujimori, Katsumi Kaneko Research Center for Exotic Nanocarbons Shinshu University

The Project in SICP Nanostructured Carbon Monoliths for Storage and Conversion of Methane (FY2009 - FY2012) Francisco Rodríguez-Reinoso Katsumi Kaneko (Universidad de Alicante) (Shinshu University)  Characterization of nanostructures  Preparation of nanostructured porous carbons from natural resources  Adsorption properties of carbons

Target: Methane H H Major component C H of natural gas H Methane CH 4 + 2O 2 = CO 2 + 2H 2 O + 890.36 kJ

Target: Methane Advantages • Efficient (high energy density) • Clean (low CO 2 emission) • Abundant (for several hundred years use) CH 4 + 2O 2 = CO 2 + 2H 2 O + 890.36 kJ

Target: Methane Bottleneck for practical use  Severe conditions required for storage (Low temperature / High pressure) Liquefied natural gas Compressed natural gas Supercritical at (LNG) (CNG) operating temperature Critical T c = 190.5 K point CH 4 solid Low boiling point T b = 111.5 K CH 4 gas

Towards More Effective Storage Larger amount Lower energy with  Adsorption on microporous materials Extremely large surface area Guest species are adsorbed in a small volume much more strongly

Adsorbent: Activated Carbons http://en.wikipedia.org/wiki/File:Activated_Carbon.jpg

Adsorbent: Activated Carbons Randomly stacked defective graphitic units Guest species • Highly porous with micropores • Light • Chemically stable

Missions Japan Spain Porous Methane Carbons Storage preparation characterization Methane Conversion Catalytic investigation

Collaborative Publications 1) "Anomaly of CH 4 Molecular Assembly Confined in Single-Wall Carbon Nanohorn Spaces” S. Hashimoto et al., J. Am. Chem. Soc. 133 , 2022-2024 (2011). IF = 9.907 2) "Ultrahigh CO 2 adsorption capacity on carbon molecular sieves at room temperature” J. Silvestre-Albero et al. , Chem. Commun. 47 , 6840-6842 (2011). IF = 6.169 3) “Effect of nanoscale curvature sign and bundle structure on supercritical H 2 and CH 4 adsorptivity of single wall carbon nanotube.” M. Yamamoto et al. , Adsorption , 17 , 643-651 (2011). IF = 2.000 4) "Well-defined mesoporosity on lignocellulosic-derived activated carbons.” A. Silvestre-Albero et al. , Carbon 50 , 66-72 (2012). IF = 5.378 5) “Formation of CO x -Free H 2 and Cup-Stacked Carbon Nanotubes over Nano-Ni Dispersed Single Wall Carbon Nanohorns.” S. Wang et al. , Langmuir 28 , 7564-7571 (2012). IF = 4.186 6) "Diffusion-Barrier-Free Porous Carbon Monoliths as a New Form of Activated Carbon.” T. Kubo et al. , ChemSusChem 5 , 2271-2277 (2012). IF = 6.827

Today’s Topics Methane Hydrate Formation in Carbon Nanospaces Ongoing study Diffusion-Barrier-Free Porous Carbon Monoliths as a New Form of Activated Carbon ChemSusChem 5 , 2271-2277 (2012). Formation of CO x -Free H 2 and Cup-Stacked Carbon Nanotubes over Nano-Ni Dispersed Single Wall Carbon Nanohorns Langmuir 28 , 7564-7571 (2012)

Porous Carbon Monolith Activated carbon powder Advantages • Easy handling • Tightly packed particles  Enhanced properties — Inter-particle porosity — Conductivity Disadvantages Activated carbon monolith • Binder required for molding • Diffusion obstacle

Preparation Mesophase pitch Ball-milled Source Pyrolysis Ethylene tar/ 733 K with KOH (Anisotropic area = Mesophase ) Vacuum residue Under N 2

Preparation 2 AC powder E-powder Wash V-powder AC monolith E-monolith Activation V-monolith 1073K Binder-free Molding under N 2 flow monoliths

Pore Properties Nitrogen adsorption isotherms at 77 K 1200 V-monolith 1000 V-powder E-monolith 800 1 mg g - E-powder Amount / Surface Micropore DR micropore 600 area volume volume [m 2 g -1 ] [mL g -1 ] [mL g -1 ] 400 2370 0.96 0.82 E-powder E-monolith 2530 0.98 0.86 200 2600 1.0 0.89 V-powder V-monolith 2820 1.1 0.97 0 0.0 0.2 0.4 0.6 0.8 1.0 Relative Pressure, P/ P 0 Enhancement of surface area and micropore volume

Methane Storage Ability Methane adsorption isotherms at 303 K V-monolith E-monolith V-powder E-powder Enhancement of methane storage capacity

Adsorption Kinetics Time course of adsorption amount on sudden pressure chanege1 Mpa−2 MPa E-powder V-powder Desorption Adsorption Desorption Adsorption 293 K 293 K 298 K 293 K 298 K 293 K 303 K 298 K 303 K 298 K E-monolith V-monolith Adsorption Desorption Adsorption Desorption 293 K 293 K 298 K 293 K 293 K 298 K 303 K 298 K 303 K 298 K Monoliths have practically acceptable diffusion rates

Summary Advantages • Tightly packed particles  Enhanced properties — Inter-particle porosity — Conductivity • Easy handling Disadvantages • Binder required for molding • Diffusion obstacle “Binder-free” porous carbon monolith

More Efficient Methane Storage “Efficient methane storage at milder conditions” 20 CNG ~250 v/v Pressure [MPa] ~200 v/v 3.5 Adsorption • Methane hydrate Milder • Nano-confinement effect 0.1 LNG Condition 600 v/v 111 191 298 Temperature [K]

Methane Hydrate • CH 4 confined in the cages of H 2 O framework • Composition: CH 4 ·5.75H 2 O • Storage capacity: 164 v/v

Nano-confinement Effect In nanospaces, high pressure phases formed at low pressure conditions. KI B2 phase formation 0.1 MPa in SWCNH (1.9 GPa in bulk state) K. Urita et al., J. Am. Chem. Soc. 133 , 10344–10347 (2011)  Quasi-high pressure factor: ∼ 19,000

Methane Hydrate Formation Assuming MH formation with the factor of “20,000”… Phase diagram of “Confined” “Bulk” bulk methane hydrate (solid) formation formation 50 MPa 2.5 kPa (300 K) (300 K) 0.13 kPa 2.6 MPa (273 K) (273 K) Much milder condition!!! Sloan and Koh “Clathrate Hydrates of Natural Gases, Third Edition”

Strategy “H 2 O pre-adsorption−CH 4 introduction” method Porous Porous MH Material Material in pore ( dry ) ( wet ) H 2 O CH 4 Methane adsorption isotherm

CH 4 adsorption on dry/wet carbons Rw*= 0.7 Rw*= 1.5 VR93-2:1-800 VR93-5:1-800 1 2 25 50 Rw:1.5_adsorp Rw:1.5_desorp 20 40 Rw:0_adsorp Rw:0_desorp n CH 4 , wt% n CH 4 , wt% 15 30 10 20 Rw:0.7_adsorp 10 5 Rw:0.7_desorp Rw:0_adsorp 0 0 Rw:0_desorp 0 20 40 60 80 100 0 20 40 60 80 100 P eq (bar) P eq (bar) Rw*= 1.8 VR93-6:1-800 3 60 Rw:1.8_adsorp Measured at 275 K Rw:1.8_desorp 50 Rw:0_adsorp • Sudden uptake at 40~60 bar Rw:0_desorp 40 n CH 4 , %wt • Similar amount uptake 30 • Hysteresis only for wet samples 20  Methane hydrate formation? 10 0 0 20 40 60 80 100 Details under investigation... P eq (bar)

Use of Stored Methane Methane storage techniques Porous carbon monolith Methane hydrate in pores • Handling • Milder condition • Capacity Uses • Fuel • Source of other chemicals - Hydrogen - Nanocarbons - C1-chemistry

H 2 Generation Reactions from CH 4 All the reactions require metal catalysts Steam reforming CH 4 + 2H 2 O  4 H 2 + CO 2 CO 2 reforming CH 4 + CO 2  2 H 2 + 2CO Partial oxidation CH 4 + O 2  2 H 2 + CO Methane decomposition Methane decomposition Merits CH 4  C + 2H 2 • No gaseous CO x impurity • Solid carbon product — Nanotube production

Catalyst for Methane Decomposition Metal species Precious metals : Pd, Pt Problem : Expensive Support Oxides : TiO 2 , Al 2 O 3 , SiO 2 , MgO... Non-Oxides : carbon fiber, carbon black... Problem : Impurity or deactivation H 2 CH 4 CH 4 CO Carbon H 2 CO 2 M M M M M M M M M M O O O O O O Non-Oxide Oxide Reaction with oxygen of oxide Carbon product covers the metal particles, affords CO and CO 2 as impurities which deactivates the catalytic metal.

Strategy Metal species Cheaper metals : Fe, Co, Ni, Cu Support Single-walled carbon nanohorns (SWCNH) • Dahlia-like assembly structure — Suitable morphology for deposition • Large surface area Large deposition amount — • Reducing agent for metal salts Easier preparation without H 2 — • Non-Oxide No CO/CO 2 evolution —

Catalyst Preparation (Ni-SWCNH) Incipient wetness Ni nanoparticles impregnation method Metal nitrate ( M II/III (NO 3 ) m ･ n H 2 O) SWCNH Mixed in EtOH (Impregnation) M II/III (NO 3 ) m /SWCNH Heat at 673 K in He flow (Reduction) M 0 /SWCNH (M = Fe, Co, Ni, Cu)

CH 4 Decomposition Reaction Mass spectrometer m / z CH 4 10% 2 (H 2 ) (reactant) 16 (CH 4 ) M/SWCNH 28 (CO) (catalyst) He T 44 (CO 2 ) (carrier) 90% 303 K→1200 K 3 K min -1

CO/CO 2 Evolution CO ( m /z = 28) Different reduction conditions a : in He at 673 K for 1 h b : in H 2 (20%)/He(80%) at 673 K for 40 min c : in He at 873 K for 40 min CO 2 ( m /z = 44) No CO/CO 2 evolution

Metal type dependency Ni Co Fe Cu

Durability Good catalytic activity 773 K kept at 723 K 823 K 723 K 873 K 673 K 1173 K

Carbon Product Cup-stacked Carbon Nanotubes Possibility for a nanocarbon growth substrate

Summary Methane storage techniques Porous carbon monolith Methane hydrate in pores • Handling • Milder condition • Capacity Use of methane Catalytic decomposition • H 2 , Nanocarbon production