Photocatalytic reduction of CO 2 in a batch slurry photoreactor ENEA - C.R. "Casaccia - 18-06-2012 Guido Spanò www.eni.it
Introduction Since the seminal work of Inoue et al [1] in 1979, the phocatalytic reduction of Carbon Dioxide gave rise to a lively interest. Thirty years have passed since the first publications, the most widely used materials for photocatalysis are still based on TiO 2, on systems equipped with artificial UV lamp and using water as the source of hydrogen. The reported productivity are still dramatically low, in the order of some μmol h -1 gcat -1. The use of a scavengers usually isopropanol, but also inorganic (Na 2 SO 3 ) have been added as well, seems to reduce recombination of the couple electron / hole created on the semiconductor by photon adsorption enhancing yield of reduction product. Indeed TiO 2 acts as photo degradation catalysts of organic water pollutant. [1] Inoue,T; Fujishima, A; Konishi, S; Honda, K. Nature 1979, 277, 637 2
System CH x (O) (H 2 ) Water Photo-splitting CO 2 (H + ) H 2 O O 2 3
State of the art 4
State of the art 10000 1000 100 2003 2007 1999 2003 2007 2002 1997 1999 2001 2005 g ctz -1 h -1 10 mol 2008 1 0 1994 2002 TiO2 (optical-fiber R) Cu/TiO2/SBA-15 5 Ti-FSM16 (fluorur) Ti- Sio2 thin film TiO2 (CO2 supercrit.) Cu/TiO2 8W Hg lamp Pt-loaded TiO2/Y-zeolite Indrakanti (A) TiO2 P25 (con Hsc.) TiO2 Ti-MCM-4, Ti-MCM-48 TiO2/Pd/Al2O3 Ti- Sio2 thin film oaded ex-ti-oxide/y-zeolite Pt-loa nanotio2 Pt/TiO2 C Fe/LaCoO3 Ti BETA TiO2 sputter BiVO4 cu-fe TiO2/SiO2 Co(Pc) - TiO2 u-k/deall.y - Pt/K2Ti6O13 Fe-Cu
Experimental setup Reactor UV lamp CO 2 inlet Thermostatic bath Magnetic stirrer CO 2 continuously bubbled and circulating Thermostatic Double jacket Continuous stirring Ca. 1 g of catalyst in 0.7 litre 20 hour reaction Room temperature and pressure.2-2 -1 W*m *nm 300 400 500 600 700 800 900 1000 Nanometers UV high mercury pressure lamp 500W power (313 nm) 580 wat/cm 2 UV low mercury pressure lamp 17W power (254 nm) 50 wat/cm 2 0.2 pa Complex hydrocarbon pool not even easy to resolve: MEOH 5.7 ppm 3.89 min ACETALDEIDE 5 ppm 3.86 min METHANOL and ACETALDEYDE overlap on HP PONA Propane and Propene on HP-PLOT/U METHANOL and t-butanol on FFAP 3.8 3.85 3.9 3.95 4 4.05 4.1 Minutes 6
Test Results without Scavenger CATALYSTS DEGUSSA STANDARD TiO 2 P25 P25 2 4 % Cu after 5h calcination at 550 C by incipient wet impregnation with Copper Nitrate 2%Cu-TiO 2 / SBA-15 (45/55) following Yang et al; Catal Lett () 131,381 ( ) Catalysts Ambient UV-lamp Yields of products condition HCHO CH3OH (μmol/gctz*h) (μmol/gctz*h) TiO 2 P25 water 17 W (254 nm) 1 1 4%Cu/TiO 2 (P25) water 17 W (254 nm) 1 1 2%Cu/TiO 2 (P25) 0,2M NaOH 17 W (254 nm) 1 1 4%Cu/TiO 2 (P25) 0,2M NaOH 17 W (254 nm) 1 1 45% (2% Cu/TiO 2 )/SBA-15 0,1M NaOH 17 W (254 nm) 1 1 T.Inoue (TiO 2 ) a water 500 W (365 nm) 6,0 48,7 I.-H. Tseng (3,3% Cu/TiO 2 sol-gel ) b 0,2M NaOH 8 W (254 nm) 15,0 I.-H. Tseng (2,0% Cu/P25) b 0,2M NaOH 8 W (254 nm) 10,0 I.-H. Tseng (TiO 2 P25) b 0,2M NaOH 8 W (254 nm) 3,8 H.-C. Yang (45% (2% Cu/TiO 2 )/SBA-15) c 0,1M NaOH 400 W (365 nm) 627,0 1 less than detectable level (0,5 ppm for liquid products). ( ) Letterature references: a T. Inoue: TiO 2 powder, 1g/100ml; 30 h; ambient T and P; lamp 500W high-p. Hg; GC-column, PEG 200 and molecular sieve. b I.-H. Tseng(2002): cat. 0.15-0.6 g in 300 ml; 6h; ca. 50 C; 101.3-135.6 kpa; lamp 8W low-p. Hg; GC-column, Porapak Q. c H.-C. Yang (): Cu/TiO2)/SBA-15 0.05 g in 550 ml; 8h; ca. 42 C; lamp 400W medium-p. met halide; GC-column, Porapak. 7
Test Results with Scavenger Products detected: hydrogen, methane, acetaldehyde, methanol, acetone, propene/propane, ethane, ethene, tert-butanol. REAGENT IPA undergo UV- photolysis [*] itself even in absence of CTZ [*] Herasymowyacnhd, O. S., Knight, A. R. Canadian Journal of Chemistry. 1972, 50, 2217. 8
Test Results Changing Scavenger Concentration Influence of 2 propanol p concentration Influence of 2 propanol concentration µmol/gct tz*h 120 100 80 60 40 20 0 Hydrogen Acetone IPA 1M 52.22 110.12 IPA 0.1M 22.26 70.09 IPA 0.01M 3.21 34.36 IPA 0.001M 0.26 4.78 µmol/gct tz*h 5 5 4 4 3 3 2 2 1 1 0 Propene Acetic Mth Methane Methanol Ethane Ethene t Butanol t Propane Aldehyde IPA 1M 0.99 1.80 1.23 0.79 0.00 0.00 0.36 IPA 0.1M 4.12 1.98 1.56 1.19 0.01 0.00 0.35 IPA 0.01M 3.92 2.11 0.92 0.86 0.21 0.00 0.63 IPA 0.001M 0.06 0.29 0.14 0.66 0.00 0.00 0.34 IPA 0.0001M 017 0.17 000 0.00 IPA 0.0001M0001M 002 0.02 002 0.02 000 0.00 010 0.10 000 0.00 000 0.00 036 0.36 Indeed IPA acts as hole scavenger Partially oxidized / reduced product follow complex reaction path Why some product increase with decreasing IPA? 9
Test Results Changing Power UV-Lamp High power lamp greatly enhance typical photolysis product 10
Test Results with Inorganic Scavenger With Inorganic scavenger only water splitting is detected 11
Test Results with Labelled CO 2 May IPA still have a role as H 2 carrier in CO 2 hydrogenation? CO CH 4 CO 2 13 C labelled CO 2 was used to rule out the origin of partially oxidised product 12
State of the art / present result 10000 1000 100 10 1999 2003 2003 2007 2002 Methane (500W) 1999 1997 2001 2005 mol g -1 ctz h - 1 2007 2008 1 0 Methane (17W) Methanol (17W) 1994 2002 Pt-loaded TiO2/Y-zeolite Indrakanti (A) TiO2 P25 (con Hsc.) TiO2 (CO2 supercrit.) Ti-FSM16 (fluorur) Ti- Sio2 thin film TiO2 (optical-fiber R) Cu/TiO2/SBA-15 Present result 13 Cu/TiO2 8W Hg lamp TiO2 Ti-MCM-4, Ti-MCM-48 TiO2 sputter BiVO4 cu-fe TiO2/SiO2 Co(Pc) - TiO2 Fe-Cu Cu-K/Deall.Y - Pt/K2Ti6O13 Ti BETA Pt/TiO2 C Fe/LaCoO3 nanotio2 TiO2/Pd/Al2O3 Ti- Sio2 thin film Pt-lo loaded ex-ti-oxide/y-zeolite
Conclusion In no case the presence of labelled 13 C could be detected in partially oxidized products overcoming the natural abundance. In our experimental condition, we have no evidence that CO 2 could show even partial photo induced reduction by means of Cu doped titania catalysts. Use of labelled 13 CO 2 is, probably, the lonely way to be confident in the identification of Carbon Dioxide photoactivation Other approaches, also by using accurate blank experimental design, can be blinded by pollution from the environment or from the catalytic system 14