Orsina VERDES a, Livia AVRAM a, A. POPA a A. ERDÕHELYI b and V. Z. SASCA a a Institute of Chemistry Timisoara-Romanian Academy b Institute of Physical Chemistry and Material Science-University of Szeged Study of the Ethanol Conversion Kinetics on Cs x H 3-x PW 12 O 40 Catalysts NEW TRENDS AND STRATEGIES IN THE CHEMISTRY NOV 2011 TIMISOARA

INTRODUCTION In the last time much attention has been paid to biomass as alternative resource to petroleum, since biomass is a renewable resource and its combustion does not lead to increased of CO 2 in the atmosphere. The search for renewable resources has stimulated the production of hydrocarbons and others organic intermediary compounds from ethanol over different acidic solid catalysts as the ethanol is the one of the main biomass- derived products. The H 3-x PW 12 O 40 and its salts, especially with Cs, are effective catalysts in ethanol conversion to ethylene and the reaction kinetics is interesting to the catalysis theory and industrial application also. NEW TRENDS AND STRATEGIES IN THE CHEMISTRY NOV 2011 TIMISOARA

EXPERIMENTAL The FTIR absorption spectra (diffuse reflectance mode) were recorded “in situ” with a Bio-Rad FTIR spectrometer equipped with diffuse reflectance attachment (Thermo-electron corporation) and BaF windows with a wave number accuracy of ± 4 cm -1. Typically 32 scans were registered. The whole optical path was purged by CO 2 and H 2 O free air generated by a Balston purge gas generator. The catalysts were pre-treated at 573 K for 30 min, and then the ethanol was introduced by bubbling of Ar gas through the ethanol at 273 K for 120 min. After, the cell was flushed with He stream for 30 min, respectively with O 2 for 20 min and finally the catalyst was heated linearly with a heating of 10 K/min from 573K to 723 K. The IR spectra were recorded for each of the experiment steps on H 3 PW and Cs x H 3-x PW, x= 2.5 and 3. FTIR measurements of ethanol adsorption-desorption NEW TRENDS AND STRATEGIES IN THE CHEMISTRY NOV 2011 TIMISOARA

EXPERIMENTAL The conversion of ethanol was studied on the H 3 PW and Cs x H 3-x PW, x= 2.5 catalysts by continuous flow of reactant technique-CFRT. A micro reactor with fixed catalyst bed of about 100 mg was connected to the heated six-port valve with a loop for sampling as it can be seen in Fig. 1. The temperatures inside the catalyst bed were between from 473 K to 623 K and the reactant mixtures (11vol % and 22 vol% of ethanol in nitrogen) were obtained in the evaporator (2) by introducing the liquid ethanol in the nitrogen flow of the 30 ccm/min with a Hamilton syringe and a device which pushes its piston. The reaction products analysis was carried out with the GC-FID equipped with a stainless steel column of 3 m length 2 mm inner diameter, packed with Porapak QS mesh. The N 2 carrier gas with the flow of the 30 cm 3 /min was used. The splitting was of 1:6 volume ratios. For a better separation of reaction products, a programme of temperature for the column was set up: 5 min at 323 K, then heating from 323 K to 473 K with the heating rate of 10 K/min and the last, an isothermal heating at 473 K for 5 min. The total time for a complete analysis was 25 min. Catalytic activity tests Figure 1. The installation scheme for the catalytic activity measurement by CFRT: 1. Four port valve; 3. Evaporator of liquid sample; 3. Micro reactor heated by electric furnace; 4. Four port valve, 5-6 Six-port valve with gas sample loop; 7. Gas-chromatograph; 8. Integrator. NEW TRENDS AND STRATEGIES IN THE CHEMISTRY NOV 2011 TIMISOARA

Catalysts primary structure. RESULTS AND DISCUSSION The cm-1 band is assigned to crystallization water- hydrogen bonded and to hydrogen- bond vibrations (hydrogen-bonds formed between neighbouring KUs). The 1715 cm-1 band is ascribed to hydroxonium ions, H 3 O + or H 5 O 2+, δ vibrations and the 1615 cm-1 band is assigned to δ vibrations of nonprotonated water molecules. The specific absorbtion bands of the Keggin Unit - [PW 12 O 40 ] 4- are: ν as P-O i -W; ; ν as W- O t, ; ν as W-O c -W, ; ν as W-O e -W, cm -1. Figure 2. The FTIR spectra: (1) H 3 PW6-7H 2 O and (2) Cs 2.5 H 0.5 PW6H 2 O. NEW TRENDS AND STRATEGIES IN THE CHEMISTRY NOV 2011 TIMISOARA

Catalysts primary structure. RESULTS AND DISCUSSION Figure 3. The FTIR spectra: (1)H 3 PWx 1 H 2 O (2) Cs 2.5 H 0.5 PWx 4 H 2 O after heating at: (a) 573 K, 1 hour and (b) 873 K, 1 hour. NEW TRENDS AND STRATEGIES IN THE CHEMISTRY NOV 2011 TIMISOARA a) b)

Catalysts. RESULTS AND DISCUSSION NEW TRENDS AND STRATEGIES IN THE CHEMISTRY NOV 2011 TIMISOARA 1) EtOH/573 K/0,5 min, 2) EtOH/573 KC/1 min, 3) EtOH/573 K/15 min, 4) EtOH/573 K /60 min, 5) EtOH/573 K /120 min, 6) He/573 K /30 min. 7) O 2 /573 K/0.5 min, 8) O 2 /573 K /20 min, 9) O 2 /623 K, 10) O 2 /673 K, 11) O 2 /723 K. 1) EtOH /573 K /1 min, 2) EtOH /573 K /15 min, 3) EtOH /573 K /60 min, 4) Et /573 K /120 min. 5) He/573 K/30 min, 6) O 2 /573 K /1 min, 7) O 2 / 573 K /20 min, 8) O 2 /673 K/ K, 9) O 2 / 623 K/ K, 10) O 2 /723 K/ K. Figure 4 a,b. The FTIR spectra registered in diffuse reflectance mode for the ethanol absorption/desorption on the H 3 PW 12 O 40 (a) and Cs 2.5 H 0.5 PW 12 O 40 (b). a) b)

Ethanol Conversion Kinetics The adsorption-desorption studies of ethanol by the FTIR in diffuse reflectance mode were carried out in purpose to observe the ethanol chemisorbed species and thus to clarify the reaction mechanism. In the FTIR spectra registered during the adsorption of ethanol at 573 K and desorption under He, respectively under O2, the main absorption bands could be assigned to: - CH 3 stretch and C-H deformation vibrations which belong to chemisorbed ethanol (1490, 1385, 1365 and 1330 cm -1 ); - O=C=O asymmetric stretch vibration of the adsorbed CO 2 at 2350 cm -1, -C=O from carbonyl between 1650 and 1780 cm -1,- OCO stretch vibration from carboxylates and carbonates at 1650 cm -1 (asymmetric), 1480 cm -1 (symmetric) and 1220 cm -1 (bending); -ethoxy group deformation vibrations in the range cm -1 ; -intermolecular H-bonded alcohol species at about 3600 cm -1 and -OH stretch vibration from molecular ethanol bonded on surface of the hydrogen– bridge bonds which gives a large broad band centered at about 3400 cm -1. The dehydration of ethanol in the presence of strong Brönsted acid sites could involve a complex series of reactions, including oligomerization, aromatization, cracking and hydrogenation. The reaction products detected on Cs x H 3-x PW catalysts were: methane, C2 fraction (ethylene, ethane), C3 (propene, propane), C4 (butane, butene), C5 (pentane, pentene), C6 (hexane, hexene) and diethyl ether. The aromatic compounds, as benzene, toluene and xylene, could be also present but in undetectable quantities. In plus, very small quantities of H 2 and CO were detected with GC-TCD. RESULTS AND DISCUSSION NEW TRENDS AND STRATEGIES IN THE CHEMISTRY NOV 2011 TIMISOARA

Reaction mechanism for ethanol conversion on Bronsted acid sites: C 2 H 5 OH + H +... O UK 2- C 2 H 5 OH O UK (1) O UK C 2 H 5 OH 2 + [-OC 2 H 5 ] UK... H 2 O... (2) [-OC 2 H 5 ] UK C 2 H 4 + H +... O UK 2- (3) and/or [-OC 2 H 5 ] UK + C 2 H 5 OH (C 2 H 5 ) 2 O + H +... O UK 2- (4) [-OC 2 H 5 ] UK could react also with C 2 H 4 according to the next equation: C 2 H 4 + [-OC 2 H 5 ] UK CH 3 - (CH 2 ) 3 – O UK (5) CH 3 – (CH 2 ) 3 – O UK 2- (CH 3 ) 2 – CH=CH 2 + O UK (6) RESULTS AND DISCUSSION NEW TRENDS AND STRATEGIES IN THE CHEMISTRY NOV 2011 TIMISOARA Ethanol Conversion Kinetics

Figure 5 a, b. The ethanol conversion on the H 3 PW 12 O 40 for 11 vol% (a) and 22 vol% (b) ethanol in N 2 at different temperatures. RESULTS AND DISCUSSION a) b) NEW TRENDS AND STRATEGIES IN THE CHEMISTRY NOV 2011 TIMISOARA Ethanol Conversion Kinetics

RESULTS AND DISCUSSION Figure 6 a, b. The ethylene and diethyl ether selectivity on the H 3 PW 12 O 40 for 11 vol% (a) and 22 vol% (b) ethanol in N 2 at different temperatures. b)a) NEW TRENDS AND STRATEGIES IN THE CHEMISTRY NOV 2011 TIMISOARA Ethanol Conversion Kinetics

RESULTS AND DISCUSSION Figure 7 a, b. The C4 hydrocarbons selectivity on the H 3 PW 12 O 40 for 11 vol% (a) and 22 vol% (b) ethanol in N 2 at different temperatures. b)a) NEW TRENDS AND STRATEGIES IN THE CHEMISTRY NOV 2011 TIMISOARA Ethanol Conversion Kinetics

RESULTS AND DISCUSSION Figure 8 a, b. The ethanol conversion on the Cs 2.5 H 0.5 PW 12 O 40 for 11 vol% (a) and 22 vol% (b) ethanol in N 2 at different temperatures. b)a) NEW TRENDS AND STRATEGIES IN THE CHEMISTRY NOV 2011 TIMISOARA Ethanol Conversion Kinetics

RESULTS AND DISCUSSION Figure 9 a, b. The ethylene and diethyl ether selectivity on the Cs 2.5 H 0.5 PW 12 O 40 for 11 vol% (a) and 22 vol% (b) ethanol in N 2 at different temperatures. b)a) NEW TRENDS AND STRATEGIES IN THE CHEMISTRY NOV 2011 TIMISOARA Ethanol Conversion Kinetics

RESULTS AND DISCUSSION Figure 10 a, b. The C4 hydrocarbons selectivity on the Cs 2.5 H 0.5 PW 12 O 40 for 11 vol% (a) and 22 vol% (b) ethanol in N 2 at different temperatures. b)a) NEW TRENDS AND STRATEGIES IN THE CHEMISTRY NOV 2011 TIMISOARA Ethanol Conversion Kinetics

RESULTS AND DISCUSSION NEW TRENDS AND STRATEGIES IN THE CHEMISTRY NOV 2011 TIMISOARA Ethanol Conversion Kinetics The measurements of catalytic activity at the temperatures of the 473 K, 498 K and 523 K for 11 mol% and 22 mol% ethanol in reaction mixture were used for kinetic parameters calculation based on the reaction rate equations: r=k[p i ] n (7), k=A*e -Ea/RT (8) where k=reaction constant rate and p i = ethanol partial pressure (kPa). The kinetic parameters of the ethanol transformation to reaction products on the Cs 2.5 H 0.5 PW 12 O 40 were calculated from the logarithmic form of the reaction rate equation (7) and reaction constant rate (8), for three temperatures at each of the two ethanol partial pressures: lnr= lnA-E a /RT+nlnp i or lnr=-(E a /R)*1/T+lnA+nlnp i (9) That is equivalent with: y=ax+b, y=lnr, x=1/T and b=lnA+nlnp i

RESULTS AND DISCUSSION NEW TRENDS AND STRATEGIES IN THE CHEMISTRY NOV 2011 TIMISOARA Figure 11 a, b. The plotting of the logarithmic form of the ethanol conversion rate vs the inverse absolute temperature on the H 3 PW 12 O 40 for 11 vol% (a) and 22 vol% (b) ethanol in N 2. Ethanol Conversion Kinetics a) b)

Figure 12 a, b. The plotting of the logarithmic form of the ethylene formation rate vs the inverse absolute temperature on the H 3 PW 12 O 40 for 11 vol% (a) and 22 vol% (b) ethanol in N 2. RESULTS AND DISCUSSION NEW TRENDS AND STRATEGIES IN THE CHEMISTRY NOV 2011 TIMISOARA Ethanol Conversion Kinetics b) a)

Figure 13. The plotting of the logarithmic form of the ethanol conversion rate vs the inverse temperature on the Cs 2.5 H 0.5 PW 12 O 40 for 11 vol% (a) and 22 vol% (b) ethanol in N 2. RESULTS AND DISCUSSION NEW TRENDS AND STRATEGIES IN THE CHEMISTRY NOV 2011 TIMISOARA Figure 14. The plotting of the logarithmic form of the ethylene formation rate vs the inverse absolute temperature on the Cs 2.5 H 0.5 PW 12 O 40 for 11 vol% (a) and 22 vol% (b) ethanol in N 2. Ethanol Conversion Kinetics

NEW TRENDS AND STRATEGIES IN THE CHEMISTRY NOV 2011 TIMISOARA Catalysts: Cs 2.5 H 0.5 PW 12 O 40 Process: Ethanol conversion E a -apparent activation energy=7.55±0.15 kJ/mol A-preexponential factor= 22584±113 and n-reaction order=1. Process: Ethylene formation: E a -apparent activation energy=37.7±2.6 kJ/mol A-preexponential factor= n-reaction order=0.5. RESULTS AND DISCUSSION

CONCLUSIONS NEW TRENDS AND STRATEGIES IN THE CHEMISTRY NOV 2011 TIMISOARA The best catalyst is the Cs 2.5 H 0.5 PW 12 O 40 with high catalytic activity and selectivity to ethylene. The values of thekinetical parameter: E a -apparent activation energy, A-preexponential factor and n-reaction order were calculated for the ethanol conversion and ethylene formation. The elucidation of the reaction mechanism needs supplementary FTIR “in situ” investigation.

Acknowledgment: Financial support of this work by Cross Border Cooperation Programme , HURO 0901, is gratefully acknowledged. NEW TRENDS AND STRATEGIES IN THE CHEMISTRY NOV 2011 TIMISOARA Two countries, one goal, joint success! The financial support of the Romanian Academy for the research programme from Institute of ChemistryTimisoara which was the basis of this cooperation project is also gratefully acknowledged.

Thank you for attention! NEW TRENDS AND STRATEGIES IN THE CHEMISTRY NOV 2011 TIMISOARA