II.2.3. X-ray diffraction (XRD)

XRD is one of the most powerful techniques for qualitative and quantitative analysis of crystalline compounds.

The technique provides information that cannot be obtained by any other way. The information obtained includes types and nature of crystalline phases present, structural make-up of phases, degrees of crystallites, amount of amorphous content, microstructure size and orientation of crystallites.

Figure 5: Simple theory of XRD analysis[13].

Figure 5 shows the principle of XRD.

In this work the crystalline phases of the catalysts as well as crystalline sizes were determined by powder X-ray diffraction.

A Siemens D-500 X-ray diffractometer with nickel-filtered CuKα₁ radiation was used to record the X-ray powder diffraction (XRD) patterns of the samples. The XRD profiles were collected between 2θ = 20 – 100˚., at a step scan of 0.05˚ counting 3˚at each step. The mean crystallite size of cobalt and copper particles was calculated with the Debye-Scherrer equation,

t=Kλ /  β cos( θ)

where K is the shape factor, λ is the x-ray wevelength, β is the line broadening at half the maximum intensity in radians and θ is the Bragg angle.

For catalysts prepared by microwave method the following experimental conditions were used:

PANalytical X’Pert PRO MPD Alpha1 powder diffractometer (radius = 240 millimetres)

Cu K₁ radiation ( = 1.5406 Å).

Work power: 45 kV – 40 mA.

Focalizing Ge (111) primary monochromator

Sample spinning at 2 revolutions per second.

Variable automatic divergence slit to get an illuminated length in the beam direction of 10 millimetres.

Mask defining a length of the beam over the sample in the axial direction of 12 millimetres

Diffracted beam 0.04 radians Soller slits

X’Celerator Detector: Active length = 2.122 º; PHD lower level: 45% (iron discrimination)

/2 scan from 4 to 100º 2 with step size of 0.017º and measuring time of 150 seconds per step.

II.2.4. Temperature programmed reduction (TPR)

Temperature-programmed reduction (TPR) profiles were recorded using a Micrometrics AutoChem II chemisorption analyzer.

TPR was used to determine the number and type of redox species present in the catalysts.

Before TPR analysis, 48mg of the sample was heated in helium at 365 K for 15 min and then cooled to room temperature. The calcined samples were heated ( 10 ^oC min^-1) under a 12 v% H₂-Ar mixture (feed flow rate: 50 mL min^-1) and hydrogen consumption was measured by a thermal conductivity detector (TCD).

II.2.5. Catalytic performance - Carbon dioxide hydrogenation reaction

Catalytic tests were performed in a Microactivity-Reference unit (PID ENG&TECH). 150 mg catalyst was mixed with inactive SiC (Prolabo, 0.5 mm) and placed in a tubular fixed-bed reactor (305 mm long, 9 mm i.d., 316-L stainless steel) up to the volume of approximately 0.5 mL. The temperature was measured by a thermocouple in a direct contact with a mixture of 10 vol% H2/Ar at 300 ˚C for 1.5 h under atmosphere pressure and then increased the pressure to 3 Mbar to re-reduced catalyst for 0.5 h. Afterwards, temperature was decreased to 240 ^oC in pure hydrogen and the catalyst was exposed to a reactant gas mixture CO­­₂/H₂ = 1/3 for ca. 1h and then was the reaction temperature increased to 250 ^oC. After further ca. 15 h reaction, the reaction temperatures was consecutively increased to 260 ˚C and 250 ^oC and maintained for ca. 5 h at each temperature. One more experiment was conducted over Cu/ZnO-2 under 4.5 Mbar with the same other parameters. The products were analyzed on-line with a GC-MS analysis system (Varian 450-GC equipped with a methanizer and TCD and FID detectors).

				300°C			300°C
				1.5 h		0.5 h	0.5 h		injection CO2+H2 (1:3)
			250°C					240°C		250°C
			20 min			increasing		20 min		1 h
		200°C				pressure
		20 min							30 min
	180°C
	20 min
25°C
10min
1 bar							30 bar
Catalyst reduction process H2 + N2 ( 1 : 1 )

Figure 6: Catalyst reduction conditions.

Before hydrogenation reaction all catalysts were reduced in a mixture of 1:1 (molar ratio) of nitrogen and hydrogen in two consecutive procedures. First, reduction was carried out at 1 bar pressure and temperature increased from room temperature to 300 °C, and then at 30 bar and temperature decreased from 300 °C to 250 °C and then was started injection process. Carbon dioxide and hydrogen with molar ratio 1:3 were injected and catalyst was ready to reaction time as shown in consecutive procedures (Figure 6).

				270°C						270°C
				5 h	0.5 h					5 h
			260°C						260°C
			5 h		increasing				5 h
250°C					pressure		250°C
15 h							15 h
30 bar						45 bar
Carbon dioxide hydrogenation reaction CO2 + H2 + N2 ( 1 : 3 : 1 )

Figure 7: Carbon dioxide hydrogenation conditions.

Figure 7 show the conditions of carbon dioxide hydrogenation carried out as follows:. First at 30 bar and temperatures 250 °C, 260 ^oC and 270 °C during 25 h and then at 45 bar pressure at similar temperatures. The procedure were analyzed with a gas chromatography.

On the output from reactor was gas chromatography device witch detect product from this reaction and gave information used for calculation.

Conversion of CO₂ was calculated from equation (1).

CO₂ conversion [%] = [Σ(n_i M_i) / M_CO2 ] 100 (1)

where n_i is the number of carbon atoms in product i, M_i – is the percentage of product i and M_CO2 is the percentage of CO₂ in the syngas feed.

The selectivity (S) to a product was based on the total number of carbon atoms in the products and defined as:

S_i = [ (n_i M_i)/ Σ(n_i M_i)] 100 (2)

II.2.7. The cost of catalysts production

Table 5: The cost of catalysts production.

Precursor	Price	Catalyst	Prize for 1 kg
Zn(NO3)2x6H2O	80 €/kg	CoCuZnLa-CM	920 €
La(NO3)3x6H2O	88 €/100g	CoCuRhZnLa-CM	4115 €
Ga(NO3)2xXH2O	1400 €/100g	CoCuZnGa-CM	3419 €
Cu(NO3)2x3H2O	250 €/kg	CoCuRhZnGa-CM	6617 €
Co(NO3)2x6H2O	450 €/kg
RhCl3x(H2O)n	800 €/2,5g
CO(NH2)2	78 €/kg

A list of the prices of the precursors needed for the synthesis of the catalyst is given in Table 5, based on current prices of the Aldrich company available on the producer website. Only the cost of materials was taken into account. In order to calculate the real cost the cost of labour, installation, energy, transportation etc. must be additionally included. The most cost-effective catalyst was CoCuZnLa-CM. The high price of gallium and ruthenium makes other catalysts not attractive for industrial use.

List of publications

[1] B.Gajdzik, A.Wyciślik, Wybrane aspekty ochrony środowiska i zarządzania środowiskowego, WPŚ Gliwice (2010).

[2] G.Dobrzański, B.M.Dobrzańska, D.Kiełczewki, Ochrona Środowiska Przyrodniczego, WEiŚ Białystok (1997).

[3] A. Budnikowski, Ochrona środowiska jako problem globalny, WE, Warszawa 1998.

[4] Świat wiedzy – dział „Planeta Ziemia”, PWN, Warszawa 2000, s.94.

[5] S.K.Wiąckowski, Przyrodnicze podstawy ochrony środowiska, Kielce (2000).

[6] Johannes S. Bruck, Clayton W. Ferry, J. Am. Chem. Soc., 1936, 58 (5), pp 854-854.

[7] J.Molenda, K.Steczko, Ochrona Środowiska w gazownictwie i wykorzystaniu gazu, WNT Warszawa (2000).

[8] B.van der Meer, Carbon Dioxide Storage in Natural Gas Reservoir,IFP, vol.60(2005), No.3, pp.527-536.

[9] Z.Jiang, T.Xiao, V.L.Kuznetsov and P.P.Edwards, Turning carbon dioxide into fuel, Phil. Trans. R. Soc. A (2010) 368, 3343-3364.

[10] International Enegy Agency, CO₂ emission from fuel combustion, Highlights (2011).

[11] B. van der Meer, Oil & Gas Science and Technology – Rev. IFP, vol.60(2005), No.3.pp.527-536.

[12] J.J.Spivey, A.Egbebi, Heterogenous catalytic synthesis of ethanol from biomass-derived syngas, Chem. Soc. Rev., 36 (2007) 1514.

[13] http://www.siint.com/en/products/icp/tec_descriptions/descriptions1_e.html.

[14] V. Choque, N. Homs, R. Cicha-Szot, P. Ramirez de la

Piscina ,“Study of ruthenium supported on Ta2O5-ZrO2 and Nb2O5-ZrO2 as catalysts for

partial oxidation of methane”, Catalysis Today, vol. 142 (2009), 308-313.

[15] S. Brunauer, P.H. Emmett, E.Teller, “Adsorption of gasses in multimolecular layers”, Journal of the American Chemical Society, 60 (1938), 309-319.

[16] S.Sugawa, K.Sayama, K.Okabe, H.Arakawa, Methanol synthesis from CO2 and H2 over silver catalyst, Pergamon, Energy Convers. Mgmi, Vol. 56, No. 6-9, pp. 665-668, 1995.

[17] J. Toyir, P.Ramirez de la Piscina, J.Luis Gierro, N.Homs, Applied Catalysis B: Environmental, vol. 29, Issue 3, 1 February 2001, Pages 207-215.

[18] J.Llorca, P.Ramirez de la Piscina, J.A.Dalmon, J. Sals, N.Homs, Applied Catalysis B: Environmental, vol. 43, Issue 4, 25 July 2003, Pages 355-363.

[19] P.Nel, D.Lau, N.Wright, Nuclear Instrumental and Method in Physic Research Section B: Beam Interaction with Materials and Atoms, vol. 251, Issue 2, October 200, Pages 89-495.

Acknowledgements

As the author of this project I would like to thank for the support and guidance of my project supervisors, Prof. dr hab. Teresa Grzybek, dr Monika Motak at the AGH University of Science and Technology, and Prof Narcis Homs of the Universitat de Barcelona throughout this project.

I also would like to thank for the patience, generosity and technical support of Dr Weijie Cai and mgr.inż. Łukasz Bednarczuk without whom I would not have been able to carry out this.

Finally, I would like to acknowledge the help, guidance and great atmosphere, both inside and outside of university, afforded to me throughout my study in Barcelona by all the remaining members of the Material and Catalyst group at the Universitat de Barcelona.