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Project Title:

Hydrogen generation through steam reforming of methanol on molecular sieve catalysts

Ref.No.: 138

Project Type and Category:

Basic research

Project Duration:

See project ref. No.: 73

Project Participants:

J. Weitkamp
Institut für Technische Chemie I, Universität Stuttgart

Sponsor:

See project ref. No.: 73

Project Budget and
Funding:

See project ref. No.: 73

Project Description and Objectives:

Hydrogen as feed for fuel cells can be generated by the catalytic conversion of methanol with water vapor (steam) at reaction temperatures of 250 oC to 300 oC. Hydrogen, carbon dioxide, carbon monoxide and, in particular at elevated temperatures, methane are formed during methanol reforming [1-3]. Catalysts which are active for methanol reforming are very similar to those known to be active in methanol synthesis. Typically, they consist of a mixture of copper oxide/zinc oxide which is deposited on an amorphous carrier (e. g., Al2O3). However, also Cu-Cr, Cu-Al, Cu-Sn, Cu-Co and Cu-Ni have been reported to be active catalysts for steam reforming of methanol [4]. It is essential for a failure-free operation of fuel cells that the supplied hydrogen is essentially free of carbon monoxide, which otherwise would result in a degradation of the anode of the fuel cell. Typical minimum CO-concentrations which arereached today amount to ca. 0.5 to 1 vol.-% of CO in the reformer product gas. This is still much too high, and additional measures have therefore to be taken to remove CO from the gas obtained by steam reforming of methanol before feeding it to the fuel cell.
It is the aim of the present project to explore the potential of modified zeolites and zeolite-like molecular sieves as catalysts for the synthesis of hydrogen from methanol via steam reforming. Particular emphasis is placed on minimizing the CO-concentration in the product gas. Zeolites and related molecular sieve materials have been selected as carriers because they possess a number of properties which render them particularly attractive as catalysts and catalyst supports: (i) they can be synthesized in a large variety of different structures and chemical compositions, (ii) they can be modified by several techniques in order to tailor their properties with respect to the envisaged application and, (iii) via ion exchange or impregnation, nearly every desired catalytically active component can be introduced in the intracrystalline pore system of the zeolite. In the present study, selected zeolites and molecular sieves are modified
by the introduction of the active components into the intracrystalline pores and cavities. Both the structure and chemical composition of the porous carrier and the nature and amount of active components are systematically varied. The prepared catalysts are then tested in a fixed bed flow-type apparatus under atmospheric pressure in the conversion of methanol with water vapor. To arrive at a deeper understanding of the catalytic behavior of the prepared materials, they are characterized by selected physico-chemical techniques. Based on the information derived from this in-depth characterization, an attempt will be made to optimize molecular sieve catalysts with respect to their activity and selectivity in the generation of hydrogen from methanol.

Technical Goals:

In the frame of this research project, zeolites selected from the groups of small-, medium- and large-pore zeolites with unidimensional or multidimensional pore system are explored as catalyst supports. The active components are introduced into the pores of the carriers via different methods (i. e., addition of a transition metal compound to the synthesis gel of the zeolite, ion exchange in aqueous suspension or via a solid-state reaction, impregnation with a suitable salt solution) with the active component. During the first stage of the project, CuO, ZnO and mixtures thereof have been introduced into the intracrystalline cavities of the molecular sieve hosts. Furthermore, the loadings of the carriers with active components have been systematically varied. It is planned to include additional selected metals or metal oxides in the study (i. e., Co, Cr, Sn). To arrive at a deeper understanding of the factors which govern activity and selectivity, the prepared materials will not only be characterized by catalytic tests
But also by physico-chemical methods, i. e., X-ray powder diffraction for a characterization of crystallinity and phase purity of the zeolitic carriers, chemical analysis, and, in particular for an in-depth characterization of the active components, temperature programmed reduction and oxidation, solid-state infrared spectroscopy and solid-state nuclear magnetic resonance spectroscopy. The catalytic experiments for an evaluation of the prepared catalysts are performed in a flow-type apparatus with a fixed bed reactor under atmospheric pressure.
Activity, selectivity and time on stream stability are determined in dependence of time on stream by on-line sampling and product analysis by capillary gaschromatography (g. c.). In addition to the g. c. analysis, the concentrations of carbon monoxide, carbon dioxide and methane in the reactor effluent are continuously monitored using non-dispersive infrared gas analyzers.

Project Status

#

Preliminary or Final Results:

As reference material, a commercially available catalyst for methanol synthesis was initially tested in the steam reforming of methanol. The catalyst consisted of a mixture of CuO/ZnO on an Al2O3 carrier. Under typical reaction conditions (T = 150 oC, W/FMeOH = 1.300 gh/mol; W: mass of dry catalyst (1.7 g); FMeOH: molar flux of methanol at the reactor inlet; PMeOH =
1.9 kPa; PH2O = 2.5 kPa; carrier gas: Argon; VAr = 20 cm3/min), methanol conversion amounts to almost 100 % at the beginning of the reaction and then slightly decreases to ca. 80 %, where a stable conversion is attained. Under these conditions, the concentration of carbon monoxide typically found in the gaseous products amounts to ca. 6000 to 8000 ppm which is far beyond the limit that can be tolerated by a fuel cell.

Related Reference Papers and Other Publications:

[1]F. Asinger, ""Methanol _ Chemie und Energierohstoff"", Springer-Verlag (1986), p. 238-245.
[2]J. C. Amphlett, M. J. Evans, R. F. Mann und R. D. Weir, Can. J. Chem. Eng. 63, 605-611 (1985).
[3]C. J. Jiang, D. L. Trimm, M. S. Mainwright und N. W. Cant, Appl. Catal. A93, 245-255 (1993).
[4] H. Kobayashi, N. Takezawa and C. Minochi, Chem. Lett., 1347-1351 (1976).
[5]S. H. Oh and R. M. Sinkevitch, J. Catal. 142, 254-262 (1993).
[6]T. Inui, S. Iwamoto, K. Matsuba, Y. Tanaka and T. Yoshida, Catal. Today 26, 23-32 (1995).

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Project Title: Hydrogen generation through steam reforming of methanol on molecular sieve catalysts		Ref.No.: 138
Project Type and Category:	Basic research
Project Duration:	See project ref. No.: 73
Project Participants:	J. Weitkamp Institut für Technische Chemie I, Universität Stuttgart
Sponsor:	See project ref. No.: 73
Project Budget and Funding:	See project ref. No.: 73
Project Description and Objectives:	Hydrogen as feed for fuel cells can be generated by the catalytic conversion of methanol with water vapor (steam) at reaction temperatures of 250 oC to 300 oC. Hydrogen, carbon dioxide, carbon monoxide and, in particular at elevated temperatures, methane are formed during methanol reforming [1-3]. Catalysts which are active for methanol reforming are very similar to those known to be active in methanol synthesis. Typically, they consist of a mixture of copper oxide/zinc oxide which is deposited on an amorphous carrier (e. g., Al2O3). However, also Cu-Cr, Cu-Al, Cu-Sn, Cu-Co and Cu-Ni have been reported to be active catalysts for steam reforming of methanol [4]. It is essential for a failure-free operation of fuel cells that the supplied hydrogen is essentially free of carbon monoxide, which otherwise would result in a degradation of the anode of the fuel cell. Typical minimum CO-concentrations which arereached today amount to ca. 0.5 to 1 vol.-% of CO in the reformer product gas. This is still much too high, and additional measures have therefore to be taken to remove CO from the gas obtained by steam reforming of methanol before feeding it to the fuel cell. It is the aim of the present project to explore the potential of modified zeolites and zeolite-like molecular sieves as catalysts for the synthesis of hydrogen from methanol via steam reforming. Particular emphasis is placed on minimizing the CO-concentration in the product gas. Zeolites and related molecular sieve materials have been selected as carriers because they possess a number of properties which render them particularly attractive as catalysts and catalyst supports: (i) they can be synthesized in a large variety of different structures and chemical compositions, (ii) they can be modified by several techniques in order to tailor their properties with respect to the envisaged application and, (iii) via ion exchange or impregnation, nearly every desired catalytically active component can be introduced in the intracrystalline pore system of the zeolite. In the present study, selected zeolites and molecular sieves are modified by the introduction of the active components into the intracrystalline pores and cavities. Both the structure and chemical composition of the porous carrier and the nature and amount of active components are systematically varied. The prepared catalysts are then tested in a fixed bed flow-type apparatus under atmospheric pressure in the conversion of methanol with water vapor. To arrive at a deeper understanding of the catalytic behavior of the prepared materials, they are characterized by selected physico-chemical techniques. Based on the information derived from this in-depth characterization, an attempt will be made to optimize molecular sieve catalysts with respect to their activity and selectivity in the generation of hydrogen from methanol.
Technical Goals:	In the frame of this research project, zeolites selected from the groups of small-, medium- and large-pore zeolites with unidimensional or multidimensional pore system are explored as catalyst supports. The active components are introduced into the pores of the carriers via different methods (i. e., addition of a transition metal compound to the synthesis gel of the zeolite, ion exchange in aqueous suspension or via a solid-state reaction, impregnation with a suitable salt solution) with the active component. During the first stage of the project, CuO, ZnO and mixtures thereof have been introduced into the intracrystalline cavities of the molecular sieve hosts. Furthermore, the loadings of the carriers with active components have been systematically varied. It is planned to include additional selected metals or metal oxides in the study (i. e., Co, Cr, Sn). To arrive at a deeper understanding of the factors which govern activity and selectivity, the prepared materials will not only be characterized by catalytic tests But also by physico-chemical methods, i. e., X-ray powder diffraction for a characterization of crystallinity and phase purity of the zeolitic carriers, chemical analysis, and, in particular for an in-depth characterization of the active components, temperature programmed reduction and oxidation, solid-state infrared spectroscopy and solid-state nuclear magnetic resonance spectroscopy. The catalytic experiments for an evaluation of the prepared catalysts are performed in a flow-type apparatus with a fixed bed reactor under atmospheric pressure. Activity, selectivity and time on stream stability are determined in dependence of time on stream by on-line sampling and product analysis by capillary gaschromatography (g. c.). In addition to the g. c. analysis, the concentrations of carbon monoxide, carbon dioxide and methane in the reactor effluent are continuously monitored using non-dispersive infrared gas analyzers.
Project Status	#
Preliminary or Final Results:	As reference material, a commercially available catalyst for methanol synthesis was initially tested in the steam reforming of methanol. The catalyst consisted of a mixture of CuO/ZnO on an Al2O3 carrier. Under typical reaction conditions (T = 150 oC, W/FMeOH = 1.300 gh/mol; W: mass of dry catalyst (1.7 g); FMeOH: molar flux of methanol at the reactor inlet; PMeOH = 1.9 kPa; PH2O = 2.5 kPa; carrier gas: Argon; VAr = 20 cm3/min), methanol conversion amounts to almost 100 % at the beginning of the reaction and then slightly decreases to ca. 80 %, where a stable conversion is attained. Under these conditions, the concentration of carbon monoxide typically found in the gaseous products amounts to ca. 6000 to 8000 ppm which is far beyond the limit that can be tolerated by a fuel cell.
Related Reference Papers and Other Publications:	[1]F. Asinger, ""Methanol _ Chemie und Energierohstoff"", Springer-Verlag (1986), p. 238-245. [2]J. C. Amphlett, M. J. Evans, R. F. Mann und R. D. Weir, Can. J. Chem. Eng. 63, 605-611 (1985). [3]C. J. Jiang, D. L. Trimm, M. S. Mainwright und N. W. Cant, Appl. Catal. A93, 245-255 (1993). [4] H. Kobayashi, N. Takezawa and C. Minochi, Chem. Lett., 1347-1351 (1976). [5]S. H. Oh and R. M. Sinkevitch, J. Catal. 142, 254-262 (1993). [6]T. Inui, S. Iwamoto, K. Matsuba, Y. Tanaka and T. Yoshida, Catal. Today 26, 23-32 (1995).