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Catalysts for H2 Production

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Catalysts for H2 Production Alma Mater Studiorum – Università di Bologna FACOLTÀ DI CHIMICA INDUSTRIALE DIPARTIMENTO DI CHIMICA INDUSTRIALE E DEI MATERIALI DOTTORATO DI RICERCA IN CHIMICA INDUSTRIALE Catalysts for H2 production Tesi di Dottorato di Ricerca di Coordinatore: Dott. Rosetti Valentina Chiar.mo Prof. Luigi Angiolini Relatore: Dr. Francesco Basile Correlatori: Prof. G. Fornasari Prof. A. Vaccari XIX CICLO Settore CHIM/04 Catalysts for H2 production KEY WORDS CATALYTIC PARTIAL OXIDATION OF METHANE STEAM REFORMING OF METHANE NI AND/OR RH ACTIVE PHASE HYDROTALCITE-TYPE CATALYST PRECURSORS PEROVSKITE –TYPE CATALYSTS STRUCTURED CATALYSTS (SIC, FECRALY ALLOY) Catalysts for H2 production The research of new catalysts for the hydrogen production described in this thesis was inserted within a collaboration of Department of Industrial Chemistry and Materials of University of Bologna and Air Liquide (Centre de Recherche Claude-Delorme, Paris). The aim of the work was focused on the study of new materials, active and stable in the hydrogen production from methane, using either a new process, the catalytic partial oxidation (CPO), or a enhanced well-established process, the steam methane reforming (SMR). Two types of catalytic materials were examined: 1) Bulk catalysts, i.e. non-supported materials, in which the active metals (Ni and/or Rh) are stabilized inside oxidic matrix, obtained from perovskite type compounds (PVK) and from hydrotalcite type precursors (HT); 2) Structured catalysts, i.e. catalysts supported on materials having high thermal conductivity (SiC and metallic foams). As regards the catalytic partial oxidation, the effect of the metal (Ni and/or Rh), the role of the metal/matrix ratio and the matrix formulation of innovative catalysts obtained from hydrotalcite type precursors and from perovskites were examined. In addition, about steam reforming process, the study was carried out first on commercial type catalysts, examining the deactivation in industrial conditions, the role of the operating conditions and the activity of different type of catalysts. Then, innovative materials bulk (PVK and HT) and structured catalysts (SiC and metallic foam) were studied and a new preparation method was developed. Catalysts for H2 production I INDEX INTRODUCTION 1 1. H2 relevance and applications 3 1.1. Ammonia synthesis 5 1.1.1. Reaction mechanism 6 1.1.2. Ammonia synthesis catalysts 7 1.1.3. Ammonia plants 11 1.2. Direct Reduction of iron ore (DRI) 15 1.3. Methanol synthesis 17 1.3.1. Methanol synthesis catalysts 18 1.3.2. Reaction mechanism 24 1.3.3. Methanol plants 26 1.4. Dimethyl ether synthesis 28 1.5. Fischer-Tropsch synthesis 31 1.5.1. FT synthesis catalysts 35 1.5.2. Thermodynamics and reaction mechanism 37 1.5.3. FT synthesis plants 42 1.6. Fuel cells 47 2. Processes for H2 and/or syngas production 53 2.1. Steam reforming process 54 2.1.1. Chemistry of steam reforming: Thermodynamics 55 2.1.2. Kinetics and reaction mechanism 62 2.1.3. Steam reforming catalysts 68 2.1.4. Carbon formation on reforming catalyst 86 2.1.5. Sintering of reforming catalysts 96 2.1.6. Catalyst shape and dimensions 102 2.1.7. Practical aspects of steam reformers 104 2.1.8. Water gas shift reaction (WGS) 110 2.2. Partial oxidation of fossil fuels (POX) 115 2.3. Autothermal reforming (ATR) 117 2.4. Catalytic partial oxidation of methane (CPO) 119 II Catalysts for H2 production EXPERIMENTAL SESSION 126 1. Catalysts preparation 126 1.1. Perovskite type catalysts (PVK) 126 1.2. Catalysts obtained from hydrotalcite type precursors 127 2. Characterization of the catalysts 128 2.1. X-Ray diffraction analysis (XRD) 128 2.2. Surface area and porosimetry analyses 129 2.3. Temperature programmed reduction (TPR) and oxidation (TPO) 129 2.4. H2 Chemisorption analysis 129 2.5. Shaping in form of the catalysts 131 2.6. CPO laboratory plant 131 2.7. SMR laboratory plant 134 RESULTS AND DISCUSSION 139 1. Aim of the work 139 2. Catalytic partial oxidation of methane 140 2.1. Perovskite (PVK) type catalysts 140 2.1.1. Effect of Rh amount (La1Fe(0.7-z)Ni0.3Rhz) 142 2.1.2. Effect of Ce amount (La(1-x)CexFe0.69Ni0.3Rh0.01) 145 2.1.3. Effect of Ni amount (La0.8Ce0.2Fe(0.98-y)NiyRh0.02) 149 2.1.4. Effect of calcination temperature: 900 or 1100°C (La0.8Ce0.2Fe0.7Ni0.25Rh0.05) 155 2.2. Catalysts obtained from hydrotalcite (HT) type precursor 159 2.2.1. Role of the M2+/M3+ ratio and role of the active metal 163 2.2.2. Role of the hydrotalcite type matrix as support 175 3. Steam reforming of methane 185 3.1. Characterization of spent industrial catalysts 185 3.1.1. Characterization of Portugal used samples 186 3.1.2. Characterization of USA used samples 194 3.1.3. Activity of industrial spent samples 202 3.2. Comparison of different commercial catalyst 216 3.2.1. Characterization of commercial catalysts 216 Catalysts for H2 production III 3.2.2. Effect of the operative parameter on the steam reforming reaction carried out in the laboratory plant 221 3.2.3. Activity of commercial catalysts 229 3.2.4. Characterization of used commercial catalysts 234 3.3. Catalyst obtained from hydrotalcite (HT) type precursor 238 3.4. Catalyst obtained from perovskite (PVK) 255 3.5. Comparison among ex-HT sil, PKV and commercial catalysts 261 3.6. Structured catalysts: support with high thermal conductivity 263 3.6.1. Ni/SiC catalysts 263 3.6.2. Electrochemical deposition of hydrotalcite type precursors on metallic foams 269 CONCLUSIONS 276 REFERENCES 281 Catalysts for H2 production 1 INTRODUCTION Hydrogen is a “building block” product of remarkable industrial interest and it is indicated as energy carrier of increasing relevance. Hydrogen is found naturally in hydrogen-rich compounds; it cannot be extracted like natural gas or oil, but needs to be released by applying energy. On the one hand, this represents a drawback because the process requires the input of primary energy carriers like coal, natural gas or biomass, of electricity or high temperatures. The advantage is that a wide range of different feedstocks and energy sources can be used for hydrogen production. It can be manufactured from a wide range of energy sources and in particular from fossil fuels, biofuels by thermochemical way and from water by electrolytic way. Currently, the main sources for the next two or three decades will remain fossil fuels and in particular the natural gas1. The synthesis gas is a mixture of hydrogen and carbon monoxide; it may contain carbon dioxide together with some nitrogen and other inert gases, depending from the used source and the production process. Synthesis gas may be manufactured by coke and biomass gasification, by steam reforming or partial oxidation of hydrocarbons, usually natural gas. Today, “hydrogen economy” is high on the political agenda and on the priorities of agencies funding research. Hydrogen is claimed to replace hydrocarbons and to provide a clean fuel with no carbon emissions for use in stationary and mobile applications as well. Fuel cells will play a key role for both applications. However, hydrogen is an energy carrier, not a fuel2. The world energy production is dominated by fossil fuels as energy sources. It amounted to 88 % in 2003 with oil responsible for 37 %. The energy consumption is growing fast in Asia (7 % in 2003), and China has become the world’s second largest consumer of oil behind the United States. The proven reserves of oil are concentrated in the Middle East (63 %) and those of natural gas in the Middle East (41 %) followed by Russia. Coal is more evenly distributed between Asia, Europe and North America. 2 Introduction With the present world production, the oil reserves known today would be used up within about 40 years. This figure should be considered with care. It does not include reserves still to be discovered and it does not include the changes in consumption (for instance the growth in Asia). It has been emphasized the need for flexibility in the energy network and the need for alternative fuels. Oil is the most versatile of the fossil fuels with high energy density and ease of transportation. The power industry is very flexible to feedstocks. Coal can be transported over long distances to big centralized power plants close to deep water harbors. Natural gas in large quantities is provided by pipeline or as liquefied natural gas (LNG). The automotive sector represents a special challenge as the energy conversion is strongly decentralized. So far oil derived products have been the solution, but in view of the limited reserves, a number of alternative fuels are being considered, such as LPG (liquefied petroleum gas), natural gas, methanol, DME (dimethyl ether), ethanol, bio-diesel, Fischer-Tropsch synthetic fuels, and hydrogen. Biofuels represent a “sustainable” response for liquid fuels. It may be based on ethanol and bio-diesel derived from conventional agricultural products or from synfuels via gasification of biomass. As an example, the manufacture of ethanol from biomass requires the use of fossil energy that for methanol from corn, the ratio of the energy from ethanol divided by the amount of no renewable energy to produce it is only slightly above one if no other waste of the process are used to recover energy. This energy is used for fertilizer, harvesting, transportation, and processing. Ethanol may be produced more efficiently from sugar cane when the bagasse is also used to produce heat, as in Brazil, but it remains a challenge to find routes converting cellulose into ethanol. Comparing the alternative fuels with conventional oil-derived fuels is a comparison against a moving target, since technologies for making and using conventional fuels are developing as well2.
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