CATALYTICALLY ACTIVE MATERIAL

Abstract: The green parts of living plants, here called phytobiomass, maintain through photosynthesis life on earth. Chlorophyll is a protein which collects energy from the sunshine required for the synthesis of to begin with carbohydrates from carbon dioxide and water. The phytobiomass also contains transport paths for reactants, intermediates and end-products. Chlorophyll or phytobiomass can according to the invention after pyrolysis be used as catalytically active materials for chemical and electrochemical processes. The catalytical activity of these abundant and very cheap materials is in certain applications on the same level as of the noble metal catalysts. Typical applications are as catalytically active materials for air electrodes for fuel cells or for denitrification of flue gases.

Description: Catalytically active material Catalysts are used in most processes. Catalytic exhaust gas cleaning has acquainted the general public with catalysis Power production in the future from fuel cell power plants will mean a further expansion of the territory of catalysis. In these new applications as well as in most of the classical processes, for instance the synthesis of ammonia, the catalys is a solid material which accelerates a reaction between gase and/or liquid reactants which is called heterogeneous catalys The catalytically or electrocatalytically active material, for instance crystallites of platinum, is in general disposed on a carrier, for instance active carbon. The performance of the catalyst is governed by the properties of the catalytical active material but also by the properties of the carrier. This field is subject to extensive phenomena oriented researc and product- and process-oriented research and development. Catalysis technology is "high-tech" in the same sense as modern electronics. Considerable progress has been made but the catalysts provided by nature for the life processes are still unsurpassed. "Man-made" catalysts are in general very expensive due to complicated manufacturing. Noble metal catalysts are frequent used for exhaust gas cleaning or as electrocatalysts for fuel cell generators which are expensive. There is also a question whether the global resources of noble metals will be sufficie •for the volumes in these applications. Some catalysts are taken directly from the kingdom of plants or the kingdom of minerals. Active carbon can be made from fossil fuel or wood and is used both as a support and as a catalyst in many different connections. Haber used powder of iron ore from the large iron mines in the north of Sweden for the synthesis of ammonia. In such cases there are no restrictions with respect to cost and available quantity. The present invention has in some way features in common with these catalysts taken from the kingdom of plants and the kingdom of minerals. Catalytically active materials of concern here are taken from the kingdom of plants that is the green parts of the living plants which maintain the photosynthesis. These green parts of living plants are here called phytobiomass. The characteristic feature for the invention is thus that it refers to catalysts and their use in chemical processes said catalysts consisting of catalytically and/or electrocata lytically active materials disposed on a carrier characterize by that the catalysts comprise the residue after pyrolysis of chlorophyll from green parts of living plants. It is immediately realized that catalysts according to the invention satisfy any desiderata with respect to costs and volume. It is, however, surprising that the these catalysts are in certain important applications as active as noble meta catalysts on a carrier of active carbon. The chlorophyll is carrying out the photosynthesis in the green parts of living plants and belongsto the group of hydr porfyrins . It exhibits ."^similarities with the catalytically active macro-cycles like porfyrin≤/ ftalocyanines etc which also active after pyrolysis. Therefore it may seem obvious in after-sight to test also the residue after pyrolysis of chlorophyll as a catalyst. However, so far nobody has carrie out such tests before this invention. Nevertheless every researcher and inventor on this earth and by the way also all other people see the green plants every day and their power to grow and the photosynthesis. The most surprising with the present invention is, however, not that chlorophyll has been identified as a particularly advantageous starting material for the manufacture of catalytically active materials by means of pyrolysis but that pyrolysis of green parts of living plants produces a particularly advantageous combination of the catalytically active material and its carrier. In after-sight one may observe that this combination effect is a reminiscence of the properties of the starting material , the green parts of the living plants. The green parts of the living plants are designed not only for the photosynthesis and its consecutive reactions but also for efficient mass transfer of the reactants primarily C0 2 andH^O to the reaction sites in the plants. The pyrolys residue of the chlorophyll molecule is thus disposed on the residue of the pyrolysis of the other parts of the plant whi mainly comprise cellulose, hemicellulose and lignin. which exhibit a very efficient structure for mass transfer. The kingdom of plants has many different species with differing growth pattern, appearence and size and one may therefore supposedly expect quite large differences between catalystsmade from different starting materials. This is, however, not the case. About the same technical effect is obtained from leaves and needles from different tree species, seaweed and algae of different kinds, green parts of the plants of the agriculture like potato haulm, corn, straw, grass, weeds etc in short the whole flora. This is due to the fact that all these species in spite of all superficial differences are designed for the photosynthesis and its associated mass transfer. The invention will now be described by means of a few embodiments. In order to accentuate the exemplification we have for starting material chosen one of our most hated weeds that is the nettle belonging to the family Urtica. The catalytic action will be demonstrated by means of an applica with air cathodes for fuel cells and an application in the enviro ental sciences, that is elimination of nitrogen oxides in fluegases by means of reduction of ammonia. The leaves from the nettle were rinsed clean from road-dust and were then milled in a mortar. The phytobiomass was washe with distilled water and dried. The material was mixed with the double quantity of support,in this case powder of carbon, in a xylene-dispersion and was then dried at 140 °C. The pyrolysis took place in nitrogen at different temperatures in the range 350-900 °C. The pyrolysis temperature and the other conditions have certain influence on the catalytical activity. Pyrolysis during two hours at 800 C was optimal in this case. So called flash pyrolysis is an alternative process of treatment. Dried powder of the phytobiomass is pyrolysed in a falling tube with a temperature in the range 700-900 C with a residence time of between 0,5-5 seconds. The equipment which was used in these experiments has been described by C. Ekstrδm, Gordon Conference Analytical Pyrolysis, New Hampshire, USA, 11-15 July 1983. In certain cases the pyro¬ lysis residue after flash pyrolysis is more reactive than the pyrolysis residue after slow pyrolysis described above. For exemplification we shall, however, here rely on conven¬ tional slow pyrolysis which does not require special equipmen The catalyst, that is the catalytically active material comprising the pyrolysis residue of the chlorophyll disposed on the carrier of the pyrolysis residue of the additional plant material in its term disposed on the carbon substrate, was in this way prepared for production of for instance air electrodes. Air electrodes for fuel cells with alkaline electrolyte was manufactured according to the state of art but with a "nettle catalyst" as described above. The electrode mass " contained 53 % catalyst as described above, 12 % carbon powder and 35 % PTFE-powder (Hostaflon TF 9202) which was dispersed in hydrocarbon solvent (D-70) ; mixed in a mixer, mille in a colloid mill, deliquefied and rolled onto, a nickel nesh Hydrogen sintering took place at 360 °C during one hour after drying at 100 °C. Figure 1 shows the performance for this air electrode at room temperature. For comparison a curve is shown for a similar electrode, however, made only from active carbon which also catalyzes the oxygen reduction. The third curve shows similar electrode with platinum on carbon catalyst, 0,5 g Pt/c 2. "The nettle electrode" exhibits a performance comparable to the "noble metal electrode". The performance for air electrodes of this kind is influenced by co-catalysts which serve as peroxide decomposers in the alkaline enviroment. Figure 2 shows how performance is in¬ fluenced by such co-catalysts. In this case separated chloro¬ phyll was used as starting material which had been precipitat on a carbon support. The iron additive gives the best voltage current curve in this study. vϊlien comparing the voltage current curves in Figure 1 and Figure 2 one has to keep in the memory that the "nettle elec¬ trode" in Figure 1 is using much less virgin chlorophyll than the electrodes on the basis of pure chlorophyll accordin to Figure 2. The electrode shows a higher activity when the : electrocatalyst is generated directly from the green parts of living plants compared to the route via separated and purified chlorophyll and a conventional carbon support. The catalyst produced as described above was also evaluated as a deNO -catalyst in comparison with the corresponding catalyst based on pyrolyzed porfyrin on carbon support. "The nettle catalyst" .exhibited the same efficiency as the much more expensive catalyst based on porphyrin. The reductio of nitrogen oxides is here taking place at at temperature around 100 °C compared to deNO -catalysts based on metal oxides. This improves the heat economy most considerably for process systems for power production etc which rely on this principle for elimination of nitrogen oxides. Similar results were obtained with catalysts produced from other plants than nettle. The technical action has been demonstrated by means of two widely different applications within the industrial catalysis. The mechanism for the reactions is not known. It is possible that nitrogen remaining after the pyrolysis -is important as well as the metal component. The structure of the carbon skeleton and the electron mobility in this skeleton may also be of importance. These circumstances in combination should enhance the formation of the active complexes with the reactants which is significant for catalysis. It should not be difficult for the artisen to find other reactions which are accelerated by means of the catalyst according to the invention. This is simplified very much by the exceedingly simple manufacturing procedure.

Claims: Claim 1. Catalytically active material for chemical and electro¬ chemical processes c h a r a c t e r i z e d in that the material consists of the residue after pyrolysis of chloro¬ phyll from the green parts of living plants. 2. Catalytically active material for chemical and electro¬ chemical processes c h a r a c t e r i z e d in that the material consists of the residue after pyrolysis of green parts of living plants containing chlorophyll. 3. Catalytically active material according to claim 1 and..2 c h a r a c t e r i z e d in that the catalytically active material has been produced by pyrolysis within the temperatur range 350-900 °C. 4. Catalytically active material according to claim 1 and 2 c h a r a c t e r i z e d in that the catalytically active material has been produced by fast pyrolysis during 0,5-5 seconds at 700-900 °C. 5. Catalytically active material according to any of the proceeding claims c h a r a c t e r i z e d in that the catalytical action has been enhanced by the addition of any of the metals iron, cobalt or nickel or mixtures thereof. 6. Use in order to carry out chemical and electrochemical processes by means of catalytically active material according to the claims 1-5.

Inventors: LINDSTROEM OLLE, LINDSTROEM, OLLE
Applicants: LINDSTROEM AB OLLE, AB OLLE LINDSTROEM
Application year: 1989
Main classification: B01J21
IPC codes: B01J21, B01J37