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Advanced batteries for electronic vehicle
N31
The concentrations of these chemicals as measured in and around the soifataric vents of the Makchatka volcanoes range from 0.4 ppb to 160 ppb of CFCs. Deep drill wells (one mile or deeper) are also a source of several organochlorine compounds and CFCs. “Dioxin” 2,3,7,8-tetrachlorodibenzo-pdioxin, was once generally thought to be the most toxic man-made chemical known. However, extensive evaluations by epidemiologists of people exposed to dioxin, such as Vietnam veterans, inhabitants of Seveso, Italy (the site of a major dioxin release in 1976) and industrial plant workers, have revealed that dioxin is not the “doomsday chemical” once believed. Nevertheless, the extraordinary toxicity of some polychlorinated dioxins (PCDDs) and related compounds, such as the polychlorinated dibenzofurans (PCDFs), in some animals is reason enough for the continued study of these compounds, especially because it is now recognised that PCDDs and PCDFs are, in fact, natural products and are ubiquitous in our environment. The production of chloromethane and other organochlorine compounds when organic material is burned, in association with the omnipresent chloride ion, led to the believe, now supported by evidence, that PCDDs could form during combustion processes. Laboratory studies have revealed that PCDDs, including “dioxin”, and PCDF’s form in parts-per-billion amounts during the combustion of wood (treated or untreated). The relatively poor efficiency and incomplete oxidation when damp vegetation and wood are burned in the presence of high chloride concentrations (70-2100 ppm in wood pulp) are conditions conducive to PCDD formation, and two research groups have concluded that
applied catalysis B: environmental
forest and brush fires are the major source of PCDDs and PCDFs in the environment. It is estimated that some 130 lb (1 lb = 0.4536 kg) of PCDDs are produced in Canadian forest fires annually. This is 1Otimes more than the amount formed in the 1976 Seveso plant accident. Because most forest fires are lightning-caused, and there are 200,000 forest fires annually worldwide that burn 27,000 square miles [l mile=l.609 km], it is logical to assume that PCDDs have been present in the environment for many centuries. An 1877 soil sample was found to contain PCDDs and PCDFs. Another milestone observation is the enzymatic conversion of chlorophenols into both PCDDs and PCDFs in the partsper-million range by horse-radish peroxidase enzyme (HRP). This extraordinary revelation opens the door to the possibility that a source of environmental PCDDs and PCDFs may be their completely natural formation from (natural) chlorophenols by soil and water microbes. Many marine and terrestrial organisms use organochlorine and other organohalogen compounds in chemical defence feeding deterents, irriiants or pesticides or in food gathering. Source: Environm. Sci. Technol., 28 (7) (1994)
Advanced Batteries for Electronic Vehicle
Gary L. Henrikson and co-workers of the Argonne National Laboratory review developments in advanced batteries for electric vehicles in the November 1994 issue of Chemtech. The lead-acid battery dominates the starting, lighting and ignition market in the US for automobiles. However, as a propulVolume 5 No. 4 -
1 April 1995
sion device for an electric vehicle is specific energy is quite low and vehicle range is limited to 60-100 milesThe nickel/cadmium battery possesses excellent power, has significantly better specific energy and longer life than the lead-acid system. However, it has a higher initial cost, There are also environmental concerns relating to the disposal of cadmium. For batteries under active investigation the sodium/sulphur and sodium/nickel chloride systems offer the highest specific energies; the former offer higher power whereas the latter offer longer life. Longterm options include the lithium polymer and lithium/iron disulphide systems. Developers of those batteries are targeting high specific energy (200 W h/kg) and specific power (400 W/kg) with service lives of 10 years. Both of these systems appear very promising and significant efforts towards their development are being carried out in the United States. The advanced battery for electric vehicles still requires an enormous research effort for many years to come, but the benefits in terms of environmental protection are such as to continue to make this a fruitful area. GERARD GRACE
Recent Advances in Designer Catalysts
Two recent publications that have appeared in Nature have highlighted the latest thinking in the design of highly structured catalysts. Parton et al. have described a novel oxidation catalyst [RF. Parton, I.F.J. Vankelecan, M.J.A. Casselman, C.P. Bezoukhanoua, J.B. Uyttehoeven and P.A. Jacobs, ‘An efficient mimic of cytochrome P-450 from a zeoliteapplied catalysis B: environmental
encaged iron complex in a polymer matrix’, Nature (London), 370 (1994) 541-544). In this they have successfully mimicked the catalytic oxidative properties of the enzyme cytochrome P-450, a quest that has eluded many scientists before them. They have used a composite catalyst system that achieves realistic mimicry as well as catalytic turnover rates that make the system industrially viable. Their catalyst incorporates iron phthalocyanine complexes encapsulated in crystals of zeolite Y which are in turn embedded in a polydimethylsiloxane membrane. The polymer was chosen to act as a mimic for the phospholipid membrane in which the cytochrome P-450 resides and acts as an interface between two immiscible phases. This design avoids the need for solvents or phase transfer catalysts. The catalyst system is shown to oxidise alkanes at room temperature at rates that are comparable to those of the enzyme. Furthermore, mechanistic studies of the biomimetic catalyst involving kinetic isotope effects are suggestive that there are close mechanistic similarities between the mimic and natural enzyme catalysts. Wan and Davis have also designed a highly structured catalyst for an asymmetric hydrogenation reaction [K.T. Wan and M.E. Davis, ‘Design and synthesis of a heterogeneous asymmetric catalyst’, Nature (London), 370 (1994) 449-4501. They have designed a heterogeneous catalyst that exactly models the specificity and reactivity of a homogeneous catalyst. The work builds on their previous paper [K.T. Wan and M.E. Davis, J. Catal., 148 (1994) l] which described a heterogeneous catalyst in which an organometallic catalytic complex is held on a film of water on a porous hydrophillic support, while the reactants and products remain within a hy-
Volume 5 No. 4 -
1 April 1995
The concentrations of these chemicals as measured in and around the soifataric vents of the Makchatka volcanoes range from 0.4 ppb to 160 ppb of CFCs. Deep drill wells (one mile or deeper) are also a source of several organochlorine compounds and CFCs. “Dioxin” 2,3,7,8-tetrachlorodibenzo-pdioxin, was once generally thought to be the most toxic man-made chemical known. However, extensive evaluations by epidemiologists of people exposed to dioxin, such as Vietnam veterans, inhabitants of Seveso, Italy (the site of a major dioxin release in 1976) and industrial plant workers, have revealed that dioxin is not the “doomsday chemical” once believed. Nevertheless, the extraordinary toxicity of some polychlorinated dioxins (PCDDs) and related compounds, such as the polychlorinated dibenzofurans (PCDFs), in some animals is reason enough for the continued study of these compounds, especially because it is now recognised that PCDDs and PCDFs are, in fact, natural products and are ubiquitous in our environment. The production of chloromethane and other organochlorine compounds when organic material is burned, in association with the omnipresent chloride ion, led to the believe, now supported by evidence, that PCDDs could form during combustion processes. Laboratory studies have revealed that PCDDs, including “dioxin”, and PCDF’s form in parts-per-billion amounts during the combustion of wood (treated or untreated). The relatively poor efficiency and incomplete oxidation when damp vegetation and wood are burned in the presence of high chloride concentrations (70-2100 ppm in wood pulp) are conditions conducive to PCDD formation, and two research groups have concluded that
applied catalysis B: environmental
forest and brush fires are the major source of PCDDs and PCDFs in the environment. It is estimated that some 130 lb (1 lb = 0.4536 kg) of PCDDs are produced in Canadian forest fires annually. This is 1Otimes more than the amount formed in the 1976 Seveso plant accident. Because most forest fires are lightning-caused, and there are 200,000 forest fires annually worldwide that burn 27,000 square miles [l mile=l.609 km], it is logical to assume that PCDDs have been present in the environment for many centuries. An 1877 soil sample was found to contain PCDDs and PCDFs. Another milestone observation is the enzymatic conversion of chlorophenols into both PCDDs and PCDFs in the partsper-million range by horse-radish peroxidase enzyme (HRP). This extraordinary revelation opens the door to the possibility that a source of environmental PCDDs and PCDFs may be their completely natural formation from (natural) chlorophenols by soil and water microbes. Many marine and terrestrial organisms use organochlorine and other organohalogen compounds in chemical defence feeding deterents, irriiants or pesticides or in food gathering. Source: Environm. Sci. Technol., 28 (7) (1994)
Advanced Batteries for Electronic Vehicle
Gary L. Henrikson and co-workers of the Argonne National Laboratory review developments in advanced batteries for electric vehicles in the November 1994 issue of Chemtech. The lead-acid battery dominates the starting, lighting and ignition market in the US for automobiles. However, as a propulVolume 5 No. 4 -
1 April 1995
sion device for an electric vehicle is specific energy is quite low and vehicle range is limited to 60-100 milesThe nickel/cadmium battery possesses excellent power, has significantly better specific energy and longer life than the lead-acid system. However, it has a higher initial cost, There are also environmental concerns relating to the disposal of cadmium. For batteries under active investigation the sodium/sulphur and sodium/nickel chloride systems offer the highest specific energies; the former offer higher power whereas the latter offer longer life. Longterm options include the lithium polymer and lithium/iron disulphide systems. Developers of those batteries are targeting high specific energy (200 W h/kg) and specific power (400 W/kg) with service lives of 10 years. Both of these systems appear very promising and significant efforts towards their development are being carried out in the United States. The advanced battery for electric vehicles still requires an enormous research effort for many years to come, but the benefits in terms of environmental protection are such as to continue to make this a fruitful area. GERARD GRACE
Recent Advances in Designer Catalysts
Two recent publications that have appeared in Nature have highlighted the latest thinking in the design of highly structured catalysts. Parton et al. have described a novel oxidation catalyst [RF. Parton, I.F.J. Vankelecan, M.J.A. Casselman, C.P. Bezoukhanoua, J.B. Uyttehoeven and P.A. Jacobs, ‘An efficient mimic of cytochrome P-450 from a zeoliteapplied catalysis B: environmental
encaged iron complex in a polymer matrix’, Nature (London), 370 (1994) 541-544). In this they have successfully mimicked the catalytic oxidative properties of the enzyme cytochrome P-450, a quest that has eluded many scientists before them. They have used a composite catalyst system that achieves realistic mimicry as well as catalytic turnover rates that make the system industrially viable. Their catalyst incorporates iron phthalocyanine complexes encapsulated in crystals of zeolite Y which are in turn embedded in a polydimethylsiloxane membrane. The polymer was chosen to act as a mimic for the phospholipid membrane in which the cytochrome P-450 resides and acts as an interface between two immiscible phases. This design avoids the need for solvents or phase transfer catalysts. The catalyst system is shown to oxidise alkanes at room temperature at rates that are comparable to those of the enzyme. Furthermore, mechanistic studies of the biomimetic catalyst involving kinetic isotope effects are suggestive that there are close mechanistic similarities between the mimic and natural enzyme catalysts. Wan and Davis have also designed a highly structured catalyst for an asymmetric hydrogenation reaction [K.T. Wan and M.E. Davis, ‘Design and synthesis of a heterogeneous asymmetric catalyst’, Nature (London), 370 (1994) 449-4501. They have designed a heterogeneous catalyst that exactly models the specificity and reactivity of a homogeneous catalyst. The work builds on their previous paper [K.T. Wan and M.E. Davis, J. Catal., 148 (1994) l] which described a heterogeneous catalyst in which an organometallic catalytic complex is held on a film of water on a porous hydrophillic support, while the reactants and products remain within a hy-
Volume 5 No. 4 -
1 April 1995