Catalytic Process Technology (2000)

The committee reviewed previous studies for their applicability to industry, consulted a variety of other printed sources, and met with a cross section of leaders in industry and academia to generate a list of potential research areas (see Table 2-1 ).

Members of the committee included industry representatives with diverse backgrounds: catalysis, including Fischer-Tropsch catalyst systems; catalytic sensor systems for monitoring combustion systems; catalytic processes for the manufacture of pharmaceutical intermediates and other specialty chemicals; catalyst characterization; noble metal catalysts; catalytic combustion catalysts and combustion system components; zeolite catalysts; catalysts for environmental applications for stationary and mobile sources; biological catalysis, including fermentation biochemistry, and microbial genetics; heterogeneous catalysis; homogeneous catalysis; catalysts and processes for the generation of acetic acid, acetic anhydride, methyl acetate, propionic acid, and propionic anhydride from synthetic gas; chemical engineering research; development of new applications for catalysts; and commercialization and scale-up of new catalytic processes. For biographical information about the committee members see Appendix B .

After the initial list was generated, each research area was debated and evaluated against five criteria: impact of the technology advance; timeliness of the impact; probability of successful development; cost of investment relative to the potential benefit; and appropriateness of government involvement. After several iterations, the committee reached a consensus. The final list was then categorized into six areas:

• alkane activation and selective oxidation

• synthesis of fine chemicals

• alternative and renewable resources

• olefin polymerization

• alkylation technology

• environmental applications

Because of the breadth and diversity of the field of catalysis, the committee was not able to prioritize these six areas. The committee strongly believes that all of them are important and that all of them offer opportunities for high-payoff research in catalysis. Within each area, the two most important opportunities for catalytic research were selected and recommended to OIT for funding.

Using current commercial processes, yields of many common organic chemicals (e.g., propylene oxide, formaldehyde, and 1,4-butanediol) are low. The economics of production of acrolein, acrylic acid, methanol, acetic acid, phthalic anhydride, and linear alcohols could be considerably improved if they could be produced from simpler feedstocks (e.g., propane instead of propylene, ethane instead of ethylene). In some cases, significant amounts of coproducts are produced (e.g., acetone is produced in phenol production from cumene, and t-butanol is produced in propylene oxide production from propylene and isobutane) so that the economics are more complicated than those of a process for producing a single product. Other reactions (e.g., methane to ethylene, methanol, or formaldehyde; ethane to ethylene, ethylene glycol, acetic acid, or acetaldehyde; propane to propylene, acrolein, acrylic acid, or 1,3-propane diol; butane to butene, 1,4-butane diol, or maleic anhydride; isobutane to methacrylic acid, linear long-chain alkanes to the alpha olefins or linear alcohols, and benzene to phenol) could be used if they were highly selective and high yield and required low investment and low operational costs.

Not only are yields of common organic chemicals low, but some reactions require more complex oxidants (e.g., hydrogen peroxide, ozone, chlorine, nitric acid, manganese oxide or potassium manganese oxide, and peroxyacids), which are more expensive than oxygen or air. Highly selective, active, stable catalysts that activate molecular oxygen could be used for alkane activation processes instead of current energy-intensive processes. New processes that could coproduce energy would be more environmentally appealing than current processes. The development of a viable process to convert alkanes into cost-efficient commodity products will require a good deal of R&D focused on the synthesis of desired materials and computational and modeling studies of catalysts and reactions.

The primary building blocks for the production of chemical intermediates and polymers are olefins and aromatics, both of which are produced from petroleum and natural-gas liquids using high-temperature, endothermic processes (e.g., cracking, dehydrogenation, and reforming). There are significant economic incentives for using alkanes rather than olefins and aromatics as starting materials because low molecular- weight alkanes, especially methane, are readily available and are less expensive than olefins or aromatics.

Alkanes have not been used because they are highly stable compared to the products and require high-energy pathways to react compared with olefins. High- energy pathways can lead to the further conversion of desired products to less useful, but more thermodynamically stable, products (e.g., hydrogen-deficient products for nonoxidative reactions and carbon oxides

for oxidation). Although both alkane and alkene prices are coupled to the price of crude oil, alkenes have substantial value as chemical feedstocks, whereas alkanes primarily have fuel value. Novel catalysts and reactions will be necessary for the selective conversion of methane, ethane, propane, and other inexpensive, readily available hydrocarbons to more valuable products.

The single greatest challenge in using hydrocarbon as raw material is the selective, economical, partial oxidation of a light hydrocarbon to produce a single, more valuable product. The primary problem is converting a low-energy material into a high-energy material by oxidation. If this process could be used, selective catalytic oxidation of organic compounds could reduce the environmental impact of a broad range of industrial processes.

Low-temperature oxydehydrogenation of alkanes is a logical area for exploration if alkanes are used as the primary starting materials in the petrochemical industry. Alkane oxydehydrogenation is exothermic and has been demonstrated without complete combustion in a number of reactions One of the earliest low-temperature examples of selective, low-temperature alkane oxidation is the conversion of ethane to ethylene using a molybdenum-vanadium based catalyst with promoters (Thorsteinson, 1981) Selectivities of 90 to 95 percent to ethylene at yields of 50 to 80 percent were achieved at temperatures between 250°C and 400°C. Propane oxydehydrogenation to propylene has been far less successful.

Under different conditions (e.g., higher pressure, added water, and recycled ethane), acetic acid could be the major product (Arne, 1986) Conversion of methane to ethylene is also appealing, and a variety of mixed-metal oxides have been shown to accomplish this reaction, both in a redox mode and in a cooxidation mode (Keller and Bhasin,1982). Catalysts containing vanadium have demonstrated selective partial alkane activation at unusually low temperatures. Iridium complexes with “pincer” ligands has also been reported for low-temperature alkane dehydrogenation (Gupta et al., 1997).

New ideas for novel catalysts based on appropriate precedents and the principles of molecular chemistry at the active site could also be investigated. Other interesting mixed-metal oxides reported to oxidize alkanes without complete combustion include oxides of nickel, molybdenum, and iron. In addition, attempts have been made to modify Group VIII metals, hopcalite, and other materials that oxidize alkanes at

very low temperatures to carbon dioxide to make them more selective towards partial oxidation products.

Recommendation. The Office of Industrial Technologies should support the development of catalysts and processes for the low-temperature, oxidative dehydrogenation of alkanes to alkenes.

A major challenge for successful alkane activation is to predict, design, and make effective new catalytic materials (particularly mixed-metal oxide materials). Specifically defined bulk materials containing only two or three metal oxides will require novel approaches (Rulkens and Tilley, 1998) Synthesis of targeted new materials with defined structures, both on the molecular scale at the active site and on a larger scale requiring specific catalyst morphology, is beyond current capabilities. To design better catalysts, one must first understand precisely how catalysts work and how alkanes can be activated at low temperatures. Improved characterization and computational capabilities will be necessary to define the factors responsible for selective and unselective pathways. Once the dynamics, kinetics, and transition states of individual reactions are understood, reaction selectivity (ratio of the desired to undesired products) can be predicted and/or used as a conceptual model that might lead to the development of an entirely new class of catalysts. Capital investment and operating costs must also be kept in mind.

For a selective-oxidation catalyst, one must consider not only the molecular design on the catalytically active site, but also catalyst morphology and bulk physical characteristics, such as crush strength or acidity, which might be very important for selectivity. Uniform large pores might result in significantly higher selectivities for partial-oxidation reactions. New methods of catalyst synthesis will be neccessary to control both active-site composition and the larger structure and physical properties of the catalyst.

Successful discoveries could be used in the conversion of ethane to ethylene or acetic acid or of propane to propylene, acrolein, or acrylic acid, or the oxidation of isobutane to methacrylic acid. Anything that accelerates the discovery and testing of catalysts, especially ingenious ways of testing new catalyst compositions or processes, will decrease the time for, and increase the probability of, discovering a new, useful catalyst for alkane activation.

Recommendation. The Office of Industrial Technologies should support the development of mixed-metal oxide catalysts for alkane activation using predictive computing methods.

Propylene oxide is a high-volume commodity chemical produced by the chlorohydrin method and by two variants of the coproduct approach (propylene oxide/styrene monomer and propylene oxide/MTBE), which is energy intensive and has a significant adverse environmental impact. An efficient, direct-oxidation process using oxygen as the oxidant would significantly change the economics of the production of propylene oxide and other higher olefins. The highly reactive allylic positions of higher olefins have presented a significant challenge to the development of a selective epoxidation process. Homogeneous routes to epoxides that work on a simple olefin (without functional groups for complexation) have not been developed, although direct heterogeneous oxidation of propylene with high selectivity has been accomplished (Haruta, 1997). Carefully designed heterogeneous materials have shown some promise of achieving this cooxidation reaction with high selectivity and is an appropriate area for research by academia.

Economical processes for converting methane to methanol, ethane to ethanol or ethylene glycol, propane to 1,3-propane diol, butane to butanol or 1,4-butane diol, and other transformations of alkanes to primary alcohols and diols could have major benefits for the chemical industry. Precedents in biological systems have demonstrated that it is possible for transition metals to selectively oxidize an alkane to a primary alcohol under mild conditions (low temperatures and pressures). However, this enzymatic process cannot yet compete with robust, heterogeneous, inorganic alternatives in terms of production rate and costs. R&D could focus on the development of ingenious heterogeneous catalyst designs that allow oxygen transfer to carbon to produce an alcohol and simultaneously prevent the further oxidation of alcohols to carbon monoxide and carbon dioxide.

Homogeneous complexes have been shown to activate alkanes noncatalytically under mild conditions, or catalytically with only limited activity (Barton, 1993). Shilov (1984) reported mild conditions for catalytic reaction of alkanes with platinum metal complexes. Electrophilic alkane activation by certain transition metals (e.g., platinum, palladium, and rhodium) has been used to convert methane to methyl sulfate with high

selectivity (Periana et al., 1998). However, rates, catalyst life, and the cost of the oxidant have not been determined.

Although biomimetic catalysts were catalytic under mild conditions for hydroxylation of certain alkanes, their potential commercial use is limited. None has been robust enough to merit continued research, and rates per volume of catalyst in the most optimistic extrapolation of possibilities are still orders of magnitude below commercial requirements. Stable, heterogeneous, mixed-metal oxide analogs might provide the same advantages as biomimetic catalysts without their limitations. They could be designed with stable inorganic “ligands” to hold a metal oxide in an active redox or coordination state, analogous to how biomimetic catalysts function. For example, single-site, metal-oxide ligated zirconium and tantalum hydrides which affect alkane deoligomerization and metathesis, respectively, at very low temperatures (< 200°C) (Basset, 1999). Additional novel nonbiomimetic-catalytic approaches to primary oxidation of alkanes to alcohols should be investigated by academia.

The recent increase in the production of fine chemicals has been driven by the increasing number of new pharmaceuticals, many of which are being synthesized as single enantiomers. The fine chemical industry is actively pursuing the use of catalysis in chiral syntheses. Given the high value and strict purity control necessary for manufacturing fine chemicals, product yield and selectivity are important criteria in the design of catalytic processes. The functional complexity of the reaction substrates and products present significant challenges to chemoselectivity, regioselectivity, and stereoselectivity.

Catalysis, which has always been an important step in the synthesis of fine chemicals, has become even more important with the advent of rational catalyst/ligand design, the use of high-throughput catalyst screening tools, and the discovery of novel catalytic reactions that provide synthetic versatility and atom economy (i.e., the simplification of substrate structure and minimization of protecting-group techniques).

In addition to metallic and organometallic catalysts, enzymes and microorganisms (both biocatalysts) are rapidly becoming attractive for chiral synthesis, especially for specific reaction steps that are difficult to achieve by other chemical methods. Biocatalysis (or biotransformation) is also proving to be valuable in the chemical modification of naturally synthesized compounds (e.g., antibiotics and enzyme inhibitors) that yield high-value fine chemicals.

The identification and exploitation of new catalysts in the synthesis of fine chemicals will require continuing development of enabling technologies. Rapid preparation and screening of candidates by high-speed automation and analytical detection systems will greatly accelerate the identification of novel catalysts, as well as provide efficient optimization within catalyst families. These preparation/screening systems parallel the use of combinatorial techniques in the fields of synthetic and medicinal chemistry. The rational design of metal ligands (the basis for many stereoselective catalysts) will be assisted by advances in computational chemistry towards predicting optimal transition-state behaviors. For heterogeneous catalysts, computational chemistry and the analysis of surface-bound intermediates will improve our understanding of catalytic mechanisms and lead to improved catalysts. And finally, the use of in-situ analytical probes to uncover catalytic reaction mechanisms will lead to better optimization of their yield and selectivity.

Catalytic processes could enable the use of simpler, cheaper substrates while minimizing prefunctionalization or the need for protecting groups. Thus, synthetic versatility would be enhanced without requiring more complex substrates. The development of selective catalytic oxidations using simple oxidants, and catalytic activation of carbon-hydrogen bonds and schemes to generate carbon-carbon bonds would all be of great benefit to the fine-chemical industry.

Recommendation. The Office of Industrial Technologies should support the development of catalysts with substantially improved synthetic versatility and atom economy.

Catalytic selectivity is essential to the synthesis of fine chemicals, where yields of products from high-value substrates are paramount and the minimization of difficult-to-remove impurities can determine the choice of synthetic options. To control regioselectivity and enantioselectivity, R&D should focus on metal ligand design and optimization, by both experimental and computational techniques, especially the secondary and tertiary orientation effects of the metal ligand complexes to optimize the active-site

effect and, therefore, their effectiveness and selectivity. In particular, the asymmetric hydrogenation of carbon-carbon, carbon-oxygen, and carbonnitrogen bonds by organometallic complexes, which is used extensively in fine-chemical processing, could be improved by the development of novel chiral ligands. Selectivity in heterogeneously catalyzed, fine-chemical reactions is also important, and the development by the commercial pharmaceutical industry of novel catalysts, chiral surface modifiers, and fundamental knowledge of reaction mechanisms will lead to improvements in selectivities.

Successful processing of a catalytic reaction step often involves optimizing of reaction conditions to increase yield and selectivity, as well as careful control of catalyst deactivation and recovery to allow for the recycling and reuse of expensive catalysts. R&D on optimizing reactions might focus on in-situ analytical probes to reveal reaction mechanisms and kinetics, both of which can be used to control selectivity. R&D on novel catalysts, catalytic ligands, and catalyst support substrates to improve the activity and performance of reactions, as well as to improve the retention of catalyst activity and increase catalyst recovery, should be supported by industry.

The efficient development of a biocatalyst for the synthesis of both fine chemicals and bulk chemicals will require the parallel development of three enabling technologies. The first key technology is efficient biocatalyst screening, which will require rapid “analytical” detection methods, particularly as they relate to chirality (e.g., chromatographic separation of race mates). Screening, miniaturization, and automation will also be required to evaluate available and potential biocatalysts. Second, the development of microchip technology for the rapid study of enzyme kinetics under a variety of chemical and physical conditions is very important for rapid process scale-up. Microchips can also enable molecular biologists to identify genes responsible for specific biocatalysts of interest. Finally, data management systems must be developed to ensure that the enormous amount of data being generated from enzyme screening and characterization can be easily retrieved and reviewed in a way that leads to a better understanding of trends in biocatalyst performance.

A number of separate steps should be investigated in the biocatalyst (enzymatic) process. The first step, and the most critical, is to design enzymes with specific characteristics (e.g., substrate specificity and stereoselectivity in chiral synthesis) to optimize the conversion rate. The second step is to stabilize this enzyme long enough to produce the desired product. The third step is to maintain the enzymatic activity in a nonaqueous environment because the organic synthetic product is often nonaqueous. The fourth step is to maintain the level of reactivity of the enzyme throughout the production period, which can be done by a cofactor generation process.

Enzymes are well known catalysts that accept not only their specific native substrates but also closely related ones. However, to increase their yield or conversion rate, the fine-chemical industry must learn how to alter their substrate specificity (e.g., their preference for a specific molecular structure as its raw material) to “construct” industrially useful enzymes with perfect stereoselectivity. Fundamental studies of enzyme structures coupled with molecular biology studies will be important for achieving this goal. The committee believes that designing enzymes with specific characteristics (e.g., substrate specificity and stereoselectivity in chiral synthesis) to optimize the conversion rate is the most critical step in biocatalysis.

Recommendation. The Office of Industrial Technologies should support the development of enzymes with substrate specificity and stereoselectivity for chiral synthesis in fine chemicals.

Currently, R&D on improving stability is focused on immobilization through covalent coupling of an enzyme to a polymer, noncovalent gel entrapment, and cross-linked enzyme crystals. Continued research in this area will have a high probability of improving enzyme stability. A fundamental knowledge base will be necessary to achieve stability at the molecular level when a biocatalyst is exposed to various environments. In addition to chemical and physical studies, methods of improving intrinsic enzyme stability through molecular biological approaches, such as directed evolution, should be investigated. The ultimate goal of this R&D is to develop enzymes/microorganisms that will remain stable in altered environments. This R&D is, and should continue to be, supported by universities and industry.

Many chemical intermediates that become enzyme substrates are insoluble in aqueous solutions, requiring that the enzyme system function in a nonaqueous environment. Frequently, this causes a considerable decrease in enzyme activity. Additional studies should be conducted to achieve equal performance in both aqueous and organic solvents, but also to enhance performance in the organic solvents. A number of specific chemical reactions (e.g., transaminations, carbon-carbon bond formation, reductive amination) that are performed with enzymes should be investigated. In the opinion of the committee, enzyme stability in nonaqueous environments is an important subject for further industry and university research.

To ensure that certain important enzymes remain active throughout the reaction, the presence of another component, called a cofactor, is necessary. As the enzymatic reaction takes place, the cofactor component is reduced and must be regenerated to maintain the same level of enzymatic activity throughout the reaction. Although in-situ regeneration with isolated NADH-dependent (nicotinamide adenine dinucleotide based) enzymes has been used, alternatives should be investigated by industry or academia, including molecular biology to modify or eliminate the need for a cofactor.

Currently, crude petroleum is the primary source of petrochemicals. As domestic reserves of crude petroleum are reduced, U.S. industries are becoming increasingly dependent on foreign sources, which has greatly compromised the competitiveness of the U.S. chemical manufacturing sector. Foreign oil-producing regions are trying to attract higher value products and higher value manufacturing jobs for their own populations, and the production of petrochemicals in proximity to the sources of crude petroleum gives them a significant cost advantage. In addition, although there is no shortage of crude petroleum today, long-term availability is a concern. In the near term, the U.S. chemical industry is likely to remain competitive because of its technological, infrastructural, and workforce advantages. In the longer term, however, the U.S. will have to find ways to reduce its reliance on foreign oil to remain competitive.

The United States still has plentiful reserves of coal and natural gas. Indeed, natural gas, which is plentiful worldwide, is increasingly being used

in fuels and chemicals. Increasing the use of these domestic resources would somewhat negate the logistical advantages of other oil-producing regions.

The large capacity of the U.S. agricultural sector is the source of a large carbon reserve and a source of specialty chemicals that has gone largely untapped by the chemical industry. In the terms of this discussion, alternative resources refers to noncrude-oil-based resources. Renewable resources refers to carbon resources available from biological, especially agricultural, sources. Catalysis will be crucial to using both alternative and renewable resources.

R&D on alternative resources should be focused on the conversion of alternative materials to synthesis gas (a mixture of hydrogen and carbon monoxide) and subsequent conversions. Natural gas and, to a much lesser extent, coal are already being used to make synthesis gas used by the chemical industry: (1) to generate methanol and, in further reactions, with carbon monoxide to generate downstream products (e.g., acetic acid, acetic anhydride, formaldehyde, formic acid); and (2) to functionalize olefins (e.g., via hydroformylation) to generate aldehydes, alcohols, carboxylic acids, and esters.

Synthesis gas has several additional, smaller scale uses in the functionalization of various chemicals. However, this potential has not been completely realized. A large number of other potential products (e.g., ethylene glycol, vinyl acetate, acetaldehyde, acrylic acid, ethanol, and isobutanol) have been conceived, demonstrated in the laboratory, and, in some cases, demonstrated on the pilot-plant scale. In many cases, the biggest hurdle to the commercialization of these chemicals is the high capital cost of generating and separating synthesis gas components. Therefore, the highest priority for the chemical industry is to increase the availability and reduce the cost of synthesis gas.

A large number of processes for the generation of chemicals based on synthesis gas are competitive or nearly competitive with existing technology. Examples include, but are not limited to, the production of ethylene glycol, ethanol, ethyl acetate, acetaldehyde, isobutanol, linear alcohols, and vinyl acetate. The high capital expenditures related to the generation and separation of synthesis gas components are the limiting factor in the implementation of these technologies. Therefore, the development of lower cost processes for generating, separating, and

delivering the components of synthesis gas, especially synthesis gas from coal, would accelerate the commercialization of these processes, as well as the development of new synthesis gas-based processes for chemicals and fuels. R&D could also focus on using waste products and biomass as feedstocks for synthesis gas.

Recommendation. The Office of Industrial Technologies should support a study of alternative, lower cost means of producing synthesis gas from alternative resources.

The chemical industry would greatly benefit from new technologies for the conversion of synthesis gas to chemicals. Most research is currently focused on the generation of oxygenates. R&D should also focus on innovative approaches to increasing the number of materials and their functionality produced from synthesis gas.

The committee has strong reservations about using carbon dioxide as a carbon source in the chemical industry because a substantial amount of energy will probably be required to reduce it to an oxidation state useful for organic synthesis. Therefore, it is not likely that carbon dioxide will be a cost-effective source of carbon, except as a means of increasing the carbon content of synthesis gas through the shift reaction or as a reaction solvent.

The transportation-fuel industry may provide a strong impetus for shifting toward alternative resources. The transportation industry is now anticipating a need to reformulate transportation fuels to reduce their environmental impact, which could require fuels with a significant oxygen content. It is widely believed that the most likely source of the oxygenated component will be a synthesis gas-derived material. If so, the availability of synthesis-gas will have to be greatly increased, which could provide the infrastructure for bringing these synthetic gas technologies to fruition. Although fuel technology is beyond the scope of this study, the committee encourages the use of these alternative resources in fuels, which will certainly involve catalysis. Opportunities for developing a range of chemicals from alternative resources, especially single-carbon molecules, should be evaluated by commercial industry and academia.

The U.S. agricultural sector has the potential to provide a large volume, as well as a wide variety, of carbon resources that can be continually renewed and may represent the only viable means of

sequestering carbon dioxide. In addition, the United States has a distinct advantage over other countries in the development of biological and genetic technologies, which should be translatable to an advantage in the development of technologies for the conversion of renewable agricultural resources to chemicals and fuels. The feasibility of biotechnology to deliver economically viable products for the chemical industry from renewable resources was recently demonstrated for 1,3-propanediol (DuPont/Genencor), ascorbic acid (Eastman/Genencor), and NatureWorks ^R (a biopolymer from DOW/Cargill). The problems facing the development of technologies for the generation of raw materials from renewable resources and their downstream conversion to chemical products on a large scale are similar to those associated with the use of biocatalysis for the generation of fine chemicals.

R&D should focus on more efficient means of converting and purifying biomass components, including (but not limited to) cellulose, sugars, amino acids, and natural polymers (e.g., polylactic acid), both for direct use and for use as feedstocks in biological and chemical conversion processes. Their industrial use will require development in several areas, including microorganisms, biological catalysts (enzymes), and traditional catalysis. Tests on biological systems have shown that transition metals can selectively oxidize an alkane to a primary alcohol under mild conditions (e.g., low temperatures and pressures). However, this enzymatic process cannot yet compete with robust, heterogeneous, inorganic alternatives in terms of production rate and costs.

Recommendation. The Office of Industrial Technologies should support the development of processes for converting biomass to feedstocks and polymers. Research should focus on microorganisms, biological catalysts (enzymes), and traditional catalysis.

Currently, biological techniques require that a large portion of the feedstock be converted to carbon dioxide to drive the chemical processes. It would be useful if alternative means of providing energy, such as through the activation of hydrogen, could be identified. This may require catalysis. Scale-up of biologically based technologies into commercial, continuously operating processes would require significant advances in engineering, particularly in separations technology and waste reduction/handling.

Technical advances in olefin polymerization catalysis (e.g., metallocene catalysts), which provide low-cost, high-performance materials, have affected a broad range of manufacturing industries and, hence, have had a substantial impact on the U.S. economy. Industry continues to pursue technical and economic progress through R&D in this area, but many critical challenges remain to be met for improved product versatility in high-performance engineering plastics, improved surface properties, and improved environmental compatibility.

R&D should focus on the development of active catalysts to polymerize olefins containing polar unsaturated monomers and to copolymerize unsubstituted olefins with olefins that contain polar substituents (e.g., carbonic, ester, ether, nitrile). The goal is to improve the properties and expand the applications of economical polymers based principally on olefins. Potential applications range from replacements for polyvinyl chloride and acrylonitrile butadiene styrene to new properties, including solvent resistance, high-temperature use, toughness, controllable surface properties, optical clarity, and “smart” polymers that respond to environmental conditions, enable easy mold release, or improve adhesion and paintability. Polyolefin chemistry, including heteroatoms, such as silicones, will provide polymers with desirable properties, especially biocompatibility or conversely hydrophobic properties. The development of multifunctional polymeric systems could provide polymers that are self-healing (capable of overcoming oxidation, depolymerization, cross-link, degradation, embrittleness) or that respond to changing environmental conditions. New ligand synthesis via synthetic combinatorial techniques would accelerate progress and improve the efficiency of research. Precious metal replacements and improved efficiencies of late-transition metals would also be helpful.

Recommendation. The Office of Industrial Technologies should support the development of catalysts that can copolymerize olefins with a diverse class of polar unsaturated monomers.

The development of high-performance polyolefin and copolymer catalysts that are tolerant of common impurities (e.g., water, amines, and sulfur) could increase the flexibility and efficiency of manufacturing processes. These catalysts could function in a variety of solvating media, including alcohols and water. R&D should be focused on more efficient and selective catalysts, particularly for copolymer systems.

Recommendation. The Office of Industrial Technologies should support the development of catalysts that are tolerant of common impurities, such as water and amines.

Concepts for macromolecular architectures have been demonstrated. R&D should now focus on development of a robust, versatile catalytic system with a macromolecular architecture that can be controlled by monomer and catalyst design combinations. R&D on new macromolecular structures that expand the current limits of polymer properties should be funded by the chemical industry to open new markets for engineering materials.

Current uses for recycled polymers and unreacted monomers are very limited. The specific properties of polymers and controlled reactivity will be required for efficient recycling. OIT could work with the Environmental Protection Agency or other government agencies to identify additional uses (markets) for recycled polymers that would encourage the chemical industry to invest in recycling processes. Academia and industry should take the lead in this area.

Two major areas are of interest in the fields of petroleum and petrochemicals. The first is aromatic alkylation to prepare petrochemical intermediates, such as ethylbenzene and cumene. The second is paraffinolefin alkylation for the manufacture of motor fuels.

The development and introduction of zeolite catalysts in the manufacture of ethylbenzene and cumene has resulted in markedly

improved selectivity, reduced by-products, and the elimination of environmental and corrosion problems. Therefore, there is little economic or environmental incentive for the development of catalysts in this area.

In the alkylation process of paraffin-olefin, there is an incentive to eliminate the environmental hazards of the existing technology. A few new catalysts that are more environmentally friendly have been developed, but they have poorer performance than hydrogen fluoride and sulfuric acid. Research to discover and develop an environmentally clean catalyst system, such as solid catalyst with performance equal to hydrogen fluoride and sulfuric acid, would be beneficial to the petroleum industry.

Highly selective alkylation processes would increase carbon efficiency and minimize separation and recycling requirements for solid-supported acid or base catalysts. Capital and operating costs would also be reduced dramatically for the synthesis of fine chemicals, aliphatic and aromatic alkylation, and pharmaceutical intermediates. Improved catalysts would simultaneously improve economics and carbon efficiency and minimize environmental impact. The use of highly selective solid catalysts will most likely also require innovations in process technologies.

Recommendation. The Office of Industrial Technologies should support the development of catalysts with ultrahigh selectivity for chemicals and fuels alkylation to reduce by-products and minimize environmental impact.

Replacements for common Lewis acids, such as boron trifluoride or aluminum trichloride, would improve efficiency and increase carbon productivity in alkylation processes. Current systems are intolerant of polar functional groups, in which the Lewis acid loses its catalytic property. Lewis acid systems (e.g., transition-metal complexes) should be studied to explore the feasibility for enhanced acid catalysis with tolerances for carbon moieties with polar functional groups.

Recommendation. The Office of Industrial Technologies should support the development of catalysts with tolerance to functional groups.

The formation of carbon-carbon bonds is a critical technology with widespread applications and extensive economic impact. Replacements of hydrogen chloride, hydrogen fluoride, and sulfuric acid with solid acids has been delayed by the instability and low number density of acid sites in solid acids. New technologies would increase active-site density, improve stability, or renew surface reactivity. R&D in this area should be supported by industry and academia.

Maintaining the quality of the environment may be the most serious challenge facing the world today. This can be demonstrated from several perspectives. In the continental United States, the federal Clean Air Act of 1990 mandates that a minimum level of air quality be maintained for good health and quality of life. In 1996, substantial portions of the United States did not meet these requirements and, therefore, were classified as nonattainment areas. The population of these areas totaled 113 million people (Environmental Protection Agency (EPA), 1996). It is estimated that by the end of 2000 as much as 60 percent of the population of the United States may reside in nonattainment areas. It is also estimated that the underdeveloped portion of the world is inhabited by 70 percent of the population but currently consumes only 20 percent of the world’s resources. As underdeveloped countries attempt to raise their standards of living, they will also increase their per capita energy consumption, which may substantially increase the environmental burden.

A major source of the environmental burden is the combustion of fossil fuels, which results in the emission of nitrogen oxides (NO_X), unburned hydrocarbons, and carbon dioxide. The challenge is to reduce these emissions while still allowing industrial growth and higher standards of living. Technology development can contribute to this objective by reducing the pollution from existing means of energy production and by increasing the cost competitiveness of more efficient means of energy production.

In the short term, technology for controlling emissions of NO_X could reduce emissions from vehicle and stationary sources and enable the widespread use of high-efficiency diesel and lean-burning gasoline engine technologies. These technologies can improve energy efficiency by 20 to 30 percent. In the long term, catalytic technology could speed up the commercialization of fuel cells with substantial improvements in fuel efficiency and markedly lower pollutant emissions. Fuel cells may provide an entirely new mass-produced, energy-generation technology for vehicle

and stationary power generation. R&D could also focus on the development of a physical understanding of, and quantitative data on, the thermal aging process that occurs in high-temperature catalytic systems. A better quantitative understanding of emissions control, catalytic combustion, and enhanced fuel processing in fuel cells and other processes would have widespread benefits.

Modern three-way catalysts simultaneously reduce emissions of carbon monoxide, hydrocarbon, and NO_X from gasoline-fueled internal-combustion engines operating at the stoichiometric air-fuel composition. Lean-burning engines and diesel engines offer fuel economy advantages of 20 to 50 percent, depending on the operating mode or usage cycle. Because lean-burning gasoline engines and diesel engines operate in a fuel-lean mode resulting in high levels of exhaust oxygen, three-way catalyst technology is not applicable for NO_X control.

In stationary combustion processes with exhaust streams containing high oxygen levels, ammonia-based reductants are very effective but are not attractive for transportation applications because of the toxicity of ammonia. The amount of NO_X in lean-engine exhaust environments cannot be controlled by NO_X decomposition, by reduction of the NO_X with an added hydrocarbon, or by any other current catalyst technology. The availability of a catalyst that could control NO_X emissions would enable the rapid development and implementation of engines with increased fuel efficiency, lower pollution, and decreased greenhouse-gas emissions. Another area for R&D would be control of emissions of particulate carbon or soot from diesel engines.

Catalyst systems using hydrocarbon reductants have been intensively investigated but without success. Future R&D could be focused on nonconventional, speculative approaches. High-throughput testing could be used to identify catalyst compositions for further development; water vapor, trace levels of sulfur, and initial catalyst deactivation would have to be taken into account. R&D should also focus on the development of detailed reaction kinetics and an understanding of reaction mechanisms. OIT should only support work that evaluates catalysts under realistic exhaust-gas conditions and includes measurements of the detailed reaction kinetics.

Recommendation. The Office of Industrial Technologies should support a study to evaluate “step-out” innovative catalyst strategies for controlling of nitrogen oxide emissions in lean environments.

Despite substantial efforts, no satisfactory method of controlling particulate emissions from diesel engines has been developed. Porous, ceramic-wall, flow filters can effectively remove particulates, but the buildup of carbon increases the pressure drop in the filter, and oxidation of the collected carbon results in excessive temperatures and short filter life. Innovative catalytic approaches to controlling diesel particulates could include using fuel additives that lead to a catalytic component in the diesel exhaust. R&D should consider cost, the possible creation of a new pollutant species, and the effect of the additive on the engine. Approaches that do not require a fuel additive might be developed based on studies of the oxidation of solid carbon on catalytic surfaces. OIT could coordinate its efforts with those of the EPA and other federal agencies to evaluate innovative approaches to controlling of diesel particulates.

Any engine or power plant equipped with technology for controlling pollution will most likely have to be equipped with sensors (onboard diagnostics) to improve engine control and to assess whether the pollution system is functioning properly. Current configurations include oxygen sensors to monitor hydrocarbon removal by three-way catalysts. This works well when hydrocarbons are high but not when emissions are reduced. Hydrocarbon sensors based on the combustion of the hydrocarbon species might be used, but they would have to be accurate enough to detect extremely low hydrocarbon concentrations consistent with emission regulations for modern engines. This technology would also be applicable to a wide variety of combustion systems, as well as to the control and optimization of combustion processes. (Several IOF industries identified a need for sensors in fuel cells and fuel-processing systems for fuel cells.)

R&D should focus on the development of sensors capable of measuring NO_x, carbon monoxide, and unburned hydrocarbon at

concentrations ranging from 1 to 1,000 parts per million (ppm), with a target of 1 to 25 ppm for all three pollutants. Sensors should be tested with realistic gas compositions and temperatures. This R&D could be done by interdisciplinary groups with expertise in the sensing platform, electronics and data handling, catalytic processes, and the synthesis of catalytic materials and should be supported by industry.

Proton-exchange membrane (PEM) fuel cell systems are extremely sensitive to sulfur compounds and carbon monoxide. The presence of sulfur compounds at the 1 ppm level will shorten the life of fuel processor system catalysts. Carbon monoxide must be below 10 ppm for fuel cell electrode performance to be acceptable. In both cases, a sensor would ensure proper system performance and system control in case of an upset in inlet conditions. Interdisciplinary R&D on sensors is likely to have substantial payoffs and should be supported by industry.

Significant advances have been made in the development of the PEM and solid- oxide fuel cell systems, which are the prime candidates for the next generation of stationary applications and vehicles fueled by natural gas and liquid fossil fuels. PEM fuel cell systems are especially attractive for vehicles and small dispersed-power applications. Solid-oxide fuel cells can use hydrocarbon fuels, especially methane, but PEM systems require hydrogen fuel that is free of sulfur and has low concentrations of carbon monoxide. Ideally, hydrocarbon fuels could be used with systems on board the vehicle to convert the hydrocarbon fuel to a hydrogen stream with the required purity.

R&D could focus on efficient, durable systems for converting liquid hydrocarbon fuel to hydrogen. Although fuel-processing technologies are already being commercialized on a large scale and are widely used in the chemical and petroleum industry, reducing these technologies to compact, fast-response systems on board vehicles will require significant advancements. New systems will also be required to convert natural gas for stationary, dispersed-power generation, and to convert liquid fuels for vehicles.

Continued development of innovative steam reforming and partial-oxidation systems could yield significant reductions in the size of processing units and decrease response times. Industry is hoping for nonpyrophoric catalyst systems, including reforming and shift catalysts, to meet the demands of small fuel-processing systems that can operate intermittently. Advanced research and innovative “step-out” approaches should be considered and supported by industry.

Supported metal-catalyst systems are used in numerous industrial processes important to a clean environment and to industry in general, such as fuel cell electrode catalysis, automotive emissions control, fuel processing to produce hydrogen for fuel cells, and a variety of other petroleum and chemical processes. Supported-metal catalysts are subject to loss in activity from a variety of mechanisms, including chemical poisoning and thermal sintering. In many processes, especially those operating at high temperature, the predominate mechanism of activity loss is thermal sintering. Although some work was done in this area with the advent of automotive emissions control in the early 1970s, the sintering process of both the support and the supported metal catalyst is not well understood. Companies directly involved in the development of automotive emission-control catalysts have developed practical solutions that minimize sintering, but thermal deactivation remains a significant deactivation mode for catalytic converters. A fundamental understanding of the sintering of both the substrate and catalyst is critical for processes using supported noble-metal catalysis under high-temperature conditions. This understanding would accelerate the development of current and next-generation materials.

The committee believes OIT should fund a program with a comprehensive approach to developing a quantitative kinetic understanding of the sintering of metals on supports. The approach should include the development of a physically realistic sintering mechanism based on elementary chemical steps, followed by the measurement of kinetics for these processes. This multiyear effort should involve interdisciplinary groups and should be reviewed periodically to assess whether it is addressing proposed objectives.

Recommendation. The Office of Industrial Technologies should support the development of a basic understanding of the sintering of supported metals.

A study of the sintering of supported metals will be limited by an inability to measure the sintering process with well characterized materials. A model system, such as a planar polycrystalline-oxide surface with deposited metal particles, could provide a convenient system for obtaining sintering data via transmission electron microscopy, scanning electron microscopy, or tunneling microscopy. An interdisciplinary team could provide both the catalysis and the instrumentation (e.g., electron microscopy or tunneling microscopy) capabilities. The committee believes that commercial corporations and universities should investigate and, if appropriate, use planar model systems to study the sintering of supported metals.