Convert Carbon Monoxide Research Articles

Clostridium autoethanogenum alters cofactor synthesis, redox metabolism, and lysine-acetylation in response to elevated H2:CO feedstock ratios for enhancing carbon capture efficiency

BackgroundClostridium autoethanogenum is an acetogenic bacterium that autotrophically converts carbon monoxide (CO) and carbon dioxide (CO2) gases into bioproducts and fuels via the Wood–Ljungdahl pathway (WLP). To facilitate overall carbon capture efficiency, the reaction stoichiometry requires supplementation of hydrogen at an increased ratio of H2:CO to maximize CO2 utilization; however, the molecular details and thus the ability to understand the mechanism of this supplementation are largely unknown.ResultsIn order to elucidate the microbial physiology and fermentation where at least 75% of the carbon in ethanol comes from CO2, we established controlled chemostats that facilitated a novel and high (11:1) H2:CO uptake ratio. We compared and contrasted proteomic and metabolomics profiles to replicate continuous stirred tank reactors (CSTRs) at the same growth rate from a lower (5:1) H2:CO condition where ~ 50% of the carbon in ethanol is derived from CO2. Our hypothesis was that major changes would be observed in the hydrogenases and/or redox-related proteins and the WLP to compensate for the elevated hydrogen feed gas. Our analyses did reveal protein abundance differences between the two conditions largely related to reduction–oxidation (redox) pathways and cofactor biosynthesis, but the changes were more minor than we would have expected. While the Wood–Ljungdahl pathway proteins remained consistent across the conditions, other post-translational regulatory processes, such as lysine-acetylation, were observed and appeared to be more important for fine-tuning this carbon metabolism pathway. Metabolomic analyses showed that the increase in H2:CO ratio drives the organism to higher carbon dioxide utilization resulting in lower carbon storages and accumulated fatty acid metabolite levels.ConclusionsThis research delves into the intricate dynamics of carbon fixation in C. autoethanogenum, examining the influence of highly elevated H2:CO ratios on metabolic processes and product outcomes. The study underscores the significance of optimizing gas feed composition for enhanced industrial efficiency, shedding light on potential mechanisms, such as post-translational modifications (PTMs), to fine-tune enzymatic activities and improve desired product yields.

Machine learning-enhanced optimal catalyst selection for water-gas shift reaction

The water-gas shift (WGS) reaction is pivotal in industries aiming to convert carbon monoxide, a byproduct of steam reforming of methane and other hydrocarbons, into carbon dioxide and hydrogen. Selecting an effective catalyst for this transformation poses a substantial challenge, as it requires a delicate balance between conversion, stability, and cost. We combine machine learning-driven prediction models with Bayesian optimization to explore and identify novel catalyst compositions. The proposed method efficiently explores the catalysis composition space for a predefined set of active metals, supports, and promoters to identify the most promising catalyst formulations. We assign weights to different performance metrics of catalysts, enabling tailored optimization according to specific industry needs. Our screening system streamlines catalyst discovery and facilitates the screening and selection of catalysts that balance conversion performance, stability, and cost-effectiveness. This approach holds significant promise for advancement in heterogeneous catalysis to meet the growing demands of efficient industrial processes.

Simulations for charge transfer and photocurrent calculations using hematite for green hydrogen production

Using the split-operator method to simulate wave propagation, it is possible to calculate the hole flux to the surface in hematite OER catalysis. The flux can then be translated to photocurrent to predict the dependence of voltage on photocurrent.

Light-driven Transformation of Carbon Monoxide into Hydrocarbons using CdS@ZnS : VFe Protein Biohybrids.

Enzymatic Fisher-Tropsch (FT) process catalyzed by vanadium (V)-nitrogenase can convert carbon monoxide (CO) to longer-chain hydrocarbons (>C2) under ambient conditions, although this process requires high-cost reducing agent(s) and/or the ATP-dependent reductase as electron and energy sources. Using visible light-activated CdS@ZnS (CZS) core-shell quantum dots (QDs) as alternative reducing equivalent for the catalytic component (VFe protein) of V-nitrogenase, we first report a CZS : VFe biohybrid system that enables effective photo-enzymatic C-C coupling reactions, hydrogenating CO into hydrocarbon fuels (up to C4) that can be hardly achieved with conventional inorganic photocatalysts. Surface ligand engineering optimizes molecular and opto-electronic coupling between QDs and the VFe protein, realizing high efficiency (internal quantum yield >56 %), ATP-independent, photon-to-fuel production, achieving an electron turnover number of >900, that is 72 % compared to the natural ATP-coupled transformation of CO into hydrocarbons by V-nitrogenase. The selectivity of products can be controlled by irradiation conditions, with higher photon flux favoring (longer-chain) hydrocarbon generation. The CZS : VFe biohybrids not only can find applications in industrial CO removal for high-value-added chemical production by using the cheap, renewable solar energy, but also will inspire related research interests in understanding the molecular and electronic processes in photo-biocatalytic systems.

Atomically Dispersed Cu–Au Alloy for Efficient Electrocatalytic Reduction of Carbon Monoxide to Acetate

Electrocatalytic carbon monoxide reduction reaction (CORR) is a promising strategy to convert carbon monoxide into high-value multi-carbon products such as acetate. Nonetheless, the activity and selectivity for CO-to-multi-carbon product conversion remains low due to the lack of efficient catalysts. Herein, we report a Cu–Au alloy catalyst with abundant atomic Cu–Au interfaces to drive efficient CORR for acetate production. The unique geometric and electronic structure of atomic Cu–Au interfaces affords improved acetate activity and selectivity, surpassing metallic Cu nanoparticles and CuAu bulk alloys. A Faradaic efficiency of 39% was achieved with a large partial current density of 217 mA cm–2 for acetate production in an alkaline flow cell. Density functional theory calculation reveals that the introduction of Au atoms into the Cu support promotes C–C coupling and improves acetate formation by weakening the binding strength of *CO +*CO on the catalyst surface.

On the Technology of Solid Oxide Fuel Cell (SOFC) Energy Systems for Stationary Power Generation: A Review

This paper presents a comprehensive overview on the current status of solid oxide fuel cell (SOFC) energy systems technology with a deep insight into the techno-energy performance. In recent years, SOFCs have received growing attention in the scientific landscape of high efficiency energy technologies. They are fuel flexible, highly efficient, and environmentally sustainable. The high working temperature makes it possible to work in cogeneration, and drive downstream bottomed cycles such as Brayton and Hirn/Rankine ones, thus configuring the hybrid system of a SOFC/turbine with very high electric efficiency. Fuel flexibility makes SOFCs independent from pure hydrogen feeding, since hydrocarbons can be fed directly to the SOFC and then converted to a hydrogen rich stream by the internal thermochemical processes. SOFC is also able to convert carbon monoxide electrochemically, thus contributing to energy production together with hydrogen. SOFCs are much considered for being supplied with biofuels, especially biogas and syngas, so that biomass gasifiers/SOFC integrated systems contribute to the “waste to energy” chain with a significant reduction in pollution. The paper also deals with the analysis of techno-energy performance by means of ad hoc developed numerical modeling, in relation to the main operating parameters. Ample prominence is given to the aspect of fueling, emphasizing fuel processing with a deep discussion on the impurities and undesired phenomena that SOFCs suffer. Constituent materials, geometry, and design methods for the balance of plant were studied. A wide analysis was dedicated to the hybrid system of the SOFC/turbine and to the integrated system of the biomass gasifier/SOFC. Finally, an overview of SOFC system manufacturing companies on SOFC research and development worldwide and on the European roadmap was made to reflect the interest in this technology, which is an important signal of how communities are sensitive toward clean, low carbon, and efficient technologies, and therefore to provide a decisive and firm impulse to the now outlined energy transition.

Effects of hydrogen addition on combustion characteristics of a free-piston linear engine with glow-assisted ignition

In this paper, the combustion characteristics of a methane-fueled free-piston linear engine (FPLE) with glow-assisted ignition (GAI) under different hydrogen fractions were studied by numerical simulations. The results showed that the chain-branching reactions start to process after the ignition source appears. The fuel-air mixture can be successfully ignited under the compression of the piston. Hydrogen addition to the fuel accelerates the elementary reaction and helps enhance the ignition and combustion processes. Compared with that of pure methane, the maximum HRR increases by 9.4%, 49.4%, 75.6%, 124.7%, and 241.4% with hydrogen fractions of 1.0%, 3.0%, 5.0%, 7.0%, and 9.0%, respectively. High hydrogen concentration (greater than 7.0%) can bring the occurring of over-advanced combustion, resulting in higher compression negative work. With the hydrogen fractions changing from 0% to 9.0%, the CA0–10 first decreases and then increases, with its minimum value atαH2=7.0%, and the CA10–90 is gradually decreased. The hydrogen addition raises the combustion temperature, which in turn, results in higher NOx emission. High combustion temperature helps convert carbon monoxide into carbon dioxide, decreasing the emission amount of CO. Hydrogen addition to methane has competition effect on soot emission. On one hand, it reduces the soot emission by soot oxidation. Another hand it causes chemical effect leading to higher soot nucleation and surface growth rates. In this paper, the result of competition suppresses soot formation.

Measurements of the impact of carbon monoxide on the performance of passive autocatalytic recombiners at containment-typical conditions in the THAI facility

Passive autocatalytic recombiners (PARs) have become one of the primary measures to mitigate the hydrogen risk for severe accidents in current and advanced water-cooled nuclear power plants (NPPs). The pgm (platinum group metals) coating of the catalyst inside the PAR is capable to oxidize hydrogen into water vapor as well as to convert carbon monoxide into carbon dioxide. The optimal efficiency of conversion requires a significant surplus of oxygen compared to the stoichiometric oxidization.A test series under containment typical boundary conditions was performed in the THAI facility (Thermal-hydraulics, Hydrogen, Aerosols and Iodine) to investigate the PAR performance under the presence of carbon monoxide. Ratios of injection mass flow rates of hydrogen and carbon monoxide into the test facility are investigated between 4:1 and 7:1, based on hypothetical release of CO by the molten core concrete interaction (MCCI). The findings are related to database on PAR performance carried out in previous OECD/NEA projects, THAI (2007–2009), THAI-2 (2011–2014), and THAI-3 (2016–2019). Special emphasis is placed on the investigation of the PAR under conditions of oxygen starvation, taking also into account a potential PAR poisoning by carbon monoxide, and under potential PAR induced ignitions at elevated hydrogen and carbon monoxide concentrations.

Methane Disintegration by Water Vapor in a Hot Chamber heated by Using a Microwave Steam Torch

An analysis of the behaviors of water and methane in a hot chamber indicates that methane and water molecules mutually help to disintegrate each other. Oxygen atoms from water disintegrate methane, and methane also self-dissociates. A substantial dissociation of methane by these processes occurs at chamber temperatures higher than T = 1500 K. Methyl (CH3) from these dissociations is very instrumental for the disintegration of water molecules. Meanwhile, the majority of methyl molecules undergo disintegration by oxygen atom, producing an abundance of formaldehyde (CH2O), which self-dissociates immediately to carbon monoxide and hydrogen molecules. Hydroxyl (OH) may convert carbon monoxide to carbon dioxide at a very high temperature of T = 1900 K. An experimental observation shows that methane dissociates in a hot steam chamber heated by a microwave torch. Methane disintegrates completely at temperature higher than 1200 °C (= 1480 K) without any catalyst, as expected from the analytical study.

Efficient electrocatalytic conversion of carbon monoxide to propanol using fragmented copper

The renewable-energy-powered electrocatalytic conversion of carbon dioxide and carbon monoxide into carbon-based fuels provides a means for the storage of renewable energy. We sought to convert carbon monoxide—an increasingly available and low-cost feedstock that could benefit from an energy-efficient upgrade in value—into n-propanol, an alcohol that can be directly used as engine fuel. Here we report that a catalyst consisting of highly fragmented copper structures can bring C1 and C2 binding sites together, and thereby promote further coupling of these intermediates into n-propanol. Using this strategy, we achieved an n-propanol selectivity of 20% Faradaic efficiency at a low potential of −0.45 V versus the reversible hydrogen electrode (ohmic corrected) with a full-cell energetic efficiency of 10.8%. We achieved a high reaction rate that corresponds to a partial current density of 8.5 mA cm–2 for n-propanol. The upgrade of carbon monoxide to higher alcohols offers a route to renewable fuels. Now, Sinton, Sargent and co-workers report a highly fragmented, copper-based catalyst with engineered interfaces between the (111) and (100) facets that promote the coupling of C1 and C2 species, leading to enhanced production of n-propanol.

Complete Genome Sequence of the Autotrophic Acetogen Clostridium formicaceticum DSM 92T Using Nanopore and Illumina Sequencing Data.

ABSTRACTHere, we report the closed genome sequence of Clostridium formicaceticum, an Rnf- and cytochrome-containing autotrophic acetogen that is able to convert carbon monoxide to acetate using the Wood-Ljungdahl pathway. The genome consists of a circular chromosome (4.59 Mb).

(Invited) Sulfur Poisoning of Ni-Based SOFC-Anodes – Short and Long Term Behavior

Solid Oxide Fuel Cells (SOFCs) enable a highly efficient, environmentally-friendly power generation. One major problem of SOFCs working under real conditions are the sulfur compounds contained in almost all available fuels as natural gas, diesel reformate or gas from hydrothermal gasification of biomass (1),(2). If the sulfur is not properly removed by an upstream desulfurization unit even small amounts of sulfur in the ppm range affect the performance of SOFCs. Previous studies showed that the initial performance loss observed after adding sulfur to the fuel is related to a poisoning of the Ni-electrocatalyst in the Ni/YSZ-cermet anode. In this contribution the impact of sulfur on the short term and long term behavior of Ni-based cermet anodes will be discussed. Sulfur species are chemisorbed on the Ni-surface (3), blocking the adsorption sites and the surface diffusion of reactants and reaction products. By means of electrochemical impedance spectroscopy and a subsequent analysis of the spectra by the distribution of relaxation times (4) two poisoning mechanisms could be decoupled (i) a deactivation of the catalytic watergas-shift-reaction (WGS) at the nickel surfaces and (ii) the electro-oxidation of hydrogen at the three phase boundaries (5),(6). The time constant of these mechanisms depends on the available Ni-surface area and the amount of H2S supplied to the anode and is typically in the range of several hours. Furthermore a restructuring of the Ni-surfaces accompanied by an enhanced Ni agglomeration results in an enhanced aging in the longer term.To improve the sulfur tolerance of SOFCs a cermet anode composed of Ni and ceria, a material combination well known as sulfur tolerant catalyst, can be applied. Impedance analysis of electrolyte supported cells exhibiting a Ni/ceria cermet anodes revealed a significantly improved sulfur tolerance. It will be shown that the impact of both poisoning mechanisms can be reduced. Cells with appropriate Ni/ceria anode layers showed the ability to convert carbon monoxide by a sufficiently fast WGS and electrooxidize hydrogen with a polarization resistance below 200 mΩ·cm².References (1) Y. Matsuzaki and I. Yasuda, Solid State Ionics, 132 (3-4), p. 261 (2000). (2) K. Föger and K. Ahmed, Journal of Physical Chemistry B, 109 (6), p. 2149 (2005). (3) C. H. Bartholomew, Applied Catalysis A: General, 212 (1), p. 17 (2001). (4) H. Schichlein, A. C. Müller, M. Voigts, A. Krügel and E. Ivers-Tiffée, Journal of Applied Electrochemistry, 32 (8), p. 875 (2002). (5) A. Kromp, S. Dierickx, A. Leonide, A. Weber and E. Ivers-Tiffée, J. Electrochem. Soc., 159 (5), p. B597 (2012). (6) A. Weber, S. Dierickx, A. Kromp and E. Ivers-Tiffée, Fuel Cells, 13, p. 487 (2013).

Catalysis: Cobalt gets in shape.

Solid cobalt-based catalysts are used commercially to convert carbon monoxide and hydrogen into synthetic fuels. It emerges that much more valuable chemicals can be produced by using a different form of cobalt catalyst. See Letter p.84 The lower olefins—chiefly ethylene, propylene and butylene—are starting materials for many plastics and other industrial products. They are usually obtained by cracking hydrocarbon feedstocks, so as petroleum reserves become depleted the urgency to switch to alternative feedstocks such as biomass increases. The 'Fischer–Tropsch to olefins' (FTO) process produces lower olefines from syngas—a mixture of hydrogen and carbon monoxide derived from biomass, coal and natural gas—but at the same time produces large amounts of unwanted methane. Here Liangshu Zhong and colleagues describe a new catalyst for the FTO conversion. Formed from cobalt carbide nanoprisms, the catalyst is active in mild reaction conditions, is highly selective for lower olefins and, critically, produces very little methane.

Photocatalytic Fischer–Tropsch Synthesis on Graphene-Supported Worm-Like Ruthenium Nanostructures

Fischer–Tropsch synthesis (FTS) converts carbon monoxide and hydrogen to liquid fuels and chemicals and is usually operated under high temperature ranges, which results in an evident increase of energy consumption and CO2 emission. A photocatalytic FTS route was proposed to efficiently harvest solar energy. Worm-like ruthenium nanostructures dispersed on graphene sheets can effectively catalyze FTS at mild conditions (150 °C, 2.0 MPa H2, and 1.0 MPa CO) under irradiation of visible light and achieve a catalytic activity as high as 14.4 molCO·molRu–1·h–1. The reaction rate of FTS can be enhanced by increasing the irradiation intensity or decreasing the irradiation wavelength. The work provides a green and efficient photocatalytic route for FTS.

Polyoxometalate-mediated electron transfer-oxygen transfer oxidation of cellulose and hemicellulose to synthesis gas.

Terrestrial plants contain ~70% hemicellulose and cellulose that are a significant renewable bioresource with potential as an alternative to petroleum feedstock for carbon-based fuels. The efficient and selective deconstruction of carbohydrates to their basic components, carbon monoxide and hydrogen, so called synthesis gas, is an important key step towards the realization of this potential, because the formation of liquid hydrocarbon fuels from synthesis gas are known technologies. Here we show that by using a polyoxometalate as an electron transfer-oxygen transfer catalyst, carbon monoxide is formed by cleavage of all the carbon-carbon bonds through dehydration of initially formed formic acid. In this oxidation-reduction reaction, the hydrogen atoms are stored on the polyoxometalate as protons and electrons, and can be electrochemically released from the polyoxometalate as hydrogen. Together, synthesis gas is formed. In a hydrogen economy scenario, this method can also be used to convert carbon monoxide to hydrogen.

The effect of loading on sintering and catalytic activity of Pt/SiO2 hybrid catalyst powders synthesized via spray pyrolysis

Platinum (Pt) is commonly used as a heterogeneous catalyst to effectively convert carbon monoxide (CO) from automobile exhaust gas into carbon dioxide (CO2). Platinum/silica (Pt/SiO2) hybrid catalyst powders with varying Pt content were synthesized via a spray pyrolysis process. The average particle size and specific surface area of the Pt nanoparticles on the Pt/SiO2 hybrid catalyst powders were characterized as-prepared and after heat treatment. As the Pt loading increased, the Pt nanoparticles grew on the surface of the SiO2 as a result of sintering, and the catalytic efficiency decreased. This work demonstrates that the Pt/SiO2 (4 wt% Pt) hybrid catalyst powder is suitable as a hightemperature automobile exhaust catalyst, compared with the Pt/SiO2 hybrid catalyst powder with high Pt loading (14 wt% Pt), indicating that metal nanoparticle loading is a key factor for determining catalytic activity.

Catalysis at the boundaries

Copper-based materials have been found that efficiently convert carbon monoxide and water to ethanol using electricity. The discovery is a major advance towards storing renewable energy in the form of a liquid fuel. See Letter p.504 Renewable electricity is often produced when it is not needed. If the surplus could be harnessed to drive the conversion of CO2 and water into liquid fuel, the energy would not go to waste and a use would be found for CO2 produced by carbon capture. All this requires efficient electrocatalysts that reduce CO2 not only to CO, but also further into fuel chemicals. Copper does this but with low efficiency and selectivity. Christina Li et al. now show that the intrinsic catalytic properties of copper can be improved by producing it from its oxide as interconnected nanocrystallites. Their enhanced catalyst generates primarily ethanol, demonstrating that a two-step conversion of CO2 to liquid fuel powered by renewable electricity might be possible.

Gold Atoms Stabilized on Various Supports Catalyze the Water–Gas Shift Reaction

For important chemical reactions that are catalyzed by single-site metal centers, such as the water-gas shift (WGS) reaction that converts carbon monoxide and water to hydrogen and carbon dioxide, atomically dispersed supported metal catalysts offer maximum atom efficiency. Researchers have found that for platinum metal supported on ceria and doped ceria in the automobile exhaust catalyst, atomic Pt-Ox-Ce species are the active WGS reaction sites. More recently, preparations of gold at the nanoscale have shown that this relatively "new material" is an active and often more selective catalyst than platinum for a variety of reactions, including the WGS reaction. The activity of gold is typically attributed to a size effect, while the interface of gold with the support has also been reported as important for oxidation reactions, but exactly how this comes about has not been probed satisfactorily. Typical supported metal catalysts prepared by traditional techniques have a heterogeneous population of particles, nanoclusters, subnanometer species, and isolated atoms/ions on the support surfaces, making the identification of the active sites difficult. Both we and other researchers have clearly shown that gold nanoparticles are spectator species in the WGS reaction. Evidence has now amassed that the gold active site for the WGS reaction is atomic, that is, Au-Ox species catalyze the reaction, similar to Pt-Ox. In this Account, we review the relevant literature to conclude that the intrinsic activity of the Au-Ox(OH)-S site, where S is a support, is the same for any S. The support effect is indirect, through its carrying (or binding) capacity for the active sites. Destabilization of the gold under reducing conditions through the formation of clusters and nanoparticles is accompanied by a measurable activity loss. Therefore, it is necessary to investigate the destabilizing effect of different reaction gas mixtures on the gold atom sites and to consider regeneration methods that effectively redisperse the gold clusters into atoms. For gold catalysts, we can remove weakly bound clusters and nanoparticles from certain supports by leaching techniques. Because of this, we can prepare a uniform dispersion of gold atoms/ions strongly bound to the support surface by this two-step (loading followed by leaching) approach. Presently, one-step preparation methods to maximize the number of the single atom sites on various supports need to be developed, specific to the type of the selected support. Often, it will be beneficial to alter the surface properties of the support to enhance metal ion anchoring, for example, by shape and size control of the support or by the use of light-assisted deposition and anchoring of the metal on photoresponsive supports. Because of their importance for practical catalyst development, synthesis methods are discussed at some length in this Account.

Biohydrogen production using native carbon monoxide converting anaerobic microbial consortium predominantly Petrobacter sp.

In this study, anaerobic mixed microbial consortium isolated from a local sewage treatment plant in Guwahati, India, was used to convert carbon monoxide (CO) to hydrogen. The consortium was initially grown in acetate containing medium and later acclimatized to utilize CO as the sole carbon source for hydrogen production. By 16S rDNA analysis, the consortium was identified to be predominantly Petrobacter sp. Statistically designed experiments were then applied to optimize the CO conversion and hydrogen production by the anaerobic mixed consortium. To evaluate the significant factors that influenced the biohydrogen production, Plackett–Burman screening design of experiments was applied, which revealed that temperature and Fe2+ influenced the most on hydrogen production with P values less than 0.05 each. The effect due to pH and Ni2+ was less with P values 0.120 and 0.132, respectively. Concentration of Fe2+ and Ni2+ in the medium was then subsequently optimized by using Central Composite Design (CCD) of experiments followed by response surface methodology (RSM) which yielded the optimum value of 213 mg/L for Fe2+ and 2.2 mg/L for Ni2+. At these optimum conditions, 60.8 mol hydrogen production was achieved which was 8% higher than that observed from the screening experiment.

Characterization of Sol-Gel Derived CuO@SiO2 Nano Catalysts towards Gas Phase Reactions

One distinct concentration of copper ions was embedded into the silica matrix to xerogel form using copper source Cu(NO 3)2�3H2O. The xerogel samples were prepared with using hydrolysis and condensation reactions of TetraEthyl Ortho-Silicate (TEOS) by the sol-gel method. In this investigation, new molar ratio of H 2O/TEOS was determined to be 11.7. Also, the necessary amount of tri-hydrated copper nitrate was added to the solution in such a manner that the concentration of the copper oxide in final solution reach to 10 wt. %. The prepared samples were characterized by Thermal Gravimetric Analysis (TGA), Transmission Electron Microscopy (TEM), surface area measurement (using BET method) and Thermal Program Reduction (TPR) methods. Finally, catalytic behavior of nano-composites was studied towards carbon monoxide (CO), nitrogen monoxide (NO) oxidation and di-nitrogen oxide (N 2O) decomposition reactions. The results were presented the systematic reactivity study of CO, NO oxidation and N 2O decomposition on dispersed copper oxide nano-catalysts over silica supports, in order to determine the ability of these materials to convert carbon monoxide, nitrogen monoxide and di-nitrogen oxide to harmless species by different reaction paths at different temperatures.