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Catalysis Applications

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ドキュメント名 Catalysis Applications
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四重極質量分析計 薄膜フィルム・プラズマ・表面技術
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DEMS装置 差分電気化学質量分析
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ハイデンアナリティカル社製 質量分析計用 サンプリングインレット
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CATALYSIS APPLICATIONS Catalysis Applications
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INTRODUCTION Catalysis Applications Catalysis is the process of increasing the rate of a chemical reaction by the addition of a substance known as a catalyst. The reaction itself does not consume the catalyst but it does allow more preferential products to be produced at a faster rate under more favourable conditions. The use of catalysts is vitally important to all areas of modern life and the economic impact of catalysis is huge, contributing 30–40% of global GDP. It is estimated that 85% of all manufactured products involve catalysis somewhere in their production chain, and such products have considerable impact in: X Energy – petrochemicals X Healthcare – pharmaceuticals X Materials – polymers, batteries X Transport – catalytic convertors X Environment – water, air quality, renewable and bio–produced materials Hiden Analytical produces a range of gas analysis systems that have been crucial in the study of the catalytic process, from catalyst characterisation and development to reaction monitoring and optimisation. B | Catalysis Applications
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Contents 2. Heterogeneous Catalysis 4. Syngas 5. Operando Spectroscopy 6. Catalyst Characterisation 8. Automotive 10. Surface Chemistry 12. Electrocatalysis 14. Biocatalysis 16. Plasma Catalysis Catalysis Applications | 1
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Heterogeneous Catalysis Heterogeneous catalysis covers an enormous range of chemical reactions. The defining feature of heterogeneous catalysis is the reaction of gas or liquid phase reactants occurring at the surface of solid catalysts. As the surface is where the reaction occurs the catalyst is generally prepared in ways that produce large surface areas per gram of catalyst. Examples of this are finely divided metals, metal gauzes, metals incorporated into supporting matrices, and metallic films. The wide variety of gas or vapour phase reactions are ideal for study with the Hiden gas analysis products. MALEIC ANYDRIDE PRODUCTION Maleic anhydride (MA) is an important intermediate chemical under different operating conditions can then be used in primarily used in the production of resins and polymers. modelling the underlying transient kinetics of this complex Commercially it is produced from the partial oxidation of reaction over the full range of studied operating conditions. n-butane by air over a vanadium pyrophosphate (VPP) catalyst. There has been huge research effort to better 6% understand the different aspects of this industrially n-butane 5% attractive reaction including mechanism, dynamic catalyst H2O Oxygen phase evolutions as well as the effect of redox operating 4% CO conditions such as gas/solid residence time, temperature, CO2 pressure and gas composition on the reaction yield. 3% MA The example shown here of the transient analysis of 2% the partial oxidation of n-butane is part of a wider 1% investigation into the effect of a range of redox conditions covering the actual conditions existing in industrial reactors. 0% The transient redox conditions are simulated using the 0 1 2 3 4 Time min Hiden CATLAB microreactor coupled to a QGA gas analyser. Characterising the transient behaviour of the VPP catalyst MS transient response. 2 | Catalysis Applications Compositions
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BIOMASS TAR Climate change and depletion of fossil fuel sources has Nevertheless, it was revealed that Ni/La0.7Sr0.3AlO3 has seen the requirement to find sustainable alternatives high activity and low carbon deposition during toluene become more pressing. Steam reforming of biomass tar steam reforming. offers one such alternative. The data shown here describes In this reaction, lattice oxygen plays an important role a study into this reaction, specifically investigating catalysts for oxidizing surface carbon and decomposing reactant that minimise the role that aromatic hydrocarbons can play toluene. Therefore, this type of experiment can be used in the deactivation of the catalyst. to confirm the relationship between lattice oxygen The biomass tar includes toluene-like compounds in its release rates from the metal oxide and reaction rates, structure. Generally, for Ni supported on metal oxide, while also determining amounts of deposited carbon by aromatic hydrocarbons tend to form carbon covered detecting the emission behaviour of lattice oxygen in/on active sites of catalyst and this deactivates the catalyst. the perovskite oxide. Analysis of lattice oxygen release and proposed reaction mechanism. Catalysis Applications | 3
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Syngas One of the most diverse areas of heterogeneous catalysis involves the use of synthesis gas or syngas. This gas comprises a mixture of carbon monoxide and hydrogen and is typically produced either by oxidising coal with steam or by the partial oxidation of methane. Syngas can be used to produce a wide range of products such as fertilizers, fuels, solvents and synthetic materials. The scheme below shows some of the range of processes that involve syngas. Cellulose acetate (CH2)n C+H CH 2O 4 Polyethylene Coal or biomass Methane (polythene) +Cellulose Ru Ni/AI2O3 Acetic acid Alkanes +CO Fe, CO CO+H Cu /ZnO Alcohols 2 CH3OH ‘Syngas’ Methanol Alkenes Rh Zeolite Ag compounds CH HCHO 3 Zeolite formaldehyde CH2OH CH4+O2 Natural gas CH2OH (CH2)n Polymers and related Petrol glycols Toluene HYDROGEN PRODUCTION evolution monitored by the HPR-20 gas analyser, it was found that zirconia supported NiO exhibited good redox Steam reforming of methane is a method for producing activity and stability during multiple CH4 reduction-air syngas and is the dominant process for industrial hydrogen oxidation cycles. production today. The complete process involves multiple steps and severe operating conditions. Although a mature process, steam reforming remains very energy intensive and emits a significant amount of CO2, aggravating global warming. The study here looks at sorption enhanced chemical looping steam methane reforming (SE-CL-SMR), a novel low-carbon process for hydrogen production. The redox activity and stability of NiO-based materials was investigated by performing methane reduction/air oxidation cycles in a thermogravimetric analyzer (TGA) unit. Evolution of gaseous products during the methane and air oxidation step as a By analysing the weight changes and gaseous species function of time in a typical redox cycle for 40%NiO/ZrO2. 4 | Catalysis Applications
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Operando Spectroscopy Operando spectroscopy is an analytical methodology that combines spectroscopic characterization with simultaneous measurement of catalytic activity and selectivity. The main concern of this methodology is to determine structure-reactivity or selectivity relationships of catalysts and thereby yield information about mechanisms. It also has applications in engineering improvements to existing catalytic materials and processes and in developing new ones. OPERANDO SPECTROSCOPY This technique allows the study of the relationship between the structural/compositional changes in AB with hydrogen Operando Raman-Mass Spectrometry investigation of desorption properties in order to elucidate the mechanisms hydrogen release by thermolysis of ammonia borane of decomposition, as well as, to clarify the benefits of confined in mesoporous materials. dispersion and destabilization of AB by nanoconfinement. Ammonia borane (NH3BH3, AB hereafter) is a white crystalline inorganic solid with 19.6 wt. % mass content of hydrogen whose thermal decomposition releases up to 2 equivalents of hydrogen below 200 ºC and therefore constitutes a promising hydrogen storage material. However, the application of AB is hindered by slow hydrogen release kinetics among other factors. Confinement of AB in scaffolding nanoporous materials has shown to improve its performance in terms of lower decomposition temperature, better kinetics and suppression of volatile impurities. However, hydrogen release mechanisms are still unclear. In this work, hydrogen thermal desorption from AB, which has been incorporated into various mesoporous carriers, has been investigated by means of operando Simultaneous acquisition of Raman spectra and Mass spectrometry profiles Raman - Mass Spectrometry methodology which consists for gases evolved during thermal decomposition of AB impregnated in in using a combination of real-time Raman spectroscopy porous SBA-15 materials. measurements and simultaneous on-line analysis of During operando Raman-MS measurements, each sample was linearly heated at 1ºC·min-1 up to 200 ºC under a 50 mL·min-1 99.9995 % N2 flow the effluents by the HPR-20 gas analyser. and Raman spectra were acquired every 600 seconds. Catalysis Applications | 5
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Catalyst Characterisation For many catalysts it is not only important to understand how a catalysts performs during a chemical reaction, it is also desirable to know about the physical properties of the catalyst. By obtaining knowledge of the physical properties this information can be used to design and adapt new catalyst technology. The important properties to understand include metal surface area of the active catalyst material, the dispersion of metal catalyst on the support structure and the number and type of reaction sites of the catalyst. Characterisation techniques such as temperature programmed as the QGA or HPR-20 R&D are used in many research desorption (TPD), reduction (TPR) and oxidation (TPO) and pulse laboratories with a variety of reactors or can be coupled to chemisorption can be used to elucidate many of the physical the Hiden CATLAB microreactor to utilise these techniques properties of the catalyst. The Hiden gas analysis systems such and provide a better overall understanding of the catalyst. NH3 TPD of desorbed NH3 and H2O, thus overcoming a limitation of the TCD detector. The surface acidic properties of a heterogeneous catalyst By tuning of the ionization potential in the ion source of the can be probed using a combination of a basic molecule HPR-20 gas analyser, it is possible to avoid H O molecule such as ammonia and the technique of temperature 2 fragmentation and related interferences with the NH m/z programmed desorption (TPD). 3 signal allowing accurate and reliable measurements and The study shown here is of the surface acidic properties flexibility in the technique employed. of oxide catalysts and carriers (Al2O3, CeO2, ZrO2, SiO2, TiO2, HZSM-5 zeolite), comparatively probing their surfaces by NH3 TPD measurements. This TPD measurement is a simple and reliable technique in which a surface, after saturation with NH3 at low temperature, is subject to a linear temperature ramp, which causes desorption of the probe molecule along with a temperature profile. By qualitatively and/or quantitatively analysing the desorption pattern, it is possible to obtain information about the adsorption/ desorption energy and the quantity of NH3 that has been adsorbed on the surface (NH3 uptake). This information can help understand the catalytic behavior of a sample, or even help in fine tuning the synthesis of new systems. Instead of using a traditional TCD Detector for this task, the HPR-20 gas analyser was used and allows for the separate analysis 6 | Catalysis Applications
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CHARACTERISATION OF H2 PRODUCTION CATALYSTS Hydrogen as an energy transport medium in combination with fuel cells is one of the emerging energy solutions in terms of sustainability and low environmental impact. There are a variety of methods for the production of hydrogen such as the partial oxidation of methane, steam reforming of methanol or ethanol and ammonia decomposition. CH4 conversion at 750 °C vs time. Conventional vs protected Rh(1wt%)/Al2O3 The top data shown here demonstrates the methane conversion reaction, collected using the HPR-20 gas analyser and is used to prove the superior thermal stability, during methane partial oxidation, of an innovative embedded Rh/Al2O3 catalyst with respect to conventional impregnated material. The second data set shown here is the comparison of the characterisation of an embedded and impregnated Ru/ZrO2 based catalyst during the ammonia decomposition reaction. NH3-TPD on embedded Ru/LSZ and impregnated Ru/LSZ catalysts. Finally, the amount and nature of coke deposited is evaluated by temperature programmed oxidation (TPO) during ethanol steam reforming on Cu/ZnO/Al2O3 based catalyst. Coke characterisation by TPO after ethanol steam reforming on Cu/ZnO/ Al2O3-C (a), Co/Cu/ZnO/ Al2O3-C (b) and Ni/Cu/ZnO/ Al2O3-C (c) and TGA analysis of the same samples (d). Catalysis Applications | 7
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Automotive Probably the most familiar use of catalysis in the wider public is the use of catalytic converters in vehicles. This automotive catalyst is used in the exhaust system of vehicles to control the emission of harmful gases, such as hydrocarbons, carbon oxides, nitrogen oxides, and other particulate matter, into the atmosphere. The catalyst helps convert harmful gases into less toxic gases such as nitrogen and carbon dioxide. NOX REMOVAL However, the reaction mechanism is not well-understood especially when using typical reaction conditions and the NOx storage and reduction (NSR) or lean NOx trap Hiden gas analysis systems can be used to investigate the (LNT) catalysts are considered to be one of the most effects of using different reactants in both lean and rich promising technologies for NOx removal from lean burn periods. The figures below show the evolution of different engine exhausts. In the NSR reaction, NOx is stored under nitrogen containing species during lean and rich periods in lean conditions and then reduced by H2 or CO LNT regeneration. or hydrocarbons to N2 during a short rich period. Evolution of 15N or 14 2 NO (m/e=30), 14N2 (m/e=28) and 15N14N (m/e=29) during LNT regeneration, in the presence of 14NO (red points) or 15NO (black points). (a) 190 ºC; (b) 340 ºC. 8 | Catalysis Applications
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Typically the analysis of automotive catalyst performance is performed by analysing the gas at the exit of the exhaust. However there are often different regions of the catalyst monolith which control different parts of the reaction. It is possible to probe these different reaction zones within the monolith by a capillary inlet system inside the monolith channels – SpaciMS. SpaciMS The SpaciMS consists of a number of capillaries that can be used to determine gaseous species and temperature The automotive catalyst used in the exhaust system of profiles in both a radial and axial orientation, with high vehicles is typically based on a metal or combination of spatial and temporal resolution, allowing mapping of metals being deposited on an inert monolithic material. temperature and species distribution. The example here The use of a monolith greatly enhances the surface area shows how the CO, CO2 and NO concentration changes of the material compared with the same weight of along the length of a catalyst monolith. powdered material and therefore enhances the performance of the overall catalyst. However, the effect that the shape of the monolith has on the catalyst efficiency is not well understood. To probe the effect of the monolith spatially resolved capillary inlet mass spectrometry (SpaciMS) has been used. 2.5cm NO CO2 CO Catalysis Applications | 9
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Surface Chemistry Catalytic reactions can only occur at the surface of the catalyst. Therefore determining how molecules interact with a surface is important when trying to understand these reactions. The adhesion of gas or liquid molecules to the surface is known as adsorption. This can be due to either chemisorption or physisorption, and the strength of molecular adsorption to a catalyst surface is critically important to the catalyst’s performance. However, it is difficult to study these phenomena in real catalyst particles, which have complex structures. Instead, well-defined single crystal surfaces of catalytically crystals multi-component materials systems can be active materials such as platinum are often used as model produced by growing ultra-thin films or particles on single catalyst and are studies under ultra high vacuum (UHV) metal crystal surfaces. conditions allowing much greater control of surface Understanding catalysts at a fundamental level can be conditions for analysis. In addition to studying single metal used to develop the next generation of catalytic materials. CO TEMPERATURE PROGRAMMED DESORPTION A commonly used technique to probe surfaces at UHV is temperature programmed desorption (TPD). The data shown here probes the dynamics of Fe intercalation on pure and nitrogen doped graphene grown on Pt(111) by CO adsorption/desorption. The CO TPD profiles compare the intercalation rate of iron (Fe) nanoparticles supported on pure graphene (G) and nitrogen doped graphene (N-G) grown on platinum Pt(111) single crystal. Carbon monoxide (CO) desorption from Fe sites is used to probe the overall quantity of Fe present on the surface. It is seen that a faster intercalation occurs when the Fe nanoparticles are deposited on N-G with respect to those supported on pure G. This phenomenon can be related to nanoholes created by pyridinic and pyrrolic functionalities and/or to the lower bond enthalpy of C-N with respect to C-C Upper: representation of the temperature vs time for the CO-TPD bonds, which allow the formation of transient holes in experiment. the graphene layer. Lower: cycles of CO-TPD (CO on Fe deposited on G/Pt(111) (left) and N-G/Pt(111) (right). 10 | Catalysis Applications
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Kinetic parameters of catalyst-surface reaction intermediates, One of the most useful techniques to obtain this information such as concentration, site coverage, reactivity, and rate on catalysed heterogeneous reactions at, or near to, constants can be obtained and processed to provide valuable molecular level is the Steady-State Isotopic Transient Kinetic information about the reaction mechanism. Analysis (SSITKA) METHANE OXIDATION BY SSITKA The catalytic process of complete methane oxidation is a highly promising alternative to flame combustion, because it makes it possible to reduce the emission of NOX, CO and non-oxidized hydrocarbons into the Earth’s atmosphere. Some of the most active catalytic materials for complete methane oxidation are supported palladium and platinum catalysts. These active metals demonstrate very high activity and selectivity. Additionally their resistance to high temperature and mechanical damage provides further benefits to their use. However, for the wide application of palladium and platinum catalysts in the industry, there is still a need for clear answers to many important questions. One of the most crucial issues is the reaction mechanism of complete methane oxidation over palladium and platinum catalysts. Here the reaction mechanism is probed using fast switching of isotopically labelled reactant and following the products with the Hiden gas analysis system. A typical model recommended for SSITKA measurements is the fast response Hiden HPR-20 TMS featuring the HAL 3F PIC detector. Effect of the switching between reaction streams including 16O2/Ar/CH4/ He and 18O2/Kr/CH4/He (X is the conversion of methane). Catalysis Applications | 11
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Electrocatalysis Electrocatalysis can be defined as the heterogeneous catalysis of electrochemical reactions, which occur at the electrode–electrolyte interface and where the electrode plays both the role of electron donor/acceptor and of catalyst. Mass spectrometry (in combination with electrochemical methods) is a powerful technique which allows both evolved off-gas and dissolved species analysis to be performed in real-time. EFFECTS OF IMPURITIES ON FUEL CELL PERFORMANCE (figure d) appear around the hydrogen evolution peak, indicating A fuel cell is an electrochemical cell impurities in the hydrogen feed gas the formation of methane and that converts the chemical energy of affects the performance of the fuel cell ethane at these low potentials. a fuel (often hydrogen) and an is important. Using mass spectrometry These results demonstrate that oxidizing agent (often oxygen) into combined with electrochemical traces of ethene in the hydrogen electricity through a pair of redox techniques gives information on not feed have a minimal effect on the reactions. The catalyst used in a only how the cell performance is performance of this PEM fuel cell. certain class of fuel cells (that use affected, but an indication of why. 20 hydrogen as a fuel) can be severely a) Using ethene as an example impurity, 10 affected by some of the impurities in 0 three different cyclic voltammograms the hydrogen while other impurities −10 (CVs) were recorded (figure a); a base −20 will have little or a moderate effect. CV, recorded in pure argon (grey), a −30 Knowledge of how and to what −400 0.2 0.4 0.6 0.8 1 1.2 CV recorded in a continuous flow of Potential / V vs DHE 20 extent the presence of different b) E = 1.2 V E = 0.1 V 100 ppm ethene contaminated argon 10 0 (blue), and a stripping CV, where the −10 −20 electrode has been exposed to ethene −30 −40 contaminated argon for some time 0.10 c) 0.08 m/z = 44 followed by purging the system prior 0.06 to recording the CV (red). The oxidation 0.04 0.02 peaks around 0.6 V (shown at 30 and 0 −0.02 145 seconds in the continuous CV scan 0.06 d) 0.04 (figure b)) corresponds nicely with the 0.02 m/z = 44 signal attributed to CO m/z = 15 2 0 (figure c), indicating that adspecies m/z = 30 −0.02 originating from ethene are oxidised m/z = 43 −0.040 20 40 60 80 100 120 140 160 180 200 to CO at potentials > 0.35 V vs RHE. time / s 2 The signals at m/z = 15 and 30 Cyclic Voltammograms recorded in a fuel cell at 80°C and 90%RH, at a scan rate of 10 mV s-1 and Labelled Fuel Cell during operation. recorded in 100 ppm ethene/argon selected m/z signals. 12 | Catalysis Applications Partial pressure / μbar Current density / mA (mg Pt) −1
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VALORISATION OF BIOMASS-DERIVED FEEDSTOCKS Electrocatalysis poses several potential advantages for the valorisation of biomass-derived feedstocks, most importantly its ability for direct conversion in acidic aqueous media. Some biomass derivatives can be converted to valuable products and precursors via partial oxidation. Combining such partial oxidations with H2 evolution or other reduction reactions (e.g. CO2) in an electrochemical cell presents an opportunity to perform electrolysis at lowered voltages, while coproducing products that are more valuable than O2. Voltammetric stripping (solid line) paired with CO -OLEMS (dotted line) On-Line Electrochemical Mass Spectrometry (OLEMS) 2 for furfural (100 mM, orange), HFN (5 using the HPR-40 gas analyser system in combination with mM, red), furan (saturated, magenta), FA (100 mM, blue), and MA (100 mM, a custom-built flow-through electrolysis cell and other yellow) after 300 s adsorption periods characterisation techniques has been used to probe the at 0.3 VRHE on Pt black in 0.25 M HClO . oxidative reaction pathways of furfural on platinum 4 catalysts in acidic electrolyte. In order to investigate the performance of the electrocatalyst and the potential reaction pathways in operation, the decomposition of furfural and several of its partially oxidized derivatives to CO2 was performed using voltammetric stripping experiments with simultaneous OLEMS. Trends in the relative yield of CO2 to other products provide insight into the relative stability and surface chemistry of each adsorbed species. Voltammetric stripping with a 5 mV/s ramp and This technique is similar in methodology to temperature hold program (a), with programmed desorption studies typically performed Faradaic responses (b) paired with CO2-OLEMS in heterogeneous catalysis. Based on the results from (c) after 5 min this research, a reaction pathway and guide for the adsorption periods of CO (saturated), 100 mM design of more active and selective electrocatalysts furfural, 100 mM FA, has been proposed. furan (saturated), and 100 mM MA in 0.25 M HClO4on Pt Black. Catalysis Applications | 13
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Biocatalysis Biocatalysis refers to the use of living systems or their parts to speed up chemical reactions. In biocatalytic processes, natural catalysts such as enzymes perform chemical transformations on organic compounds. Enzymes have pivotal role in the catalysis of hundreds of reactions that include production of alcohols from fermentation and cheese by breakdown of milk proteins. Currently, there are many different biocatalytic processes that have been implemented in various pharma, biochemical, food, and agro-based industries. With further development, enzymes could also catalyse many of the industrial reactions that produce the chemicals and materials that are essential for our modern world. MEASUREMENT OF GENERATED NITRIC OXIDE Membrane inlet mass spectrometry (MIMS) is a reproducible and reliable method for the measurement of nitric oxide in aqueous solution with a lower limit of detection of 10 nM and a linear response to 50 µM. The HPR-40 gas analyser (with the specially designed enzyme compatible inlet) has been used to develop an enzyme assay for nitric oxide synthase. Shown below are the measurement of NO generated chemically from nitrite and MAHMA NONOate as well as enzymatically by nitric oxide synthase (NOS). Calibration of the m/z 30 ion current by the (A) stepwise addition of sodium nitrite to the reaction vessel. (B) MIMS calibration curve relating nitrite derived NO to ion current. HPR-40 Enzyme Kinetics Probe. MIMS calibration curve relating MAHMA NONOate Direct, continuous, real-time assay generated nitric oxide to ion current at m/z 30 measuring enzymatically generated NO. showing the linear response to 50 µM. 14 | Catalysis Applications
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OXALATE OXIDASE ENZYME Oxalate oxidase is a manganese containing enzyme that catalyzes the oxidation of oxalate to carbon dioxide in a reaction that is coupled with the reduction of oxygen to hydrogen peroxide. Oxalate oxidase from Ceriporiopsis subvermispora (CsOxOx) is the first fungal and bicupin enzyme identified that catalyzes this reaction. Potential applications of oxalate oxidase for use in pancreatic cancer treatment, the prevention of scaling in paper pulping, and in biofuel cells have highlighted the need to understand the extent of the hydrogen peroxide inhibition of the CsOxOx catalyzed oxidation of oxalate. A membrane inlet mass spectrometry (MIMS) assay The production of 13CO2 and consumption of O2 (in arbitrary ion currents) (using the HPR-40 gas analyser and a special designed during the CsOxOx catalyzed oxidation of 13C2-mesoxalate. The ion currents enzyme compatible inlet) was used to directly measure initial for the dissolved gases at their respective peak heights were recorded: blue, CO2 at m/z 45; orange, O2 at m/z 32. rates of carbon dioxide formation and oxygen consumption in the presence and absence of hydrogen peroxide (top figure). In order to distinguish the CO2 generated by CsOxOx from CO2 dissolved in the reaction mixtures, 13C labelled oxalate was employed. The bottom data shown (performed with and without hydrogen peroxide present) do not appear to have significant different x-intercepts and they are not significantly different from zero suggesting that CsOxOx is not inactivated upon addition of hydrogen peroxide within the time frame of the kinetic assay. The curve with hydrogen peroxide present has a smaller slope and goes through the approximate origin which is consistent with hydrogen peroxide being a reversible non-competitive inhibitor of the CsOxOx catalyzed oxidation of oxalate and an irreversible inactivator. The build-up of the turnover-generated hydrogen peroxide product leads to the inactivation of the enzyme. The introduction of catalase to reaction mixtures protects Plot of Vmax app versus [E]t of the CsOxOx catalyzed oxidation of oxalate with (blue, 10 mM) and without (black) hydrogen peroxide present. Each point the enzyme from inactivation allowing reactions to proceed represents a Vmax app determination at five concentrations of oxalate (0.2, 0.5, to completion. 1.0, 5.0, and 10.0 mM). Catalysis Applications | 15
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Plasma Catalysis The combination of a plasma discharge with material that has catalytic properties is known as plasma catalysis. Although a range of plasmas could be used, the most common are non-thermal, atmospheric pressure plasmas and solid catalysts with gas phase reactions. Plasma catalysis is gaining increasing interest for various gas created in the plasma. Plasma consist of a mixture of many conversion applications, such as CO2 conversion into value- different types of reactive species such as electrons, ions, added chemicals and fuels, synthesis of NH3 from N2 fixation radicals and neutral gas molecules, but due to the nature or NOx, and CH4 conversion into higher hydrocarbons or of these species the selectivity of the reactions are difficult oxygenates. Additionally, it has been shown to be useful for to control. air pollution control by reducing volatile organic compounds On the other hand a catalyst can offer excellent selectivity (VOC’s) in waste gas treatment. but traditionally may need to operate at high temperature Plasma allows thermodynamically difficult reactions to and or pressure. By combining the plasma with a traditional proceed at an ambient pressure and temperature because heterogeneous catalyst new reaction pathways can be the gas molecules are activated by energetic electrons formed under more favourable conditions. NTP ASSISTED METHANE OXIDATION formation, suggesting that CO formation occurs via a different reaction pathway than that of CO2. This CO The effect of Non Thermal Plasma (NTP) was investigated formation is likely to predominantly take place through on the methane oxidation reaction. Methane is difficult to gas phase reaction under plasma conditions. oxidise due to its high C-H bond strength and the reaction has been extensively investigated under standard thermal conditions. Relatively high temperatures are usually required to oxidise methane even over Pt and Pd catalysts especially in the presence of water. The application of NTP offers a low temperature route to methane oxidation. One effective catalytic candidate for this reaction is Pd/Al2O3 This figure shows the influence of plasma voltage on CH4 conversion as well as CO/CO2 productions over 2% Pd/Al2O3. A significant change in gas phase species detected by the HPR-20 gas analyser was observed when increasing the peak voltage from 5 to 6 kV. The conversion increased to 60% over 35 minutes on stream, a similar trend was also observed for the production of CO2. However, the change in CO formation did not follow Changes in CH4 conversion, CO2 and CO formation as a function of plasma the same variation as for the CH4 conversion and CO2 voltage applied to 2% Pd/Al2O3 under 0.5% CH4 + 10% O2 reaction conditions. 16 | Catalysis Applications
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CONTRIBUTORS HETEROGENEOUS CATALYSIS: X Ali Shekari, École Polytechnique de Montréal, Canada X Yasushi Sekine, Waseda University, Japan SYNGAS: X Eleni Heracleous, Angeliki. A. Lemonidou, Dragomir B. Bukur International Hellenic University (IHU), Aristotle University of Thessaloniki, Greece & Texas A and M University at Qatar OPERANDO SPECTROSCOPY: X Maria J. Valero-Pedraza, Instituto de Catálisis y Petroleoquímica, CSIC, Spain CATALYST CHARACTERISATION: X Paolo Fornasiero University of Trieste, Italy X Roberto Di Chio, Università degli Studi di Messina, Italy AUTOMOTIVE: X Sarayute Chansai, Queen’s University Belfast, UK SURFACE CHEMISTRY: X Mattia Cattelan, University of Padova, Italy X Marek Rotko, Andrzej Machocki, University of Maria Curie-Skłodowska, Poland ELECTROCATALYSIS: X K. Kortsdottir, R. W. Lindström, G. Lindbergh, KTH-Royal Institute of Technology, Sweden X A.M. Román, J.C. Hasse, J.W. Medlin, A. Holewinski, University of Colorado, USA BIOCATALYSIS: X J.M. Goodwin, H. Rana, J. Ndungu, G. Chakrabarti, E.W. Moomaw, Kennesaw State University, USA PLASMA CATALYSIS: X S. Chansai, C. Hardacre, University of Manchester, UK Catalysis Applications | 17
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Hiden’s quadrupole mass spectrometer systems address a broad application range in: GAS ANALYSIS dynamic measurement of reaction gas streams catalysis and thermal analysis molecular beam studies dissolved species probes fermentation, environmental and ecological studies SURFACE ANALYSIS UHV TPD SIMS - Quadrupole and ToF end point detection in ion beam etch elemental imaging – 3D mapping Hiden Analytical Ltd. 420 Europa Boulevard Warrington WA5 7UN England PLASMA DIAGNOSTICS T +44 [0] 1925 445 225 F [ ] plasma source characterisation +44 0 1925 416 518 E etch and deposition process reaction kinetic studies info@hiden.co.uk W analysis of neutral and radical species www.HidenAnalytical.com VACUUM ANALYSIS Sales Offices: partial pressure measurement and control of process gases We have sales offices situated around reactive sputter process control the globe. Visit our website for further vacuum diagnostics information. vacuum coating process monitoring TECHNICAL DATA SHEET 209