Non-catalytic Material Research Articles

Non-thermal plasma assisted CO2 conversion to CO: Influence of non-catalytic glass packing materials

The current research is focused on the decomposition of carbon dioxide (CO2) into carbon monoxide (CO) and oxygen (O2) in a non-thermal plasma reactor using dielectric barrier discharge (DBD) at ambient conditions. Pure CO2 was injected into the DBD reactor at a flow rate of 30 mL min-1, and the voltage was varied between 16 kV to 22 kV. The filamentary micro discharges generated during plasma has a significant effect on CO2 conversion. The effect of packing materials on CO2 conversion was investigated by packing non-catalytic materials such as quartz wool, glass capillary, glass wool, and glass beads in the discharge zone of the DBD reactor. Among the studied packing materials, quartz wool exhibited a maximum CO2 conversion of 9.3 % at a discharge power of 2.0 W and specific energy input (SEI) of 4.0 J mL-1. However, glass capillary exhibited the highest energy efficiency of 1.2 mmol kJ-1 at an SEI of 3.5 J mL-1.

Gas-Phase Hydrogen-Atom Measurement above Catalytic and Noncatalytic Materials during Ethane Dehydrogenation

Gas-Phase Hydrogen-Atom Measurement above Catalytic and Noncatalytic Materials during Ethane Dehydrogenation

Numerical study of influence of surface reaction and heat-loss on flame intensity of methane-air flames

This paper reports a numerical study of influence of radical quenching and heat loss on bulk flame characteristics in narrow parallel channels. Flame-wall interaction is an important phenomenon on combustors. Especially, the wall effects on the flame characteristics in a small scale combustor become larger than those on normal scale one. The wall effects are caused by heat loss and surface reaction. The surface reaction on many common non-catalytic materials may weaken or quench the flames, although those for a catalytic wall can strengthen the flames. Authors have investigated the influence of the surface reaction and the heat loss on a noncatalytic wall using numerical simulation. In this study, a two-dimensional slit burner between two parallel plates with or without surface reaction is modelled. The wall temperature is 500 and 1200 K. The flame behavior and heat release rate distributions are examined when the distance between two plates is changed.

Electrocatalytic dechlorination of polychloroethylenes at silver cathode

In this study, silver was considered as a catalytic electrodic material for the reduction of polychloroethylenes for possible application in environmental remediation and/or as an auxiliary process in the industrial chlorination of ethylene for production of vinyl chloride monomer. The electroreduction of tetrachloroethylene (PCE) and trichloroethylene (TCE), which are the most hazardous chlorinated ethylenes, was investigated at a Ag electrode in DMF under conditions of controlled proton availability. For the sake of comparison also 1,1-dichloroethylene (1,1-DCE) and 1,2-dichloroethylene were considered. Voltammetric investigations point out that Ag possesses good catalytic activities for the reduction of PCE, TCE, and 1,1-DCE as attested by the remarkable positive shifts (up to 0.46 V) of the reduction potentials with respect to GC, considered to be a non-catalytic material. In contrast, Ag shows no appreciable catalytic effect for 1,1-DCE. Apart from the case of 1,1-DCE, the presence of acetic acid (HAc) exalts the catalytic activity of silver, increasing the anodic shifts of the reduction potentials to about 0.57–0.70 V with respect to GC. Controlled-potential electrolyses have shown that both PCE and TCE are mainly reduced to acetylene and ethylene with overall yields exceeding 95 % after 100 % conversion. The distribution between these two products as well as formation of intermediates, which however remained always quite low, was found to be affected by the presence of proton donors such as H2O and HAc. A common reduction mechanism observed for both PCE and TCE involves the α,β-elimination of two Cl− ions triggered by the electron transfer. This leads to the formation of dichloroacetylene or chloroacetylene, which are further reduced at the electrode according to a sequential hydrodehalogenation leading to acetylene. The latter can be further reduced to ethylene.

Kinetic and Titration Methods for Determination of Active Site Contents of Enzyme and Catalytic Antibody Preparations

Kinetic characterization of enzymes and analogous catalysts such as catalytic antibodies requires knowledge of the molarity of functional sites. Various stoichiometric titration methods are available for the determination of active-site concentrations of some enzymes and these are exemplified in the second part of this article. Most of these are not general in that they require the existence of certain types of either intermediate or active-site residues that are susceptible to specific covalent modification. Thus they are not readily applicable to many enzymes and they are rarely available currently for titration of catalytic antibody active sites. In the first part of the article we discuss a general kinetic method for the investigation of active-site availability in preparations of macromolecular catalysts. The method involves steady-state kinetics to provide Vmax and Km and single-turnover first-order kinetics using excess of catalyst over substrate to provide the analogous parameters klimobs and Kappm. The active-site contents of preparations that contain only active catalyst (Ea) and inert material (Ei) may be calculated as [Ea]T = Vmax/klimobs. This is true even if nonproductive binding to Ea occurs. For polyclonal catalytic antibody preparations, which may contain binding but noncatalytic material (Eb) in addition to Ea and Ei, the significance of Vmax/klimobs is more complex but provides an upper limit to Ea. This can be refined by consideration of the relative values of Km and the equilibrium dissociation constant of EbS. Analysis of the Ea, Eb, Ei system requires the separate determination of Ei. For catalytic antibodies this may be achieved by analytical affinity chromatography using an immobilized hapten or hapten analog and an ELISA procedure to ensure the clean separation of Ei from the Ea + Eb mixture.

A general kinetic approach to investigation of active-site availability in macromolecular catalysts

A potentially general kinetic method for the investigation of active-site availability in preparations of macromolecular catalysts was developed. Three kinetic models were considered: (a) the conventional two-step model of enzyme catalysis, where the preparation contains only active catalyst (E(a)) and inert (i.e. non-binding, non-catalytic) material (E(i)); (b) an extension of the conventional model (a) involving only E(a) and E(i), but with non-productive binding to E(a) (in addition to productive binding); (c) a model in which the preparation contains also binding but non-catalytic material (E(b)), predicted to be present in polyclonal catalytic antibody preparations. The method involves comparing the parameters V(max) and K(m) obtained under catalytic conditions where substrate concentrations greatly exceed catalyst concentration with those (klim/obs, the limiting value of the first-order rate constant, k(obs), at saturating concentrations of catalyst; and Kapp/m) for single-turnover kinetics, in which the reverse situation obtains. The active-site contents of systems that adhere to model (a) or extensions that also lack E(b), such as the non-productive binding model (b), may be calculated using [E(a)](T)=V(max)/klim/obs. This was validated by showing that, for alpha-chymotrypsin, identical values of [E(a)](T) were obtained by the kinetic method using Suc-Ala-Ala-Pro-Phe-4-nitroanilide as substrate and the well-known 'all-or-none' spectroscopic assay using N-trans-cinnamoylimidazole as titrant. For systems that contain E(b), such as polyclonal catalytic antibody preparations, V(max)/klim/obs is more complex, but provides an upper limit to [E(a)](T). Use of the kinetic method to investigate PCA 271-22, a polyclonal catalytic antibody preparation obtained from the antiserum of sheep 271 in week 22 of the immunization protocol, established that [E(a)](T) is less than approx. 8% of [IgG], and probably less than approx. 1% of [IgG].

触媒性壁面上の熱流束予備試験

This paper describes laboratory experiments of effect of wall catalysis on aerodynamic heating in high- temperature gases. Heat fluxes on two kinds of catalytic material, stainless steel and alumina ceramic, were measured in an arc-heated wind tunnel. Stainless steel was considered as near fully catalytic material whereas alumina ceramic was selected as non-catalytic material. In order to investigate the effect of wall catalysis, heat fluxes were measured in three different arc-keated gases, argon, nitrogen and air. Measured results showed that the stainless steel to alumina ceramic heat flux ratios for air were 38% larger than those for argon and nitrogen. This implies that the recombination of oxygen atoms on the wall due to catalysis of wall material partly controls heat flux.

Proposed Mechanism of CO Mitigation in PEMFCs by Using Dilute H2O2 in the Anode Humidifier

CO poisoning in proton exchange membrane fuel cells (PEMFCs) can be mitigated by using dilute H 2 O 2 in the anode humidifier. However, mitigation appears to be provided by an unintended O 2 bleed produced by decomposition of H 2 O 2 in the humidifier, rather than by H 2 O 2 vapors transported from the humidifier to the anode. CO mitigation was effective when significant levels of O 2 were present in the anode feed. The effectiveness of CO mitigation disappeared when non-catalytic materials were used to suppress H 2 O 2 decomposition in the humidifier. (Safety Note: H 2 O 2 decomposition in the anode humidifier may produce flammable compositions in the anode feed).

Control of Volatile Organic Compounds by the Catalytic Reverse Process

The catalytic reverse process employs a fixed catalyst bed placed between two beds of noncatalytic material. The gas flow direction in such a «sandwich» is periodically switched from one end to the other. Using a mathematical model of this unsteady-state process, this work discusses the efficiency of the catalytic reverse process for the purification of industrial off-gases containing various volatile organic compounds. A method of process economics optimization is considered. Advantages of the catalytic reverse process in comparison with the traditional steady-state catalytic and regenerative incineration processes of volatile organic compound control are discussed. Potential application of the reverse process and first steps made in this direction by industry are discussed

Stirred autoclave apparatus for study of the Fischer-Tropsch synthesis in a slurry bed. 1. Reactor and trapping procedures

A mechanically stirred autoclave provides advantages over other types of reactors for fundamental studies of liquid-phase Fischer-Tropsch synthesis, but no information appears to have been published on such use. Particular attention must be paid to obtaining complete suspension of the catalyst, use of non-catalytic materials of construction, and procedures to avoid loss of portions of the wide range of products formed. Many of the aspects of design and operation are applicable to stirred autoclave reactors in general.

Chemical factors in carbon brush wear

Chemical factors involved in the wear of carbon brushes on metal slip rings are discussed. Under conditions of elevated temperature operation in an oxidizing atmosphere, a correlation is found between the oxidation characteristics and the wear rates of carbon brushes. It is demonstrated that temperatures in the oxidation range can readily be generated by current converging through high resistance constrictions in the contact zone. Copper and other metals present in the slip ring can act as catalysts for the oxidation, the metal oxide particles migrating into the interior of the brush and causing enhanced gasification rates and increased porosity. Treatment of the brush with oxidation inhibitors, such as phosphorus oxychloride, and surface alloying of the ring with non-catalytic materials, such as zinc, can reduce the wear rate at elevated temperatures under favorable conditions. Graphite surfaces are also attacked by reactive gaseous species such as atomic nitrogen and oxygen, ozone and nitrogen oxides which may form near the brush surface during arcing.

Surface catalysis in dissociated, chemically frozen air boundary layers with variable transport properties

This work is concerned with the effects of surface catalysis and variable transport properties on the structure of chemically frozen, dissociated air boundary layers enveloping flat plates and slender wedges. Our main interest is in nonsimilar hypersonic flows past catalytic segments placed aft of leading edges or stagnation points coated with noncatalytic materials. The problems are solved numerically; the method of solution is shown to be reliable and applicable in general to the solution of nonsimilar boundarylayer equations. Local convective heat transfer and heat release due to catalysis of atoms are computed separately. These results show that variable transport properties and non-similarity of the flow field have a significant influence on the heat flux due to catalysis and suggest possible serious errors in available diagnostic formulas for catalytic gauges.