Reactions of coal with discharge-generated (excited) nitrogen species

Reaction between coal and nitrogen in a discharge furnishes hydrogen cyanide and smaller amounts of cyanogen, as well as some carbon monoxide and carbon dioxide; the cumulative yields of hydrogen cyanide and cyanogen depend upon rank. The apparent activation energies for formation of hydrogen cyanide and cyanogen are in the order of 2–4 kcal mol⁻¹ but increase sharply to ≈13–14 kcal mol⁻¹ at ≈200 °C (possibly coincident with incipient thermal decomposition of the coal). The cyanogen/hydrogen cyanide ratio increases with rank, and also depends upon the reaction temperature — falling with increasing temperature up to ≈200 °C, and thereafter rising progressively. Rate measurements and i.r. spectral changes accompanying the reaction suggest that hydrogen cyanide is mainly formed from non-aromatic carbon-hydrogen configurations in the coal, and that cyanogen derives for the most part from aromatic carbon — though some can also be generated from non-aromatic CH in competition with formation of hydrogen cyanide.     

Reaction of coal with nitrogen in a microwave discharge

In a microwave discharge in nitrogen, high-volatile bituminous coal produces gaseous products, namely hydrogen cyanide, acetylene, small amounts of cyanogen and lowmolecular-weight hydrocarbon gases, and nitrogen-containing compounds, in addition to the usual hydrogen and carbon oxides. The reaction of coal in the nitrogen discharge occurs in two stages: interaction of active nitrogen with the coal molecule to cause rapid volatilization of gaseous products, and slow gasification of residual char by active nitrogen. Various factors influencing product type, yield, and distribution are examined. Under conditions where the gaseous products can be quickly quenched or removed, as by trapping at a very low temperature, more than 42% of carbon in the coal can be converted mainly to hydrogen cyanide and acetylene, which together constitute about 90% of the total products.     

Catalysis with homogeneous membranes loaded with nanoscale metallic clusters and their preparation

Catalytically powerful, non-porous membranes were manufactured from two highly gas permeable poly(amide imides) consisting of structures with moieties of 3,3'-dimethylnaphthidine and hexafluoroisopropylidene (6F) or hexafluoroisopropylidene 2,2-bis(phthalic acid anhydride) (6FDA) and 6F. The catalysts are pure precious metals or precious metal alloys dispersed on a nanoscale uniformly throughout the membrane. The membranes are characterized by electron microscopy, gas permeability, hydrogen uptake and, as a model reaction, the decomposition of nitrous oxide by hydrogen to nitrogen and water catalyzed by Pd/Ag. The permeance to hydrogen and nitrous oxide is round 2–10^-6 cm³ (STP) /cm²·s·cmHg for membranes of 40–50μm in thickness.     

Catalytic radiant burner for stationary and mobile applications

In present discussions on energy conversion processes aimed at producing both thermal and process heat, catalytic burners provide an alternative approach for future applications. Catalytic burners are advantageous in that they cause only low pollutant emissions during the process of converting chemical energy into heat. In addition, novel engineering concepts require the complete combustion of a variety of fuels and fuel mixtures. Against this background, a novel catalytic radiant burner was developed at the Research Centre Jülich. Under near-stoichiometric conditions, this catalytic burner burns both natural gas with hydrogen admixture in a heat recovery boiler for stationary heat production and methanol with hydrogen admixture in a reformer producing process heat to be used in a fuel cell drive system. The emission data of the catalytic heater were recorded at a nominal power of 11.5 kW, a nominal air/fuel ratio of 1.15 and different hydrogen ratios between 0% and 50% and were 7–3 mg/kW h for carbon monoxide and 3.3–3.9 mg/kW h for nitrogen oxides. The test runs for a catalytic burner to be used for heating a compact reformer in a fuel cell vehicle were carried out at a power density of 15–60 kW/m², a nominal air/fuel ratio of 1.1 and different hydrogen, carbon dioxide and water ratios. For nitrogen oxides emissions of less than 0.4 mg/kW h, the measured carbon monoxide amount ranges between 0 and 13 mg/kW h.     

Selective reduction of nitric oxide with propene over platinum-group based catalysts: Studies of surface species and catalytic activity

The reduction of nitric oxide by propene in the presence of oxygen over platinum-group metals supported on TiO₂, ZnO, ZrO₂, and Al₂O₃ has been investigated by combined diffuse reflectance FT-IR spectroscopy and catalytic activity studies under flow reaction conditions at 523–673 K and atmospheric pressure. The catalytic activity for the selective reduction of nitric oxide and the intensity of the IR bands due to reaction species depended strongly on the nature of the support, type of supported metal, reaction time and temperature. The main surface species detectable by IR were adsorbed hydrocarbons (2900–3080 cm⁻¹), isocyanate (2180, and 2232–2254 cm⁻¹), cyanide (2125 cm⁻¹), nitrosonium (1901 cm⁻¹), CO₂ (2343–2357 cm⁻¹), CO (2058 cm⁻¹) and carbonate (1300–1650 cm⁻¹) species. In the case of rhodium containing catalysts, when supported on Al₂O₃, they exhibited both the highest concentration of surface species and the highest activity for nitric oxide reduction and selectivity to nitrogen. The catalytic activity and the IR intensities of the nitrosonium and isocyanate bands increased with reaction temperature, reached their maximum between 570 and 620 K, and then decreased at higher temperatures. The IR band intensities due to nitrogen containing surface species were found to be strongly correlated to the activity for nitric oxide conversion and only slightly related to the selectivity to dinitrogen.     

Evolution of toxic gases from heated plastics

A brief investigation has been carried out into the nature and quantity of the toxic gases evolved during the thermal decomposition of polyurethane, urea-formaldehyde, nylon and acrylonitrile in air and in nitrogen. The weight fractions of the polymers evolved as hydrogen cyanide are given, together with the lowest temperatures at which hydrogen cyanide, carbon monoxide, ammonia and nitrogen oxides are evolved. Apparent activation energies for the evolution of hydrogen cyanide and carbon monoxide have been determined. A brief discussion of the experimental data is given.     

Reactions of acetylene and ammonia in a continuous-flow microwave discharge reactor

Both pure acetylene and mixtures of acetylene and ammonia have been passed continuously through a microwave discharge reactor. The reaction products from the gas mixtures were hydrogen cyanide, hydrogen and nitrogen. When the input reactant ratio (ammonia to acetylene) was below a critical value, the extent of reaction was negligible. When the critical ratio was exceeded, high conversions were obtained. When reaction did occur, the conversions of both reactants were linear functions of the power absorption in the discharge. The conversion of acetylene to hydrogen cyanide varied linearly with the input volumetric flow rate. Comparison of the present work with previous studies shows that hydrogen cyanide is not produced exclusively by the route when mixtures of benzene and ammonia react in a microwave discharge.     

Study of the NOχ reaction with reducing gases on Fe/ZrO2 catalyst

The Fe/ZrO₂ catalyst (1% Fe by weight) shows a strong adsorption capacity toward the nitric oxide (at room temperature the ratio NOFe is ca. 0.5) as a consequence of the formation of a highly dispersed iron phase after reduction at 500–773 K. Nitric oxide is adsorbed mainly as nitrosyl species on the reduced surface where the Fe²⁺ sites are prevailing, but it is easily oxidised by oxygen forming nitrito and nitrato species adsorbed on the support. However, in the presence of a reducing gas such as hydrogen, carbon monoxide, propane and ammonia at 473–573 K the Fe-nitrosyl species react producing nitrogen, nitrous oxide, carbon dioxide and water, as detected by FTIR and mass spectrometers. The results show that nitric oxide reduction is more facile with hydrogen containing molecules than with CO, probably due the co-operation of spillover effects. Experiments carried out with the same gases in the presence of oxygen show, however, a reduced dissociative activity of the surface iron sites toward the species NO_χ formed by NO oxidation and therefore the reactivity is shifted to higher temperatures.     

Graphite nanofibers prepared from catalytic graphitization of electrospun poly(vinylidene fluoride) nanofibers and their hydrogen storage capacity

Electrospun poly(vinylidene fluoride) nanofibers were carbonized with iron(III) acetylacetonate to induce catalytic graphitization within the temperature range 800–1800 °C. Carbonization in the presence of the catalyst produced graphite nanofibers (GNFs). Their structural properties and morphology were investigated. GNFs with a high surface area of 377–473 m²/g showed the typical Type II containing mesopore in nitrogen adsorption–desorption isotherms. The hydrogen storage capacity of these GNFs was evaluated by the gravimetric method using a magnetic suspension balance (MSB) at room temperature and about 80 bar. The hydrogen storage capacity was 0.11–0.18 wt.%. The effective pore size for hydrogen storage compared to the diameter of the hydrogen molecule is discussed.     

Carbon gasification in the presence of metal catalysts

The development of new processes for the production of gaseous fuels from carbon-containing solids is essential in meeting the energy needs of the nation. In this paper, catalysed carbon gasification is examined. The change in the reactivity of the interface between gaseous reactant (hydrogen or steam) and solid carbon has been measured in the presence of various metal catalysts. With platinum it is found that over a range of temperatures the specific rate of methane production is of the same magnitude as the rate of hydrogen atomization. The catalytic effect is interpretable in terms of an enhanced rate of hydrogen dissociation on the metal surface, followed by surface diffusion across the metal/carbon interface and reaction with carbon. The gas formation rate during the interaction of water vapour with catalyst-activated carbons has been increased by more than an order of magnitude by depositing small weight fractions of active metal catalyst on the carbon surface. At the temperatures employed in this study (975–1175 K), carbon monoxide and hydrogen are the products of the catalysed reaction for each of the catalysts examined.     

Nitrogen evolution during rapid hydropyrolysis of coal

The behavior of nitrogen evolution during rapid hydropyrolysis of coal has been investigated at temperatures ranging from 923 to 1123 K and hydrogen pressure up to 5 MPa using a continuous free fall pyrolyzer. Three coals have been tested in this study. The dominant nitrogen gaseous species is ammonia, together with a little amount of HCN because most of HCN is converted to NH₃ through secondary reactions. The results show that the evolution of nitrogen in coal is caused mainly by devolatilization at temperatures below 973 K, while the evolution of volatile nitrogen in char is accelerated with increasing temperature and hydrogen pressure. The mineral matter in coal act as catalysts to promote the evolution of volatile nitrogen in char to N₂ apparently at high temperatures of 1123 K, as found during pyrolysis of coal by Ohtsuka et al. A pseudo-first-order kinetic model was applied to the evolution of nitrogen in coal during rapid hydropyrolysis. The model shows the activation energy for the nitrogen evolution from coal is 36.6–58.6 kJ/mol while the rate of the nitrogen evolution depends on hydrogen pressure in the order of 0.16–0.24.     

Oxidation of H2S on activated carbon KAU and influence of the surface state

Properties of the oxidized activated carbon KAU treated at different temperatures in inert atmosphere were studied by means of DTA, Boehm titration, XPS and AFM methods and their catalytic activity in H₂S oxidation by air was determined. XPS analysis has shown the existence of three types of oxygen species on carbon catalysts surface. The content of oxygen containing groups determined by Boehm titration is correlated with their amount obtained by XPS. Catalytic activity of the KAU catalysts in selective oxidation of hydrogen sulfide is connected with chemisorbed charged oxygen species (O_3.1 oxygen type with BE 536.8–537.7 eV) present on the carbons surface.

Formation of dense sulfur layer (islands of sulfur) on the carbons surface and removal of active oxygen species are the reason of the catalysts deactivation in H₂S selective oxidation. The treatment of deactivated catalyst in inert atmosphere at 300 °C gives full regeneration of the catalyst activity at low temperature reaction but only its partial reducing at high reaction temperature. The last case is connected with transformation of chemisorbed charged oxygen species into CO groups.

The KAU samples treated in flow of inert gas at 900–1000 °C were very active in H₂S oxidation to elemental sulfur transforming up to 51–57 mmol H₂S/g catalyst at 180 °C with formation of 1.7–1.9 g S_x/g catalyst.     

Effect of hydrogen on the mesopore development of pitch-based spherical activated carbon containing iron during activation by steam

In the present paper, pitch-based spherical activated carbon (PSAC) was activated by steam under various carrier gases such as nitrogen, mixture of nitrogen and hydrogen (H₂/N₂: 1/3 mol/mol) and pure hydrogen. The results showed that hydrogen inhibited the uncatalyzed C–H₂O reaction while accelerated the iron-catalyzed one. Furthermore, the effects of hydrogen became much more remarkable as the proportion of hydrogen increased. In this case, the ratio of mesopore volume of the resultant PSAC increased, but the micropore volume and micropore surface area decreased remarkably. The ratio of mesopore could reach more than 90%, and the mesopore mainly distributed at 10–50 nm. Thus, the PSAC with higher ratio of mesopore can be prepared by the aid of hydrogen as well as iron.     

Aromatization of ethane over modified pentasils

Aromatization of ethane over high silica zeolites modified by Zn, Ga or Pt was studied in the presence of intermetallic hydrogen acceptor Zr₂Fe. Elimination of hydrogen formed during the reaction at 500–550°C by acceptor resulted in 4–6 fold higher aromatics yield, aromatization selectivity reaching 74–90%. In the similar conditions the effect of hydrogen absorption by Zr₂Fe on ethane dehydrogenation appeared to be negligible over supported Ga₂O₃ or Cr₂O₃ and strongly negative in the case of Pt-containing catalysts. General considerations of the reaction mechanism are discussed.     

Harmful by-products in selective catalytic reduction of nitrogen oxides by olefins over alumina

The selective reduction of nitrogen dioxide and nitrogen monoxide by olefins (ethene, propene) has been studied over two different -aluminium oxides in the temperature range 473–873 K. Nitrogen dioxide was reduced more effectively than nitrogen monoxide with both, ethene and propene, as a reductant. At temperatures exceeding 700 K, ammonia was formed as a by-product over one type of alumina. Concentrations in the range 30–40 ppm were determined for propene in combination with both, NO and NO₂, while no ammonia was produced with ethene as a reductant. In addition, significant formation of hydrogen cyanide up to 70 ppm was observed with propene over both aluminium oxides starting from either NO or NO₂. In contrast, hydrogen cyanide formation remained below 10 ppm with ethene as a reductant. Nitrous oxide formation did not exceed 10 ppm for all investigations. The results show that for alumina catalysts ethene is a more suitable reductant than propene due to its lower tendency to form undesired by-products.     

Characterization of palladium supported on sulfated zirconia catalysts by DRIFTS, XAS and n-butane isomerization reaction in the presence of hydrogen

Palladium supported on sulfated zirconia (PdSZ) has been characterized by the n-butane isomerization reaction in the presence of hydrogen, X-ray absorption spectroscopy (XAS) and diffuse reflectance Fourier transform infrared spectroscopy (DRIFTS) of adsorbed carbon monoxide. Catalyst calcination at 873 K followed by hydrogen reduction at 513 K results in the formation of 30–40 Å Pd metal clusters, but the surface can only weakly adsorb CO, though stronger than Pd-free, sulfated zirconia catalysts. In the presence of hydrogen, PdSZ has a lower n-butane isomerization activity than SZ, and the Pd function cannot stabilize the reaction at low H₂/n-butane ratios.     

Mass transfer resistances in the palladium-catalysed hydrogenation of 1-methoxy-2,4-(nitrophenyl)-ethane

Hydrogenation of 1-methoxy-2,4-(nitrophenyl)-ethane (MNPE) to 1-methoxy-2,4-(aminophenyl)-ethane (MAPE) over Pd/C catalyst was studied in a three-phase stirred slurry reactor. The reaction was performed in a kinetic region (no internal and external mass transfer resistances) at temperatures ranging from 293 to 320 K, hydrogen pressure 200 kPa using powdered pellets of 1–4% Pd on carbon support. The rates have been correlated with power law and Hougen–Watson kinetic models. The rate expression which best fit the data is

which postulates a reaction between adsorbed MNPE (marked by B) and hydrogen (marked by A).     

Hydrogenation of anthracene over active carbon-supported nickel catalyst

Hydrogen transfer behavior over active carbon and carbon-supported Ni catalyst was examined in the hydrogenation of anthracene with three kinds of hydrogen sources: hydrogen gas, hydrogen-donor tetralin and the combination of both. In tetralin, active carbon itself provided higher conversions of anthracene in the temperature range of 350–400°C than Ni/C catalyst, while under the pressure of hydrogen gas, the addition of Ni metal onto active carbon remarkably promoted the hydrogenation of anthracene, providing a complete conversion at 300°C. When both tetralin and hydrogen gas were used together, an apparent improvement in both conversion and product distribution was observed with active carbon, whereas with Ni/C catalyst, the rate of hydrogen consumed in the hydrogenation was apparently low in the temperature range of 300–320°C, compared to that observed at the same temperatures using hydrogen gas alone.     

Reaction of nitric oxide and nitric oxide + carbon monoxide with amorphous Fe-Co-B alloy powders

The activity of amorphous Fe---Co---B alloy powder was investigated for the decomposition and the reduction of nitrogen monoxide. The transient response technique and a fixed bed reactor were applied to study the interactions of the Fe---Co---B alloy with two gas mixtures: NO + Ar at 353 and 573 K and NO + CO + Ar at 333–573 K. Moessbauer spectroscopy and X-ray photoelectron spectroscopy (XPS) were used to study the state of the initial sample and the samples utilized in both gas mixtures. It is shown that the amorphous Fe---Co---B alloy powder has an activity for the direct decomposition of nitric oxide to nitrous oxide and nitrogen at a high gas space velocity (26 000 h⁻¹). Oxygen from the decomposed nitric oxide poisons the surface for the formation of nitrogen. In the presence of carbon monoxide (a NO + CO + Ar gas mixture) nitric oxide is reduced to nitrous oxide at 333–353 K and fully reduced to nitrogen at 373–573 K. The quantities of the carbon dioxide formed are not equal to the values expected from the stoichiometry of the NO + CO reaction. Probably, the interaction of carbon monoxide with the adsorbed oxygen (left on the surface by the decomposed nitric oxide) enhances the rate of nitric oxide decomposition to nitrous oxide and nitrogen. The rate limiting steps for both reactions of nitric oxide decomposition, as indicated by the transient response data, change with increasing temperature. The data from the Moessbauer spectroscopy and the X-ray photoelectron spectroscopy (XPS) studies have shown that the amorphous Fe---Co---B alloy powder undergoes phase changes under the conditions of both, the NO + Ar and the NO + CO + Ar gas mixtures. Boron migrates to the surface of globules and serves the accumulation of oxygen by the formation of B₂O₃ (or B(OH)₃).     

Effects of surface chemistry on the reactive adsorption of hydrogen cyanide on activated carbons

Two activated carbons of different origins were modified by heating at 950 °C either with or without previous urea impregnation. The treatment causes changes in surface chemistry and porosity. The materials obtained were used as adsorbents for hydrogen cyanide in dry air at ambient conditions. The samples before and after adsorption were characterized using nitrogen adsorption, potentiometric titration, elemental analysis and thermal analysis. On selected samples extraction was carried out to identify surface reaction products soluble in alcohols. The results indicated differences in the amount adsorbed and the products of surface reactions on specific surface features. The presence of nitrogen incorporated in the carbon matrix leads to an enhanced performance owing to the basic environment and the ability of the surface to activate oxygen. These lead to complex surface reactions in which the derivatives of hydrogen cyanide form oxamide, and are incorporated in the carbon matrix, or are deposited as the bulky insoluble polymers of paracyanogen on the surface. The reactions mainly occur in pores with sizes between 10 and 20 Å where the functional groups can be present and HCN, or its derivatives, and water can take part in the reactions.