Enhanced activity of metal oxide-doped Ga2O3–Al2O3 for NO reduction by propene

Effect of additives, In₂O₃, SnO₂, CoO, CuO and Ag, on the catalytic performance of Ga₂O₃–Al₂O₃ prepared by sol–gel method for the selective reduction of NO with propene in the presence of oxygen was studied. As for the reaction in the absence of H₂O, CoO, CuO and Ag showed good additive effect. When H₂O was added to the reaction gas, the activity of CoO-, CuO- and Ag-doped Ga₂O₃–Al₂O₃ was depressed considerably, while an intensifying effect of H₂O was observed for In₂O₃- and SnO₂-doped Ga₂O₃–Al₂O₃. Of several metal oxide additives, In₂O₃-doped Ga₂O₃–Al₂O₃ showed the highest activity for NO reduction by propene in the presence of H₂O. Kinetic studies on NO reduction over In₂O₃–Ga₂O₃–Al₂O₃ revealed that the rate-determining step in the absence of H₂O is the reaction of NO₂ formed on Ga₂O₃–Al₂O₃ with C₃H₆-derived species, whereas that in the presence of H₂O is the formation of C₃H₆-derived species. We presumed the reason for the promotional effect of H₂O as follows: the rate for the formation of C₃H₆-derived species in the presence of H₂O is sufficiently fast compared with that for the reaction of NO₂ with C₃H₆-derived species in the absence of H₂O. Although the retarding effect of SO₂ on the activity was observed for all of the catalysts, SnO₂–Ga₂O₃–Al₂O₃ showed still relatively high activity in the lower temperature region.     

Conversion of naphthenes to a high value steamcracker feedstock using H-ZSM-5 based catalysts in the second step of the ARINO-process

Future regulations for the limitation of sulfur and aromatics in fuels driven by the European Auto Oil Program (AOP II) stimulate the need for an alternative utilization of the resulting surplus of pyrolysis gasoline (pygas). The conversion of heavy pyrolysis gasoline into valuable steam cracker feedstock with a maximum yield of C₂–C₄ n-alkanes is achieved via the ARINO^® two-step process, jointly developed by Linde, VEBA Oil and Süd-Chemie. The first step involves a hydrogenation of aromatics to naphthenes followed by the subsequent ring opening and cracking in the second step.

Süd-Chemie developed a new commercial cracking catalyst for the second step of the ARINO^® process with the aim to maximize the yield of C₂–C₄ n-alkanes at low formation of methane and aromatics. The ring opening and cracking reaction of naphthenes was studied in a bench scale tubular reactor over extruded H-ZSM-5 based zeolite catalysts.

In a series of screening tests using a commercial, hydrogenated and desulphurized heavy pyrolysis gasoline, the influence of the preparation parameters such as zeolite acidity, palladium content as well as the type of binder were investigated. Furthermore, the influence of the process conditions space velocity and temperature was studied.

High yields of C₂–C₄ n-alkanes at low formation of undesired methane and aromatics were achieved over an alumina bound zeolite with medium Brønsted acidity loaded with palladium.

The reduction of the space velocity resulted in an increase in the C₂–C₄ n-alkane yield and lower formation of aromatics, but a simultaneous increase in the methane make. Raising the temperature from 280 to 370 °C significantly increased the catalyst activity.     

The effect of coal rank on flash hydropyrolysis of Chinese coal

Fourteen kinds of Chinese coal were flash hydropyrolysed in a small entrained reactor at 750°C and hydrogen atmosphere. The results indicated that carbon content and yields of liquid hydrocarbon, H/C and yields of gaseous hydrocarbon, oxygen content and yields of CO, CO₂ and H₂O show better corresponding relations. The correlations between yields of CH₄, C₂ and C₂H₆ and H/C can be expressed as Y_CH4=−42.2+100(H/C)(0.51<0.59), Y_CH4=15.8+1.67(H/C)(0.59<1.11), Y_C2=0.347+4.78(H/C), Y_C2H6=0.352+4.74(H/C); The correlations between yields of CO₂ and water and oxygen content can be expressed as: Y_CO2=−0.0437+0.0355(O); Y_H2O=0.726+0.467(O). The cutoff points of flash hydropyrolysis for coal are that H/C is 0.6 and carbon content is 85%. The coal which H/C is lower than 0.6 and carbon content is higher than 85% is usually not good for flash hydropyrolysis. It is found that influence of coal rank on yields of liquid, gas product and total yields of product in flash hydropyrolysis can be expressed as of H/C in coal.     

CO, H2 or C3H8 assisted catalytic combustion of methane over supported LaMnO3 monoliths

The effect of the addition of a second fuel such as CO, C₃H₈ or H₂ on the catalytic combustion of methane was investigated over ceramic monoliths coated with LaMnO₃/La-γAl₂O₃ catalyst. Results of autothermal ignition of different binary fuel mixtures characterised by the same overall heating value show that the presence of a more reactive compound reduces the minimum pre-heating temperature necessary to burn methane. The effect is more pronounced for the addition of CO and very similar for C₃H₈ and H₂. Order of reactivity of the different fuels established in isothermal activity measurements was: CO>H₂≥C₃H₈>CH₄. Under autothermal conditions, nearly complete methane conversion is obtained with catalyst temperatures around 800 °C mainly through heterogeneous reactions, with about 60–70 ppm of unburned CH₄ when pure methane or CO/CH₄ mixtures are used. For H₂/CH₄ and C₃H₈/CH₄ mixtures, emissions of unburned methane are lower, probably due to the proceeding of CH₄ homogeneous oxidation promoted by H and OH radicals generated by propane and hydrogen pyrolysis at such relatively high temperatures.

Finally, a steady state multiplicity is found by decreasing the pre-heating temperature from the ignited state. This occurrence can be successfully employed to pilot the catalytic ignition of methane at temperatures close to compressor discharge or easily achieved in regenerative burners.     

Hydroisomerisation of n-alkanes over partially reduced MoO3: Promotion by CoAlPO-11 and relations to reaction mechanism and rate-determining step

The reaction mechanism and the rate-determining step (RDS) of the isomerisation of n-alkanes (C₄–C₆) over partially reduced MoO₃ catalysts were studied through the effects of the addition of an alkene isomerisation catalyst (i.e. CoAlPO-11). When an acidic CoAlPO-11 sample was mechanically mixed with the MoO₃, a decrease of the induction period and an increase of the steady-state conversion of n-butane to isobutane were observed. These data support previous assumptions that a bifunctional mechanism occurred over the partially reduced MoO₃ (a complex nanoscale mixture of oxide-based phases) during n-butane isomerisation and that the RDS was the skeletal isomerisation of the linear butene intermediates. The only promotional effect of CoAlPO-11 on the activity of partially reduced MoO₃ for C₅–C₆ alkane hydroisomerisation was a reduction of the induction period, as the RDS at steady-state conditions appeared to be dehydrogenation of the alkane in this case. However, lower yields of branched isomers were observed in this case, the reason of which is yet unclear.     

Single-event microkinetics for coke formation during the catalytic cracking of (cyclo)alkane/1-octene mixtures

A single-event microkinetic model (SEMK) is applied to model initial coking rates during the catalytic cracking of (cyclo)alkane/1-octene mixtures at 693–753 K and (cyclo)alkane and 1-octene inlet partial pressures of 26.6 and 4.8 kPa on a REUSY equilibrium catalyst. Three types of irreversible alkylations involving both gas phase and surface coke precursors, viz., alkylation of phenyl substituted carbenium ions with C₃–C₅ alkenes, alkylation of the nucleus of monoaromatics with C₃–C₅ alkylcarbenium ions, and alkylation of C₈–C₁₀ alkylcarbenium ions with C₃–C₅ alkenes, have been considered as rate-determining steps in coke formation. The bulky alkylated species formed out of these alkylations are considered as coke. The activation energies for these alkylations obtained via non-isothermal regression are independent of the feedstock within the parameters confidence limits reflecting the fundamental character of the SEMK. The negative effect of temperature on the experimentally observed coking rates is qualitatively described and is explained in terms of an overcompensation of the increase of the rate coefficient by a lower surface coke precursor concentration.     

Pyrolysis of oil sand from the Whiterocks deposit in a rotary kiln

A rotary kiln reactor was evaluated for thermal recovery of oil from Utah oil sands. A series of continuous-flow pyrolysis experiments was conducted. Process variables investigated included temperature (748–848 K), solids retention time (10–27 min) and sweep gas flow rate (1.27–2.83 m_s³ h⁻¹). The results indicated that the pyrolysis temperature and the solids retention time were the two most important variables affecting the liquid and gas yields. The liquid yield (C₅⁺]) decreased and the gas yield (C₁–C₄) increased with increasing temperature. The liquid yield increased with decreasing solids retention time, while the gas yield decreased. No significant effect of the sweep gas flow rate on the product distribution and yields was observed. The quality of the bitumen-derived liquids was significantly better than that of the bitumen. A preliminary process kinetics model which conforms to the observed trends was proposed.     

Synthesis and crystal structure of carbonate cancrinite Na8[AlSiO4]6CO3(H2O)3.4, grown under low-temperature hydrothermal conditions

The synthesis of cancrinite in the system Na₂O–SiO₂–Al₂O₃–Na₂CO₃–H₂O was studied under low-temperature hydrothermal conditions in the 353 K<T<473 K interval. The aim was to reveal the suitable range for the crystallization of pure-phase carbonate cancrinite with the ideal composition Na₈[AlSiO₄]₆CO₃(H₂O)₂ without cocrystallization of sodalite or intermediate disordered phases between cancrinite and sodalite. It was found that cancrinite formation reacts very sensitive on the temperature within the autoclaves whereas the concentration of reactants and the alkalinity of the hydrothermal solution have a much lower influence on the phase formation. Thus the temperature of crystallization of carbonate cancrinite without any by-products should not remain below 473 K. At the lower reaction temperature of 353 K the formation of a disordered intermediate phase between the cancrinite and the sodalite structure has been obtained in every case, independent of the template concentrations and the base. Some problems to detect this in a typical powder product mixture are discussed. Besides the ²⁹Si and ²⁷Al MAS NMR characterization of the products, the crystal structure refinement of pure carbonate cancrinite of ideal composition Na₈[AlSiO₄]₆CO₃(H₂O)_3.4, has been carried out from X-ray powder data using the Rietveld method: P6₃, a=1271.3(1) pm, c=518.6(1) pm, R_WP=0.073, R_F=0.016 for 347 structure factors and 45 variable positional parameters.     

Reversible sorption–desorption of NOx by mixed oxides under various atmospheres

Characteristics of MnO_y–ZrO₂ and Pt–ZrO₂–Al₂O₃ as reversible sorbents of NO_x were investigated under dynamic changes in atmosphere. These sorbents can be used reversibly with a change of C₃H₈ concentration in the reaction gases. Catalytic reduction of NO occurred in the presence of propane, which was more pronounced on Pt–ZrO₂–Al₂O₃ than on MnO_y-ZrO₂ due to high activity of Pt surface for this reaction on MnO_y in MnO_y–ZrO₂. The sorption was observed as soon as the atmosphere changed from a reducing to an oxidizing one. This implies that a high equilibrium partial pressure of O₂ is necessary for NO uptake since the sorbed NO⁻₃ species becomes stable. The beginning of NO_x desorption atmospheres was somewhat dependent on the amount of stored NO_x. The presence of propane in the gas phase strongly affected the characteristic sorption and desorption properties of MnO_y–ZrO₂ and Pt–ZrO₂–Al₂O₃. The sorption and desorption properties are different for MnO_y–ZrO₂ and Pt–ZrO₂–Al₂O₃, since the noble metal or metal oxide possesses unique activity for the NO reaction with C₃H₈ and the amount of oxygen available for oxidative sorption of NO.     

Methanol formation from methane partial oxidation in CH4–O2–NO gaseous phase at atmospheric pressure

The reaction condition for high yield of methanol in a gaseous reaction between methane and oxygen in the presence of NO at atmospheric pressure was explored. Methane partial oxidation without NO (CH₄–O₂) gave only 1% conversion of methane at 966 K. The addition of NO led to a remarkable increase in methane conversion and to high selectivity to C₁-oxygenates. The conversion of methane attained 10% at 808 K in the presence of NO (0.5%) where the selectivities to methanol and formaldehyde were 22.1 and 24.1%, respectively. Nitromethane and carbon oxides were also observed in the product gas. The amount of nitromethane was almost equal and/or near to that of initial NO. The carbon monoxide produced was several times higher than carbon dioxide. Influences of NO concentration, ratio of methane to oxygen, water vapor, and dilution with helium gas on product distribution were measured. Low concentration of NO (0.35–0.55%) was favorable for methanol formation. High selectivity to methanol was obtained at low value of the ratio of methane to oxygen (2.0–3.0) or low concentration of dilution gas (<16%). The NO₂ added promoted methane partial oxidation and selectivity to methanol. Therefore, it was assured that NO_x promoted the formation of CH₃√ and CH₃O√ in the gas phase reaction for CH₄–O₂–NO.     

Surface properties and reactivity of Cu/γ-Al2O3 catalysts for NO reduction by C3H6: Influences of calcination temperatures and additives

The influences of calcination temperatures and additives for 10 wt.% Cu/γ-Al₂O₃ catalysts on the surface properties and reactivity for NO reduction by C₃H₆ in the presence of excess oxygen were investigated. The results of XRD and XPS show that the 10 wt.% Cu/γ-Al₂O₃ catalysts calcined below 973 K possess highly dispersed surface and bulk CuO phases. The 10 wt.% Cu/γ-Al₂O₃ and 10 wt.% Mn–10 wt.% Cu/γ-Al₂O₃ catalysts calcined at 1073 K possess a CuAl₂O₄ phase with a spinel-type structure. In addition, the 10 wt.% La–10 wt.% Cu/γ-Al₂O₃ catalyst calcined at 1073 K possesses a bulk CuO phase. The result of NO reduction by C₃H₆ shows that the CuAl₂O₄ is a more active phase than the highly dispersed and bulk CuO phase. However, the 10 wt.% Mn–10 wt.% Cu/γ-Al₂O₃ catalyst calcined at 1073 K possesses significantly lower reactivity for NO reduction than the 10 wt.% Cu/γ-Al₂O₃ catalyst calcined at 1073 K, although these catalysts possess the same CuAl₂O₄ phase. The low reactivity for NO reduction for 10 wt.% Mn–10 wt.% Cu/γ-Al₂O₃ catalyst calcined at 1073 K is attributed to the formation of less active CuAl₂O₄ phase with high aggregation and preferential promotion of C₃H₆ combustion to CO_x by MnO₂. The engine dynamometer test for NO reduction shows that the C₃H₆ is a more effective reducing agent for NO reduction than the C₂H₅OH. The maximum reactivity for NO reduction by C₃H₆ is reached when the NO/C₃H₆ ratio is one.     

Selective catalytic reduction of NO by C3H8 over CoOx/Al2O3: An investigation of structure–activity relationships

A series of CoO_x/Al₂O₃ catalysts was prepared, characterized, and applied for the selective catalytic reduction (SCR) of NO by C₃H₈. The results of XRD, UV–vis, IR, Far-IR and ESR characterizations of the catalysts suggest that the predominant oxidation state of cobalt species is +2 for the catalysts with low cobalt loading (≤2 mol%) and for the catalysts with 4 mol% cobalt loading prepared by sol–gel and co-precipitation. Co₃O₄ crystallites or agglomerates are the predominant species in the catalysts with high cobalt loading prepared by incipient wetness impregnation and solid dispersion. An optimized CoO_x/Al₂O₃ catalyst shows high activity in SCR of NO by C₃H₈ (100% conversion of NO at 723 K, GHSV: 10,000 h⁻¹). The activity of the selective catalytic reduction of NO by C₃H₈ increases with the increase of cobalt–alumina interactions in the catalysts. The influences of cobalt loading and catalyst preparation method on the catalytic performance suggest that tiny CoAl₂O₄ crystallites highly dispersed on alumina are responsible for the efficient catalytic reduction of NO, whereas Co₃O₄ crystallites catalyze the combustion of C₃H₈ only.     

CO hydrogenation over a rhodium vanadate catalyst: Reduction and regeneration of RhVO4 on SiO2

The hydrogenation of CO over an Rh vanadate (RhVO₄) catalyst supported on SiO₂ (RhVO₄/SiO₂) has been investigated after H₂ reduction at 500°C, and the results are compared with those of vanadia-promoted (V₂O₅–Rh/SiO₂) and unpromoted Rh/SiO₂ catalysts. The mean size of Rh particles, which were dispersed by the decomposition of RhVO₄ after the H₂ reduction, was smaller (41 Å) than those (91–101 Å) of V₂O₅–Rh/SiO₂ and Rh/SiO₂ catalysts. The RhVO₄/SiO₂ catalyst showed higher activity and selectivity to C₂ oxygenates than the unpromoted Rh/SiO₂ catalyst after the H₂ pretreatment. The CO conversion of the RhVO₄/SiO₂ catalyst was much higher than that of V₂O₅–Rh/SiO₂ catalyst, and the yield of C₂ oxygenates increased. We also found that the RhVO₄/SiO₂ catalyst can be regenerated by calcination or O₂ treatment at high temperature after the reaction.     

Selective catalytic reduction of NO by C2H2 over MoO3/HZSM-5

Molybdenum impregnated HZSM-5 zeolite catalysts with MoO₃ loading from 1 to 8 wt.% were studied in detail for the selective catalytic reduction (C₂H₂-SCR) of NO by acetylene. A 83.9% of NO could be removed by the reductant at 350 °C under 1600 ppm of NO, 800 ppm of C₂H₂ and 9.95% of O₂ in He over 2%MoO₃/HZSM-5 catalyst with a specific activity of in NO elimination and the competitiveness factor (c.f.) of 33.6% for the reductant. The NO elimination level and the c.f. value were ca. 3–4 times as high as those using methane or propene as reductant over the catalyst in the same reaction condition. About same reaction rate was estimated in NO oxidation as that in the NO reduction over each xMoO₃/HZSM-5 (x = 0–8%) catalyst, which confirms that NO₂ is a crucial intermediate for the aimed reaction over the catalysts. Appropriate amount of Mo incorporation to HZSM-5 considerably enhanced the title reaction, both by accelerating the intermediate formation and by strengthening the adsorption NO_x on the catalyst surface under the reaction conditions. Rather lower adsorption tendency of acetylene compared with propene on the catalysts explains the catalyst's steady performance in the C₂H₂-SCR of NO and rapid deactivation in the C₃H₆-SCR of NO.     

Selective catalytic reduction of NO by hydrocarbons on Ga2O3/Al2O3 catalysts

Catalytic properties of supported gallium oxides have been examined for the selective reduction of NO by CH₄ in excess oxygen. The activity was greatly affected by the support; Ga₂O₃/Al₂O₃ (Al₂O₃ supported Ga₂O₃) and Ga₂O₃–Al₂O₃ mixed oxide exhibited high activity and selectivity as comparable to Ga-ZSM-5, while unsupported Ga₂O₃ and the other supported Ga₂O₃ were ineffective. For Ga₂O₃/Al₂O₃, the activity changed with Ga₂O₃ content, and was highest at about 30 wt% Ga₂O₃, which corresponds to a theoretical monolayer coverage. Gallium oxide highly dispersed on Al₂O₃ is considered to be responsible for the high activity and selectivity. The reaction characteristics of Ga₂O₃/Al₂O₃ were studied and compared with Ga-ZSM-5 and Co-ZSM-5. Ga₂O₃/Al₂O₃ exhibited the highest activity and selectivity at high temperature. In addition, Ga₂O₃/Al₂O₃ showed higher tolerance against water than Ga-ZSM-5. C₃H₈ and C₃H₆ were also evaluated as reducing agents, and Ga₂O₃/Al₂O₃ showed higher activity than Ga-ZSM-5 above 723 K achieving almost complete reduction of NO to N₂.     

Synthesis, crystal structure and thermal stability of tetrahydroborate sodalite Na8[AlSiO4]6(BH4)2

Tetrahydroborate sodalite formation was investigated in the system Na₂O–SiO₂–Al₂O₃–NaBH₄–H₂O under mild hydrothermal conditions. Due to the high degree of decomposition of hydroborates in aqueous solutions synthesis conditions were tuned by variation of the parameters alkalinity, liquid/solid ratio, reaction temperature and reaction time. The insertion of 8–16 molar NaOH solution was crucial for the higher stability of pure tetrahydroborate salt under strong alkaline conditions. Synthesis at 393 K and 24 h reaction time reveal tetrahydroborate sodalite Na₈[AlSiO₄]₆(BH₄)₂ beside a small amount of amorphous material within the total batch. Structure, composition and thermal stability of this new sodalite was investigated using XRD, NMR, infrared and TG/DTA methods. The crystal structure of tetrahydroborate sodalite has been refined in the space group P-43n with a = 891.61(2) pm. The Si- and Al-atoms of the aluminosilicate framework are completely ordered. The boron atoms of the tetrahydroborate anions are located at the centre of the sodalite cage whereas the hydrogen atoms are positionally disordered. Na₈[AlSiO₄]₆(BH₄)₂ shows a high stability under inert gas conditions. At atmospheric conditions the group can be oxidized to borate and boroxide anions suggesting the formation of hydrogen which leaves the sodalite cages. Future investigation of reloading properties of the oxidized form could be highly interesting for the hydrogen storage capabilities of these sodalites.     

Mineral matter effects on the rapid pyrolysis and hydropyrolysis of a bituminous coal. 1. Effects on yields of char,tar and light gaseous volatiles

The effects of minerals on product compositions from rapid pyrolysis of a Pittsburgh Seam bituminous coal were investigated. Whole, demineralized, and mineral treated samples of pulverized coal were heated in 100 KPa helium or 6.9 MPa hydrogen at 1000 K s^?1 to temperatures of up to 1300 K. Yields of char, tar and individual gaseous products were determined as a function of time-temperature conditions. Clays, iron-sulphur minerals, and quartz had few effects on pyrolysis in helium. Calcium minerals decreased yields of hydrocarbon products and increased yields of CO in helium pyrolysis. Calcite and clays decreased yields of CH₄ from hydropyrolysis, whereas iron-sulphur minerals had little effect on pyrolysis at 6.9 MPa H₂. Whole coal results were similar to demineralized coal results under all conditions.     

Relative rates of various steps of NO–CH4–O2 reaction catalyzed by Pd/H-ZSM-5

Reaction mechanism of the reduction of nitrogen monoxide by methane in an oxygen excess atmosphere (NO–CH₄–O₂ reaction) catalyzed by Pd/H-ZSM-5 has been studied at 623–703 K in the absence of water vapor, in comparison with the mechanism for Co-ZSM-5. Kinetic isotope effect for the N₂ formation in NO–CH₄–O₂ vs. NO–CD₄–O₂ reactions was 1.65 at 673 K and decreased with a decrease in the reaction temperature. In addition, H–D isotopic exchange took place significantly in NO–(CH₄+CD₄)–O₂ reaction. These results are in marked contrast with the case of Co-ZSM-5, for which the C–H dissociation of methane is the only rate-determining step, and show that the C–H dissociation is slow but not the only rate-determining step in the case of Pd/H-ZSM-5.

A reaction scheme was proposed, in which the relative rates of the three steps ((i)–(iii) below) vary depending on the reaction conditions.

Further, in contrast to Co-ZSM-5, NO_x–CH₄–O₂ reaction was much slower than CH₄–O₂ reaction for Pd/H-ZSM-5; the presence of NO_x retards the reaction of CH₄ over the latter catalyst, while it accelerates the reaction over the former. It is suggested that CH₄ is activated directly by the Pd atoms in the case of Pd/H-ZSM-5, but by NO₂ strongly adsorbed on Co ion for Co-ZSM-5. The reaction order of the NO–CH₄–O₂ reaction with respect to NO pressure was consistent with this mechanism; 1.05 for Pd/H-ZSM-5 and 0.11 for Co-ZSM-5.     

Cu-ZSM-5 zeolite highly active in reduction of NO with decane under water vapor presence: Comparison of decane, propane and propene by in situ FTIR

Selective catalytic reduction of NO_x (SCR-NO_x) with decane, and for comparison with propane and propene over Cu-ZSM-5 zeolite (Cu/Al 0.49, Si/Al 13.2) was investigated under presence and absence of water vapor. Decane behaves in SCR-NO_x like propene, i.e. the Cu-zeolite activity increased under increasing concentration of water vapor, as demonstrated by a shift of the NO_x–N₂ conversion to lower temperatures, in contrast to propane, where the NO_x–N₂ conversion is highly suppressed. In situ FTIR spectra of sorbed intermediates revealed similar spectral features for C₁₀H₂₂– and C₃H₆–SCR-NO_x, where –CH_x, R–NO₂, –NO₃⁻, Cu⁺–CO, –CN, –NCO and –NH species were found. On contrary, with propane –CH_x, R–NO₂, NO₃⁻, Cu⁺–CO represented prevailing species. A comparison of the in situ FTIR spectra (T–O–T and intermediate vibrations) recorded at pulses of propene and propane, moreover, under presence and absence of water vapor in the reaction mixture, revealed that the Cu²⁺–Cu⁺ redox cycle operates with the C₃H₆–SCR-NO_x reactions in both presence/absence of water vapor, while with C₃H₈–SCR-NO_x, the redox cycle is suppressed by water vapor. It is concluded that decane cracks to low-chain olefins and paraffins, the former ones, more reactive, preferably take part in SCR-NO_x. It is concluded that formation of olefinic compounds at C₁₀H₂₂–SCR-NO_x is decisive for the high activity in the presence of water vapor, while water molecules block propane activation. The increase in NO_x–N₂ conversion due to water vapor in C₁₀H₂₂–SCR-NO_x should be connected with the increased reactivity of intermediates. These are suggested to pass from R–NO_x → –CN → –NCO → NH₃; the latter reacts with another activated NO_x molecule to molecular nitrogen. The positive effect of water vapor on the NO_x–N₂ conversion is attributed to increased hydrolysis of –NCO intermediates.     

Conversion of waste plastics into fuels: Recycling polyethylene in FCC

Low density polyethylene was dissolved into toluene and converted at 500 °C over three different commercial FCC catalysts in a laboratory Riser Simulator reactor. Short reaction-times up to 12 s were used. All the catalysts had qualitatively similar behaviors. The specific contribution of the polymer to the product slate of FCC was centered in hydrocarbons in the range of gasoline, with high aromatic content and highly olefinic C₃–C₄ gases. Saturated C₄–C₅ products were mainly isoparaffins. The additional coke formed by the polymer would make coke yields to increase moderately in relation to the standard operation. These facts confirmed that this recycling option, which is based on a proven technology, represents an interesting alternative to solve a major environmental problem.