Complete N2O Conversion Research Articles

Thermodynamic and mechanism study of syngas production via integration of nitrous oxide decomposition and methane partial oxidation in the presence of 10%NiO–La0.3Sr0.7Co0.7Fe0.3O3−δ

10%NiO–La0.3Sr0.7Co0.7Fe0.3O3−δ (10%NiO-LSCF3773) was synthesized using the EDTAcitrate complexing method. Non-catalytic and catalytic nitrous oxide decomposition and methane partial oxidation using 10%NiO–LSCF3773 was experimentally studied, assuming that the reactions occurred separately in a membrane reactor at feed side and permeate side. The experimental results are in good agreement with the chemical equilibrium composition calculated using Aspen Plus, and the changes of standard Gibbs free energy of each relevant elementary reactions. The mechanism of the reactions was proposed to follow Eley–Rideal surface reaction. The optimal temperature was 800 °C, under atmospheric pressure, where (1) NO2 formation was not detected (2) no production of C2 + and C3 + (3) complete conversion of N2O, CH4 and O2 were achieved (4) high purity syngas was obtained with no significant amount of undesired products and (5) readily utilizable syngas at the ratio of two was achieved.

Nitrous oxide decomposition over La0.3Sr0.7Co0.7Fe0.3O3−δ catalyst

Nano-sized La0.3Sr0.7Co0.7Fe0.3O3-δ (LSFC3773) was prepared as a catalyst for nitrous oxide (N2O) decomposition by a sonochemical method. The catalyst provided a complete conversion of N2O at 450 °C, showing the best performance among most recent industrial catalysts, and offered 99.7–100% conversion at higher temperatures, e.g., 540–600 °C. A suitable operating temperature range for the reaction to avoid NOx formation is from 400 to 600 °C. The activation energy and the pre-exponential factor were 42.96 kJ/mol and 161,135.35 mol/gcat h bar. Oxygen inhibition was observed and was more obvious as the sample approached full surface coverage ( $$\theta \; = \;1$$ ) at 375 °C using a 100% N2O feed. The reaction occurred via the Eley–Rideal mechanism. Two possible model mechanisms were suggested according to the experimental phenomenon and the rate coefficient order of each elementary steps.

Effect of copper precursors on the catalytic performance of Cu-ZSM-5 catalysts in N 2 O decomposition

Abstract Five Cu-ZSM-5 catalysts were obtained by treating Na-ZSM-5 (Si/Al ratio = 15) with aqueous solutions of different Cu precursors (CuCl2, Cu(NO3)2, CuSO4, Cu(CH3COO)2, and ammoniacal copper (II) complex ion). After being pretreated in flowing He at 500 °C to form active Cu+, these catalysts exhibited quite different activities in catalytic decomposition of N2O. CZM-AC(II) (prepared by ammoniacal copper (II) complex ion) with 9.4 wt% Cu content was the most active among these Cu-ZSM-5 catalysts, achieving almost complete N2O conversion at 400 °C. CZM-CA (prepared using Cu(CH3COO)2 as the Cu precursor) with 2.8 wt% Cu content was the second most active catalyst among these Cu-ZSM-5 catalysts, achieving almost complete N2O conversion at 425 °C. CZM-CC, CZM-CN, and CZM-CS prepared by using CuCl2, Cu(NO3)2, or CuSO4 as the Cu precursor with similar Cu contents (≈ 1.7 wt%) were the least active among these Cu-ZSM-5 catalysts, achieving ca. 90% N2O conversion at 500 °C. XRD, ICP, SEM, TEM, EDX-mapping, and CO-IR experiments were conducted to characterize relevant samples. The superior activity of CZM-AC(II) can be attributed to the high contents of total Cu+ and dimeric Cu+ among these samples. The influence of co-fed O2 or H2O on the catalytic performance of typical samples was also studied.

Metal phosphate-supported RuOx catalysts for N2O decomposition

RuOx/M–P–O (M=Mg, Al, Ca, Fe, Co, Zn, La) catalysts were prepared by impregnating commercial metal phosphates with RuCl3, followed by calcination in air at 500°C. The catalytic performance in N2O decomposition was studied. Among these catalysts, RuOx/Ca–P–O (also denoted as RuOx/HAP, HAP=hydroxyapatite) showed the highest activity, achieving complete N2O conversion at 400°C. RuOx/Mg–P–O was the second most active, showing 46.3% N2O conversion at 400°C. The presence of 5.0vol.% O2 or 2.0vol.% H2O in the reaction mixture inhibited the catalytic activity of RuOx/HAP to some extent, but the inhibiting effect was reversible, i.e., the activity was restored after O2 or H2O was retracted. The influences of pretreatment by H2 as well as different Ru-containing precursors on the catalytic performance of RuOx/HAP were also studied. The characterization data indicate that RuOx/HAP has a not-so-small surface area (49.5m2/g), highly dispersed amorphous RuOx species, as well as relatively abundant basic sites, O2-adsorption sites, and surface hydroxyls.

Effect of Alkali Promoters (K) on Nitrous Oxide Abatement Over Ir/Al2O3 Catalysts

The promoting impact of potassium (0–1 wt% K) on nitrous oxide (N2O) catalytic decomposition over Ir/Al2O3 is investigated under both oxygen deficient and oxygen excess conditions. All samples were characterized by means of X-ray powder diffraction (XRD), temperature-programmed reduction (H2-TPR), ammonia desorption (NH3-TPD) and Fourier Transform Infrared Spectroscopy of pyridine adsorption (FTIR-Pyridine). The results reveal that the K-free Ir/Al2O3 catalyst consists mainly of the IrO2 phase, exhibiting also significant Lewis acidity, which is gradually eliminated by the addition of K. Catalytic performance results showed that the deN2O performance in the absence of O2 in the feed mixture is negatively affected upon increasing potassium loading. However, under oxygen excess conditions, a pronounced effect of K is observed. Although the catalytic performance of the un-doped catalyst is drastically hindered by the presence of O2, the K-promotion notably prohibits the oxygen poisoning. The optimum deN2O performance under oxygen excess conditions is obtained with potassium loading of 0.5 wt% K, which offers complete conversion of N2O at 580 °C, instead of the corresponding 50 % N2O conversion achieved with the un-modified sample. On the basis of characterization results, it was concluded that alkali-doping in combination with oxygen excess conditions are required towards the formation of active Ir entities.

The use of CeO2-Co3O4oxides as a catalyst for the reduction of N2O emission

The morphological characterization of a series of cobalt-cerium oxide composites prepared by the deposition of CeO2 onto Co3 O4 powder with a molar ratio of cerium oxide to Co3O4 in the range of 0 to 1 was performed. The powders were also impregnated with a solution of K2 CO3 to obtain the theoretical content of potassium atoms 2at·nm−2 . To investigate the effect of adding specific amount of CeO2 on the catalytic activity, the X-ray diffraction, SEM-EDX, laser particle size distribution and BET surface area measurements were used. The catalysts were tested through the low-temperature decomposition of nitrous oxide in the temperature range of 50°C to 700°C. The addition of CeO2 and K always moved the temperature of a complete N2O conversion towards lower temperatures (480°C-540°C to 340°C-420°C). The best catalytic properties were shown by the samples in which the ratio of cerium oxide to cobalt oxide ranged from 0.4 to 0.7.

Coupling of N2O decomposition with CO2 reforming of CH4 in novel cobalt-free BaFe0.9Zr0.05Al0.05O3−δ oxygen transport membrane reactor

Coupling of N2O decomposition with CO2 reforming of CH4 was demonstrated in cobalt-free perovskite BaFe0.9Zr0.05Al0.05O3−δ (BFZ-Al) membrane reactor. Perovskite oxide BFZ-Al was synthesized by EDTA–citric acid complexing method. The stability of BFZ-Al and BaFexZryCo1−x−yO3−δ (BFZ-Co) was studied under hydrogen atmosphere. X-ray diffraction analysis indicates that BFZ-Al shows a better stability compared to cobalt-based perovskite BFZ-Co. The oxygen permeation rate of BFZ-Al dense membrane was investigated from 810 to 960°C, and the oxygen permeation rate reached 0.85mlmin−1cm−2 at 960°C. N2O decomposition in BFZ-Al membrane reactor was studied under three different sweep gas atmospheres including He, He/CH4, and He/CH4/CO2. Comparatively, a higher N2O conversion was achieved by using the sweep gas mixture He/CH4/CO2 than only using He or He/CH4. Therefore, the simultaneous N2O decomposition and syngas production via dry reforming was studied in BFZ-Al membrane reactor by using N2O and He/CH4/CO2 as feed gas and sweep gas, respectively. At 900°C, almost complete N2O conversion was achieved owing to the efficient in situ removal of the inhibitor oxygen through BFZ-Al membrane. CH4 conversion was found to be around 97% with 94% CO selectivity at 900°C, and no obvious decline in the activity and selectivity was observed even after 100h of the operation.

Catalytic decomposition of N2O over RhOx supported on metal phosphates

RhOx/M–P–O (M=Mg, Al, Ca, Fe, Co, Zn, La) catalysts were tested in N2O decomposition. RhOx/Ca–P–O showed the highest activity, achieving complete N2O conversion at 300°C. RhOx/La–P–O is the second most active catalyst, achieving almost complete conversion at 375°C. RhOx/Mg–P–O, RhOx/Co–P–O, and RhOx/Al–P–O showed lower activities, whereas RhOx/Fe–P–O and RhOx/Zn–P–O were completely inactive. The high activity of RhOx/Ca–P–O is ascribed to the presence of very small RhOx particles, more basic sites, and the easiness of desorbing O2 at low temperatures. The inhibiting effects of co-fed O2 and/or H2O on the catalytic activity of RhOx/Ca–P–O are reversible.

Insights into the twofold role of Cs doping on deN2O activity of cobalt spinel catalyst—towards rational optimization of the precursor and loading

Cobalt spinel catalysts promoted with different cesium loadings from various precursors (Cs2CO3, CsNO3, CH3COOCs, and CsOH) were prepared by incipient wetness impregnation. The catalysts were characterized by XRF, XRD, SEM, XPS and Raman Spectroscopy. The work function studies were used to optimized the surface doping and monitor the retention of surface oxygen. The stability of cesium promoter was evaluated by means of species resolved – thermal alkali desorption method. The catalytic activity of N2O decomposition over the synthesized catalysts was studied by temperature programmed reaction. The role of cesium precursor was evaluated in terms of dispersion and the nature of the counterion. The results show that the most active deN2O catalysts are obtained for cesium carbonate at the narrow loading range of 2–3atoms/nm2 (complete N2O conversion at T<200°C). The twofold promotional effect is discussed in terms of modification of the electronic properties of the spinel catalyst (stimulation of dissociation step: N2O+e=N2+O–) and stability of the surface oxygen species (recombination step: O–=½O2+e).

Reduction of N2O by CO over Fe- and Cu-BEA zeolites: An experimental and computational study of the mechanism

The catalytic reduction of N2O by CO over two types of modified beta zeolite (BEA) catalysts, i.e. Fe modified beta (Fe-BEA) and Cu modified beta (Cu-BEA), was investigated. Catalytic tests for N2O direct decomposition and reduction by CO over Fe-BEA prepared by liquid ion exchange method were performed through a fixed-bed reactor. The experimental results showed that N2O conversion is apparently improved using CO as reductant; Fe-BEA starts to reduce N2O from 513K; a complete N2O conversion is achieved at 650K; and the required temperature for this reaction is reduced by ca. 150K. The reaction mechanism over Fe-BEA was investigated by in situ FTIR and DFT methods with 5T [(Si(OH)3)4AlO4(Fe) or (FeO)] cluster models. For Cu-BEA, a 5T [(Si(OH)3)4AlO4(Cu)] cluster model was established to optimize the geometries of reactants, transition states, and products. Two different reaction routines, namely the redox mechanism and the associative mechanism, have been investigated for the reduction of N2O by CO over both Fe- and Cu-BEA. It was found that for Fe-BEA, the energy barrier over the [Fe]+ active site is much lower than that over [FeO]+ active site; the redox mechanism is preferred for both Fe- and Cu-BEA; and the energy barrier on [Cu]+ active site is higher than that on [Fe]+ active site, indicating that Fe-BEA is superior to Cu-BEA for the reduction of N2O by CO.

Support mediated promotional effects of rare earth oxides (CeO2 and La2O3) on N2O decomposition and N2O reduction by CO or C3H6 over Pt/Al2O3 structured catalysts

The N2O decomposition and reduction by CO or C3H6 over rare earth oxides (REOs)-modified Pt/Al2O3 structured catalysts, i.e., coated on ceramic honeycomb monoliths, were comparatively investigated in a wide temperature interval of 100–600°C, either in the presence or in the absence of excess O2 and H2O. It was shown that the de-N2O efficiency can be remarkably enhanced via modification of Al2O3 support with rare earth oxides (REOs). In specific, complete conversion of N2O can be attained over REOs-modified catalysts at a relatively low temperature (ca. 480°C) even in the presence of excess O2, which in general depresses de-N2O efficiency, in opposite to the unmodified Pt/Al2O3 catalyst, over which, 20% N2O conversion is never exceeded for temperatures up to 600°C. In terms of turnover frequency (TOF), optimally modified (by REOs) Pt–Al2O3 catalyst exhibits one order of magnitude higher activity compared to that of the unpromoted Pt/Al2O3 sample. Under reducing conditions the N2O conversion is strongly enhanced by C3H6 and especially by CO, whereas marginal inhibition is induced by reducing agents under excess oxygen conditions. Water was found to induce a detrimental influence on N2O decomposition, with its effect however, to be partially reversible. An in situ diffuse reflectance infrared Fourier transform spectroscopic (DRIFTS) study, using CO as a probe molecule, was performed over both unmodified and REOs-modified Pt/Al2O3 catalysts to correlate their surface characteristics with their de-N2O efficacy. The results revealed that the superior catalytic performance of promoted samples could be mainly attributed to the increase of Pt dispersion as well as to the development of Pt sites with exceptional electron density, located on the metal–support interfacial area.

Catalytic decomposition of N2O over CeO2 promoted Co3O4 spinel catalyst

A series of CeO2 promoted cobalt spinel catalysts were prepared by the co-precipitation method and tested for the decomposition of nitrous oxide (N2O). Addition of CeO2 to Co3O4 led to an improvement in the catalytic activity for N2O decomposition. The catalyst was most active when the molar ratio of Ce/Co was around 0.05. Complete N2O conversion could be attained over the CoCe0.05 catalyst below 400°C even in the presence of O2, H2O or NO. Methods of XRD, FE-SEM, BET, XPS, H2-TPR and O2-TPD were used to characterize these catalysts. The analytical results indicated that the addition of CeO2 could increase the surface area of Co3O4, and then improve the reduction of Co3+ to Co2+ by facilitating the desorption of adsorbed oxygen species, which is the rate-determining step of the N2O decomposition over cobalt spinel catalyst. We conclude that these effects, caused by the addition of CeO2, are responsible for the enhancement of catalytic activity of Co3O4.

The Characteristics of Heat Transfer and the Decomposition of N2O in a Double-Spiral Heat Exchanger/Catalytic Reactor.

The use of a double-spiral heat exchanger/catalytic reactor is proposed to decompose nitrous oxide (N2O) gas, which is widely used as anesthetic in the operating rooms of hospitals. Air contaminated with N2O enters one spiral passage with a rectangular cross-section at the periphery of the reactor, is heated by exchange with the outflowing stream of air, and passes through an Rh/Al2O3 or Pd/Al2O3 catalyst layer in which N2O is decomposed to N2 and O2. The purified air is then heated electrically in the central core and finally passes through the other spiral passage to the periphery where it is exhausted into the surroundings. With this device, a sufficiently high temperature is produced in the layer of catalyst to attain an essentially complete conversion of N2O with a minimal electrical input and a minimal elevation of the temperature of the exiting air. The characteristics of heat transfer and the decomposition of N2O in a double-spiral heat exchanger/catalytic reactor for this service were investigated experimentally and computationally. As an example, with an electrical heat input of 130 watts at the core and a volumetric rate of flow of 20 L/min of air plus 60 ppm of N2O, the device produced a heat refluxing rate of over 200%, a temperature of 973 K for the air in the core, a temperature of 333 K in the exiting air, and a greater than 90% decomposition of N2O.

Catalytic Conversion of N2O to N2 over Metal-Based Catalysts in the Presence of Hydrocarbons and Oxygen

The catalytic conversion of N2O to N2 in the presence or the absence of propene and oxygen was studied. The catalysts examined in this work were synthesized impregnating metals (Rh, Ru, Pd, Co, Cu, Fe, In) on different supports (Al2O3, SiO2, TiO2, ZrO2 and calcined hydrotalcite MgAl2(OH)8·H2O). The experimental results varied both with the type of the active site and with the type of the support. Rh and Ru impregnated on γ-alumina exhibited the highest activity. The performance of the above most promising catalysts was studied using various hydrocarbons (CH4, C3H6, C3H8) as reducing agents. These experimental results showed that the type of reducing agent does not affect the reaction yield. The temperature where complete conversion of N2O to N2 was measured was independent of the reductant type. The activity of the most active catalysts was also measured in the presence of SO2 and H2O in the feed. A shift of the N2O conversion versus temperature curve to higher temperatures was observed when SO2 and H2O were added, separately or simultaneously, to the feed. The inhibition caused by SO2 was attributed to the formation of sulfates and that caused by water to the competitive chemisorption of H2O and N2O on the same active sites.