Complete Oxidation Of Ethylene Research Articles

Kinetic model of ethylene oxidation in the presence of both ethylene dichloride (1,2-dichloroethane) and carbon dioxide over a highly selective silver catalyst

Experiments were conducted to obtain the kinetic model of ethylene oxidation over a commercial highly selective catalyst αAl2O3/Ag-Cs-Re, for the first time. A gas mixture of 4.15–7.5% O2, 24.23% C2H4, 0–3.464% CO2, 0.56 ppm C2H4Cl2 and N2 at 17.4 bar and 208–240 °C was deployed, similar to that in industry. An adsorbed atomic oxygen and a gaseous ethylene molecule through modified or original Eley-Rideal mechanisms were responsible for both the partial and complete oxidation of ethylene. The partial oxidation engaged an additional uncovered active site in surface reaction compared to the complete oxidation. The surface reaction was the rate-limiting step under the experimental conditions. The proposed model is in remarkable agreement with the experimental data. The addition of CO2 to the feed was proved detrimental to the EO selectivity, only suppressing the EO production rate. Temperature raise was much in favor of the CO2 production rate, decreasing the EO selectivity.

Decomposition of Gas-Phase Organic Pollutants over Nanocrystalline Tungsten Oxide Photocatalysts under Visible-Light Irradiation

Abstract We have prepared visible-light-sensitive tungsten oxide (WO3) nanoparticle photocatalysts by a thermal plasma method and subsequent annealing treatment. The WO3 photocatalysts effectively decomposed acetaldehyde under visible-light irradiation and the activity increased with the annealing temperature. The WO3 annealed at 600 °C exhibited fivefold higher photocatalytic activity than nitrogen-doped TiO2 and commercial WO3. The high photocatalytic activity of the WO3 nanoparticles was attributed to their high crystallinity and large surface area. It was also found that the acetaldehyde decomposition rate over the WO3 nanoparticles was significantly enhanced by the addition of metal oxides such as ZrO2. The ZrO2 additive functions as an adsorbent of the acetic acid (reaction intermediate) to remove the acetic acid from the WO3 surface. Furthermore, the complete oxidation of acetaldehyde into CO2 and H2O was achieved using a Ru (0.02 wt%)-loaded WO3-ZrO2 mixed oxide under visible-light irradiation, and this catalyst exhibited excellent durability for the reaction.

Ethylene Oxidation in an Oxygen‐Deficient Environment: Why Ceria is an Active Support?

AbstractPt/CeO2, Ru/CeO2, Ir/CeO2 and the corresponding unsupported nanoparticles (Pt, Ru and Ir) were evaluated for their performance in the complete oxidation of ethylene in the presence and absence of oxygen. The lattice oxygen and oxygen storage capacity (OSC) of CeO2 had a significant influence on the interaction with the supported metal nanoparticles, which caused different catalytic behaviours in the absence of oxygen. Overall, Ru/CeO2 was more stable than Ir/CeO2 and Pt/CeO2, which results in transient promotional rate enhancement ratio (ρMSI; MSI=metal–support interaction) values that reach 200 in the first 25 min. These results were attributed to the corresponding interaction with CeO2 and negligible carbon deposition. A proposed relationship between ρMSI and the O2− consumed from CeO2 is discussed, which was suggested as a possible tool to estimate the extent of the MSI. In general, an increase in ρMSI corresponded to an increase in O2− consumed from ceria.

Complete oxidation of acetaldehyde over a composite photocatalyst of graphitic carbon nitride and tungsten(VI) oxide under visible-light irradiation

Graphitic carbon nitride (g-C3N4) was prepared by heating melamine and then its specific surface area was enlarged by hydrothermal treatment in aqueous sodium hydroxide solution. The g-C3N4 samples were blended with tungsten(VI) oxide (WO3) using a planetary mill in order to improve photocatalytic activity. The composite photocatalyst with optimized amounts of these contents showed higher photocatalytic activity for decomposition of acetaldehyde under visible-light irradiation than did original samples. From the results, we concluded that the composite photocatalyst utilizes both high oxidation ability of WO3 and high reduction ability of g-C3N4 by Z-scheme charge transfer.

Low-Temperature Complete Combustion of Volatile Organic Compounds over Novel Pt/CeO2–ZrO2–SnO2/γ-Al2O3 Catalysts

Abstract Catalytic combustion of volatile organic compounds (VOCs) such as ethylene, toluene, and acetaldehyde over novel Pt/CeO2–ZrO2–SnO2/γ-Al2O3 catalysts prepared by a coprecipitation method was investigated. The introduction of a small amount of SnO2 within the CeO2–ZrO2 lattice as a promoter was considerably effective to enhance the oxygen release and storage abilities of the catalysts, so that complete oxidation of VOCs was markedly activated. This improvement of the reducibility of the catalyst can be ascribed to the simultaneous reduction of Ce4+ and Sn4+ in the CeO2–ZrO2–SnO2 solid solutions. By the optimization of the composition and the Pt amount, complete oxidation of ethylene, toluene, and acetaldehyde was realized at temperatures as low as 55, 110, and 140 °C over a Pt(10 wt %)/Ce0.68Zr0.17Sn0.15O2.0(16 wt %)/γ-Al2O3 catalyst, respectively.

Complete oxidation of acetaldehyde on Pt/CeO 2–ZrO 2–Bi 2O 3 catalysts

Pt/CeO 2–ZrO 2–Bi 2O 3 catalysts for catalytic combustion of acetaldehyde, which is one of volatile organic compounds (VOCs), were prepared by a wet impregnation method in the presence of polyvinylpyrrolidone K25 (PVP). The addition of PVP in the preparation process was effective to enhance the specific surface area and the Pt 2+ ratio on the surface. Additionally, the pore volume and size of the catalysts were modified by the PVP addition. The Pt/CeO 2–ZrO 2–Bi 2O 3 catalysts are specific for the total acetaldehyde oxidation and CO and any acetaldehyde-derivative compounds were not observed as by-products. The catalytic activity of the Pt/CeO 2–ZrO 2–Bi 2O 3 catalysts was significantly promoted by the PVP addition and the total oxidation temperature decreased. By the optimization of the amount of platinum, the complete oxidation of acetaldehyde was realized at a temperature as low as 140 °C on a 10 wt%Pt/CeO 2–ZrO 2–Bi 2O 3 catalyst.

Complete oxidation of acetaldehyde and toluene over a Pd/WO3 photocatalyst under fluorescent- or visible-light irradiation

Acetaldehyde was completely oxidized to CO(2) over a Pd/WO(3) photocatalyst under fluorescent-light irradiation in a flow-type reactor, and Pd/WO(3) was also used to completely oxidize toluene to CO(2) in a batch reactor under visible-light irradiation.

Complete Oxidation of Ethylene over Supported Gold Nanoparticle Catalysts

Complete oxidation of ethylene was performed over supported noble metals or transition metals oxide catalysts and on monoliths under atmospheric pressure. Gold nanoparticles on Al2O3 or MxOy(M = Mo, Fe, Mn) were prepared by impregnation, coprecipitation, deposition, and dispersion methods. Nanoparticles prepared by impregnation method were irregular and very large above 25 nm, but those by coprecipitation and deposition method were uniformly nanosized at 4-5 nm. The gold nanoparticle were outstandingly active in catalyzing oxidation of ethylene. The activity order of these catalysts with preparation methods was deposition > coprecipitation > impregnation, and Au/Co3O4 prepared by deposition method showed the best performance in ethylene oxidation. The addition of gold particles to MxOy/Al2O3 catalyst enhanced the ethylene oxidation activity significantly. The main role of the gold nanoparticles apparently was to promote dissociative adsorption of oxygen and to enhance the reoxidation of the catalyst.

Complete Oxidation of Ethylene over Supported Gold Nanoparticle Catalysts

Aluminum Nitride (AIN) nanoparticles were synthesized using a Reactive Gas Condensation (RGC) technique in which a mixture of ammonia (NH3) and nitrogen (N2) gases were used for the nitridation of aluminum. NH3 served as the reactive gas, while N2 served as both a carrier gas and the inert source for particle condensation. X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) analyses revealed that at reactive gas compositions greater than 10% NH3 in N2, samples were composed entirely of hexagonal AIN nanoparticles. Electron diffraction patterns showed single crystal hexagonal AIN structure. The particle size was controlled by varying the pressure of the gas mixture. AIN nanoparticles were dispersed in a liquid matrix to enhance thermal conductivity. Results showed that a minimal addition of AIN increased the thermal conductivity of hydrocarbon pump oil by approximately 27%. The thermal conductivity became constant after reaching a maximum above 0.01 wt% AIN. Temporal stability of AIN was studied by XRD. Samples exposed to air for extended periods of time and analyzed by XRD show no degradation of crystalline AIN nanoparticles.

Rapid and complete oxidation of acetaldehyde on TiO 2 photocatalytic filter supported by photo-induced activated hydroxyapatite

The new TiO 2 photocatalytic filter supported by photo-induced activated hydroxyapatite (HAp Ca 10(PO 4) 6(OH) 2) was developed and the complete oxidation of acetaldehyde on the filter was investigated. The photocatalytic filter was fabricated by coating TiO 2 and HAp on the porous ceramics body. In the decomposition of acetaldehyde using this composite filter, CO 2 generation came to maximum at 20 min after starting of UV (254 nm) irradiation and the value was the stoichiometric to the complete oxidation. The rapid and complete oxidative decomposition of acetaldehyde can be achieved using the new photocatalytic composite filter in spite of the very small contact time, about 0.4 s through the filter and one path method. This effect would not be explained alone by the absorption capacity of HAp for acetaldehyde. Synergic and composite effect of HAp followed by radical formation under light is maximum at 254 nm.

Complete Oxidation of Ethylene by Co-Modified Mordenites under Microwave Irradiation

Addition of cobalt oxide (Co 3 O 4 ) as a heating promoter, absorbing microwave energy with high efficiency, was suggested in order to accelerate microwave heating of zeolite adsorbent or catalyst. The effect of the addition of Co 3 O 4 on the microwave heating of Co-modified mordenites prepared by the impregnation method and physical mixing was investigated. Catalytic oxidation of ethylene on Co-modified mordenites was also examined under microwave irradiation. Co 3 O 4 promoted microwave heating of the mordenite bed when Co 3 O 4 and mordenite were mixed physically. The physical mixture with Co 3 O 4 of 50 wt% was heated up to 518 K by microwave irradiation. The desorption peak of water for pellet type Co-modified mordenite was very sharp in microwave heating after pre-adsorption of water vapor and most of adsorbed water desorbed in the initial stage of the microwave heating. The sharp desorption peak of water indicates that the pelletized sample was heated to higher temperatures than powder one. In the case of the pelletized Co-modified mordenite with Co 3 O 4 of 75 wt%, adsorbed water on mordenite was almost desorbed during microwave irradiation. Co 3 O 4 had both functions of the heating promoter and catalyst, and ethylene was removed with high conversion (93%) when the pelletized mixture of Co 3 O 4 (75 wt%) and mordenite was irradiated by microwave under steady feed of ethylene, water vapor, and oxygen.

The Study of the Nature of Adsorbed Species to Build a Bridge between Surface Science and Catalysis: Problems of Pressure and Material Gap

This review substantiates the molecular approach to the study of the catalytic action of various systems, which consists in the comparative study of the nature and reactivity of adsorbed species and considering the problems of pressure and material gaps. The pressure gap problem can be solved by a continuous increase in the pressure of the reaction mixture, including carrying out in situ studies. The solution to the problem of material gap is possible when one passes from bulk to dispersed samples, which model real supported catalysts. As the last step that can build a bridge between surface science and catalysis, the study of nanoparticle reactivity toward the reactants of a catalytic reaction with varying sizes of nanoparticles is proposed. The scope of such an approach is demonstrated by the study of silver catalysts of ethylene epoxidation. It was found that the catalytic action of silver in the process of ethylene oxide synthesis is determined by the possibility of formation of electrophilic adsorbed atomic oxygen. Its formation is more efficient under the action of reaction mixtures at high pressures and on the surfaces of silver species with sizes smaller than 50 nm. It is shown that the reaction center should also contain the nucleophilic form of Oads, which itself is only active in the complete oxidation of ethylene but creates the Ag1+ sites for ethylene adsorption. The disappearance of Onucl with a decrease in the size of silver particles below 50 nm leads to a drastic decrease in the rate of ethylene epoxidation. The reaction mechanism made it possible to propose systems with an abnormally high value of selectivity to ethylene oxide (>90%).

Electrochemical promotion of RuO 2-catalysts for the gas phase combustion of C 2H 4

The electrochemical promotion of RuO 2 catalysts interfaced with yttria stabilised zirconia was studied for the combustion of ethylene. The complete oxidation of ethylene can be described by an Eley–Rideal type mechanism. In situ work function measurements were used to proof the mechanism. A linear dependence between the catalyst work function and the surface coverage of the only adsorbed reactant, chemisorbed oxygen, was found. Cyclic voltammetric measurements were used to study the RuO 2/YSZ interface. The electrochemically active zone was located at the RuO 2/YSZ interface and next to the three-phase boundary with only a small extension on the gas-exposed catalyst surface.

In situ controlled electrochemical promotion of catalyst surfaces: Pd-catalysed ethylene oxidation

The catalytic activity of polycrystalline Pd films deposited on 8 mol% Y2O3-stabilized–ZrO2 (YSZ), an O2−-conductor, can be altered reversibly by varying the potential of the Pd catalyst film via the effect of nonfaradaic electrochemical modification of catalytic activity (NEMCA) or electrochemical promotion. The complete oxidation of ethylene was investigated as a model reaction in the temperature range 290–360 °C and atmospheric total pressure. The rate of C2H4 oxidation can be reversibly enhanced by up to 45% by supplying O2− to the catalyst via positive current application. The steady-state rate change is typically 103–104 times larger than the steady-state rate I/2F of electrochemical supply or removal of promoting oxide ions. The observed behaviour is discussed on the basis of previous NEMCA studies and the mechanism of the reaction.

Acetaldehyde Gas‐Sensing Properties and Surface Chemistry of SnO2 ‐ Based Sensor Materials

Acetaldehyde gas‐sensing properties of , loaded with and without a noble metal, were investigated, and the results are discussed in terms of the level of sensor resistance in air and oxidation behavior of acetaldehyde over sensor materials. Of the noble metals tested, Rh was found to be the best sensitizer, and the highest sensitivity was achieved with loaded with 0.1 wt % Rh at 350°C. The sensitivity enhancement is explained by the increased sensor resistance in air due to the electronic interaction between Rh and . In addition, the almost complete oxidation of acetaldehyde and its derivatives at 350°C is also found to be responsible for its high sensitivity. © 1999 The Electrochemical Society. All rights reserved.

Theoretical studies on the catalytic activity of Ag surface for the oxidation of olefins

Systematic theoretical studies for the mechanisms of the epoxidation and complete oxidation of ethylene and propylene over silver surface as well as the reactivity and the stability of oxygen species on Cu, Ag, and Au surfaces have been presented. The . . dipped adcluster model DAM combined with the ab initio Hartree)Fock HF , second- . order Moller-Plesset MP2 , and SACrSAC-CI symmetry-adapted clusterrconfiguration . interaction methods are used. These studies clarify the origin of silver as a unique effective catalyst for the epoxidation of ethylene and the different mechanisms for the oxidation of olefins over silver surface. For the epoxidation of ethylene, the superoxide O y , which is molecularly adsorbed in bent end-on geometry on the silver surface, is the 2 active species. The origin of the unique catalytic activity of silver for the epoxidation of ethylene is due to its ability to adsorb oxygen as the superoxide species. Such an adsorbed species cannot be stable or exist on Cu and Au surfaces. For the oxidation of propylene, both reaction mechanisms initiated by the activation of olefinic carbon and by the activation of the allyl hydrogen exist. The activation of the allyl hydrogen is the origin of the complete oxidation of some olefins over silver surface. The present results not only let us have a better understanding of the reaction mechanisms of olefins over silver surface but also supply a basic idea for the new catalyst design of the epoxidation

Non-Faradaic Electrochemical Modification of Catalytic Activity: VIII. Rh-Catalyzed C 2H 4 Oxidation

The catalytic activity of polycrystalline Rh films deposited on 8 mol% Y 2O 3-stabilized ZrO 2, (YSZ), an O 2-− conductor, can be altered dramatically and reversibly by varying the potential of the Rh catalyst film. The complete oxidation of ethylene was investigated as a model reaction in the temperature range 300 to 400°C and at atmospheric total pressure. The rate of C 2H 4 oxidation can be reversibly enhanced by up to 100 times by supplying O 2− to the catalyst via positive potential application (up to 1.5 V). This is the highest rate enhancement observed so far with in situ electrochemical promotion studies. The steady-state rate increase is typically 10 4 times larger than the steady-state rate of O 2− supply to the catalyst. It was also found that varying the catalyst potential causes the appearance of the well-known compensation effect with an isokinetic point at 372°C. As in previous studies of the effect of non-Faradaic electrochemical modification of catalytic activity (NEMCA) the observed behaviour is due to the promotional action of back-spillover oxide ions which migrate from the YSZ solid electrolyte onto the catalyst surface under the influence of the applied potential. The back-spillover oxide ions are less reactive with C 2H 4 than normally chemisorbed oxygen and act as promoters by affecting the binding strength of chemisorbed oxygen and ethylene.

Modifying action of carbon dioxide in catalytic oxidation of ethylene on silver

Carbon dioxide exerts a strong inhibitory effect on oxygen adsorption and complete oxidation of ethylene on silver but has little effect on the rate of ethylene oxidation to ethylene oxide.

Poisoning and promoting effects of additives on the catalytic behavior of metal clusters

Extended Hückel calculations are used to explain the mechanisms by which additives such as Cu, Ag, Cl, and S affect the catalytic behavior of Pt or Ag clusters. The complete oxidation of ethylene over Pt Al 2O 3 , the oxidation of CO over Pt Al 2O 3 , and the ethylene epoxidation over supported silver catalysts are used as examples. It is found that Cu or Ag, unlike S, change mainly the net atomic population (the localized electrons around each atom) and very slightly the bond population among the atoms of the Pt clusters. The increased electron density at the surface of Pt clusters due to the electron transfer from Cu or Ag facilitates the electron transfer from the cluster to the π ∗ antibonding MO of adsorbed O 2. As a result, the dissociative chemisorption of O 2 over Cu- or Ag-treated Pt catalyst is enhanced and the reaction rates for the complete oxidation of C 2H 4 and the oxidation of CO are increased. The electronic effect of Cu on the electron redistribution in the clusters is stronger than that of Ag. Sulfur inhibits these reactions because it is a strong electron acceptor and the competition for electrons, as well as the destabilization of the MOs of the cluster, reduces the dissociative chemisorption of O 2. The inhibition effect of sulfur overcomes the promoting effect of Cu or Ag. Two forms of chemisorbed O 2 molecule, normal and parallel to the surface of a Ag (111) cluster, have been assumed in the calculations. For both forms, the coadsorption of chlorine results in a significant energy shift of the O 2 dissociation curves toward higher energies, thus inhibiting the chemisorption of O 2 and its dissociation. As a consequence, a loss in overall activity occurs, while the selectivity for epoxidation is higher. In the presence of chlorine, the O 2 adsorbed normal to the surface seems to be more stable than the O 2 adsorbed parallel to the surface. In the absence of chlorine, the former form becomes less stable than the latter if the elongation of the OO bond is larger than 1.4 Å.

The oxidation of ethylene over a supported platinum catalyst

AbstractThe complete oxidation of ethylene over a 0.3% Pt/Al2O3 catalyst, at ethylene concentration of ≤ 1.0 mol/m3 and oxygen concentrations of 0.16 to 8.6 mol/m3, was studied in a recycle reactor at temperatures of 362 to 472 K. The activity of the catalyst was influenced by pretreatment and reaction conditions causing fluctuations in rate measurements. Nevertheless, a simple rate function, r =Ae−E/RT[O2]/[C2H4], fitted the data as well as more complicated rate functions.