Continuous Catalytic Oxidation Research Articles

Plasma driven exsolution of Ca as the adjacent dechlorinated site in La0.8Ca0.2MnO3 perovskite: A highly mineralization chlorobenzene oxidation catalyst

The degradation of chlorine-containing volatile organic compounds (CVOCs) catalytic combustion technology is subject to the catalyst chlorine poisoning, which is resulted from the chlorination of active phases, even though the structural stable perovskite. The reaction between Ca species and dissociated chlorine species is demonstrated as an efficient way to inhibited chlorine poisoning of the active phase. Herein, a Ca substituted partial La prepared La0.8Ca0.2MnO3 (named as L8C2MO) perovskite was treated by 5% H2/Ar plasma driven route (the treated sample was denoted as L8C2MO-P), which was applied for the chlorobenzene oxidation removal. The integrated characterization results of XRD, XPS, HRTEM, etc. confirmed that Ca (mainly exhibited as CaCO3) was successfully exsolved from La0.8Ca0.2MnO3 and simultaneously leaved oxygen vacancies on the surficial layers. The continuous catalytic oxidation experiments illustrated that the conversion efficiency of L8C2MO was unexpectedly decreased compared with that of LaMnO3 (LMO in short) sample, while that of L8C2MO-P was nearly maintained the oxidation capacity, with approximately 12 °C of 90% chlorobenzene conversion temperature (T90) higher than that of LMO. Importantly, the CO2 and inorganic chlorine species yields were significantly enhanced for L8C2MO and L8C2MO-P. The characteristic of used samples showed a possible chlorinated Ca species formation while the status of Mn phases was hardly changed, suggesting the exsolved Ca could inhibit the poison of Mn sites by binding with dissociative chlorine species. Additionally, oxygen vacancies that generated along with Ca exsolution process was definitely contributed to the deep oxidation of chlorobenzene. The possible reaction route was also studied by in situ DRIFTS and GCMS. The work provides a potential route as in situ growth of adjacent sites to protect active phases from chlorine poison in CVOCs catalytic oxidation process.

Key factors maintaining catalytic ammonium oxidation activity of manganese oxide active filter media: The role of bicarbonate

The removal of ammonium (NH4+-N) via the catalytic oxidation of manganese oxide (MnOx) active filter media is a new technology. In this study, three different types of water (groundwater, surface water, and deionized water) were used to investigate the key factors affecting the sustainability of the catalytic activity of active MnOx filter media. The NH4+-N removal performance of the MnOx active filter media differed in different water environments, especially in deionized water, and the removal ability of NH4+-N was gradually decreased with increasing the running time. The continuous NH4+-N removal kinetics in different water environments were investigated. The rate constant k of the NH4+-N removal kinetics gradually decreased with NH4+-N removal, even in the groundwater environment, and the rate constant k decreased from 1.18 to 0.97 to 0.19. The addition of bicarbonate enhanced the ability to remove NH4+-N again, which confirmed that bicarbonate was the driving force for the continuous catalytic oxidation of NH4+-N. Based on the FTIR and XPS analysis results, the bicarbonate structure was consumed during the continuous removal of NH4+-N. Moreover, bicarbonate could affect the structure of MnOx, and then affected the electron transfer process of different valence manganese ions during the catalytic oxidation of NH4+-N, especially the conversion of Mn3+ to Mn2+. This study provides new insights into the theory of continuous catalytic oxidation by MnOx for NH4+-N removal.

Continuous selective conversion of methane to methanol over a Cu-KFI zeolite catalyst using a water-O2 mixture as the oxygen source.

The continuous catalytic oxidation of methane to methanol on a Cu-KFI zeolite using water-O2 mixture as the oxidant is reported. A high methanol space-time yield of 880.3 mmol molCu-1 h-1 with 83% selectivity is achieved at 450 °C. Isotopic labelling experiments show that both H2O and O2 provide the oxygen source in this catalytic methane-to-methanol conversion reaction.

Rapid Discrimination of Adsorbed Oxygen and Lattice Oxygen in Catalysts by the Cataluminescence Method.

Adsorbed oxygen and lattice oxygen are crucial parameters for catalyst characterization and catalytic oxidation mechanism. Therefore, rapid discrimination of adsorbed oxygen and lattice oxygen is highly desired. Herein, a direct correlation between cataluminescence (CTL) kinetic curve and oxygen species was discovered. The adsorbed oxygen-catalyzed CTL only lasted for a few minutes, whereas the lattice oxygen-catalyzed CTL could exhibit hours of continuous luminescence. The long-term CTL was attributed to the slow migration of lattice oxygen in a slow and continuous catalytic oxidation reaction. In addition to the discrimination between the adsorbed oxygen and lattice oxygen by the CTL kinetic processes, the corresponding CTL intensity was positively proportional to their amounts. Accordingly, the developed catalytic oxidation-related CTL can be used as an indicator for rapid discrimination and determination of adsorbed oxygen and lattice oxygen in catalysts. Oxygen species detected by the proposed CTL method not only matched well with those obtained by conventional X-ray photoelectron spectroscopy and O2-temperature programmed methods but also offered some distinguished advantages, such as convenient operation, fast response, and low cost. It can be expected that the established oxygen-responsive CTL probe has great potential in distinguishing adsorbed oxygen and lattice oxygen in various catalysts.

Super-high N-doping promoted formation of sulfur radicals for continuous catalytic oxidation of H2S over biomass derived activated carbon

N-doped biomass derived activated carbon (NBAC) with superhigh content of surface N atom (17.2 at.%) and microchannel structure was prepared successfully via one-step pyrolysis method using supramolecular melamine cyanurate (MCA) as nitrogen source, and the breakthrough sulfur capacity was very high up to 1872 mg/g for catalytic oxidation of H2S under room temperature. The superhigh content of N atoms (17.2 at.%) provided massive active sites for the catalytic oxidation of H2S and formation of sulfur radicals which further helped the dissociation of H2S and O2, resulting in continuous catalytic oxidation of H2S over NBAC after the coverage of nitrogenous sites by multilayer sulfur. Moreover, the microchannel structure with enhanced mesopore volume promoted the mass transfer of reactants and emigration of product elemental sulfur to form multilayer sulfur. This work could provide an insight into the NBAC with superhigh N-doping content for continuous catalytic oxidation of H2S at room temperature.

Silicotungstic acid modified CeO2 catalyst with high stability for the catalytic combustion of chlorobenzene

The catalysts’ redox capacity and surface acidity was important during the catalytic combustion of chlorobenzene (CB). CeO2 showed great attractiveness due to its high oxygen storage capacity. Furthermore, the increase of acidity on the catalyst surface could improve the resistance to the chlorine poisoning. In this work, the silicotungstic (HSiW) modified CeO2 catalysts prepared by four cerium salts and exhibited the different morphologies and catalytic activity. The HSiW modified CeO2 catalyst prepared by Ce(CH3COO)3 (Cat-A) exhibited the best catalytic activity due to its abundant surface weak acid sites, more Ce3+ species and surface adsorption oxygen. The HSiW mainly located on the CeO2 (111) planes of the Cat-A, which was conducive to redox property of CeO2, thus promoting the deep oxidation of CB. Meanwhile the redox ability together with the weak acidity influenced the catalytic efficiency at low temperature. And the redox ability played a major role at high temperature. In addition, the Cat-A still possessed high stability and water resistance and maintained high activity after continuous catalytic oxidation of CB at 235 and 295 °C for 100h, exhibiting the possibility of industrial application.

Continuous Catalytic Oxidation of Glycerol to Carboxylic Acids Using Nanosized Gold/Alumina Catalysts and a Liquid-Phase Flow Reactor.

Here, we report the development of catalysts comprising highly dispersed Au on an alumina (Al2O3) support for the oxidation of glycerol to high-value carboxylic acids in a liquid-phase flow reactor. The catalysts were prepared by means of a deposition–precipitation method. To ensure that the catalysts could be used for long-term catalytic conversions in a liquid-phase flow reactor, we chose an alumina support with high temperature stability and a particle size (50–200 μm) large enough to prevent leakage of the catalyst from the reactor. One of the five catalysts had a high catalytic activity for the conversion of glycerol to the high-value carboxylic acids, glyceric acid and tartronic acid (conversion of glycerol >70%), and the catalyst retained its catalytic activity over long-term use (up to 1770 min). Pretreatment of the catalyst with fructose, a mild reductant, increased the activity of the catalyst. Scanning transmission electron microscopy revealed three Au species highly dispersed on the surface of the alumina support—Au nanoparticles (mode = 7.5–10 nm), Au clusters (1–2 nm), and atomic Au.

Continuous Heterogeneously Catalyzed Oxidation of Benzyl Alcohol in a Ceramic Membrane Packed-Bed Reactor

A ceramic membrane reactor was investigated for the continuous catalytic oxidation of benzyl alcohol with oxygen. The reactor had a concentric configuration. An inner tube created an annulus for the catalyst packed-bed (0.9 wt % Au− Pd/TiO2, particle size 90−125 μm) through which the liquid phase (benzyl alcohol, neat or dissolved in o-xylene) flowed. This was followed by the tubular ceramic membrane, which consisted of layers of alumina and a zirconia top layer with a nominal average pore size of 50 nm. The role of the membrane was to provide an interface for gas and liquid to come in contact. Pure oxygen was fed to the opposite side of the membrane in the outer shell of the reactor. Temperature affected conversion but not selectivity, possibly because of insufficient supply of oxygen. However, increasing catalyst contact time or decreasing benzyl alcohol concentration improved selectivity and conversion, indicating that a key parameter was the balance between oxygen supply by the membrane vs oxygen demand by the reaction. By adjusting the operating parameters, reaction performance improved. Selectivity to benzaldehyde 88% and conversion of benzyl alcohol 75% were obtained at 3.2 bara of gas pressure, 24444 gcat·s/galcohol catalyst contact time, 0.5 M benzyl alcohol concentration, and temperature of 120 °C. This performance was comparable to simulated trickle bed operation, where oxygen and substrate were premixed before entering the catalyst packed bed. The membrane reactor offers safer operation, since flammable oxygen/organic mixtures formed in the trickle bed are avoided.

Ni supported on Mg–Al oxides for continuous catalytic wet air oxidation of Crystal Violet

The continuous catalytic oxidation of aqueous Crystal Violet (CV) solutions has been investigated using a nickel catalysts (7wt%) supported over Mg–Al mixed oxides in a trickle-bed reactor. The influence of the temperature, pressure, gas flow and dye initial concentration were studied in the catalytic wet air oxidation of CV. The catalyst showed a very stable activity up to 350h on stream with an average total organic carbon (TOC) conversion of 64%. CV and TOC removal were very sensitive to the temperature. Dye conversion augmented from 44.7% at 120°C to 86.1% at 180°C. Dye conversion varied from 62.6 to 18.4%, TOC from 59.5 to 18.7% and TN from 66.6 to 14.0% within 10 to 50ppm of initial dye concentration. The leaching of Ni was 6wt% of the initial metal present in the catalyst and a 0.59% of carbonaceous deposit was formed onto the catalyst surface.

Low temperature catalytic oxidation of aldehydes using wood fly ash and molecular oxygen

Aldehydes, such a 2-methylbutanal (2-MB) and 3-methylbutanal (3-MB), are odorous and regulated VOCs generated in the poultry rendering process that are ineffectively removed in chemical wet scrubbers. It was theorized that wood fly ash or selective crystalline phases in the ash could act to catalyze the oxidation of aldehydes at room temperature in the presence of ClO2, resulting in a low-cost/energy air pollution control method. Results indicate that wood fly ash catalyzed the oxidation (i.e., breakdown) of 2-MB and 3-MB both in the presence of ClO2 and with just O2 (i.e., air) itself, potentially via a free radical mechanism. Aldehyde oxidation did not occur at measurable rates without the wood fly ash or activated carbon. The presence of ClO2 did not increase the rate, but altered the end products of oxidation. Wood fly ash also catalyzed the oxidation of 2-MB in the presence of air, leading to the appearance of 2-butanone, compared to acetone from 3-MB. Contact times of 30s reduced 3-MB levels by ∼40% in bench scale, batch reactors. Similar results were found using activated charcoal (i.e., in terms of contact times), except that higher molecular weight compounds appeared to be formed. Continuous catalytic oxidation of 3-MB using wood fly ash was also demonstrated in a fixed-bed reactor at room temperature; the overall oxidation rate appeared to be first order with respect to 3-MB and a representative conversion of 20% at an inlet concentration of 67ppmv and 2s residence time (GHSV 18001/h, 25°C, 1atm) was measured. Results indicate the potential of using inexpensive solid waste materials to breakdown C5 aldehydes in rendering emissions to CO2, H2O, and less odor offensive compounds, but a carbon balance on the reaction and complete identification of end products are required for implementation.

Continuous catalytic oxidation of solid alcohols in supercritical CO 2: A parametric and spectroscopic study of the transformation of cinnamyl alcohol over Pd/Al 2O 3

Cinnamyl alcohol was oxidized to cinnamaldehyde in a continuous fixed-bed reactor with molecular oxygen over an alumina-supported palladium catalyst in supercritical carbon dioxide modified with toluene. A strong dependence of the reaction performance on pressure and oxygen concentration in the feed was found. Optimization of the reaction conditions resulted in a higher catalytic activity than in the liquid phase. At 120 bar, 80 °C, and double stoichiometric oxygen concentration, a turnover frequency of 400 h −1 at a selectivity of 60% to cinnamaldehyde was achieved. Spectroscopic investigations and the knowledge of the selectivity pattern turned out to be crucial for a deeper understanding of the reaction allowing a rational optimization. Under almost all experimental conditions (even at high oxygen concentration) hydrogenated byproducts, stemming from internal hydrogen transfer reactions, were detected in the effluent. This indicated that alcohol dehydrogenation was the first reaction step; this finding was further confirmed by spectroscopic investigations. In situ XANES and EXAFS revealed that in the entire experimental range investigated, the palladium constituent was mainly in a reduced state, and its surface could be oxidized only in the absence of cinnamyl alcohol in the feed. Bulk-phase behavior studies and investigations at the catalyst–fluid interface, performed by visual inspection and combined transmission and ATR-IR spectroscopy, demonstrated that the reaction performed best in the biphasic region. Moreover, cinnamaldehyde and carbon dioxide, but hardly any toluene and cinnamyl alcohol, were detected inside the porous catalyst, indicating a significantly different product composition inside the porous catalyst compared with the bulk phase.

5755977 Continuous catalytic oxidation process : Gurol Mirat; Lin Shu-Sung Philadelphia, PA, United States assigned to Drexel University

5755977 Continuous catalytic oxidation process : Gurol Mirat; Lin Shu-Sung Philadelphia, PA, United States assigned to Drexel University