Catalytic performance of Co3O4/CeO2 and Co3O4/CeO2–ZrO2 composite oxides for methane combustion: Influence of catalyst pretreatment temperature and oxygen concentration in the reaction mixture

The influence of catalyst pre-treatment temperature (650 and 750 °C) and oxygen concentration (λ = 8 and 1) on the light-off temperature of methane combustion has been investigated over two composite oxides, Co₃O₄/CeO₂ and Co₃O₄/CeO₂–ZrO₂ containing 30 wt.% of Co₃O₄. The catalytic materials prepared by the co-precipitation method were calcined at 650 °C for 5 h (fresh samples); a portion of them was further treated at 750 °C for 7 h, in a furnace in static air (aged samples).

Tests of methane combustion were carried out on fresh and aged catalysts at two different WHSV values (12 000 and 60 000 mL g⁻¹ h⁻¹). The catalytic performance of Co₃O₄/CeO₂ and Co₃O₄/CeO₂–ZrO₂ were compared with those of two pure Co₃O₄ oxides, a sample obtained by the precipitation method and a commercial reference. Characterization studies by X-ray diffraction (XRD), BET and temperature-programmed reduction (TPR) show that the catalytic activity is related to the dispersion of crystalline phases, Co₃O₄/CeO₂ and Co₃O₄/CeO₂–ZrO₂ as well as to their reducibility. Particular attention was paid to the thermal stability of the Co₃O₄ phase in the temperature range of 750–800 °C, in both static (in a furnace) and dynamic conditions (continuous flow). The results indicate that the thermal stability of the phase Co₃O₄ heated up to 800 °C depends on the size of the cobalt oxide crystallites (fresh or aged samples) and on the oxygen content (excess λ = 8, stoichiometric λ = 1) in the reaction mixture. A stabilizing effect due to the presence of ceria or ceria–zirconia against Co₃O₄ decomposition into CoO was observed.

Moreover, the role of ceria and ceria–zirconia is to maintain a good combustion activity of the cobalt composite oxides by dispersing the active phase Co₃O₄ and by promoting the reduction at low temperature.     

Experimental Evaluation of Thermal Properties of Grouting Materials

This study is aimed at the thermal analysis of sealant mortar （usually a mixtures of bentonite and cemem with addition of sand） used in geothermal cooling and heating. In particular, thermal conductivity and diffusivity measurements were performed on differem sealant mixtures by using Hot Disk thermal constants analyzer in order to identify the interesting thermal properties of grouting materials. The grouting materials that we considered are of porous nature and, if used in the presence of groundwater, have different levels of imbibitions. It is important to know the thermal behavior of these materials at different water content. A first set of measurements was performed on a not-tinted material at room temperature; then the samples were led to saturation conditions by contact capillary imbibitions with a cotton wool layer moistened in water. The determination of thermal conductivity in these test conditions appears to be critical compared to the measuremems on non-timed sample. The thermal conductivity tests have revealed how the thermal behavior of the samples analyzed is essentially determined by the density and water content of the material： in fact, the thermal conductivity increases of two to three times the value of the not-tinted material.     

Kinetic study of 1,5-cyclooctadiene hydro-isomerization on Pd/pumice catalysts

A new route for obtaining 1,4-cyclooctadiene by catalytic isomerization of 1,5-cyclooctadiene at low temperature in presence of H₂ in a three-phase reactor is presented. Wei, Prater and Silvestri methods are used for the kinetic studies. A comparison of the activity-selectivity patterns of the Pd/pumice catalysts with Pd on silica and Pt and Pd–Pt on pumice catalysts is performed. Although Pt catalysts are not active in the hydro-isomerization of 1,5-cyclooctadiene, the presence of small amount of Pt in Pd/pumice catalysts increases the yield to 1,4-cyclooctadiene. Besides the catalyst characteristics, temperature and H₂ pressure influence the production of 1,4-cyclooctadiene. A mechanism of the process is proposed. This revised version was published online in July 2006 with corrections to the Cover Date.     

Insights into SO2 Interaction with Pd/Co3O4–CeO2 Catalysts for Methane Oxidation

The catalytic performance and the sulphur resistance of a Pd (0.7 wt%) catalyst supported over Co₃O₄(30 wt%)–CeO₂(70 wt%) mixed oxide were investigated in the oxidation of methane under stoichiometric and lean conditions. The catalytic behaviour was compared with that of two reference catalysts, palladium supported over pure Co₃O₄ and CeO₂. Catalysts were characterized by XRD, BET, XPS and FTIR measurements. Regeneration by a CH₄-reducing treatment at 600 °C was investigated.     

Rheology of cellulose nanofibrils and silver nanowires for the development of screen-printed antibacterial surfaces

Journal of Materials Science - TEMPO (2,2,6,6-tetramethylpiperidine-N-oxyl)-oxidized cellulose nanofibrils (T-CNF) and silver nanowires (Ag NWs) were formulated as active inks. Their rheological...     

CoMo catalysts supported on aluminosilicates: synergy between support and sodium effects

The structural properties and the hydrodesulfurization (HDS) activity of sodium doped and sodium free CoMo catalysts supported on amorphous aluminosilicates (ASA) were investigated as a function of different SiO₂:Al₂O₃ ratios. The support yielding the most active catalyst, (66% alumina) doped with different amounts of sodium, was used for a series of similar catalysts in order to study the effect of the alkali ion on the catalytic performance. The supports were prepared by sol–gel method and the catalysts were prepared by incipient wet impregnation method. The structure and the surface of the various samples were investigated by X-ray diffraction (XRD), temperature-programmed reduction (TPR) and X-ray photoelectron spectroscopy (XPS). The catalytic behaviour was tested in the hydrodesulfurization of thiophene carried out in a continuous flow system at atmospheric pressure, in a range of temperature between 603 and 633 K. Changes of activity with the support composition were observed. The presence of sodium, modifying the Brønsted acidity of the supports, enhances such effect. Moreover, the increase of the activity with increasing amount of sodium was a clear indication of the promoting effect of the alkali ion.     

Pd/Co3O4 catalyst for CH4 emissions abatement: study of SO2 poisoning effect

A catalyst with 0.7 wt% Pd load supported over Co₃O₄ oxide was investigated in the methane oxidation by operating under CH₄/O₂ stoichiometric conditions. The effect of the noble metal addition on the activity of bare Co₃O₄ was evaluated. Samples were characterized by BET, XRD, TPR and XPS analyses. The SO₂ poisoning of Pd catalyst and Co₃O₄ was studied by performing CH₄ oxidation tests under stoichiometric conditions in SO₂ (1 ppm or 10 ppm)_. Experiments evidenced that in our conditions the low amount of SO₂ doesn’t influence the Pd behaviour, whereas in presence of 10 ppm of SO₂ some deactivation occurs that becomes more evident above 450 °C at which the catalyst doesn’t reach 100% of methane conversion. Catalytic tests performed over Co₃O₄ and the Pd supported catalyst, after a treatment at 350 °C for 15 h in 10 ppm SO₂/He, suggest that Co₃O₄ is a sulphating support, as confirmed by XPS analysis. Therefore, an important role in lowering the sulphur poisoning of Pd may be played by Co₃O₄.     

Combined CO/CH4 oxidation tests over Pd/Co3O4 monolithic catalyst: Effects of high reaction temperature and SO2 exposure on the deactivation process

CO and CH₄ combined oxidation tests were performed over a Pd (70 g/ft³)/Co₃O₄ monolithic catalyst in conditions of GHSV = 100,000 h⁻¹ and feed composition close to that of emission from bi-fuel vehicles. The effect of SO₂ (5 ppm) on CO and CH₄ oxidation activity under lean condition (λ = 2) was investigated. The presence of sulphur strongly deactivated the catalyst towards methane oxidation, while the poisoning effect was less drastic in the oxidation of CO. Saturation of the Pd/Co₃O₄ catalytic sites via chemisorbed SO₃ and/or sulphates occurred upon exposure to SO₂. A treatment of regeneration to remove sulphate species was attempted by performing a heating/cooling cycle up to 900 °C in oxidizing atmosphere. Decomposition of PdO and Co₃O₄ phases at high temperature, above 750 °C, was observed. Moreover, sintering of Pd⁰ and PdO particles along with of CoO crystallites takes place.     

Oxidative degradation properties of Co-based catalysts in the presence of ozone

Four series of cobalt-based catalysts, such as bare Co₃O₄ and CoO, CoO_x–CeO₂ mixed oxides, CoO_x supported over alumina and alumina–baria and CoMgAl and CoNiAl hydrotalcites have been synthesized and investigated for the oxidative degradation of phenol in the presence of ozone. Characterizations were obtained by several techniques in order to investigate the nature of cobalt species and their morphological properties, depending on the system. Analyses by XRD, BET, TPR, UV–visible diffuse reflectance spectroscopy and TG/DT were performed.

The CoNiAl hydrotalcite exhibits, after 4 h of reaction, the highest phenol ozonation activity followed by Co(3 wt%)/Al₂O₃–BaO and CoMgAl. The samples Co(1 wt%)/Al₂O₃–BaO and Co(1 and 3 wt%)/Al₂O₃ show a comparable medium activity, while the oxidation properties of bare oxides Co₃O₄, CoO and CoO_x–CeO₂ are really low. Leaching of cobalt ions in the water solution was detected during the reaction, the amount varied depending on the nature of catalysts. A massive release was observed for the CoMgAl and CoNiAl hydrotalcites, while cobalt catalysts over alumina and alumina–baria look much more stable. The recycle of CoO_x/Al₂O₃ and CoO_x/Al₂O₃–BaO was studied by performing three consecutive cycles in the phenol oxidation. Because of the potential interest of the cobalt-supported catalysts in the ozonation process, the oxidative degradation of naphtol blue black was also investigated.

On the basis of TPR and UV–visible results it appears that highly dispersed Co²⁺ ions especially present over Co(3 wt%)/Al₂O₃–BaO are the main active sites for phenol and naphtol blue black oxidative degradation by ozone.     

Alumina and Alumina–Baria Supported Cobalt Catalysts for DeNO x : Influence of the Support and Cobalt Content on the Catalytic Performance

Co/Al₂O₃ and Co/Al₂O₃–BaO catalysts with low cobalt loading (0.1, 0.3 and 1 wt%) for the selective catalytic reduction (SCR) of NO _x by C₃H₆ were prepared. The distribution of cobalt species was investigated by UV–vis diffuse reflectance spectroscopy and by H₂-TPR in order to identify the active cobalt species in hydrocarbons (HC)-selective catalytic reduction (SCR). It was found that the nature of cobalt species strongly depends on the cobalt loading as well as on the properties of the support. The barium addition to the alumina slows down solid state diffusion processes, improving the thermal stability of the support and preventing diffusion of cobalt into the bulk. Highly dispersed surface Co²⁺ species over alumina were identified as active sites in the NO-SCR process. Accordingly, a high concentration of surface Co²⁺ sites in Co 1 wt%/Al₂O₃ improves the catalytic performance in NO-SCR, the long term stability as well as the water tolerance. On the contrary, the formation of Co₃O₄ particles in Co 1 wt%/Al₂O₃–BaO promotes the propylene oxidation by oxygen, decreasing the activity and selectivity of the catalyst in NO reduction.