Plasma catalysis:distinguishing between thermal and chemical effects

The goal of this study is to develop a method to distinguish between plasma chemistry and thermal effects in a Dielectric Barrier Discharge nonequilibrium plasma containing a packed bed of porous particles. Decomposition of CaCO 3 in Ar plasma is used as a model reaction and CaCO 3 samples were prepared with different external surface area, via the particle size, as well as with different internal surface area, via pore morphology. Also, the effect of the CO 2 in gas phase on the formation of products during plasma enhanced decomposition is measured. The internal surface area is not exposed to plasma and relates to thermal effect only, whereas both plasma and thermal effects occur at the external surface area. Decomposition rates were in our case found to be influenced by internal surface changes only and thermal decomposition is concluded to dominate. This is further supported by the slow response in the CO 2 concentration at a timescale of typically 1 minute upon changes in discharge power. The thermal effect is estimated based on the kinetics of the CaCO 3 decomposition, resulting in a temperature increase within 80 °C for plasma power from 0 to 6W. In contrast, CO 2 dissociation to CO and O 2 is controlled by plasma chemistry as this reaction is thermodynamically impossible without plasma, in agreement with fast response within a few seconds of the CO concentration when changing plasma power. CO forms exclusively via consecutive dissociation of CO 2 in the gas phase and not directly from CaCO 3 . In ongoing work, this methodology is used to distinguish between thermal effects and plasma-chemical effects in more reactive plasma, containing, e.g., H 2 . </p

Magnetically-extractable hybrid of magnetite, mesoporous silica and titania for the photo-degradation of organic compounds in water

This work addresses the development of a magnetically extractable magnetite-silica-titania photocatalyst to be applied in the degradation of organic compounds in water. MCM-41 silica was successfully deposited on magnetite, providing large surface area for anchoring of TiOx species, and preventing thermally induced conversion of magnetite to hematite. A good correlation between the calculated values and amount of titania deposited on the silica-covered magnetite particles was obtained for a synthesis route involving the treatment of magnetite-silica in boiling ethanolic Ti-precursor solution. Photocatalytic activity in conversion of 4-chlorophenol could only be observed for compositions containing larger than ∼50 wt% titania, whereas increasing the titania content did not significantly improve performance. Experiments carried out at pH ∼ 3.0 and ∼7.2 demonstrated the performance is relatively pH-independent. The structure activity-correlation of the materials is briefly discussed.</p

Catalytic effect of water on calcium carbonate decomposition

The search for cheap solutions for carbon dioxide capture in order to prevent global warming is still challenging. Calcium oxide may be a suitable sorbent, but the regeneration process from calcium carbonate requires too high temperatures, causing sintering and decreasing sorption capacity. In this study the effect of steam on the decomposition of the carbonate is investigated. A clear rate-enhancing effect up to a factor of 4 is observed when steam concentrations up to 1.25% are applied during isothermal reactions at temperatures between 590 and 650°C. This results in a decrease of the apparent activation barrier from 201 to 140kJmol-1, caused by the opening of a new reaction pathway. The kinetics of steam catalyzed decomposition of CaCO3 is discussed and a simple reaction scheme is proposed, including estimation of kinetic constants. The new pathway proceeds via formation of a stable surface bicarbonate followed by decomposition to surface OH groups, which then decompose by desorbing H2O

Synergy between dielectric barrier discharge plasma and calcium oxide for reverse water gas shift

This study reports on synergy between Dielectric Barrier Discharge plasma and calcium oxide as a catalyst for the Reverse Water Gas Shift (RWGS). Any effect of the presence of the catalyst on the contribution of plasma chemistry, i.e. chemical conversion in the plasma, is minimized by using a fixed bed of α-Al2O3 particles as a blank experiment and adding a small amount of calcium oxide, with similar dielectric constant, particle size and shape. This approach results in constant plasma power and ensures also that the residence time and specific energy input remain unchanged. Furthermore, synergy is determined based on reaction rates at fixed conditions, i.e. concentrations and temperature, based on kinetic equations derived from integral experiments, describing both thermal operation and plasma operation and both in absence and presence of calcium oxide. This approach has not been applied so far to study plasma-catalysis synergy. The experimental results in thermal and plasma operation are well described with kinetic equations based on power rate laws. Synergy is observed at the lower operational temperatures (640°C) with a rate-enhancement factor of 1.7, steadily decreasing with increasing temperature until disappearing at 750°C. The concentrations of CO2, H2 and H2O have no significant influence. Synergy is attributed to a new reaction pathway involving interaction of plasma activated intermediates with the CaO surface, with a relatively low apparent activation barrier of 40 kJ mol-1. Much higher activation barriers are observed for both thermal-catalytic RWGS on CaO (140 kJ mol-1) as well as for plasma operation with Al2O3 only (90 kJ mol-1). We suggest that reaction of surface CaCO3 with plasma generated H radicals is the rate determining step, in contrast to plasma chemistry where CO2 cannot be activated with H radicals

Plasma catalysis: distinguishing between thermal and chemical effects

The goal of this study is to develop a method to distinguish between plasma chemistry and thermal effects in a Dielectric Barrier Discharge nonequilibrium plasma containing a packed bed of porous particles. Decomposition of CaCO 3 in Ar plasma is used as a model reaction and CaCO 3 samples were prepared with different external surface area, via the particle size, as well as with different internal surface area, via pore morphology. Also, the effect of the CO 2 in gas phase on the formation of products during plasma enhanced decomposition is measured. The internal surface area is not exposed to plasma and relates to thermal effect only, whereas both plasma and thermal effects occur at the external surface area. Decomposition rates were in our case found to be influenced by internal surface changes only and thermal decomposition is concluded to dominate. This is further supported by the slow response in the CO 2 concentration at a timescale of typically 1 minute upon changes in discharge power. The thermal effect is estimated based on the kinetics of the CaCO 3 decomposition, resulting in a temperature increase within 80 °C for plasma power from 0 to 6W. In contrast, CO 2 dissociation to CO and O 2 is controlled by plasma chemistry as this reaction is thermodynamically impossible without plasma, in agreement with fast response within a few seconds of the CO concentration when changing plasma power. CO forms exclusively via consecutive dissociation of CO 2 in the gas phase and not directly from CaCO 3 . In ongoing work, this methodology is used to distinguish between thermal effects and plasma-chemical effects in more reactive plasma, containing, e.g., H 2

Plasma catalysis:distinguishing between thermal and chemical effects

\u3cp\u3e The goal of this study is to develop a method to distinguish between plasma chemistry and thermal effects in a Dielectric Barrier Discharge nonequilibrium plasma containing a packed bed of porous particles. Decomposition of CaCO \u3csub\u3e3\u3c/sub\u3e in Ar plasma is used as a model reaction and CaCO \u3csub\u3e3\u3c/sub\u3e samples were prepared with different external surface area, via the particle size, as well as with different internal surface area, via pore morphology. Also, the effect of the CO \u3csub\u3e2\u3c/sub\u3e in gas phase on the formation of products during plasma enhanced decomposition is measured. The internal surface area is not exposed to plasma and relates to thermal effect only, whereas both plasma and thermal effects occur at the external surface area. Decomposition rates were in our case found to be influenced by internal surface changes only and thermal decomposition is concluded to dominate. This is further supported by the slow response in the CO \u3csub\u3e2\u3c/sub\u3e concentration at a timescale of typically 1 minute upon changes in discharge power. The thermal effect is estimated based on the kinetics of the CaCO \u3csub\u3e3\u3c/sub\u3e decomposition, resulting in a temperature increase within 80 °C for plasma power from 0 to 6W. In contrast, CO \u3csub\u3e2\u3c/sub\u3e dissociation to CO and O \u3csub\u3e2\u3c/sub\u3e is controlled by plasma chemistry as this reaction is thermodynamically impossible without plasma, in agreement with fast response within a few seconds of the CO concentration when changing plasma power. CO forms exclusively via consecutive dissociation of CO \u3csub\u3e2\u3c/sub\u3e in the gas phase and not directly from CaCO \u3csub\u3e3\u3c/sub\u3e . In ongoing work, this methodology is used to distinguish between thermal effects and plasma-chemical effects in more reactive plasma, containing, e.g., H \u3csub\u3e2\u3c/sub\u3e . \u3c/p\u3

Magnetically-extractable hybrid of magnetite, mesoporous silica and titania for the photo-degradation of organic compounds in water

This work addresses the development of a magnetically extractable magnetite-silica-titania photocatalyst to be applied in the degradation of organic compounds in water. MCM-41 silica was successfully deposited on magnetite, providing large surface area for anchoring of TiOx species, and preventing thermally induced conversion of magnetite to hematite. A good correlation between the calculated values and amount of titania deposited on the silica-covered magnetite particles was obtained for a synthesis route involving the treatment of magnetite-silica in boiling ethanolic Ti-precursor solution. Photocatalytic activity in conversion of 4-chlorophenol could only be observed for compositions containing larger than ∼50 wt% titania, whereas increasing the titania content did not significantly improve performance. Experiments carried out at pH ∼ 3.0 and ∼7.2 demonstrated the performance is relatively pH-independent. The structure activity-correlation of the materials is briefly discussed

Il 'De miseria humanae conditions' nel suo tempo

Il contributo analizza il significato dell'opera composta da Innocenzo III prima di divenire pontefice, collocandola nei generi letterari allora diffusi e nella biografia dell'autore

Magnetically-extractable hybrid of magnetite, mesoporous silica and titania for the photo-degradation of organic compounds in water

This work addresses the development of a magnetically extractable magnetite-silica-titania photocatalyst to be applied in the degradation of organic compounds in water. MCM-41 silica was successfully deposited on magnetite, providing large surface area for anchoring of TiOx species, and preventing thermally induced conversion of magnetite to hematite. A good correlation between the calculated values and amount of titania deposited on the silica-covered magnetite particles was obtained for a synthesis route involving the treatment of magnetite-silica in boiling ethanolic Ti-precursor solution. Photocatalytic activity in conversion of 4-chlorophenol could only be observed for compositions containing larger than ∼50 wt% titania, whereas increasing the titania content did not significantly improve performance. Experiments carried out at pH ∼ 3.0 and ∼7.2 demonstrated the performance is relatively pH-independent. The structure activity-correlation of the materials is briefly discussed