Catalytic micro-combustors have been developed via deposition of active layers of Pt/γ-Al2O3, LaM... more Catalytic micro-combustors have been developed via deposition of active layers of Pt/γ-Al2O3, LaMnO3/γ-Al2O3 and Pt-LaMnO3/γ-Al2O3 on FeCralloy and α-Al2O3 slabs. Diffusional resistance in the gas phase have been experimental excluded, even if catalyst is present on only one side of the reactor. Pt/γ-Al2O3 gave best performances in the combustion of H2 while LaMnO3/γ-Al2O3 revealed to be the best catalyst for
The adsorption of NO at 80°C on Cu-overexchanged ZSM-5 (Si/Al=80) has been investigated in a flow... more The adsorption of NO at 80°C on Cu-overexchanged ZSM-5 (Si/Al=80) has been investigated in a flow apparatus. The formation of N2O during a transient phase was observed after He pretreatment of the zeolite at 550°C. A negligible amount of N2O was detected, in contrast, from O2 pretreated zeolite. The formation of N2O has been associated to the reoxidation from Cu+
ABSTRACT Commercial H-ZSM5 zeolites with a Si/Al ratio equal to 25 and 75 have been exchanged usi... more ABSTRACT Commercial H-ZSM5 zeolites with a Si/Al ratio equal to 25 and 75 have been exchanged using copper acetate aqueous solutions with different concentrations. Copper saturation is reached at the 130 and 230% level of Cu exchange for Si/Al equal to 25 and 75, respectively, although FTIR spectra showed that a fraction of Al-OH exchange positions is still available. Catalytic activity experiments of NO decomposition have been carried out at 450°C in a fixed bed reactor. Catalysts have been characterized with H 2 TPR and NO adsorption experiments at 120 ° C. All samples are partially reduced upon thermal treatment under inert flow (He) leading to the formation of Cu + -containing sites in addition to a fraction of differently reduced copper spe- cies. The Cu + -containing sites, also responsible for NO adsorption and subsequent production of N 2 O at 120 ° C, have been proposed to be the active centers. A quantitative estimation of these species, likely having multi-ionic structure, has been provided.
ABSTRACT A study of the nature and accessibility of internal and external protonic and cationic s... more ABSTRACT A study of the nature and accessibility of internal and external protonic and cationic sites has been carried out on protonic and partially Co- or Cu-exchanged ZSM5zeolite samples through UV-Vis and FT-IR spectroscopies. The samples were prepared by ionic exchange. o-toluonitrile has been chosen as a probe for the external surface of the zeolites. The existence of Cu2+ and Co2+ sites at positions different from those exchanging the active protons of the zeolites is emphasized.
... lowering CO conversion. As also observed by Avgouropoulos and Ioannides, 29 this effect is mo... more ... lowering CO conversion. As also observed by Avgouropoulos and Ioannides, 29 this effect is more pronounced at low temperature, while at 200 °C, CO conversion is substantially unaffected by the presence of CO 2 . figure Figure 5 ...
ABSTRACT The autothermal oxidative dehydrogenation of ethane in short contact time reactors can b... more ABSTRACT The autothermal oxidative dehydrogenation of ethane in short contact time reactors can be carried out with high ethylene yields on LaMnO3-based non-noble-metal catalysts. The performance of LaMnO3 honeycomb monoliths is evaluated in direct comparison with state-of-the-art Pt catalyst in an autothermal reactor configuration at varying external heating, N2 dilution, C2H6/O2 ratio, and total flow rate. LaMnO3 and Pt are also compared after the addition of a secondary fuel. Evidence is present that H2 and especially CO addition are the means of increasing ethylene selectivity above 80% on LaMnO3, as preferentially this is oxidized in place of ethane. The lower activity of Pt toward CO oxidation makes CO addition ineffective on such a catalyst.
ABSTRACT Novel monolithic catalysts for the high-temperature combustion of methane have been deve... more ABSTRACT Novel monolithic catalysts for the high-temperature combustion of methane have been developed with a dual-site nature, to combine low and high temperature activity within a single system and widen its operating range. Such catalysts are based on strongly interacting Pd and LaMnO3 active phases supported onto La/γ-alumina and applied as a thick washcoat on ceramic honeycombs. Optimization of the preparation procedure and catalyst characterization were performed with respect to the effects of Pd deposition method, catalyst activation strategy, and thermal history in comparison with previously developed catalysts based only on supported perovskite. Extensive methane combustion tests (steady state and transient) were run under both isothermal and autothermal lean premixed conditions in order to study intrinsic oxidation activity, light-off behavior, and real life performance in the middle to high temperature range. Experimental evidence is presented for improved activity, stability, and durability of the catalytic system, and for a self-regenerative behavior of Pd active sites through reversible interaction with perovskite lattice. Implications of novel combined catalyst functionalities are addressed with respect to operation of a fully catalytic burner.
Fluidized-bed combustion of premixed lean methane-air mixtures over a copper-based catalyst (1-mm... more Fluidized-bed combustion of premixed lean methane-air mixtures over a copper-based catalyst (1-mm diameter) has been tested. Combustion experiments have been performed in a 100-mm externally heated fluidized-bed reactor. Effects of methane inlet concentration, gas superficial velocity, and bed height on reactor performance have been evaluated. 100% combustion efficiency could be achieved at suitable gas space-time values and no permanent bypass of methane in the bubble phase onsets under the experimental ...
Catalytic micro-combustors have been developed via deposition of active layers of Pt/γ-Al2O3, LaM... more Catalytic micro-combustors have been developed via deposition of active layers of Pt/γ-Al2O3, LaMnO3/γ-Al2O3 and Pt-LaMnO3/γ-Al2O3 on FeCralloy and α-Al2O3 slabs. Diffusional resistance in the gas phase have been experimental excluded, even if catalyst is present on only one side of the reactor. Pt/γ-Al2O3 gave best performances in the combustion of H2 while LaMnO3/γ-Al2O3 revealed to be the best catalyst for
The adsorption of NO at 80°C on Cu-overexchanged ZSM-5 (Si/Al=80) has been investigated in a flow... more The adsorption of NO at 80°C on Cu-overexchanged ZSM-5 (Si/Al=80) has been investigated in a flow apparatus. The formation of N2O during a transient phase was observed after He pretreatment of the zeolite at 550°C. A negligible amount of N2O was detected, in contrast, from O2 pretreated zeolite. The formation of N2O has been associated to the reoxidation from Cu+
ABSTRACT Commercial H-ZSM5 zeolites with a Si/Al ratio equal to 25 and 75 have been exchanged usi... more ABSTRACT Commercial H-ZSM5 zeolites with a Si/Al ratio equal to 25 and 75 have been exchanged using copper acetate aqueous solutions with different concentrations. Copper saturation is reached at the 130 and 230% level of Cu exchange for Si/Al equal to 25 and 75, respectively, although FTIR spectra showed that a fraction of Al-OH exchange positions is still available. Catalytic activity experiments of NO decomposition have been carried out at 450°C in a fixed bed reactor. Catalysts have been characterized with H 2 TPR and NO adsorption experiments at 120 ° C. All samples are partially reduced upon thermal treatment under inert flow (He) leading to the formation of Cu + -containing sites in addition to a fraction of differently reduced copper spe- cies. The Cu + -containing sites, also responsible for NO adsorption and subsequent production of N 2 O at 120 ° C, have been proposed to be the active centers. A quantitative estimation of these species, likely having multi-ionic structure, has been provided.
ABSTRACT A study of the nature and accessibility of internal and external protonic and cationic s... more ABSTRACT A study of the nature and accessibility of internal and external protonic and cationic sites has been carried out on protonic and partially Co- or Cu-exchanged ZSM5zeolite samples through UV-Vis and FT-IR spectroscopies. The samples were prepared by ionic exchange. o-toluonitrile has been chosen as a probe for the external surface of the zeolites. The existence of Cu2+ and Co2+ sites at positions different from those exchanging the active protons of the zeolites is emphasized.
... lowering CO conversion. As also observed by Avgouropoulos and Ioannides, 29 this effect is mo... more ... lowering CO conversion. As also observed by Avgouropoulos and Ioannides, 29 this effect is more pronounced at low temperature, while at 200 °C, CO conversion is substantially unaffected by the presence of CO 2 . figure Figure 5 ...
ABSTRACT The autothermal oxidative dehydrogenation of ethane in short contact time reactors can b... more ABSTRACT The autothermal oxidative dehydrogenation of ethane in short contact time reactors can be carried out with high ethylene yields on LaMnO3-based non-noble-metal catalysts. The performance of LaMnO3 honeycomb monoliths is evaluated in direct comparison with state-of-the-art Pt catalyst in an autothermal reactor configuration at varying external heating, N2 dilution, C2H6/O2 ratio, and total flow rate. LaMnO3 and Pt are also compared after the addition of a secondary fuel. Evidence is present that H2 and especially CO addition are the means of increasing ethylene selectivity above 80% on LaMnO3, as preferentially this is oxidized in place of ethane. The lower activity of Pt toward CO oxidation makes CO addition ineffective on such a catalyst.
ABSTRACT Novel monolithic catalysts for the high-temperature combustion of methane have been deve... more ABSTRACT Novel monolithic catalysts for the high-temperature combustion of methane have been developed with a dual-site nature, to combine low and high temperature activity within a single system and widen its operating range. Such catalysts are based on strongly interacting Pd and LaMnO3 active phases supported onto La/γ-alumina and applied as a thick washcoat on ceramic honeycombs. Optimization of the preparation procedure and catalyst characterization were performed with respect to the effects of Pd deposition method, catalyst activation strategy, and thermal history in comparison with previously developed catalysts based only on supported perovskite. Extensive methane combustion tests (steady state and transient) were run under both isothermal and autothermal lean premixed conditions in order to study intrinsic oxidation activity, light-off behavior, and real life performance in the middle to high temperature range. Experimental evidence is presented for improved activity, stability, and durability of the catalytic system, and for a self-regenerative behavior of Pd active sites through reversible interaction with perovskite lattice. Implications of novel combined catalyst functionalities are addressed with respect to operation of a fully catalytic burner.
Fluidized-bed combustion of premixed lean methane-air mixtures over a copper-based catalyst (1-mm... more Fluidized-bed combustion of premixed lean methane-air mixtures over a copper-based catalyst (1-mm diameter) has been tested. Combustion experiments have been performed in a 100-mm externally heated fluidized-bed reactor. Effects of methane inlet concentration, gas superficial velocity, and bed height on reactor performance have been evaluated. 100% combustion efficiency could be achieved at suitable gas space-time values and no permanent bypass of methane in the bubble phase onsets under the experimental ...
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