Our research project concerns the H2S purification from a biogas stream by direct and selective o... more Our research project concerns the H2S purification from a biogas stream by direct and selective oxidation to sulphur and water at low temperature. Biogas is a renewable energy source that can be produced from biomass, agricultural and industrial waste and sewage sludge. Its main components are CH4, CO2 but unfortunately sulphur based compounds such as H2S, COS are also present. The main limitation of the biogas utilization as fuel in Molten Carbonate Fuel Cells is due to the presence of sulphur compounds such as H2S that can poison the main components of the fuel cell. The partial H2S oxidation reaction is carried out in presence of vanadium-based catalysts that are active and very selective toward Sulphur formation. The aim of the work is to study the preparation procedure of V2O5/CeO2 structured catalysts from the washcoating with CeO2-ZrO2 to the deposition of the active phase (V2O5) for the abatement of H2S at 150-200°C. The catalytic tests were carried out in a fixed bed flow reactor, made of a steel tube 21 cm long and a 14 mm of internal diameter. The reactor is inserted in an electrical furnace equipped with a PID electronic temperature controller. A thermocouple is inserted in a steel sheath concentric to the reactor. The catalytic tests were carried out in the temperature range 150-250 °C, with a GHSV of 180,000 h-1 , by feeding 500 ppm of H2S, 250 ppm of O2 and N2 to balance. In Figure 1, the scheme of the laboratory plant is shown.
• CeO 2-ZrO 2 is a promising support for the methanation catalysts. • Ruthenium acts as a promote... more • CeO 2-ZrO 2 is a promising support for the methanation catalysts. • Ruthenium acts as a promoter in Ni/CeO 2-ZrO 2 formulations. • RuNi/CeO 2-ZrO 2 formulations have better catalytic performances with low Ru loadings. • Ruthenium acetylacetonate is an excellent precursor salt for catalysts preparation. • 0.5Ru-10Ni/CeO 2-ZrO 2 is a very active and stable catalyst for CO 2 methanation.
International Journal of Hydrogen Energy, Jul 1, 2016
The catalytic activity of bimetallic PteNi/CeO 2 eZrO 2 powders and foams, with a silicon carbide... more The catalytic activity of bimetallic PteNi/CeO 2 eZrO 2 powders and foams, with a silicon carbide carrier and containing silica or boehmite as binder, was investigated for ethanol steam reforming in the low temperature range (400e500 C). A parametric experimental study was preliminary performed to analyze the effect of different operative conditions (temperature, water/ethanol ratio and contact time) on coke selectivity: low temperatures and space velocities as well as high water contents in the feeding stream minimized carbon deposits formation and reactor plugging. Moreover, once analyzed the individual influence of C 2 H 4 O, C 3 H 7 OH, C 4 H 9 OH and C 5 H 11 OH, selected among the main bioethanol contaminants, on catalyst deactivation, a model mixture, containing 1% mol of all the impurities, was fed to the reformer at 15,000 h À1 , T ¼ 450 C and water/ethanol ratio equal to 6. In order to test catalytic behavior in more stressful conditions, contact time was decreased and the stability of powder and foam catalysts was investigated at 50,000 h À1. Despite very similar H 2 selectivities were recorded, the structured samples, containing boehmite as binder, showed the most interesting catalytic performance, as total ethanol conversion was assured for more than 1 day of time-on-stream. Foams geometry, in fact, enhanced coke gasification reactions, limiting, at the same time, plugging phenomena.
Laminar burning velocity of biosyngas was measured by means of heat flux burner. Numerical result... more Laminar burning velocity of biosyngas was measured by means of heat flux burner. Numerical results from detailed kinetic mechanism were compared with experiments. Empirical mixing rules for laminar burning velocity estimation were evaluated. NOx kinetic mechanisms were investigated by means of sensitivity analysis.
Vanadium-based catalysts supported on ceria were studied for the direct and selective oxidation o... more Vanadium-based catalysts supported on ceria were studied for the direct and selective oxidation of H 2 S to sulphur and water at low temperature. Catalysts with two vanadium loading (20e50 wt% of V 2 O 5) were prepared, characterized and tested at temperature of 150e200 C in order to identify the best catalytic formulation. The most promising catalyst was the sample with the 20 wt% of V 2 O 5 that showed 99% of sulphur selectivity and equilibrium H 2 S conversion at 150 C. The effect of the components of a typical biogas stream (CH 4 , CO 2 and H 2 O) was studied at 150 C in order to investigate the possible formation of secondary products such COS, CS 2. No significant effect was observed in terms of H 2 S conversion (99%) and selectivity to SO 2 (<1%) by adding CH 4 and CO 2 to the feed stream. Furthermore, the effect of the H 2 S inlet concentration, temperature, contact time and molar feed ratio (O 2 /H 2 S) were also investigated at a reaction temperature of 80 C. Finally, time on stream tests of 30 h were performed at 80 and 120 C, in order to examine the catalyst stability.
The growing demand of natural gas inspires existing and new projects in topographical areas where... more The growing demand of natural gas inspires existing and new projects in topographical areas where the hydrocarbon extraction meets severe safety challenges due to the presence of hydrogen sulfide (H 2 S) in natural gas, i.e. sour gas. Indeed, the combined effect of flammability and toxicity of such gases has the critical potential to increase the hazard level in the industrial installation, thus aggravating the consequences for human and assets. In this work, a detailed kinetic model was validated and adopted to estimate the laminar burning velocity and the flammability limits of sour gas at different initial temperatures, within the range 250-325 K, equivalence ratio from 0.4 to 2.5, and content of H 2 S up to 15%v/v with respect to methane. For larger amount of the acid, almost negligible variations of the burning velocity of the mixtures have been observed, even if slight variations are detected either at lean (decrease) or rich (increase) conditions. On the contrary, flammability limits results show also that the addition of H 2 S has a strong relevance on safety parameters, more specifically for the upper flammability limit.
International Journal of Hydrogen Energy, Dec 1, 2014
ABSTRACT CeO2 supported vanadium catalysts at different V2O5 loads (2.55e20.00 wt%) were tested f... more ABSTRACT CeO2 supported vanadium catalysts at different V2O5 loads (2.55e20.00 wt%) were tested for the selective catalytic H2S oxidation to sulfur at low temperature. The aim of the work is to investigate the effect of temperature and contact time in order to realize in one step a very high H2S conversion, minimizing SO2 formation. Catalytic activity tests showed in the range 2.55e20.00 wt% the effect of the vanadium loading plays a major role on sulfur selectivity. In particular, the 20.00 wt% V2O5/CeO2 catalyst was the most interesting sample with a selectivity to sulfur of 99%. The H2S conversion calculated experimentally at 150 �C is 98.7%, very close to that obtained by thermodynamic equilibrium calculations, corresponding to 99%. Interesting results were also obtained from the preliminary tests on the effect of the contact time, suggesting information relating to the reaction behavior as well as helping to identify the optimal operating conditions capable of minimizing SO2 selectivity.
This article is an open access article distributed under the terms and conditions of the Creative... more This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY
ABSTRACT Temperature-programmed desorption (TPD) of carbon oxides from partially oxidized carbon ... more ABSTRACT Temperature-programmed desorption (TPD) of carbon oxides from partially oxidized carbon black has been performed to investigate the uncatalysed and catalysed carbonoxygen reactions (Walker, Jr., et al., Carbon, 29 (1991) 411–421 [1]). TPD data have been elaborated to obtain the distribution function of the desorption energies of carbon-oxygen surface complexes. The catalysed oxidation of carbon black was carried out in the presence of a potassium-copper-vanadium catalyst which substantially decreases the temperatures of carbon black burn-off. TPD measurements of carbon oxides and elaborations of the results have shown that the presence of catalyst noticeably increases the number of surface complexes, giving rise to gaseous carbon dioxide, and dramatically modifies the desorption energy distribution functions of carbon-oxygen surface complexes by lowering the peak energy values.
The water gas shift (WGS) is an equilibrium exothermic reaction, whose corresponding industrial p... more The water gas shift (WGS) is an equilibrium exothermic reaction, whose corresponding industrial process is normally carried out in two adiabatic stages, to overcome the thermodynamic and kinetic limitations. The high temperature stage makes use of iron/chromium-based catalysts, while the low temperature stage employs copper/zinc-based catalysts. Nevertheless, both these systems have several problems, mainly dealing with safety issues and process efficiency. Accordingly, in the last decade abundant researches have been focused on the study of alternative catalytic systems. The best performances have been obtained with noble metal-based catalysts, among which, platinum-based formulations showed a good compromise between performance and ease of preparation. These catalytic systems are extremely attractive, as they have numerous advantages, including the feasibility of intermediate temperature (250-400 • C) applications, the absence of pyrophoricity, and the high activity even at low loadings. The particle size plays a crucial role in determining their catalytic activity, enhancing the performance of the nanometric catalytic systems: the best activity and stability was reported for particle sizes < 1.7 nm. Moreover the optimal Pt loading seems to be located near 1 wt%, as well as the optimal Pt coverage was identified in 0.25 ML. Kinetics and mechanisms studies highlighted the low energy activation of Pt/Mo 2 C-based catalytic systems (Ea of 38 kJ•mol −1), the associative mechanism is the most encountered on the investigated studies. This review focuses on a selection of recent published articles, related to the preparation and use of unstructured platinum-based catalysts in water gas shift reaction, and is organized in five main sections: comparative studies, kinetics, reaction mechanisms, sour WGS and electrochemical promotion. Each section is divided in paragraphs, at the end of the section a summary and a summary table are provided.
Plasma science has attracted the interest of researchers in various disciplines since the 1990s. ... more Plasma science has attracted the interest of researchers in various disciplines since the 1990s. This continuously evolving field has spawned investigations into several applications, including industrial sterilization, pollution control, polymer science, food safety and biomedicine. nonthermal plasma (NTP) can promote the occurrence of chemical reactions in a lower operating temperature range, condition in which, in a conventional process, a catalyst is generally not active. The aim, when using NTP, is to selectively transfer electrical energy to the electrons, generating free radicals through collisions and promoting the desired chemical changes without spending energy in heating the system. Therefore, NTP can be used in various fields, such as NO x removal from exhaust gases, soot removal from diesel engine exhaust, volatile organic compound (VOC) decomposition, industrial applications, such as ammonia production or methanation reaction (Sabatier reaction). The combination of NTP technology with catalysts is a promising option to improve selectivity and efficiency in some chemical processes. In this review, recent advances in selected nonthermal plasma assisted solid-gas processes are introduced, and the attention was mainly focused on the use of the dielectric barrier discharge (DBD) reactors.
The depletion of fossil fuels and the growing concerns related to the environmental impact of the... more The depletion of fossil fuels and the growing concerns related to the environmental impact of their processing has progressively switched the interest towards the utilization of biomassderived materials for a large variety of processes. Among them, biogas, which is a CH4-rich gas deriving from anaerobic digestion of biomass, has acquired a lot of interest as a feedstock for reforming processes. The main issue in employing biogas is related to the carbon deposition and active metal sintering, which are both responsible for the deactivation of the catalyst. In this work, bimetallic and monometallic Rh-and Ni-based formulations were supported on alumina and ceria with the aim of evaluating their activity and stability in biogas oxidative steam reforming. The Rh addition to the monometallic Ni/-Al2O3 formulation enhances its catalytic performances; nevertheless, this induces a higher coke deposition, thus suggesting a preferential coke formation on Rh sites. The initial activity of the CeO2-supported catalysts was found to be lower than the Al2O3supported catalysts, but the 5%Ni/CeO2 sample showed a very good stability during the test and, despite the lower activity, 0.5%Rh-5%Ni/CeO2 did not show coke deposition. The results suggest that the promotion of Ni/CeO2 catalysts with other active metals could lead to the selection of a highly stable and performing formulation for biogas oxidative steam reforming.
This article is an open access article distributed under the terms and conditions of the Creative... more This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY
Abstract The reaction of H 2 S selective partial oxidation to elemental sulfur was studied on cor... more Abstract The reaction of H 2 S selective partial oxidation to elemental sulfur was studied on cordierite honeycomb-structured catalysts in the range of temperature of 150–200 °C. The preparation procedure of catalytic cordierite monoliths has been studied, from the washcoating with CeO 2 to the deposition of V 2 O 5 by wet impregnation. Two different preparation washcoating procedures deposition were studied: in one case the washcoat had been already added with the salts precursors of the active species ( joint impregnation method ), in other case the active species were added only after the deposition step of the washcoat on the monolith, by impregnation in a solution of the salt precursor ( distinct impregnation method ). The catalysts prepared with the two different methods were characterized and the stability was investigated in catalytic activity tests. The catalysts prepared with the “joint impregnation” method have shown a poor catalytic activity and tendency to the deactivation. Very different results were found for the catalysts prepared with the “distinct impregnation” method, for which the effect of the vanadium content (2–19 V 2 O 5 wt %) was also studied at 200 °C. Good catalytic performances were obtained for both samples that have shown a high H 2 S conversion (∼90%), low SO 2 selectivity (3%) and a high stability. The catalytic tests performed to varying the contact time with the temperature have allowed to identify the possible reaction pathway and the optimal operating conditions for which were obtained good catalytic performance.
International Journal of Hydrogen Energy, May 1, 2019
The activity and selectivity to hydrogen of alumina-supported nickel or platinum catalysts doped ... more The activity and selectivity to hydrogen of alumina-supported nickel or platinum catalysts doped with Ce and La for the oxidative reforming of hexadecane were studied. The influence of both thermal stabilizer and activity promoter, such as lanthanum and cerium oxide, respectively, over hydrogen yield and catalyst durability was investigated. Catalytic activity was found to depend strongly on the type of metal, platinum showing lower specific activities per atom of metal exposed and a higher selectivity to combustion products than the Ni counterparts. The characterization results achieved with H 2 chemisorption, XRD, TPR and XPS showed differences in surface metal concentrations and metal-support interactions which depend on the presence of cerium and/or lanthanum in the support composition. For both based metal catalysts higher reforming activities were found when active metals were deposited on Ce-La-Al 2 O 3 substrate. For Pt-based catalysts, the increase in activity observed for the sample using Ce-La-modified alumina as support is suggested to be related with a participation of lanthanum in the reaction more than modifications on coke resistance or dispersion and state of platinum-induced by lanthanum. In the case of Ni-based catalysts, a lower carbon deposition and a higher thermal stability of metallic Ni particles under reaction conditions were observed for catalyst using Ce-La-modified alumina as support. It is suggested that the higher number of NiCe and Ni-Al surface interactions developed Ce-La-Al 2 O 3-supported Ni catalysts are responsible of the better catalytic behaviour of this sample in the oxidative reforming of hexadecane.
h i g h l i g h t s A preliminary chemical kinetic model for H 2 S oxidation has been developed. ... more h i g h l i g h t s A preliminary chemical kinetic model for H 2 S oxidation has been developed. Experimental data were compared with model results at different operating conditions. H 2 yield, SO 2 selectivity of the model are higher than the experimental data at 900°C. The model predictions at 1100°C are in good agreement with the experimental values. The model should be revised and optimized to fit better to the experimental results.
Diesel particulate filter (DPF), consisting in alternately plugged parallel square channels with ... more Diesel particulate filter (DPF), consisting in alternately plugged parallel square channels with porous walls that trap the soot particles, must be periodically regenerated. In this work, a new procedure for the preparation of microwave susceptible catalytic DPFs based on a preliminary controlled chemical erosion of the porous structure was optimized, so obtaining catalytic filters with higher catalyst load (30 %wt CuFe2O4). The filters showed pressure drop values very similar to that pertaining to the uncatalysed filters and a higher regeneration activity: consequently their microwave assisted regeneration phase, compared to the traditional fuel postinjection, allowed an energy saving of about 60 %.
Similar conversion profile above 350°C were recorded over Pt-Ni and Ni-Co catalysts. • The highes... more Similar conversion profile above 350°C were recorded over Pt-Ni and Ni-Co catalysts. • The highest extent of deactivation was observed for the Pt-Co catalyst. • The system can be effectively kinetically described by 4 main reactions. • Ni-Co catalyst showed lower activation energies and a reduced extent of deactivation.
The aim of the present work is to study the application of a fluidized bed reactor for oxidative ... more The aim of the present work is to study the application of a fluidized bed reactor for oxidative steam reforming of ethanol (OESR) over a bimetallic 3wt% Pt-10wt% Ni/CeO 2-SiO 2 catalyst. In particular, the effect of cerium salt precursor (nitrate (N), ammonium nitrate (AN) and acetylacetonate (AC)) on catalyst activity and stability was investigated. Three catalysts were synthetized. In all cases, the support was composed of a CeO 2-SiO 2 mixed oxide and the ceria content for all the catalysts was fixed to 30 wt%. The tests were carried out at a steam to ethanol ratio (f.r.) of 4 and oxygen to ethanol ratio (o.r.) of 0.5; temperature was fixed to 500°C and the weigh hourly space velocity (WHSV) to 12.3 h-1. All the samples displayed a partial deactivation with timeon-stream and ethanol was completely converted only for few hours. The initial H 2 yield was very close to the predicted thermodynamic value (41.5%) and a gradual yield lowering was observed over the three catalysts. However, after 80 h of test, all the samples reached a plateau condition, with no more variation in selectivity. It is worthwhile noting that, for the sample AC, the final conversion was attested to 75%, while the other two catalysts displayed a similar behaviour with plateau conversion of almost 60%. In addition, a higher H 2 yield (20%) was recorded after 100 h of test for the sample AC and the carbon formation rate measured after the test on the latter catalyst was almost 1 half of the values found for the catalysts N and AN: in the case of acetylacetonate, the organic group of the salt probably assures a templanting effect, which protects ceria molecules, improving their dispersion and increasing catalyst activity towards both reforming and carbon gasification reactions.
Our research project concerns the H2S purification from a biogas stream by direct and selective o... more Our research project concerns the H2S purification from a biogas stream by direct and selective oxidation to sulphur and water at low temperature. Biogas is a renewable energy source that can be produced from biomass, agricultural and industrial waste and sewage sludge. Its main components are CH4, CO2 but unfortunately sulphur based compounds such as H2S, COS are also present. The main limitation of the biogas utilization as fuel in Molten Carbonate Fuel Cells is due to the presence of sulphur compounds such as H2S that can poison the main components of the fuel cell. The partial H2S oxidation reaction is carried out in presence of vanadium-based catalysts that are active and very selective toward Sulphur formation. The aim of the work is to study the preparation procedure of V2O5/CeO2 structured catalysts from the washcoating with CeO2-ZrO2 to the deposition of the active phase (V2O5) for the abatement of H2S at 150-200°C. The catalytic tests were carried out in a fixed bed flow reactor, made of a steel tube 21 cm long and a 14 mm of internal diameter. The reactor is inserted in an electrical furnace equipped with a PID electronic temperature controller. A thermocouple is inserted in a steel sheath concentric to the reactor. The catalytic tests were carried out in the temperature range 150-250 °C, with a GHSV of 180,000 h-1 , by feeding 500 ppm of H2S, 250 ppm of O2 and N2 to balance. In Figure 1, the scheme of the laboratory plant is shown.
• CeO 2-ZrO 2 is a promising support for the methanation catalysts. • Ruthenium acts as a promote... more • CeO 2-ZrO 2 is a promising support for the methanation catalysts. • Ruthenium acts as a promoter in Ni/CeO 2-ZrO 2 formulations. • RuNi/CeO 2-ZrO 2 formulations have better catalytic performances with low Ru loadings. • Ruthenium acetylacetonate is an excellent precursor salt for catalysts preparation. • 0.5Ru-10Ni/CeO 2-ZrO 2 is a very active and stable catalyst for CO 2 methanation.
International Journal of Hydrogen Energy, Jul 1, 2016
The catalytic activity of bimetallic PteNi/CeO 2 eZrO 2 powders and foams, with a silicon carbide... more The catalytic activity of bimetallic PteNi/CeO 2 eZrO 2 powders and foams, with a silicon carbide carrier and containing silica or boehmite as binder, was investigated for ethanol steam reforming in the low temperature range (400e500 C). A parametric experimental study was preliminary performed to analyze the effect of different operative conditions (temperature, water/ethanol ratio and contact time) on coke selectivity: low temperatures and space velocities as well as high water contents in the feeding stream minimized carbon deposits formation and reactor plugging. Moreover, once analyzed the individual influence of C 2 H 4 O, C 3 H 7 OH, C 4 H 9 OH and C 5 H 11 OH, selected among the main bioethanol contaminants, on catalyst deactivation, a model mixture, containing 1% mol of all the impurities, was fed to the reformer at 15,000 h À1 , T ¼ 450 C and water/ethanol ratio equal to 6. In order to test catalytic behavior in more stressful conditions, contact time was decreased and the stability of powder and foam catalysts was investigated at 50,000 h À1. Despite very similar H 2 selectivities were recorded, the structured samples, containing boehmite as binder, showed the most interesting catalytic performance, as total ethanol conversion was assured for more than 1 day of time-on-stream. Foams geometry, in fact, enhanced coke gasification reactions, limiting, at the same time, plugging phenomena.
Laminar burning velocity of biosyngas was measured by means of heat flux burner. Numerical result... more Laminar burning velocity of biosyngas was measured by means of heat flux burner. Numerical results from detailed kinetic mechanism were compared with experiments. Empirical mixing rules for laminar burning velocity estimation were evaluated. NOx kinetic mechanisms were investigated by means of sensitivity analysis.
Vanadium-based catalysts supported on ceria were studied for the direct and selective oxidation o... more Vanadium-based catalysts supported on ceria were studied for the direct and selective oxidation of H 2 S to sulphur and water at low temperature. Catalysts with two vanadium loading (20e50 wt% of V 2 O 5) were prepared, characterized and tested at temperature of 150e200 C in order to identify the best catalytic formulation. The most promising catalyst was the sample with the 20 wt% of V 2 O 5 that showed 99% of sulphur selectivity and equilibrium H 2 S conversion at 150 C. The effect of the components of a typical biogas stream (CH 4 , CO 2 and H 2 O) was studied at 150 C in order to investigate the possible formation of secondary products such COS, CS 2. No significant effect was observed in terms of H 2 S conversion (99%) and selectivity to SO 2 (<1%) by adding CH 4 and CO 2 to the feed stream. Furthermore, the effect of the H 2 S inlet concentration, temperature, contact time and molar feed ratio (O 2 /H 2 S) were also investigated at a reaction temperature of 80 C. Finally, time on stream tests of 30 h were performed at 80 and 120 C, in order to examine the catalyst stability.
The growing demand of natural gas inspires existing and new projects in topographical areas where... more The growing demand of natural gas inspires existing and new projects in topographical areas where the hydrocarbon extraction meets severe safety challenges due to the presence of hydrogen sulfide (H 2 S) in natural gas, i.e. sour gas. Indeed, the combined effect of flammability and toxicity of such gases has the critical potential to increase the hazard level in the industrial installation, thus aggravating the consequences for human and assets. In this work, a detailed kinetic model was validated and adopted to estimate the laminar burning velocity and the flammability limits of sour gas at different initial temperatures, within the range 250-325 K, equivalence ratio from 0.4 to 2.5, and content of H 2 S up to 15%v/v with respect to methane. For larger amount of the acid, almost negligible variations of the burning velocity of the mixtures have been observed, even if slight variations are detected either at lean (decrease) or rich (increase) conditions. On the contrary, flammability limits results show also that the addition of H 2 S has a strong relevance on safety parameters, more specifically for the upper flammability limit.
International Journal of Hydrogen Energy, Dec 1, 2014
ABSTRACT CeO2 supported vanadium catalysts at different V2O5 loads (2.55e20.00 wt%) were tested f... more ABSTRACT CeO2 supported vanadium catalysts at different V2O5 loads (2.55e20.00 wt%) were tested for the selective catalytic H2S oxidation to sulfur at low temperature. The aim of the work is to investigate the effect of temperature and contact time in order to realize in one step a very high H2S conversion, minimizing SO2 formation. Catalytic activity tests showed in the range 2.55e20.00 wt% the effect of the vanadium loading plays a major role on sulfur selectivity. In particular, the 20.00 wt% V2O5/CeO2 catalyst was the most interesting sample with a selectivity to sulfur of 99%. The H2S conversion calculated experimentally at 150 �C is 98.7%, very close to that obtained by thermodynamic equilibrium calculations, corresponding to 99%. Interesting results were also obtained from the preliminary tests on the effect of the contact time, suggesting information relating to the reaction behavior as well as helping to identify the optimal operating conditions capable of minimizing SO2 selectivity.
This article is an open access article distributed under the terms and conditions of the Creative... more This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY
ABSTRACT Temperature-programmed desorption (TPD) of carbon oxides from partially oxidized carbon ... more ABSTRACT Temperature-programmed desorption (TPD) of carbon oxides from partially oxidized carbon black has been performed to investigate the uncatalysed and catalysed carbonoxygen reactions (Walker, Jr., et al., Carbon, 29 (1991) 411–421 [1]). TPD data have been elaborated to obtain the distribution function of the desorption energies of carbon-oxygen surface complexes. The catalysed oxidation of carbon black was carried out in the presence of a potassium-copper-vanadium catalyst which substantially decreases the temperatures of carbon black burn-off. TPD measurements of carbon oxides and elaborations of the results have shown that the presence of catalyst noticeably increases the number of surface complexes, giving rise to gaseous carbon dioxide, and dramatically modifies the desorption energy distribution functions of carbon-oxygen surface complexes by lowering the peak energy values.
The water gas shift (WGS) is an equilibrium exothermic reaction, whose corresponding industrial p... more The water gas shift (WGS) is an equilibrium exothermic reaction, whose corresponding industrial process is normally carried out in two adiabatic stages, to overcome the thermodynamic and kinetic limitations. The high temperature stage makes use of iron/chromium-based catalysts, while the low temperature stage employs copper/zinc-based catalysts. Nevertheless, both these systems have several problems, mainly dealing with safety issues and process efficiency. Accordingly, in the last decade abundant researches have been focused on the study of alternative catalytic systems. The best performances have been obtained with noble metal-based catalysts, among which, platinum-based formulations showed a good compromise between performance and ease of preparation. These catalytic systems are extremely attractive, as they have numerous advantages, including the feasibility of intermediate temperature (250-400 • C) applications, the absence of pyrophoricity, and the high activity even at low loadings. The particle size plays a crucial role in determining their catalytic activity, enhancing the performance of the nanometric catalytic systems: the best activity and stability was reported for particle sizes < 1.7 nm. Moreover the optimal Pt loading seems to be located near 1 wt%, as well as the optimal Pt coverage was identified in 0.25 ML. Kinetics and mechanisms studies highlighted the low energy activation of Pt/Mo 2 C-based catalytic systems (Ea of 38 kJ•mol −1), the associative mechanism is the most encountered on the investigated studies. This review focuses on a selection of recent published articles, related to the preparation and use of unstructured platinum-based catalysts in water gas shift reaction, and is organized in five main sections: comparative studies, kinetics, reaction mechanisms, sour WGS and electrochemical promotion. Each section is divided in paragraphs, at the end of the section a summary and a summary table are provided.
Plasma science has attracted the interest of researchers in various disciplines since the 1990s. ... more Plasma science has attracted the interest of researchers in various disciplines since the 1990s. This continuously evolving field has spawned investigations into several applications, including industrial sterilization, pollution control, polymer science, food safety and biomedicine. nonthermal plasma (NTP) can promote the occurrence of chemical reactions in a lower operating temperature range, condition in which, in a conventional process, a catalyst is generally not active. The aim, when using NTP, is to selectively transfer electrical energy to the electrons, generating free radicals through collisions and promoting the desired chemical changes without spending energy in heating the system. Therefore, NTP can be used in various fields, such as NO x removal from exhaust gases, soot removal from diesel engine exhaust, volatile organic compound (VOC) decomposition, industrial applications, such as ammonia production or methanation reaction (Sabatier reaction). The combination of NTP technology with catalysts is a promising option to improve selectivity and efficiency in some chemical processes. In this review, recent advances in selected nonthermal plasma assisted solid-gas processes are introduced, and the attention was mainly focused on the use of the dielectric barrier discharge (DBD) reactors.
The depletion of fossil fuels and the growing concerns related to the environmental impact of the... more The depletion of fossil fuels and the growing concerns related to the environmental impact of their processing has progressively switched the interest towards the utilization of biomassderived materials for a large variety of processes. Among them, biogas, which is a CH4-rich gas deriving from anaerobic digestion of biomass, has acquired a lot of interest as a feedstock for reforming processes. The main issue in employing biogas is related to the carbon deposition and active metal sintering, which are both responsible for the deactivation of the catalyst. In this work, bimetallic and monometallic Rh-and Ni-based formulations were supported on alumina and ceria with the aim of evaluating their activity and stability in biogas oxidative steam reforming. The Rh addition to the monometallic Ni/-Al2O3 formulation enhances its catalytic performances; nevertheless, this induces a higher coke deposition, thus suggesting a preferential coke formation on Rh sites. The initial activity of the CeO2-supported catalysts was found to be lower than the Al2O3supported catalysts, but the 5%Ni/CeO2 sample showed a very good stability during the test and, despite the lower activity, 0.5%Rh-5%Ni/CeO2 did not show coke deposition. The results suggest that the promotion of Ni/CeO2 catalysts with other active metals could lead to the selection of a highly stable and performing formulation for biogas oxidative steam reforming.
This article is an open access article distributed under the terms and conditions of the Creative... more This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY
Abstract The reaction of H 2 S selective partial oxidation to elemental sulfur was studied on cor... more Abstract The reaction of H 2 S selective partial oxidation to elemental sulfur was studied on cordierite honeycomb-structured catalysts in the range of temperature of 150–200 °C. The preparation procedure of catalytic cordierite monoliths has been studied, from the washcoating with CeO 2 to the deposition of V 2 O 5 by wet impregnation. Two different preparation washcoating procedures deposition were studied: in one case the washcoat had been already added with the salts precursors of the active species ( joint impregnation method ), in other case the active species were added only after the deposition step of the washcoat on the monolith, by impregnation in a solution of the salt precursor ( distinct impregnation method ). The catalysts prepared with the two different methods were characterized and the stability was investigated in catalytic activity tests. The catalysts prepared with the “joint impregnation” method have shown a poor catalytic activity and tendency to the deactivation. Very different results were found for the catalysts prepared with the “distinct impregnation” method, for which the effect of the vanadium content (2–19 V 2 O 5 wt %) was also studied at 200 °C. Good catalytic performances were obtained for both samples that have shown a high H 2 S conversion (∼90%), low SO 2 selectivity (3%) and a high stability. The catalytic tests performed to varying the contact time with the temperature have allowed to identify the possible reaction pathway and the optimal operating conditions for which were obtained good catalytic performance.
International Journal of Hydrogen Energy, May 1, 2019
The activity and selectivity to hydrogen of alumina-supported nickel or platinum catalysts doped ... more The activity and selectivity to hydrogen of alumina-supported nickel or platinum catalysts doped with Ce and La for the oxidative reforming of hexadecane were studied. The influence of both thermal stabilizer and activity promoter, such as lanthanum and cerium oxide, respectively, over hydrogen yield and catalyst durability was investigated. Catalytic activity was found to depend strongly on the type of metal, platinum showing lower specific activities per atom of metal exposed and a higher selectivity to combustion products than the Ni counterparts. The characterization results achieved with H 2 chemisorption, XRD, TPR and XPS showed differences in surface metal concentrations and metal-support interactions which depend on the presence of cerium and/or lanthanum in the support composition. For both based metal catalysts higher reforming activities were found when active metals were deposited on Ce-La-Al 2 O 3 substrate. For Pt-based catalysts, the increase in activity observed for the sample using Ce-La-modified alumina as support is suggested to be related with a participation of lanthanum in the reaction more than modifications on coke resistance or dispersion and state of platinum-induced by lanthanum. In the case of Ni-based catalysts, a lower carbon deposition and a higher thermal stability of metallic Ni particles under reaction conditions were observed for catalyst using Ce-La-modified alumina as support. It is suggested that the higher number of NiCe and Ni-Al surface interactions developed Ce-La-Al 2 O 3-supported Ni catalysts are responsible of the better catalytic behaviour of this sample in the oxidative reforming of hexadecane.
h i g h l i g h t s A preliminary chemical kinetic model for H 2 S oxidation has been developed. ... more h i g h l i g h t s A preliminary chemical kinetic model for H 2 S oxidation has been developed. Experimental data were compared with model results at different operating conditions. H 2 yield, SO 2 selectivity of the model are higher than the experimental data at 900°C. The model predictions at 1100°C are in good agreement with the experimental values. The model should be revised and optimized to fit better to the experimental results.
Diesel particulate filter (DPF), consisting in alternately plugged parallel square channels with ... more Diesel particulate filter (DPF), consisting in alternately plugged parallel square channels with porous walls that trap the soot particles, must be periodically regenerated. In this work, a new procedure for the preparation of microwave susceptible catalytic DPFs based on a preliminary controlled chemical erosion of the porous structure was optimized, so obtaining catalytic filters with higher catalyst load (30 %wt CuFe2O4). The filters showed pressure drop values very similar to that pertaining to the uncatalysed filters and a higher regeneration activity: consequently their microwave assisted regeneration phase, compared to the traditional fuel postinjection, allowed an energy saving of about 60 %.
Similar conversion profile above 350°C were recorded over Pt-Ni and Ni-Co catalysts. • The highes... more Similar conversion profile above 350°C were recorded over Pt-Ni and Ni-Co catalysts. • The highest extent of deactivation was observed for the Pt-Co catalyst. • The system can be effectively kinetically described by 4 main reactions. • Ni-Co catalyst showed lower activation energies and a reduced extent of deactivation.
The aim of the present work is to study the application of a fluidized bed reactor for oxidative ... more The aim of the present work is to study the application of a fluidized bed reactor for oxidative steam reforming of ethanol (OESR) over a bimetallic 3wt% Pt-10wt% Ni/CeO 2-SiO 2 catalyst. In particular, the effect of cerium salt precursor (nitrate (N), ammonium nitrate (AN) and acetylacetonate (AC)) on catalyst activity and stability was investigated. Three catalysts were synthetized. In all cases, the support was composed of a CeO 2-SiO 2 mixed oxide and the ceria content for all the catalysts was fixed to 30 wt%. The tests were carried out at a steam to ethanol ratio (f.r.) of 4 and oxygen to ethanol ratio (o.r.) of 0.5; temperature was fixed to 500°C and the weigh hourly space velocity (WHSV) to 12.3 h-1. All the samples displayed a partial deactivation with timeon-stream and ethanol was completely converted only for few hours. The initial H 2 yield was very close to the predicted thermodynamic value (41.5%) and a gradual yield lowering was observed over the three catalysts. However, after 80 h of test, all the samples reached a plateau condition, with no more variation in selectivity. It is worthwhile noting that, for the sample AC, the final conversion was attested to 75%, while the other two catalysts displayed a similar behaviour with plateau conversion of almost 60%. In addition, a higher H 2 yield (20%) was recorded after 100 h of test for the sample AC and the carbon formation rate measured after the test on the latter catalyst was almost 1 half of the values found for the catalysts N and AN: in the case of acetylacetonate, the organic group of the salt probably assures a templanting effect, which protects ceria molecules, improving their dispersion and increasing catalyst activity towards both reforming and carbon gasification reactions.
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Papers by Vincenzo Palma