Salvatore Vaccaro

Catalytic oxidation of soot from diesel exhaust gases: 1. Screening of metal oxide catalysts by TG-DTG-DTA analysis

Abstract Thermal analysis was employed as a screening technique to evaluate the activity of catalysts for the oxidation of soot produced during combustion. Oxidation took place over metal-oxide-based catalysts at temperatures much lower than in the absence of catalyst. Best results were displayed by a Cu/V/K-supported catalyst which is very active at about 330 °C. In the absence of oxygen, 16% of soot was oxidised by the oxygen of the catalyst, suggesting that a redox mechanism is involved.

Catalytic combustion of carbon particulate

Abstract The catalytic combustion of carbon particulate was investigated with the aim of developing a catalyst for the abatement of soot in diesel exhausts. In the presence of a Cu/V/K based catalyst a strong increase of the rate of carbon combustion and a marked decrease of the apparent activation energy were observed. The carbon reactivity showed a linear dependence upon the initial ratio of the mass of catalyst to the mass of carbon and a square root dependence upon the oxygen partial pressure. However, catalytic combustion of diesel soot and partially graphitized carbon black confirmed previous results obtained for other carbon materials. In particular, kinetic data follow a model proposed for the catalytic combustion of amorphous carbon black [1]. An extension of this model, incorporating the influence of carbon-catalyst contact on the catalyst performances, has been presented.

Catalytic oxidation of an amorphous carbon black

Abstract The oxidation of an amorphous carbon black in the presence of a potassium-copper-vanadium catalyst supported on α-alumina has been studied. Burnoff temperatures in the presence of catalyst were lowered by about 300 K with respect to those for uncatalyzed combustion. Cycles of temperature-programmed reduction and oxidation, along with TG-MS analyses demonstrated that a redox mechanism is at the basis of the catalyst strong activity. A differential flow reactor was employed to perform kinetic tests. The progress of the catalytic combustion process was followed measuring the concentrations of carbon oxides in the product stream at the reactor outlet with on-line NDIR analyzers. The dependence of the reaction rate on the relevant variables was investigated. In particular, the apparent activation energy for the catalytic oxidation was found to be less than half that of the corresponding uncatalyzed process, while the carbon reactivity showed a linear dependence upon the amount of catalyst and a square root dependence upon the oxygen partial pressure. The results allowed the formulation of a mechanism for the catalytic oxidation of carbon black and suggest that the limiting step of the overall process is that of catalyst reduction. On the basis of such findings a kinetic equation for catalytic carbon black oxidation is proposed.

Performances of a catalytic foam trap for soot abatement

Abstract A catalytic trap for soot particles was prepared by deposition of Cu–V–K–Cl catalyst on a ceramic foam. Catalytic trap performances were evaluated by treating the exhaust of a gas oil burner under different operating conditions. The results obtained showed that ceramic foam is a particularly suitable support for this application since it yields low gas pressure drop, good soot collection efficiency (“deep bed” filtration mechanism), high thermal shock resistance and good contact throughout the filter between soot particles and catalyst surface. In addition, the catalytic foam trap is able to spontaneously regenerate at operating conditions comparable to those typical of diesel engine exhaust and after more than 70 test hours it retains its activity towards soot oxidation.

Low temperature carbon particulate oxidation on a supported Cu/V/K catalyst

Abstract The oxidation of carbon black on a supported potassium-copper-vanadium catalyst was studied with the aim of characterise the mechanism of carbon gasification which is the basis of a treatment process based on catalytic post-combustion of particulate at the exhausts of oil fired power plants. In the presence of catalyst the temperatures of carbon black burn off were strongly lowered. Catalyst characterization suggested that a redox mechanism is responsible for the strong activity of the catalyst. Carbon oxides TPD measurements gave evidence that the energy of desorption of the carbon-oxygen surface complexes is dramatically modified by the presence of catalyst.

The role of NO in the regeneration of catalytic ceramic filters for soot removal from exhaust gases

Abstract The effect of NO and H2O on the activity of a Cu/V/K/Cl/Ti based catalytic filter in the combustion of soot generated in the flame of a gas-oil burner has been investigated. Temperature programmed oxidation (TPO) of soot collected on a ceramic filter supporting the Cu/V/K/Cl/Ti catalyst was performed with a flow micro-reactor in the absence and in the presence of NO and H2O in the reactant gas. The presence of NO and H2O resulted in a substantial increase of the rate of carbon combustion, and also affected the selectivity (CO2/CO ratio). The enhanced activity is mainly due to carbon oxidation by NO2 formed by NO oxidation on the same catalyst. TPO test performed after sulphation of the catalytic filter evidenced a marked loss of activity. However, in the presence of NO and H2O the activity of soot oxidation was mostly preserved.

Deep filtration and catalytic oxidation: an effective way for soot removal

Catalytic and uncatalytic axial flow ceramic foam traps for soot removal were prepared and tested at the exhaust of a gas oil burner. Soot filtration efficiencies of uncatalytic and catalytic traps were comparable and depended on the burner operating conditions. A threshold temperature of the catalyst of about 330 °C was determined. Above such a temperature while the pressure drop through the uncatalytic trap increases continuously because of soot load, that through the catalytic trap reaches a steady-state value where the soot amounts captured and burned on the trap were equivalent. Also radial flow ceramic foam traps were prepared and tested at the exhaust of a common rail diesel engine. Their behaviours reflected those of the corresponding axial flow traps. A model descriptive of the relevant phenomena (filtration, combustion and pressure drop time evolution) occurring all over the traps was formulated. It is able to yield the overall trap performances although further improvements are needed in the catalytic case.

Kinetics of Soot Oxidation on Potassium-Copper-Vanadium Catalyst

Abstract Combustion of carbonaceous materials such as Diesel engine soot, carbon black and graphite on a potassium-copper-vanadium catalyst supported on α- alumina has been studied. Catalyst characterization by thermal analysis and X-ray diffraction indicates the formation of mixed K/Cu/Cl and K/V/O phases after calcination at 700° C. The presence of KCl has been also detected. Soot combustion experiments show a dramatic effect of the catalyst, burn off temperatures being about 300° C lower than those obtained with thermal combustion. Kinetics of soot catalytic combustion has been investigated in a differential flow reactor. A linear dependence on both soot mass and oxygen partial pressure has been found. Comparable reaction rates with the same dependence on the reactant concentrations have been determined also in the case of carbon black. The apparent energy of activation for the catalytic process is 85–100 kJ/mol. The kinetic equation enables to describe the process of catalytic combustion up to conversions of 50%.

Catalytic Combustion of Methane Soot

Abstract The performances of a Cu-V-K catalyst in the oxidation of soot collected in a methane-rich flame have been studied in a tubular flow reactor. Burn-off temperatures were lowered by about 300 K with respect to uncatalyzed combustion. The dependence of the reaction rate on the relevant variables was investigated. The apparent activation energy for the catalytic oxidation was found to be about a half of the one of the uncatalyzed process, while the carbon reactivity showed a linear dependence on the initial soot to catalyst mass ratio. A square root dependence on the oxygen partial pressure was found. The results of soot combustion confirm previous findings obtained with other carbon materials. Moreover, kinetic data follow a model proposed for the catalytic combustion of amorphous carbon black (Ciambelli et al, 1994a). An extension of this model, incorporating the influence of carbon-catalyst contact on the catalyst performances, has been presented.

Simultaneous Filtration and Catalytic Oxidation of Carbonaceous Particulates

Two catalytic filters prepared by the deposition of Cu–V–K–Cl catalyst on different ceramic supports, foam and sintered aluminosilicate monolith, were employed for the removal of soot from the exhaust of a gas-oil burner. The foam filter was more suitable than the sintered filter for this application allowing better soot–catalyst contact, lower gas pressure drop and easier spontaneous filter regeneration.