Commercial Oxidation Catalyst Research Articles

Extensive Gaseous Emissions Reduction of Firewood-Fueled Low Power Fireplaces by a Gas Sensor Based Advanced Combustion Airflow Control System and Catalytic Post-Oxidation

In view of the tremendous emissions of toxic gases and particulate matter (PM) by low-power firewood-fueled fireplaces, there is an urgent need for effective measures to lower emissions to keep this renewable and economical source for private home heating available in the future. For this purpose, an advanced combustion air control system was developed and tested on a commercial fireplace (HKD7, Bunner GmbH, Eggenfelden, Germany), complemented with a commercial oxidation catalyst (EmTechEngineering GmbH, Leipzig, Germany) placed in the post-combustion zone. Combustion air stream control of the wood-log charge combustion was realized by five different control algorithms to describe all situations of combustion properly. These control algorithms are based on the signals of commercial sensors representing catalyst temperature (thermocouple), residual oxygen concentration (LSU 4.9, Bosch GmbH, Gerlingen, Germany) and CO/HC-content in the exhaust (LH-sensor, Lamtec Mess- und Regeltechnik für Feuerungen GmbH & Co. KG, Walldorf (Germany)). The actual flows of the combustion air streams, as calculated for the primary and secondary combustion zone, are adjusted by motor-driven shutters and commercial air mass flow sensors (HFM7, Bosch GmbH, Gerlingen, Germany) in separate feedback control loops. For the first time, the residual CO/HC-content (CO, methane, formaldehyde, etc.) in the flue gas is in-situ monitored with a long-term stable AuPt/YSZ/Pt mixed potential high-temperature gas sensor, which allows continuous estimation of the flue gas quality with an accuracy of about ±10%. This parameter is not only an essential input for advanced combustion air stream control but also provides monitoring of the actual combustion quality and logging of this value over a whole heating period. By many firing experiments in the laboratory and by field tests over four months, it could be demonstrated that with this long-term stable and advanced automated firing system, depression of the gaseous emissions by about 90% related to manually operated fireplaces without catalyst could be achieved. In addition, preliminary investigations at a firing appliance complemented by an electrostatic precipitator yielded PM emission depression between 70% and 90%, depending on the firewood load.

Energy assessment of an electrically heated catalyst in a hybrid RCCI truck

Reactivity controlled compression ignition (RCCI) combustion showed great advantages in terms of engine-out NOx and soot emissions reduction. However, HC and CO emissions are larger than with conventional diesel combustion. Commercial oxidation catalysts can deal with the amount of HC and CO generated during the RCCI combustion only at warm conditions, thus limiting the implementation of this concept in conventional vehicles and in RCCI hybrid applications due to the large engine stop periods. This work aims to study the behaviour of an electrically heated catalyst used in a hybrid medium-duty truck operating with diesel-gasoline RCCI combustion. A parallel P2 full hybrid medium-duty truck is studied in transient conditions by means of numerical simulations validated with experimental data. The results are compared to those from the commercial diesel non-hybrid truck and the RCCI non-hybrid concept with a commercial oxidation catalyst. The results show that the fuel consumption increases about 2 % in combined cycles and 5 % in urban cases with respect to the non-hybrid RCCI case with a commercial oxidation catalyst. Finally, it was found that the RCCI hybrid concept with the electrically heated catalyst allows to achieve the EUVI targets for all the pollutant emissions with CO2 levels of 15 %.

Activating low-temperature diesel oxidation by single-atom Pt on TiO2 nanowire array

Supported metal single atom catalysts (SACs) present an emerging class of low-temperature catalysts with high reactivity and selectivity, which, however, face challenges on both durability and practicality. Herein, we report a single-atom Pt catalyst that is strongly anchored on a robust nanowire forest of mesoporous rutile titania grown on the channeled walls of full-size cordierite honeycombs. This Pt SAC exhibits remarkable activity for oxidation of CO and hydrocarbons with 90% conversion at temperatures as low as ~160 oC under simulated diesel exhaust conditions while using 5 times less Pt-group metals than a commercial oxidation catalyst. Such an excellent low-temperature performance is sustained over hydrothermal aging and sulfation as a result of highly dispersed and isolated active single Pt ions bonded at the Ti vacancy sites with 5 or 6 oxygen ions on titania nanowire surfaces.

Fluidized Bed Plasmas Reactor for Catalyst Synthesis and Pretreatment. Application for Pollution Abatement in Stationary and Mobile Sources

The preparation of automotive catalysts and commercial oxidation catalysts in stationary sources use a large amount of noble metal precursors. Moreover, during their preparation high energy (gas and temperature) is necessary for treatment processes. In order to develop a higher sustainable process, the plasma-assisted catalysts synthesis could be a solution. The use of plasmas for catalysis is already well developed and plasma treatment was already used in a low pressure system to replace the thermal calcination steps of the catalysts. Fluidized bed reactors offer the possibility to lead to homogenous treatment and have the additional advantage of excellent heat transfer rates between the gas and the particles, so that it can modify the catalytic properties of the prepared materials. The aim of our work is to prepare plasma-assisted catalysts dedicated to pollution abatement in stationary or mobile sources. For stationary sources, the first prepared catalysts are palladium based catalysts, which were chosen since the main reducing agent in combine heat power is methane. In the case of mobile sources, we have worked with silver based catalysts since ethanol could be chosen as a sustainable alternative reducing agent to replace ammonia. After the preparation of the different catalysts, the low fluidized bed plasma reactor was used to modify Pd/ γ-alumina and Ag/γ-alumina catalysts. A comparison with “classical calcination” in air at 500°C was performed in order to show the advantages of plasma treatments. The first catalytic results show that plasma treated catalysts lead to higher pollutant abatement than classically prepared ones. Thus, concerning the plasma process, we have studied the role of the plasma treatment time as well as the nature of the gas treatment. The characterization of the catalysts is in course in order to understand the influence of plasma treatment parameters on catalytic results.

Synergistic Effect in Selective Reduction of NO by Alkanes over Mechanically Mixed Oxide Catalysts

The process of selective catalytic reduction of nitrogen oxides by propane in the presence of O2, as well as in the presence or absence of CO, was studied over series of commercial oxide catalysts used in petrochemical processes. For the first time synergistic effect was observed for catalytic systems consisting of mechanical mixtures of Cu–Zn–Ni–Al (catalyst I) + Fe–Cr (catalyst II) and Cu–Zn–Ni–Al (catalyst I) + Ni–Cr (catalyst III). The activity of these mixtures in nitrogen oxides reduction by propane was greater than that of individual components in each case. The worked-out catalytical systems showed high effectivity in the process of simultaneous removal of several toxic components: NO x , CO, hydrocarbons – from model gas mixtures, as well as from real exhausts of automotive transport.

Selective NO reduction by propane over commercial oxide catalysts and their mechanical mixture: II. Intermediate complexes and reaction mechanism

Based on a spectrokinetic study (simultaneous measurements of the concentrations of surface complexes and reaction rate usingin situ IR spectroscopy), a hypothesis is proposed which explains synergism in the reaction of NO reduction by propane on a mechanical mixture of commercial oxide catalysts.

Selective NO reduction by propane over commercial oxide catalysts and their mechanical mixture: I. Synergistic effect

In the reaction of NO reduction by propane in excess oxygen, the activity of a binary mixture of commercial oxide catalysts is higher than should be expected if it were proportional to the activities of separate catalyst components. This synergism reveals itself in the fact that the conversion of NO and C3H8 is higher when the catalyst is a mechanical mixture than the sum of conversions over separate catalysts, all other conditions being the same. Based on the kinetic and thermal desorption measurements, the experimental conditions are found under which the synergism is observed. A hypothetical mechanism is proposed.

Fast catalytic oxidation of phenol in supercritical water

The catalytic oxidation of phenol in water over a commercial oxidation catalyst, CARULITE 150, was investigated in a fixed bed flow reactor at 250 atm and temperatures from 380°C to 430°C. The phenol and oxygen concentrations at the reactor entrance varied between 0.070 and 1.24 mmol/l, and 9.60 and 39.6 mmol/l, respectively. The reaction conditions produced phenol conversions and selectivities to CO 2 much higher than those produced by non-catalytic oxidation. The kinetics of phenol disappearance and of CO 2 formation were both roughly first-order, and the activation energies were 31 and 47 kcal/mol, respectively. The catalyst did not undergo continuous deactivation during the catalytic oxidation, but rather maintained a high activity even after several days of continuous operation.

Utilization of hydrogen sulfide from acidic gases produced in treatment with amines

Treatment with amines is the basic method for removing hydrogen sulfide from gases. When such treatment is used, there is a problem in utilizing the acidic regeneration gases, which consist of carbon dioxide, hydrogen sulfide, and C{sub 1}-C{sub 4} hydrocarbons. If the concentration of hydrogen sulfide in these gases is below 20%, it is best removed by direct oxidation by oxygen to form sulfur or sulfur dioxide, over solid or liquid catalysts. Here we are reporting on an investigation of the activity and selectivity of commercial oxide catalysts in this reaction. Commercial catalysts were used in the direct oxidation of gas containing hydrogen sulfide (2-4% hydrogen sulfide, 1-4% C{sub 1}-C{sub 4} hydrocarbons, remainder carbon dioxide) in a laboratory flow unit with a fixed bed of catalyst. The compositions of the feed and the reaction products were determined by gas-liquid chromatography. The oxidation of hydrogen sulfide may proceed with the formation of either sulfur dioxide or sulfur. Catalyst activity was rated on the basis of the total conversion of hydrogen sulfide, the percentage conversions to elemental sulfur and sulfur dioxide, and the selectivity for the formation of elemental sulfur. The catalyst activities were investigated at temperatures of 170-270{degrees}C, space velocity ofmore » feed 300 h{sup -1}, hydrogen sulfide concentration 2-4%, and O{sub 2}: H{sub 2}S ratio 1.« less

Deep oxidation of hydrocarbons

The activity of two commercial oxidation catalysts was investigated for the oxidation of a humidified air stream containing 500 ppm of a mixture of C 5 to C 9 hydrocarbons over an extended period of time (ten months). The composition of the feed stream was similar to that obtained from air-strippers used for groundwater clean-up. The reaction was conducted continuously in fixed bed reactors at constant total conversion (> 99%). The temperature was increased, when needed, to compensate for the catalyst deactivation and maintain a constant conversion. A 0.1% Pt/3% Ni/Al 2O 3 catalyst (G-43A, United Catalysts, Inc., Louisville, KY) did not lose any activity at 430 ° C when used continuously for 253 days-on-stream. On the other hand, a ceria-promoted hopcalite catalyst suffered considerable deactivation and required a temperature increase of 85° C over 297 days-on-stream to maintain the total conversion above 99%. However, the final temperature (400 ° C) required to maintain > 99% conversion over the hopcalite catalyst was still lower than the initial temperature required for the operation of the Pt/Ni catalyst (430° C). No partial oxidation products were formed over either of the catalysts. Also, the only total carbon oxidation product was carbon dioxide. A simple first order deactivation model fits the time-temperature relationship over the hopcalite catalyst and predicts a hopcalite catalyst lifetime of 362 days for a maximum operating temperature of 500° C.