Rachid Brahmi

Removal of oxygenated volatile organic compounds by catalytic oxidation over Zr-Ce-Mn catalysts.

The composition-activity relationship of Zr-Ce-Mn-O materials was investigated for the catalytic removal of Oxygenated Volatile Organic Compounds (OVOC) emitted by stationary sources. Using a sol-gel method, very high surface specific areas, small crystallite sizes and high redox properties were obtained for Zr(0.4)Ce(0.6-x)Mn(x)O(2) catalytic systems after calcination at 500°C. The textural and redox properties were improved when Mn content increased in the material, especially for x=0.36. As a result the most active and selective catalyst in the butanol (model of OVOC) oxidation was obtained for the nominal composition Zr(0.4)Ce(0.24)Mn(0.36)O(2) due to a high oxygen mobility and surface Mn(4+) concentration.

Comparison of Catalyst Support Between Monolith and Pellet in Hydrogen Peroxide Thrusters

The effect of catalyst support on the performance of monopropellant thrusters was investigated. In the present study, two support materials (monolith honeycombs and alumina pellets) were tested and their relative performances were compared. A reference catalyst (Na 0.2 MnO 2 ) was coated on both catalyst supports, and 90 wt% hydrogen peroxide was used as the monopropellant. Two test thrusters of different sizes were fabricated, and the performance of each thruster when using monolith honeycomb and alumina pellets as the catalyst bed was evaluated by measuring the product-gas temperature at the rear end of the catalyst bed and the pressure of the gas at the front and rear ends of the catalyst bed; during these measurements, the feed pressure of the propellant was fixed. Under the given test conditions, the performance of the thrusters was better when using alumina pellets as the catalyst support than when using monolith honeycomb. Since the monolith support was less reactive than the pellets, pressure buildup in the former case was relatively small; consequently, the chamber pressure and temperature were lower when using the monolith support than when using the pellet support. The pressure drop across the catalyst bed was moderate in both cases (0.02-0.1 bar in the case of a monolith and 0.3-0.7 bar in the case of a pellet catalyst).

Transient Behavior of H2O2 Thruster: Effect of Injector Type and Ullage Volume

ROCKET-GRADE hydrogen peroxide has been used as a monopropellant and a storable oxidizer. However, because of the demand for a higher specific impulse, hydrazine andN2O4 are being used as the monopropellant and storable oxidizer, respectively. Recently, due to concerns regarding propellant toxicity, there has been a renewed interest [1] in the use ofH2O2 in propulsion systems [2–10]. A monopropellant thruster is operated in either the continuous or pulse mode. The thrust force and pressure instability are important issues in the continuous mode. For generating the desired thrust, the catalytic reactor size required for completely decomposing the propellant must be determined [8]. However, in the pulse mode (the main operationmode for attitude control systems), the response characteristics of the thruster are important. The catalyst activity, thruster component design (including the injector design), manifold volume, ullage volume in the reactor, and operating pressure influence the thruster response time. Tian et al. investigated the response time when using a combination of PbO and MnO2 catalysts [11]; they found that Ir=Al2O3 is unsuitable for use as a catalyst in a H2O2 monopropellant thruster [12]. Xu et al. studied the activities of various catalysts during H2O2 decomposition [13]. El-Aiashy et al. reported that the catalyst activity ofMnO2 increased when ZnO was added [14]. Hasan et al. reported that the activity ofMnO2 increased when promoters such as Ni, Cu, Bi, and Ce were added [15]. None of the aforementioned studies have addressed the effect of thruster design parameters on response times, although a few researchers have measured the thruster response time. Optimization of the thruster design (determination of the appropriate injector and ullage volume in the reaction chamber) can also influence the response characteristics. Therefore, we investigate the response characteristics of H2O2 monopropellant thrusters for three different thruster designs andmeasure the response times by varying the injector type, reactor volume, and catalyst grain size. AMnO2=Al2O3 catalyst is used for the decomposition of concentrated H2O2 (90 wt%).

Photocatalytic Degradation of Organic Pollutants in Wastewater

Even today the efficient treatment of industrial wastewaters is not evident. The effluents may contain large amounts of harmful organic compounds that are not easily removed with conventional methods. This study focuses on the photocatalytic treatment of four organic pollutants originated from different types of industry. The pollutants are diuron (herbicide), p-coumaric acid (agro-industrial wastewater), bisphenol A and phthalic anhydride (plasticizers), which all are widely used and cause significant health and environmental problems. To get deeper understanding, the photocatalytic degradation of the model molecules was studied both in synthetic solutions and in industrial wastewater matrix over TiO2 P25 in two different batch photoreactors under UV-A irradiation. The effects of catalyst loading, pH and initial concentration were studied. To gain understanding on the reactivity of molecules and costs of treatment, the kinetic modelling and energy modelling were compared and the specific applied energy (ESAE) was estimated. ESAE is proposed as a useful value to estimate the energy needed to degrade one mole of pollutant and further to calculate the operating costs to treat the wastewater. Of the model pollutants, diuron was removed the most efficiently and its removal consumed the least amount of energy in terms of the specific applied energy. Bisphenol A was found to be the most difficult to be removed by photocatalysis. The industrial wastewater matrix affected negatively the removal results.

Monolithic catalysts for the decomposition of energetic compounds

Abstract Pellet-based catalysts have been developed more than 60 years ago for the decomposition of hydrogen peroxide and hydrazine for propulsion applications. Cellular ceramic supports are now proposed to replace such catalyst support for monopropellant decomposition or bipropellant ignition. Different honeycomb supports have been manufactured by CTI Company and used as catalyst support for lab-scale reactor as well as for full-scale application. The support parameters are the chemical nature (cordierite, mullite, mullite–zircone, SiC…), the channel shape and density. For full-scale reactors, dedicated apparatus have been developed to control the key parameters during the preparation of the catalysts: quality and homogeneity of the wash-coating layer, impregnation conditions to reach a high loading level of active phase.

Copper-zinc oxide catalyst. Part II. Preparation, IR characterization and thermal properties of novel bimetallic precursors

Four new bimetallic model precursors of copper-zinc oxide catalysts for methanolization were prepared: Zn(NH3)2Cu(CN)3 (ZCA), [Zn(en)3]6[Cu5(CN)17]·nH2O (n = 8.4) (ZCE3), Zn(en)Cu(CN)3 (ZCE1) and [Zn1 − xCux(en)][Cu(CN)3] (ZCCE1). The new compounds were characterized by elemental analysis, IR spectroscopy, and thermal analysis under dynamic conditions. Thermal stability increases in the order ZCE3 (65) < ZCA (120) < ZCE1 or ZCCE1 (155°C). Thermal decomposition in air proceeds via the following steps: dehydration (if water molecules are present), deamination, redox decomposition of the cyano groups with formation of metallic copper and ZnO, and finally re-oxidation of copper to CuO. In the case of en-containing compounds an unexplained phase transition was observed at 800°C.

Bi-propellant Micro-Rocket Engine

Micro-satellites (from 10 kg up to 100 kg) have mass, volume, and electrical power constraints due to their low dimensions. These limitations lead to the lack in currently available active orbit control systems in micro-satellites. Therefore, a micro-propulsion system with a high thrust to mass ratio is required to increase the potential functionality of small satellites. Mechatronic is presently working on a liquid bipropellant micro-rocket engine under contract with ESA (Contract No.16914/NL/Sfe - Microturbomachinery Based Bipropellant System Using MNT). The advances in Mechatronics project are to realise a micro-rocket engine with propellants pressurised by micro-pumps. The energy for driving the pumps would be extracted from a micro-turbine. Cooling channels around the nozzle would be also used in order to maintain the wall material below its maximum operating temperature. A mass budget comparison with more traditional pressure-fed micro-rockets shows a real benefit from this system in terms of mass reduction. In the paper, an overview of the project status in Mechatronic is presented.

Catalytic decomposition of energetic compounds - Influence of catalyst shape and ceramic substrate

Catalytic decomposition of energetic compounds is used for different purposes like propulsion application (launcher, satellites and missiles) and gas generator (e.g. rescue systems). The energetic liquids (H 2O2, N 2H4, ionic liquids, N 2O, …) are decomposed on catalytic beds which must present very good thermal and mechanical properties to resist frequent thermal shocks and high flow rates. Compared to conventional alumina-based supports developed specifically for this application about 30 years ago (extrudates, pellets, spheres), honeycomb monolith catalysts show many advantages: (i) lower pressure drop, (ii) better thermal shock and attrition resistance, (iii) uniform flow distribution and mass/heat transfer conditions, (iv) shorter diffusion length, and (v) large heritage from cleaning of car exhaust gases. Therefore, monolithic reactors represent very attractive alternatives to traditional systems with the future ability to develop chemical micro-propulsion systems. These new monolith applications demand a careful control of the substrate chemical nature, the surface impregnation by the thin porous wash-coat layer and the impregnation of this layer by the active phase precursor. An overview is given and two applications to the decomposition of hydrogen peroxide and ionic liquid solutions are presented and discussed.

Copper-zinc oxide catalysts. Part IV. Thermal treatment in air, argon and hydrogen and XRD study of new bimetallic precursors-direct formation of alloys

Abstract Four new CuZn bimetallic precursors of model catalysts for methanolization of syngas, Zn(NH 3 ) 2 Cu(CN) 3 (ZCA), [Zn(en) 3 ] 6 [Cu 5 (CN) 17 ]· n H 2 O ( n = 8.4) (ZCE3), [Zn( en )] [Cu(CN) 3 ] (ZCE1) and [Zn 1− x Cu x (en)] [Cu(CN) 3 ] (ZCCE1), were thermally treated in air, hydrogen and argon atmosphere between 200 and 900°C. The calcinations in air yield firstly a mixture of cyano-ligand-containing compounds which transform at temperatures above 300°C to CuO and ZnO; the crystallite size of both oxides increases with temperature. The reduction in hydrogen at 300°C gives zinc cyanide and metallic copper which are converted at 450°C mainly to β′-brass including some α- and γ-alloys. The thermal treatment in argon displays the very high thermal stability of zinc cyanide to 900°C and formation of copper or α-CuZn alloy. Only the hydrogen treatment avoids the segregation of both metallic elements. The results are discussed on the basis of thermodynamic data.

Assessment of Catalysts for Hydrogen-Peroxide-Based Thrusters in a Flow Reactor

Hydrogen peroxide is a candidate propellant for rocket-propulsion applications with the potential to replace highly toxic propellants currently used. Decomposition of hydrogen peroxide yields a high-temperature oxygen-steam mixture, which can be used as monopropellant or as oxidizer in a bipropellant configuration. This work examines different types of cellular ceramic-based catalysts for hydrogen-peroxide decomposition at miniature scale of nominal mass flows of 0.3  g s−1. An exhaustive investigation of different catalysts in a flow reactor configuration similar to a propulsion application is conducted. The test matrix includes honeycomb monoliths with different channel geometries, densities, lengths, different carrier materials, and wash-coating procedures, as well as different types of catalysts such as pellets and foams. Thirty nine catalyst configurations with a total of 121 catalysts have been experimentally investigated based on their transient and stationary performance at design mass-flow levels...