Hydrogen Peroxide Decomposition: Testing and Characterization of MnOx-based Catalysts
Creators: name:  S. CARLOTTI 
name:   F. MAGGI 
Publisher: name: Proceedings of  the 9th European Conference for Aerospace Sciences. Lille, France, 27 June - 1 July, 2022
Year: 2022
Subjects: PROPULSION PHYSICS
NEW PROPELLANTS

description: Nowadays, the research towards green alternatives to the most widely employed propellants, such as hydrazine and nitrogen tetroxide/monomethylhydrazine (NTO/MMH), is greatly increased pushed by a worldwide shared interest for improved environmental safety and consequent economic benefits. Hydrogen peroxide is considered one of the best candidates for near-future storable and green space propulsion, because of the advantages of low toxicity, low environmental impact, and because its decomposition produces no pollutant species. Highly concentrated hydrogen peroxide, known as high-test hydrogen peroxide (HTP), can exothermically decompose into water vapor and oxygen. The adiabatic decomposition predicted by thermochemistry can produce hot gases at a temperature range of 898-1269 K, depending on the H2O2 concentration (85-100%). Then, the hot decomposition products can be directly expanded in a nozzle or injected in a combustion chamber to react with a solid or liquid fuel. In the former case, exploiting a monopropellant configuration, high-test hydrogen peroxide can deliver specific impulse between 150 and 180 seconds, while in a bipropellant rocket system, more than 300 seconds can be achieved. As an example, HTP-ethanol combination leads to satisfactory performance, only about 10% lower than NTO/MMH couple. One of the most important technology challenges in the realization of hydrogen peroxide-based rockets is the development of reliable and efficient catalysts. The catalyst has to fulfill several requirements, such as high stability, longevity and short response time. Moreover, it has to provide reproducible performance in a wide range of operating conditions, spanning from high-test peroxide liquid injection at high pressure to the resulting decomposition products at elevated temperature. Additionally, long-term stability, high thermal and mechanical strength associated with ignition/shut down cycles, as well as low cost are typical features required from catalysts. Nowadays, mainly grids, pellets, or beads coated with the catalytic substances have been employed, granting the maximization of surface-to-volume ratio. Different metals and/or metallic oxides (such as silver, platinum, iron oxides, alkali permanganates, manganese oxides and others) have been investigated as the active phase. Among the others, manganese oxides (MnOx) based catalysts represent an interesting yet cheap solution, demanding thorough analysis regarding their characteristics and their production technique. The aim of this work is to present the current study performed at the Space Propulsion Laboratory of Politecnico di Milano about the catalysts based on manganese oxides for the decomposition of hydrogen peroxide. In particular, a procedure for catalyst preparation based on an impregnation process using potassium permanganate as precursor in aqueous solution and commercial aluminum oxide as support, is proposed. The active phase content is determined by weighting the catalysts under preparation, and it is defined as the ratio of mass increase in the overall process to the original mass of the pellets. Additionally, surface characterization by means of scanning electron microscopy (SEM) is discussed. Catalysts reactivity and decomposition rate are quantified by investigating the decomposition of a defined amount of 87.5% high-test hydrogen peroxide at lab-scale level. Furthermore, results related to the scale-up of the process are discussed. In fact, a decomposition system has been designed and implemented at SPLab, and a preliminary experimental campaign in relevant conditions is presented.